Physical
Activity
and
Health

A Report of the Surgeon General

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
The President's Council on Physical Fitness and Sports


Suggested Citation

U.S. Department of Health and Human Services. Physical Activity and Health:
A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and
Human Services, Centers for Disease Control and Prevention, National
Center for Chronic Disease Prevention and Health Promotion, 1996.

For sale by the Superintendent of Documents,
P.O. Box 371954, Pittsburgh, PA 15250-7954,
      s/No17-023-00196-5


Message from Donna E. Shalala
Secretary of HeaIth and Human Services

The United States has led the world in understanding and promoting the
benefits of physical activity. In the 1950s we launched the first national effort to
encourage young Americans to be physically active, with a strong emphasis on
participation in team sports. In the 1970s we embarked on a national effort to
educate Americans about the cardiovascular benefits of vigorous activity, such as
running and playing basketball. And in the 1980s and 1990s we made break-
through findings about the health benefits of moderate-intensity activities, such as
walking, gardening, and dancing.

Now, with the publication of this first Surgeon General's report on physical
activity and health, which I commissioned in 1994, we are poised to take another
bold step forward. This landmark review of the research on physical activity and
health-the most comprehensive ever-has the potential to catalyze a new physical
activity and fitness movement in the United States. It is a work of real significance,
on par with the Surgeon General's historic first report on smoking and health
published in 1964.

This report is a passport to good health for all Americans. Its key finding is that
people of all ages can improve the quality of their lives through a lifelong practice
of moderate physical activity. You don't have to be training for the Boston Marathon
to derive real health benefits from physical activity. A regular, preferably daily
regimen of at least 30-45 minutes of brisk walking, bicycling, or even working
around the house or yard will reduce your risks of developing coronary heart
disease, hypertension, colon cancer, and diabetes. And if you're already doing that,
you should consider picking up the pace: this report says that people who are
already physically active will benefit even more by increasing the intensity or
duration of their activity.

This watershed report comes not a moment too soon. We have found that 60
percent-well over half-of Americans are not regularly active. Worse yet, 25
percent of Americans are not active at all. For young people-the future of our
country-physical activity declines dramatically during adolescence. These are
dangerous trends. We need to turn them around quickly, for the health of our
citizens and our country.

We will do so only with a massive national commitment-beginning now, on
the eve of the Centennial Olympic Games, with a true fitness Dream Team drawing
on the many forms of leadership that make up our great democratic society.
Families need to weave physical activity into the fabric of their daily lives. Health
professionals, in addition to being role models for healthy behaviors, need to
encourage their patients to get out of their chairs and start fitness programs tailored
to their individual needs. Businesses need to learn from what has worked in the past


and promote worksite fitness, an easy option for workers. Community leaders need
to reexamine whether enough resources have been devoted to the maintenance of
parks, playgrounds, community centers, and physical education. Schools and
universities need to reintroduce daily, quality physical activity as a key component
of a comprehensive education. And the media and entertainment industries need to
use their vast creative abilities to show all Americans that physical activity is
healthful and fun-in other words, that-it is attractive, maybe even glamorous!
We Americans always find the will to change when change is needed. I believe
we can team up to create a new physical activity movement in this country. In doing
so, we will save precious resources, precious futures, and precious lives. The time
for action-and activity-is now.


Foreword

This first Surgeon General's report on physical activity is being released on the
eve of the Centennial Olympic Games- the premiere event showcasing the worlds
greatest athletes. It is fitting that the games are being held in Atlanta, Georgia, home
of the Centers for Disease Control and Prevention (CDC), the lead federal agency
in preparing this report. The games' loo-year celebration also coincides with the
CDC's landmark 50th year and with the 40th anniversary of the President's Council
on Physical Fitness and Sports (PCPFS), the CDC's partner in developing this
report. Because physical activity is a widely achievable means to a healthier life, this
report directly supports the CDC's mission- to promote health and quality of life
by preventing and controlling disease, injury, and disability. Also clear is the link
to the PCPFS; origin-ally established as part of a national campaign to help shape up
America's younger generation, the Council continues today to promote physical
activity, fitness, and sports for Americans of all ages.
The Olympic Games represent the summit of athletic achievement. The
Paralympics, an international competition that will occur later this summer in
Atlanta, represents the peak of athletic accomplishment for athletes with disabili-
ties. Few of us will approach these levels of performance in our own physical
endeavors. The good news in this report is that we do not have to scale Olympian
heights to achieve significant health benefits. We can improve the quality of our lives
through a lifelong practice of moderate amounts of regular physical activity of
moderate or vigorous intensity. An active lifestyle is available to all.
Many Americans may be surprised at the extent and strength of the evidence
linking physical activity to numerous health improvements. Most significantly,
regular physical activity greatly reduces the risk of dying from coronary heart
disease, the leading cause of death in the United States. Physical activity also reduces
the risk of developing diabetes, hypertension, and colon cancer; enhances mental
health; fosters healthy muscles, bones and joints; and helps maintain function and
preserve independence in older adults.

The evidence about what helps people incorporate physical activity into their
lives is less clear-cut. We do know that effective strategies and policies have taken
place in settings as diverse as physical education classes in schools, health promo-
tion programs at worksites, and one-on-one counseling by health care providers.
However, more needs to be learned about what helps individuals change their
physical activity habits and how changes in community environments, policies, and
social norms might support that process.

Support is greatly needed if physical activity is to be increased in a society as
technologically advanced as ours. Most Americans today are spared the burden of
excessive physical labor. Indeed, few occupations today require significant physical


acttvtty, and most people use motorized transportation to get to work and to perform
routine errands and tasks. Even leisure time is increasingly filled with sedentary
behaviors, such as watching television, "surfing" the Internet, and playing video
games.

Increasing physical activity is a formidable public health challenge that we must
hasten to meet. The stakes are high, and the potential rewards are momentous:
preventing premature death, unnecessary illness, and disability; controlling health
care costs\ and maintaining a high quality of life into old age.

David Satcher, M.D., Ph.D.                 Philip R. Lee, M.D.

Director
Centers for Disease Control
and Prevention

Assistant Secretary
for Health

Florence Griffith Joyner
Tom McMillen
Co-Chairs
President's Council on
Physical Fitness and Sports


    Preface
from the Surgeon General
U.S. Public Health Service

I am pleased to present the first report of the Surgeon General on physical
activity and health. For more than a century, the Surgeon General of the Public
Health Service has focused the nation's attention on important public health issues.
Reports from Surgeons General on the adverse health consequences of smoking
triggered nationwide efforts to prevent tobacco use. Reports on nutrition, violence,
and HIV/AIDS-to name but a few-have heightened America's awareness of
important public health issues and have spawned major public health initiatives.
This new report, which is a comprehensive review of the available scientific
evidence about the relationship between physical activity and health status, follows
in this notable tradition.

Scientists and doctors have known for years that substantial benefits can be
gained from regular physical activity. The expanding and strengthening evidence
on the relationship between physical activity and health necessitates the focus this
report brings to this important public health challenge. Although the science of
physical activity is a complex and still-developing field, we have today strong
evidence to indicate that regular physical activity will provide clear and substantial
health gains. In this sense, the report is more than a summary of the science-it is
a national call to action.

We must get serious about improving the health of the nation by affirming our
commitment to healthy physical activity on all levels: personal, family, community,
organizational, and national. Because physical activity is so directly related to
preventing disease and premature death and to maintaining a high quality of life,
we must accord it the same level of attention that we give other important public
health practices that affect the entire nation. Physical activity thus joins the front
ranks of essential health objectives, such as sound nutrition, the use of seat belts,
and the prevention of adverse health effects of tobacco.

The time for this emphasis is both opportune and pressing. As this report
makes clear, current levels of physical activity among Americans remain low, and
we are losing ground in some areas. The good news in the report is that people can
benefit from even moderate levels of physical activity. The public health implica-
tions of this good newsare vast: the tremendous health gains that could be realized
with even partial success at improving physical activity among the American
people compel us to make a commitment and take action. With innovation,
dedication, partnering, and a long-term plan, we should be able to improve the
health and well-being of our people.


This report is not the final word. More work will need to be done so that we can
determine the most effective ways to motivate all Americans to participate in a level
of physical activity that can benefit their health and well-being. The challenge that
lies ahead is formidable but worthwhile. 1 strongly encourage all Americans to join
us in this effort.

Audrey F. Manley, M.D`., M.P.H.
Surgeon General (Acting)


Physical Activity and Health

Acknowledgments

Editors

Steven N. Blair, P.E.D., Senior Scientific Editor,
Director of Research and Director, Epidemiology
and Clinical Applications, The Cooper Institute for
Aerobics Research, Dallas, Texas.

Adele L. Franks, M.D., Scientific Editor, Assistant
Director for Science, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Dana M. Shelton, M.P.H., Managing Editor,
Epidemiologist, Office on Smoking and Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

John R. Livengood, M.D., M.Phil., Coordinating
Editor, Deputy Director, Epidemiology and
Surveillance Division, National Immunization
Program, (formerly, Associate Director for Science,
Division of Chronic Disease Control and Community
Intervention, National Center for Chronic Disease
Prevention and Health Promotion), Centers for
Disease Control and Prevention, Atlanta, Georgia.

Frederick L. Hull, Ph.D., Technical Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Byron Breedlove, M.A., Technical Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

This report was prepared by the Department of
Health and Human Services under the direction of
the Centers for Disease Control and Prevention,
National Center for Chronic Disease Prevention and
Health Promotion, in collaboration with the
President's Council on Physical Fitness and Sports.

David Satcher, M.D., Ph.D., Director, Centers for
Disease Control and Prevention, Atlanta, Georgia.

J~~I~CS S. Marks, M.D., M.P.H., Director, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prcvcntion, Atlanta, Georgia.

Virginia S. Bales, M.P.H., Deputy Director, National
Ccntcr for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
f'rcvcntion, Atlanta, Georgia.

f.isa A. Daily, Assistant Director for Planning,
f:valuation, and Legislation, National Center for
(:hronic Disease Prevention and Health Promotion,
(:cntcrs for Disease Control and Prevention,
)\tlanta, Georgia.

Marjorie A. Speers, Ph.D., Behavioral and Social
\cicnccs Coordinator, Office of the Director,
(lormcrly, Director, Division of Chronic Disease
(:oritrol and Community Intervention, National
(:ctircr for Chronic Disease Prevention and Health
Promotion), Centers for Disease Control and
f'rcvention, Atlanta, Georgia.

f:rcclerick L. Trowbridge, M.D., Director, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Ccmcrs for Disease Control and Prevention, Atlanta,
Georgia.

l'lorcnce Griffith Joyner, Co-Chair, President's
C:ouncil on Physical Fitness and Sports, Washington,
D.C.

C. Thomas McMillen, Co-Chair, President's Council
on Physical Fitness and Sports, Washington, D.C.
5lmh-a P. Perlmutter, Executive Director, President's
Council on Physical Fitness and Sports, Washington,
D.C.

Editorial Board

Carl J. Caspersen, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Aaron R. Folsom, M.D., M.P.H., Professor, Division
of Epidemiology, School of Public Health, University
of Minnesota, Minneapolis, Minnesota.

vii


A Report of the Surgeon General

William L. Haskell, Ph.D., Professor of Medicine,
Stanford University, Palo Alto, California.

Arthur S. Leon, M.D., M.S., Henry L. Taylor Professor
and Director of the Laboratory of Physiological
Hygiene and Exercise Science, Division of Kinesiology,
University of Minnesota, Minneapolis, Minnesota.

James F. Sallis, Jr., Ph.D., Professor, Department of
Psychology, San Diego State University, San Diego,
California.

Martha L. Slattery, Ph.D., M.P.H., Professor,
Department of Oncological Sciences, University of
Utah Medical School, Salt Lake City, Utah.

Christine G. Spain, `M.A., Director, Research,
Planning, and Special Projects, President's Council
on Physical Fitness and Sports, Washington, D.C.

Jack H. Wilmore, Ph.D., Professor, Department of
Kinesiology and Health Education, University of
Texas at Austin, Austin, Texas.

Planning Board

Terry L. Bazzarre, Ph.D., Science Consultant,
American Heart Association, Dallas, Texas.

Steven N. Blair, P.E.D., Senior Scientific Editor,
Director of Research and Director, Epidemiology and
Clinical Applications, The Cooper Institute for
Aerobics Research, Dallas, Texas.

Willis R. Foster, M.D., Office of Disease Prevention
and Technology Transfer, National Institute of
Diabetes and Digestive and Kidney Diseases, National
Institutes of Health, Bethesda, Maryland.

Patty Freedson, Ph.D., Department of Exercise
Science, University of Massachusetts, Amherst,
Massachusetts. Represented the American Alliance
for Health, Physical Education, Recreation and Dance.

William R. Harlan, M.D., Associate `Director for
Disease Prevention, Office of the Director, National
Institutes of Health, Bethesda, Maryland.

James A. Harrell, M.A., Deputy Commissioner,
Administration on Children, Youth, and Families,
(formerly, Deputy Director, Office of Disease
Prevention and Health Promotion, Office of the
Assistant Secretary for Health, Department of Health
and Human Services), Washington, D.C.

Richard W. Lymn, Ph.D., Muscle Biology Branch,
National Institute of Arthritis and Musculoskeletal
and Skin Diseases, National Institutes of Health,
Bethesda, Maryland.

Russell R. Pate, Ph.D., Chairman, Department of
Exercise Science, University of South Carolina,
Columbia, South Carolina. Represented the American
College of Sports Medicine.

Sandra P. Perlmutter, Executive Director, President's
Council on Physical FitnessandSports, Washington,
D.C.

Bruce G. Simons-Morton, Ed.D., M.P.H., Behavioral
Scientist, Prevention Research Branch, National
Institute of Child Health and Human Development,
National Institutes of Health, Bethesda, Maryland.

Denise G. Simons-Morton, M.D., Ph.D., Leader,
Prevention Scientific Research Group, DECA,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

Contributing Authors

Lynda A. Anderson, Ph.D., Public Health Educator,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Carol C. Ballew, Ph.D., Epidemiologist, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Jack W. Berryman, Ph.D., Professor, Department of
Medical History and Ethics, School of Medicine,
University of Washington, Seattle, Washington.

Lawrence R. Brawley, Ph.D., Professor, University of
Waterloo, Ontario, Canada.

David R. Brown, Ph.D., Health Scientist, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

.
VIII


Physical Activity and Health

Lee S. CupIan, M.D., Ph.D., Medical Epidemiologist,
Epidcruiology and Statistics Branch, Division of
C&lnccr prevention and Control, National Center for
Cllronic Disease Prevention and Health Promotion,
Ccntcrs for Disease Control and Prevention, Atlanta,
Georgia.

R,+h J. Coatcs, Ph.D., Chief, Epidemiology Section,
Division of Cancer Prevention and Control, National
ccntcr for Chronic Disease Prevention and Health
f'romotion, Centers for Disease Control and
frcvcntion, Atlanta, Georgia.

C,lrlos J. Crespo, Dr.P.H., M.S., F.A.C.S.M., Public
flculth Analyst, National Heart, Lung, and Blood
Itlstitutc, National Institutes of Health, Bethesda,
Xlaryland.

I.orctta DiPietro, Ph.D., M.P.H., Assistant Fellow
and Assistant Professor of Epidemiology and
I'ublic Health, The John B. Pierce Laboratory and
Y;IIC University School of Medicine, New Haven,
(;onnccticut.

124 K. Dishman, Ph.D., Professor, Department of
f:scrcisc Science, University of Geoigia, Athens,
Georgia.

Michael M. Engelgau, M.D., Chief, Epidemiology
:~nd Statistics Branch, Division of Diabetes
Translation, National Center for Chronic Disease
I'rcvcntionand Health Promotion, Centers for Disease
(:ontrol and Prevention, Atlanta, Georgia.

\Valtcr H. Ettinger, M.D., Professor, Internal Medicine
and Public Health Sciences, Bowman Gray School of
Medicine, Winston-Salem, North Carolina.

David S. Freedman, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Frederick Fridinger, Dr.P.H., C.H.E.S.., Public Health
Educator, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for
Disease Control and Prevention, Atlanta, Georgia.

Gregory W. Heath, D.Sc., M.P.H., Epidemiologist/
Exercise Physiologist, Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Wendy A. Holmes, M.S., Health Communications
Specialist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for
~Disease Control and Prevention, Atlanta, Georgia.

Elizabeth H. Howze, Sc.D., Associate Director for
Health Promotion, Division* of Nutrition and
Physical Activity, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Laura K. Kann, Ph.D., Chief, Surveillance Research
Section, Division of Adolescent and School Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Abby C. King, Ph.D., Assistant Professor of Health
Research and Policy and Medicine, Stanford
University School of Medicine, Palo Alto, California.

Harold W. Kohl, III, Ph.D., Director of Research,
Baylor College of Medicine, Baylor Sports Medicine
Institute, Houston, Texas.

Jeffrey P. Koplan, M.D., M.P.H., President, Prudential
Center for Health Care Research, Atlanta, Georgia.

Andrea M. Kriska, Ph.D., M.S., Assistant Professor,
Department of Epidemiology, Graduate School of
Public Health, University of Pittsburgh, Pittsburgh,
Pennsylvania.

Barbara D. Latham, R.D., M.P.H., Public Health
Nutritionist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for
Disease Control and Prevention, Atlanta, Georgia.

I-Min Lee, M.B.B.S., Sc.D., Assistant Professor
of Medicine, Harvard Medical School, Boston,
Massachusetts.

ix


A Report of the Surgeon General

Elizabeth Lloyd, M.S., Statistician, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Bess H. Marcus, Ph.D., Associate Professor of
Psychiatry and Human Behavior, Division of Behavior
and Preventive Medicine, Miriam Hospital and Brown
University School of Medicine, Providence, Rhode
Island.

DyannMatson-Koffman,Dr.P.H.,M.P.H., C.H.E.S.,
Public Health Educator, Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease ControI and Prevention, Atlanta,
Georgia.

Marion R. Nadel, Ph.D., Epidemiologist, Epidemiology
and Statistics Branch, Division of Cancer Prevention
and Control, National Center for Chronic Disease
Preventionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Eva Obarzanek, Ph.D., M.P.H., R.D., Nutritionist,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

Christine M. Plepys, M.S., Health Statistician, Division
of Health Promotion Statistics, National Center for
Health Statistics, Centers for Disease Control and
Prevention, Hyattsville, Maryland.

Michael L. Pollock, Ph.D., Professor of Medicine,
Physiology and Health and Human Performance;
Director, Center for Exercise Science, University of
Florida, Gainesville, Florida.

Michael Pratt, M.D., M.P.H., Medical Epidemiologist,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Paul T. Raford;M.D., M.P.H.,Special Assistant to the
Regional Health Administrator, Environmental
Justice Programs, Office of Public Health Science,
Region VIII, Department of Health and Human
Services, U.S. Public Health Service, Denver,
Colorado.

W. Jack Rejeski, Ph.D., Professor, Health and Sports
Science, Wake Forest University, Winston-Salem,
North Carolina.

Richard B. Rothenberg, M.D., M.P.H., F.A.C.P.,
Professor and Director, Preventive Medicine
Residency Program, Department of Family and
Preventive Medicine, Emory University School of
Medicine, Atlanta, Georgia.

Mary K. Serdula, M.D., M.P.H., Acting Branch Chief,
Chronic Disease Prevention Branch, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Charlotte A. Schoenborn, M.P.H., Health Statistician,
National Center for Health Statistics, Centers for
Disease Control and Prevention, Hyattsville,
Maryland.

Denise G. Simons-Morton, M.D., Ph.D., Leader,
Prevention Scientific Research Group, DECA,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

Elaine J. Stone, Ph.D., M.P.H., Health Scientist
Administrator, Division of Epidemiology and Clinical
Applications, National Heart, Lung, and Blood
Institute, National Institutes of Health, Bethesda,
Maryland.

Marlene K. Tappe, Ph.D., Visiting Behavioral
Scientist, Division of Adolescent and School Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Wendell C. Taylor, Ph.D., M.P.H., Assistant Professor
of Behavioral Sciences, School of Public Health,
University of Texas Health Science Center at Houston,
Houston, Texas.

CharlesW. Warren, Ph.D., Statistician/Demographer,
Division of Adolescent and School Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Deborah R. Young, Ph.D., Assistant Professor of
Medicine, Division of Internal Medicine, The Johns
Hopkins School of Medicine, Baltimore, Maryland.

X


Physical Activity and Health

Senior Reviewers

Elizabeth A. Arendt, M.D., Associate Professor of
Orthopaedics, University of Minnesota, Minneapolis,
>jtnnesota. Member, President's Councilon Physical
Fitness and Sports.

Elsworth R. Buskirk, Ph.D., Professor of Applied
Physiology, Emeritus, Pennsylvania State University,
University Park, Pennsylvania.

B. Don Franks, Ph.D., Professor and Chair,
Department of Kinesiology, Louisiana State
University, Baton Rouge, Louisiana. Senior Program
Advisor, President's Council on Physical Fitness
and Sports.

\Villiam R. Harlan, M.D., Associate Director for
Disease Prevention, Office of the Director, National
Institutes of Health, Bethesda, Maryland.

William P. Morgan, Ed.D., Professor, Department of
Kincsiology, University of Wisconsin-Madison,
Madison, Wisconsin.

Ralph S. Paffenbarger,Jr., M.D., Dr.P.H., Professor of
Epidemiology (Retired-Active), Stanford University
School of Medicine, Stanford, California.

Russell R. Pate, Ph.D., Chairman, Department of
Escrcise Science, University of South Carolina,
cIolumbia,SouthCarolina. Represented the American
(:ollcge of Sports Medicine.

Roy J. Shephard, M.D., Ph.D., D.P.E., F.A.C.S.M.,
Professor EmeritusofApplied Physiology, University
of Toronto, Toronto, Canada.

Peer Reviewers

Barbara E. Ainsworth, Ph.D., M.P.H., Associate
Professor, Department of Epidemiology and
Biosratistics, Department ofExercise Science, School
of Public Health, University of South Carolina,
Columbia, South Carolina.

Tom Baranowski, Ph.D., Professor, Department of
Behavioral Science, University of Texas, M. D.
.-\nderson Cancer Center, Houston, Texas.

Oded Bar-Or, M.D., Professor of Pediatrics and
Director, Children's Exercise and Nutrition Centre,
McMaster University, Chedoke Hospital Division,
Hamilton, Ontario, Canada.

Charles B. Corbin, Ph.D., Professor, Department of
Exercise Science and Physical Education, Arizona
State University, Tempe, Arizona.

Kirk J. Cureton, Ph.D., Professor and Head,
Department of Exercise Science, University of
Georgia, Athens, Georgia.

Gail P. Dalsky, Ph.D., Assistant Professor ofMedicine
(in residence), University of Connecticut Health
Center, Farmington, Connecticut.

Nicholas A. DiNubile, M.D., Clinical Assistant
Professor, Department of Orthopaedic Surgery,
Hospital of the University of Pennsylvania; Chief,
Orthopaedic Surgery and Sports Medicine, Delaware
County Memorial Hospital, Drexel Hill, Pennsylvania.

BarbaraL. Drinkwater, Ph.D., Research Physiologist,
Pacific Medical Center, Seattle, Washington.

Andrea L. Dunn, Ph.D., Associate Director, Division
of Epidemiology and Clinical Applications, The
Cooper Institute for Aerobics Research, Dallas, Texas.

Leonard H. Epstein, Ph.D., Professor, Department of
Psychology, State University of New York at Buffalo,
Buffalo, New York.

Katherine M. Flegal, Ph.D., Senior Research
Epidemiologist, National Center for Health Statistics,
Centers for Disease Control and Prevention,
Hyattsville, Maryland.

Christopher D. Gardner, Ph.D., Research Fellow,
Stanford Center for Research in Disease Prevention,
Stanford University, Palo Alto, California.

Glen G. Gilbert, Ph.D., Professor and Chairperson,
Department of Health Education, University of
Maryland, College Park, Maryland.

Andrew P. Goldberg, M.D., Professor of Medicine
and Director, Division of Gerontology, University of
Maryland School of Medicine, Baltimore, Maryland.

John 0. Holloszy, M.D., Professor of Internal
Medicine, Washingtonuniversity SchoolofMedicine,
St. Louis, Missouri.

Melbourne F. Hovell, Ph.D., M.P.H., Professor of
Health Promotion; Director, Center for Behavioral
Epidemiology, Graduate School of Public Health,
College of Health and Human Services, San Diego
State University, San Diego, California.

xi


A Report of the Surgeon General

Caroline A. Macera, Ph.D., Director, Prevention
Center, School of Public Health, University of South
Carolina, Columbia, South Carolina.

JoAnn E. Manson, M.D., Dr.P.H., Co-Director of
Women's Health, Brigham and Women's Hospital,
Harvard Medical School, Boston, Massachusetts.

Jere H. Mitchell, M.D., Professor of Internal Medicine
and Physiology; Director, Harry S. Moss Heart Center,
University of Texas Southwestern Medical Center,
Dallas, Texas.

James R. Morrow, Jr., Ph.D., Professor and Chair,
Department of KHPR, University of North Texas,
Denton, Texas.

Neville Owen, Ph.D., Professor of Human Movement
Science, Deakin University, Melbourne, Australia.
Roberta J. Park, Ph.D., Professor of the Graduate
School, University of California, Berkeley, California.

Peter B. Raven, Ph.D., Professor and Chair,
Department of Integrative Physiology, University of
North Texas Health Science Center, Fort Worth,
Texas.

Judith G. Regensteiner, Ph.D., Associate Professor of
Medicine, University of Colorado Health Sciences
Center, Denver, Colorado.

Bruce G. Simons-Morton, Ed.D., M.P.H., Behavioral
Scientist, Prevention Research Branch, National
Institute of Child Health and Human Development,
National Institutes of Health, Bethesda, Maryland.

Denise G. Simons-Morton, M.D., Ph.D., Leader,
Prevention Scientific Research Group, DECA,
National Heart, Lung, and Blood Institute, National
Institutes of Health, Bethesda, Maryland.

James S. Skinner, Ph.D., Professor, Department of
Kinesiology, Indiana University, Bloomington,
Indiana.

Thomas Stephens, Ph.D., Principal, Thomas Stephens
and Associates, Ottawa, Canada.

Anita Stewart, Ph.D., Associate Professor in
Residence, University of California, San Francisco,
San Francisco, California.

C. Barr Taylor, M.D., Professor of Psychiatry,
Department of Psychiatry and Behavioral Sciences,
Stanford University School of Medicine, Stanford,
California.

Charles M. Tipton, Ph.D., F.A.C.S.M., Professor of
Physiology and Surgery, University of Arizona,
Tucson, Arizona.

Zung Vu Tran, Ph.D., Senior Research Scientist,
Center for Research in Ambulatory Health Care
Administration, Englewood, Colorado.

Other Contributors

Melissa M. Adams, Ph.D., Assistant Director for
Science, Division of Reproductive Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Indu Ahluwalia, M.P.H., Ph.D., EISOfficer, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Betty A. Ballinger, Technical Information Specialist,
Technical Information and Editorial Services Branch,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Sandra W. Bart, Policy Coordinator, Office of the
Secretary, Executive Secretariat, Department of
Health and Human Services, Washington, D.C.

Mary Bedford, Proofreader, Cygnus Corporation,
Rockville, Maryland.

Caryn Bern, M.D., Medical Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Karil Bialostosky, M.S., Nutrition Fellow, National
Center for Health Statistics, Centers for Disease
Control and Prevention, Hyattsville, Maryland.

xii


Physical Activity and Health

Thomas E. Blakeney, Program Analyst, National
Center for Injury Prevention and Control, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Ronctte R. Briefel, Dr.P.H.. Nutrition Policy Advisor,
National Center for Health Statistics, Centers for
Disease Control and Prevention, Hyattsville,
htaryland.

L. Diane Clark, M.P.H., Public Health Nutritionist,
Division of Nutrition and Physical Activity, National
Ccntcr for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

jancl L. Coil' Ins, Ph.D., Chief, Surveillance and
Evaluation Research Branch, Division of Adolescent
and School Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Janet B. Croft, Ph.D.,Epidemiogist,DivisionofAdult
;tnd Community Health, National Center for Chronic
Discasc Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Ann M. Cronin, Program Analyst, National Institute
for Occupational Safety and Health, Centers for
Discase Control and Prevention, Atlanta, Georgia.

(iail A. Cruse, M.L.I.S., Technical Information
Specialist, Technical Information and Editorial
Scrviccs Branch, National Center for Chronic Disease
Prcventionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

John M. Davis, M.P.A., R.D., Public Health Analyst,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Earl S. Ford, M.D., M.P.H., Senior Scientist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Christine S. Fralish, M.L.I.S., Chief, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Emma L. Frazier, Ph.D., Mathematical Statistician,
Division of Diabetes Translation, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Deborah A. Galuska, M.P.H., Ph.D., EIS Fellow,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Dinamarie C. Garcia, M.P.H., C.H.E.S., Intern,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Linda S. Geiss, M.A., Health Statistician, Division of
Diabetes Translation, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Wayne H. Giles, M.D., M.S., Epidemiologist,
Cardiovascular Health Section, Division of Adult
and Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Kay Sissions Golan, Public Affairs Specialist, Office
of Communication (proposed), Centers for Disease
Control and Prevention, Atlanta, Georgia.

Betty H. Haithcock, Editorial Assistant, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Helen P. Hankins, Writer-Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

. . .
XIII


A Report of the Surgeon General

Rita Harding, Graphic Designer, Cygnus Corporation,
Rockville, Maryland.

William A. Harris, M.M., Computer Specialist,
Division of Adolescent and School Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Charles G. Helmick, III, M.D., Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Elizabeth L. Hess, Technical Editor, Cygnus
Corporation, Rockville, Maryland.

Mary Ann Hill, M.P.P., Director of Communications,
President's Council on Physical Fitness and Sports,
Washington, D.C.

Thomya L. Hogan, Proofreader, Cygnus Corporation,
Rockville, Maryland.

Judy F. Horne, Technical Information Specialist,
Technical Information and Editorial ServicesBranch,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Catherine A. Hutsell, M.P.H., Public Health Educator,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Robert Irwin, Special Assistant, Office of the Director,
Centers for Disease Control and Prevention,
Washington, D.C.

Sandra E. Jewell, MS., Statistician, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Loretta G. Johnson, Secretary, Division of Nutrition
and Physical Activity, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Deborah A. Jones, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Wanda K. Jones, M.P.H., Dr.P.H., Associate Director
for Women's Health, Office of Women's Health,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Robert E. Keaton, Consultant, Cygnus Corporation,
Rockville, Maryland.

Delle B. Kelley, Technical Information Specialist,
Technical Information and Editorial ServicesBranch,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Mescal J. Knighton, Writer-Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Sarah B. Knowlton, J.D., M.S.W., Attorney Advisor,
Office of the General Council, Centers for Disease
Control and Prevention, Atlanta, Georgia.

FredKroger,ActingDirector,HealthCommunication,
Office of Communication (proposed), Centers for
Disease Control and Prevention, Atlanta, Georgia.

Sarah A. Kuester, M.P.H., R.D., Public Health
Nutritionist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Becky H. Lankenau, M.S., R.D., M.P.H., Dr.P.H.,
Public Health Nutritionist, Division of Nutrition and
Physical Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Nancy C. Lee, M.D., Associate Director for Science,
Division of Cancer Prevention and Control, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

xiv


Physical Activity and Health

Leandris C. Liburd, M.P.H., Public Health Educator,
Division of Diabetes Translation, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Richard Lowry, M.D., M.S., Medical Epidemiologist,
Division of Adolescent and School Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Salvatore J. Lucido, M.P.A., Program Analyst,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta,, Georgia.

Gene W. Matthews, Esq., Legal Advisor to CDC and
ATSDR, Office of the General Council, Centers for
Disease Control and Prevention, Atlanta, Georgia.

Urcnda W. Mazzocchi, M.S.L.S., Technical
Information Specialist, Technical Information and
Editorial Services Branch, National Center for
Chronic Disease Prevention and Health Promotion,
Ccntcrs for Disease Control and Prevention, Atlanta,
(icorgia.

Sharon McDonnell, M.D., M.P.H., Medical
Ilpidcmiologist, Division of Nutrition and Physical
:\ctivity, National Center for Chronic Disease
I'rcvcntionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Michael A. McGeehin, Ph.D., M.S.P.H., Chief, Health
9udics Branch, Division of Environmental Hazards
and Health Effects, National Center for Environmental
1 icalth, Centers for Disease Control and Prevention,
Atlanta, Georgia.

ZU~UO Mei, M.D., M.P.H. Visiting Scientist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease . Control and
Prcvcntion, Atlanta, Georgia.

lames M. Mendlein, Ph.D., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
frcvenlion, Atlanta, Georgia.

Robert K. Merritt, M.A., Behavioral Scientist, Office
on Smoking and Health, National Center for Chronic
,Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta,
Georgia.

Gaylon D. Morris, M.P.P., Program Analyst, Office
of Program Planning and Evaluation, Centers for
Disease Control and Prevention, Atlanta, Georgia.

Melba Morrow, M.A., Division Manager, The Cooper
Institute for Aerobics Research, Dallas, Texas.

Marion R. Nadel, Ph.D., Epidemiologist, Division of
Cancer Prevention and Control, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

David E. Nelson, M.D., M.P.H., Medical Officer,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Reba A. Norman, M.L.M., Technical Information
Specialist, Technical Information and Editorial
Services Branch, National Center for Chronic Disease
Prevention andHealth Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Ward C. Nyholm, Graphic Designer, Cygnus
Corporation, Rockville, Maryland.

Stephen M. Ostroff, M.D., Associate Director for
Epidemiologic Science, National Center for Infectious
Diseases, Centers for Disease Control and Prevention,
Atlanta, Georgia.

Ibrahim Parvanta, MS., Acting Deputy Chief,
Maternal and Child Health Branch, Division of
Nutrition and Physical Activity, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Terry F. Pechacek, Ph.D., Visiting Scientist, Office
on Smoking and Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

xv


A Report of the Surgeon General

Geraldine S. Perry, Dr.P.H., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Todd M. Phillips, M.S., Deputy Project Director,
Cygnus Corporation, Rockville, Maryland.

Audrey L. Pinto, Writer-Editor, Technical
Information and Editorial Services Branch, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Kenneth E. Powell, M.D., M.P.H., Associate Director
for Science, Division of Violence Prevention, National
Center for Injury Prevention and Control, Centers
for Disease Control and Prevention, Atlanta,Georgia.

Julia H. Pruden, M.Ed., R.D., Public Health
Nutritionist, Division of Nutrition and Physical
Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

David C. Ramsey, M.P.H., Public Health Educator,
Division of Nutrition and Physical Activity, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Brenda D. Reed, Secretary, Division of Adult and
Community Health, National Center for Chronic
Disease Prevention and Health Promotion, Centers
for Disease Control and Prevention, Atlanta, Georgia.

Susan A. Richardson, Writer-Editor, Cygnus
Corporation, Rockville, Maryland.

Christopher Rigaux, Project Director, Cygnus
Corporation, Rockville, Maryland.

Angel Rota, Program Analyst, National Center for
Chronic Disease Prevention and Health Promotion,
Centers for Disease Control and Prevention, Atlanta,
Georgia.

Cheryl V. Rose, Computer Specialist, Division of
Health Promotion Statistics, National Center for
Health Statistics,. Centers for Disease Control and
Prevention, Hyattsville, Maryland.

Patti Schwartz, Graphic Designer, Cygnus Corporation,
Rockville, Maryland.

Bettylou Sherry, Ph.D., Epidemiologist, Maternal
and Child Health Branch, Division of Nutrition and
Physical Activity, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Margaret Leavy Small, Behavioral Scientist, Division
of Adolescent and School Health, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia

Joseph B. Smith, Senior Project Officer, Disabilities
Prevention Program, National Center for
Environmental Health, Centers for Disease Control
and Prevention, Atlanta, Georgia.

Terrie D. Sterling, Ph.D., Research Psychologist,
Division of Adult and Community Health, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Emma G. Stupp, M.L.S., Technical Information
Specialist, Technical Information and Editorial
ServicesBranch, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

William I. Thomas, M.L.I.S., Technical Information
Specialist, Technical Information and Editorial
Services Branch, National Center for Chronic Disease
Prevention and Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Patricia E. Thompson-Reid, M.A.T., M.P.H.,
Program Development Consultant/Community
Interventionist, Division of Diabetes Translation,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Jenelda Thornton, Staff Specialist, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

xvi


Physical Activity and Health

Nancy B. Watkins, M.P.H., Health Education
Specialist, Division of Adult and Community Health,
National Center for Chronic Disease Prevention and
Health Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Howell Wechsler, Ed.D., M.P.H., Health Education
Research Scientist, Division of Adolescent and School
Health, National Center for Chronic Disease
Preventionand Health Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

Julie C. Will, Ph.D., M.P.H., Epidemiologist, Division
of Nutrition and Physical Activity, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Lynda S. Williams, Program. Analyst, National
Center for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

David F. Williamson, Ph.D., Acting Director,
Division of Diabetes Translation, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia.

Stephen W. Wyatt, D.M.D., M.P.H., Director, Division
of Cancer Prevention and Control, National Center
for Chronic Disease Prevention and Health
Promotion, Centers for Disease Control and
Prevention, Atlanta, Georgia,

Matthew M. Zack, M.D.; M.P.H., Medical
Epidemiologist, Division of Adult and Community
Health, National Center for Chronic Disease
Prevention andHealth Promotion, Centers for Disease
Control and Prevention, Atlanta, Georgia.

xvii


PHYSICAL ACTIVITV AND HEALTH

Chapter 1: Introduction, Summary, and Chapter Conclusions   ....................... 1
Chapter 2: Historical Background, Terminology, Evolution of Recommendations
andbleasurement   .......................................................... 9

Western Historical Perspective  ............................................... .12
Terminology of Physical Activity, Physical Fitness, and Health  ..................... .2O
Evolution of Physical Activity Recommendations  .................................. 22
Summary of Recent Physical Activity Recommendations ........................... .28
Measurement of Physical Activity, Fitness, and Intensity  .......................... .29
Chapter 3: Physiologic Responses and Long-Term Adaptations to Exercise  ............ .61
Physiologic Responses to Episodes of Exercise  .................................. .61
Long-Term Adaptations to Exercise Training .................................... .67
Maintenance, Detraining, and Prolonged Inactivity  ............................... .71
Special Considerations  ..................................................... .73

Chapter 4: The Effects of Physical Activity on Health and Disease  ................... .81
Overall Mortality  ........................................................... .85

  Cardiovascular Diseases  .................................................... .87

  Cancer ................................................................ ..112
Non-Insulin-Dependent Diabetes Mellitus ..................................... .125

  Osteoarthritis                                                .129
                ................. , ..........................................
  Osteoporosis ........................................................... ..13 0
Obcsity..................................................................13 3
  McntalHealth .......................................................... ..13 5
  Health-Related Quality of Life ............................................... .141
  Adverse Effects of Physical Activity  .......................................... .142
  Occurrence of Adverse Effects  .............................................. .144
  Nature of the Activity/Health Relationship  ..................................... .144

Cllaptcr 5: Patterns and Trends in Physical Activity  ............................... 173
  Physical Activity among Adults in the United States  ............................. .177
Physical Activity among Adolescents and Young Adults in the United States  ........... 186

Chapter 6: Understanding and Promoting Physical Activity   ....................... ,209
  Theories and Models Used in Behavioral and Social Research on
   PhysicalActivity.. .................................................... ..211
  Behavioral Research on Physical Activity among Adults  .......................... .215
Behavioral Research on Physical Activity among Children and Adolescents  ........... .234
  Promising Approaches, Barriers, and Resources  ................................. .243
List of Tables and Figures   ................................................... .261

Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...265


        CHAPTER 1
INTRODUCTION, SUMMARY,
AND CHAPTER CONCLUSIONS

Contents

Introduction  ................................................................. 3
Development of the Report  ................................................... 3
MajorConclusions  ......................................................... 4

Summary . .._................................................,............._ 4

Chapter Conclusions  .......................................................... 6
Chapter 2: Historical Background and Evolution of Physical Activity Recommendations  . . 6
Chapter 3: Physiologic Responses and Long-Term Adaptations to Exercise  ............. 7
Chapter 4: The Effects of Physical Activity on Health and Disease  .................... 7
Chapter 5: Patterns and Trends in Physical Activity  ............................... 8
Chapter 6: Understanding and Promoting Physical Activity  ......................... 8


CHAPTER 1

htroduction

T his is the first Surgeon General's report to ad-
dress physical activity and health. The main
message of this report is that Americans can substan-
tially improve their health and quality of life by
including moderate amounts of physical activity in
their daily lives. Health benefits from physical activ-
ity arc thus achievable for most Americans, includ-
ing those who may dislike vigorous exercise and
those who may have been previously discouraged by
rhc difficulty of adhering to a program of vigorous
cscrcise. For those who are alreadyachievingregular
modcrate amounts of activity, additional benefits
c.an bc gained by further increases in activity level.
This report grew out of an emerging consensus
:~mong epidemiologists, experts in exercise science,
;1nc1 health professionals that physical activity need
not be of vigorous intensity for it to improve health.
Morcovcr, health benefits appear to be proportional
10 amount of activity; thus, every increase in activity
~lds some benefit. Emphasizing the amount rather
lhan the intensity of physical activity offers more
options for people to select from in incorporating
physical activity into their daily lives. Thus, a mod-
crate amount of activity can be obtained in a 30-
minute brisk walk, 30 minutes of lawn mowing or
raking leaves, a 1%minute run, or 45 minutes of
playing volleyball, and these activities can be varied
from day to day. It is hoped that this different
elnphasis on moderate amounts of activity, and the
ncsibility to vary activities according to personal
prcfcrcnce and life circumstances, will encourage
more people to make physical activity a regular and
sustainable part of their lives.

The information in this report summarizes a
diverse literature from the fields of epidemiology,
cscrcisc physiology, medicine, and the behavioral
sciences. The report highlights what is known about

INTRODUCTION, SUMMARY,
AND CHAPTER CONCLUSIONS

physical activity and health; as well as what is being
learned about promoting phjrsical activity among
adults and young people.

Development of the Report
In July 1994, the Office of the Surgeon General
authorized the Centers for Disease Control and Pre-
vention (CDC) to serve as lead agency for preparing
the first Surgeon General's report on physical activity
and health. The CDC was joined in this effort by the
President's Council on Physical Fitness and Sports
(PCPFS) as a collaborative partner representing the
Office of the Surgeon General. Because of the wide
interest in the health effects of physical activity, the
report was planned collaboratively with representa-
tives from the Office of the Surgeon General, the
Office of Public Health and Science (Office of the
Secretary), the Office of Disease Prevention (Na-
tional Institutes of Health [NIH]), and the following
institutes from the NIH: the National Heart, Lung,
and Blood Institute; the National Institute of Child
Health and Human Development; the National Insti-
tute of Diabetes and Digestive and Kidney Diseases;
and the National Institute of Arthritis and Muscu-
loskeletal and Skin Diseases. CDC's nonfederal part-
ners-indluding the American Alliance for Health,
Physical Education, Recreation, and Dance; the
American College of Sports Medicine; and the Ameri-
can Heart Association-provided consultation
throughout the development process.
The major purpose of this report is to summarize
the existing literature on the role of physical activity in
preventing disease and on the status of interventions to
increase physical activity. Any report on a topic this
broad must restrict its scope to keep its message clear.
This report focuses on disease prevention and there-
fore does not include the considerable body of evi-
dence on the benefits of physical activity for treatment or


Physical Activity and Health

rehabilitation after disease has developed. This report
concentrates on endurance-type physical activity (ac-
tivity involving repeated use of large muscles, such as
in walking or bicycling) because the health benefits of
this type of activity have been extensively studied. The
importance of resistance exercise (to increase muscle
strength, such as by lifting weights) is increasingly
being recognized as a means to preserve and enhance
muscular strength and endurance and to prevent falls
and improve mobility in the elderly. Some promising
findings on resistance exercise are presented here, but
a comprehensive review of resistance training is be-
yond the scope of this report. In addition, a review of the
special concerns regarding physical activity for preg-
nant women and for people with disabilities is not
undertaken here, although these important topics de-
serve more research and attention.
Finally, physical activity is only one of many every-
day behaviors that affect health. In particular, nutri-
tional habits are linked to some of the same aspects of
health as physical activity, and the two may be related
lifestyle characteristics. This report deals solely with
physical activity; a Surgeon General's Report on Nutri-
tion and Health was published in 1988.
  Chapters 2 through 6 of this report address dis-
tinct areas of the current understanding of physical
activity and health. Chapter 2 offers a historical per-
spective: after outlining the history of belief and
knowledge about physical activity and health, the
chapter reviews the evolution and content of physical
activity recommendations. Chapter 3 describes the
physiologic responses to physical activity-both the
immediate effects of a single episode of activity and the
long-term adaptations to a regular pattern of activity.
The evidence that physical activity reduces the risk of
cardiovascular and other diseases is presented in
Chapter 4. Data on patterns and trends of physical
activity in the U.S. population are the focus of Chapter
5. Lastly, Chapter 6 examines efforts to increase
physical activity and reviews ideas currently being
proposed for policy and environmental initiatives.

Major Conclusions
1. People of all ages, both male and female, benefit
from regular physical activity.
2. Significant health benefits can be obtained by
including a moderate amount of physical activity
(e.g., 30 minutes of brisk walking or raking

3.

4.

5.

6.

7.

leaves, 15 minutes of running, or 45 minutes of
playing volleyball) on most, if not all, days of the
week. Through a modest increase in daily activity,
most Americans can improve their health and
quality of life.

Additional health benefits can be gained through
greater amounts of physical activity. People who
can maintain a regular regimen of activity that is
of longer duration or of more vigorous intensity
are likely to derive greater benefit.
Physical activity reduces the. risk of premature
mortality in general, and of coronary heart dis-
ease, hypertension, colon cancer, and diabetes
mellitus in particular. Physical activity also im-
proves mental health and is important for the
health of muscles, bones, and joints.
More than 60 percent of American adults are not
regularly physically active. In fact, 25 percent of
all adults are not active at all.
Nearly half of American youths 12-21 years of age
are not vigorously active on a regular basis. More-
over, physical activity declines dramatically dur-
ing adolescence.

Daily enrollment in physical education classes
has declined among high school students from 42
percent in 1991 to 25 percent in 1995.

8. Research on understanding and promotingphysi-
cal activity is at an early stage, but some interven-
tions to promote physical activity through schools,
worksites, and health care settings have been
evaluated and found to be successful.

Summary

The benefits of physical activity have been extolled
throughout western history, but it was not until the
second half of this century that scientific evidence
supporting these beliefs began to accumulate. By the
1970s enough information was available about the
beneficial effects of vigorous exercise on cardiorespi-
ratory fitness that the American College of Sports
Medicine (ACSM), the American Heart Association
(AHA), and other national organizations began issu-
ing physical activity recommendations to the public.
These recommendations generally focused on car-
diorespiratory endurance and specified sustained
periods of vigorous physical activity involving large
muscle groups and lasting at least 20 minutes on 3 or

4


more days per week. As understanding of the ben-
efitsoflessvigorousactivitygrew, recommendations
followed suit. During the past few years, the ACSM,
the CDC, the AHA, the PCPFS, and the NIH have all
recommended regular, moderate-intensity physical
activity as an option for those who get little or no
exercise. The Healthy Peopfe2OOOgoals for the nation's
health have recognized the importance of physical
activity and have included physical activity goals.
The 1995 Dietary Guidelinesfor Americans, the basis
of the federal government's nutrition-related pro-
grams, included physical activity guidance to main-
tain and improve weight-30 minutes or more of
moderate-intensity physical activity on all, or most,
days of the week.

Underpinning such recommendations is a grow-
ing understanding of how physical activity affects
physiologic function. The body-responds to physical
activity in ways that have important positive effects
on musculoskeletal, cardiovascular, respiratory, and
endocrine systems. These changes are consistent
with a number of health benefits, including a re-
duced risk of premature mortality and reduced risks
of coronary heart disease, hypertension, colon can-
cer, and diabetes mellitus. Regular participation in
physical activity also appears to reduce depression
and anxiety, improve mood, and enhance ability to
perform daily tasks throughout the life span.
The risks associated with physical activity must
also be considered. The most common health prob-
lems that have been associated with physical activity
are musculoskeletal injuries, which can occur with
excessive amounts of activity or with suddenly be-
ginning an activity for which the body is not condi-
tioned. Much more serious associated health
problems (i.e., myocardial infarction, sudden death)
are also much rarer, occurring primarily among
sedentary people with advanced atherosclerotic dis-
ease who engage in strenuous activity to which they
are unaccustomed. Sedentary people, especially those
with preexisting health conditions, who wish to
increase their physical activity should therefore
gradually build up to the desired level of activity.
Even among people who are regularly active, the risk
of myocardial infarction or sudden death is some-
what increased during physical exertion, but their
overall risk of these outcomes is lower than that
among people who are sedentary.

Introduction, Summary, and Chapter Conclusions

  Research on physical activity continues to evolve.
This report includes both well-established findings
and newer research results that await replication and
amplification. Interest has been developing in ways
to differentiate between the various characteristics of
physical activity that improve health. It remains to be
determined how the interrelated characteristics of
amount, intensity, duration, frequency, type, and
pattern of physical activity are related to specific
health or disease outcomes.

Attention has been drawn recently to findings
from three studies showing `that cardiorespiratory
fitness gains are similar when physical activity oc-
curs in several short sessions (e.g., 10 minutes) as
when the same total amount and intensity of activity
occurs in one longer session (e.g., 30 minutes).
Although, strictly speaking, the health benefits of
such intermittent activity have not yet been demon-
strated, it is reasonable to expect them to be similar
to those of continuous activity. Moreover, for people
who are unable to set aside 30 minutes for physical
activity, shorter episodes are clearly better than none.
Indeed, one study has shown greater adherence to a
walking program among those walking several times
per day than among those walking once per day,
when the total amount of walking time was kept the
same. Accumulating physical activity over the course
of the day has been included in recent recommenda-
tions from the CDC and ACSM, as well as from the
NIH Consensus Development Conference on Physi-
cal Activity and Cardiovascular Health.
Despite common knowledge that exercise is
healthful, more than 60 percent of American adults
are not regularly active, and 25 percent of the adult
population are not active at all. Moreover, although
many people have enthusiastically embarked on vig-
orous exercise programs at one time or another, most
do not sustain their participation. Clearly, the pro-
cesses of developing and maintaining healthier hab-
its are as important to study as the health effects of
these habits.

The effort to understand how to promote more
active lifestyles is of great importance to the health of
this nation. Although the study of physical activity
determinants and interventions is at an early stage,
effective programs to increase physical activity have
been carried out in a variety of settings, such as
schools, physicians' offices, and worksites. Determin-
ing the most effective and cost-effective intervention

5


Physical Activity and Health

approaches is a challenge for the future. Fortu-
nately, the United States has skilled leadership and
institutions to support efforts to encourage and
assist Americans to become more physically active.
Schools, community agencies, parks, recreational
facilities, and health clubs are available in most
communities and can be more effectively used in
these efforts.

School-based interventions for youth are particu-
larly promising, not only for their potential scope-
almost all young people between the ages of 6 and 16
years attend school-but also for their potential im-
pact. Nearly half of young people 12-21 years of age
are not vigorously active; moreover, physical activity
sharply declines during adolescence. Childhood and
adolescence may thus be pivotal times for preventing
sedentary behavior among adults by maintaining the
habit of physical activity throughout the school years.
School-based interventions have been shown to be
successful in increasing physical activity levels. With
evidence that success in this arena is possible, every
effort should be made to encourage schools to require
daily physical education in each grade and to promote
physical activities that can be enjoyed throughout life.
  Outside the school, physical activity programs
and initiatives face the challenge of a highly techno-
logical society that makes it increasingly convenient
to remain sedentary and that discourages physical
activity in both obvious and subtle ways. To increase
physical activity in the general population, it may be
necessary to go beyond traditional efforts. This re-
port highlights some concepts from community
initiatives that are being implemented around the
country. It is hoped that these examples will spark
new public policies and programs in other places as
well. Special efforts will also be required to meet the
needs of special populations, such as people with
disabilities, racial and ethnic minorities, people with
low income, and the elderly. Much more informa-
tion about these important groups w-ill be necessary
to develop a truly comprehensive national initiative
for better health through physical activity. Chal-
lenges for the future include identifying key deter-
minants of physically active lifestyles among the
diverse populations that characterize the United
States (including special populations, women, and
young people) and using this information to design
and disseminate effective programs.

Chapter Conclusions
Chapter 2: Historical Background and
Evolution of Physical Activity
Recommendations

1.

Physical activity for better health and well-being
has been an important theme throughout much
of western history.

2.

Public health recommendations have evolved
from emphasizing vigorous activity for cardio-
respiratory fitness to including the option of
moderate levels of activity for numerous health
benefits.

3.

Recommendations from experts agree that for
better health, physical activity should be per-
formed regularly. The most recent recommenda-
tions advise people of all ages to include a
minimum of 30 minutes of physical activity of
moderate intensity (such as brisk walking) on
most, if not all, days of the week. It is also
acknowledged that for most people, greater health
benefits can be obtained by engaging in physical
activity of more vigorous intensity or of longer
duration.

4.

Experts advise previously sedentary people em-
barking on a physical activity program to start
with short durations of moderate-intensity activ-
ity and gradually increase the duration or inten-
sity until the goal is reached.

5.

6

Experts advise consulting with a physician before
beginning a new physical activity program for
people with chronic diseases, such as cardiovas-
cular disease and diabetes mellitus, or for those
who are at high risk for these diseases. Experts
also advise men over age 40 and women over age
50 to consult a physician before they begin a
vigorous activity program.
Recent recommendations from experts also sug-
gest that cardiorespiratory endurance activity
should be supplemented with strength-devel-
oping exercises at least twice per week for
adults, in order to improve musculoskeletal
health, maintain independence in performing
the activities of daily life, and reduce the risk of
falling.

6


Introduction, Summary, and Chapter Conclusions

Chapter 3: Physiologic Responses and Long-
Term Adaptations to Exercise

Physical activity has numerous beneficial physi-
ologic effects. Most widely appreciated are its
effects on the cardiovascular and musculoskel-
eta1 systems, but benefits on the functioning of
metabolic, endocrine, and immune systems are
also considerable.

Many of the beneficial effects of exercise training-
from both endurance and resistance activities-
diminish within 2 weeks if physical activity is
substantially reduced, and effects disappear within
2 to 8 months if physical activity is not resumed.

,. People of all ages, both male and female, undergo
beneficial physiologic adaptations to physical
activity.

Chapter 4: The Effects of Physical Activity
on Health and Disease

Overall Mortality
I. Higher levels of regular physical activity are asso-
ciated with lower mortality rates for both older
and younger adults.
2. Even those who are moderately active on a regu-
lar basis have lower mortality rates than those
who are least active.

Cardiovascular Diseases
1. Regular physical activity or cardiorespiratory fit-
ncss decreases the risk of cardiovascular disease
mortality in general and of coronary heart disease
mortality in particular. Existing data are not con-
clusive regarding a relationship between physical
activity and stroke.

1. The level of decreased risk of coronary heart
disease attributable to regular physical activity is
similar to that of other lifestyle factors, such as
keeping free from cigarette smoking.
3. Regular physical activity prevents or delays the
development of high blood pressure, and exer-
cise reduces blood pressure in people with
hypertension.

Cancer

1. Regular physical activity is associated with a
decreased risk of colon cancer.

2.








3.

There is no association between physical activity
and rectal cancer. Data are too sparse to draw
conclusions regarding a relationship between
physical activity and endometrial, ovarian, or
testicular cancers.

Despite numerous studies on the subject, exist-
ing data are inconsistent regarding an association
between physical activity and breast or prostate
cancers.

Non-Insulin-Dependent Diahefes Mellifus
1.) Regular physical activity lowers the risk of devel-
oping non-insulin-dependent diabetes mellitus.

Osteoarthritis

1. Regular physical activity is necessary for main-
taining normal muscle strength, joint structure,
and joint function. In the range recommended for
health, physical activity is not associated with
joint damage or development of osteoarthritis
and may be beneficial for many people with
arthritis.

2. Competitive athletics may be associated with the
development of osteoarthritis later in life, but
sports-related injuries are the likely cause.

Osteoporosis
1.






2.

Weight-bearing physical activity is essential for
normal skeletal development during childhood
and adolescence and for achieving and maintain-
ing peak bone mass in young adults.
It is unclear whether resistance- or endurance-
type physical activity can reduce the accelerated
rate of bone loss in postmenopausal women in the
absence of estrogen replacement therapy.

Falling

1. There is promising evidence that strength train-
ing and other forms of .exercise in older adults
preserve the ability to maintain independent liv-
ing status and reduce the risk of falling.

Obesif y
1. Low levels of activity, resulting in fewer kilocalo-
ries used than consumed, contribute to the high
prevalence of obesity in the United States.
2. Physical activity may favorably affect body fat
distribution.


Physical Activity and Health

Mental Health

1. Physical activity appears to relieve symptoms of
depression and anxiety and improve mood.
2. Regular physical activity may reduce the risk of
developing depression, although further research
is needed on this topic.

Health-Related Qualify of Life
1. Physical activity appears to improve health-re-
lated quality of life by enhancing psychological
well-being and by improving physical function-
ing in persons compromised by poor health.

Adverse Effects
1. Most musculoskeletal injuries related to physical
activity are believed to be preventable by gradu-
ally working up to a desired level of activity and
by avoiding excessive amounts of activity.
2. Serious cardiovascular events can occur with
physical exertion, but the net effect of regular
physical activity is a lower risk of mortality from
  cardiovascular disease.

Chapter 5: Patterns and Trends
in Physical Activity
Adults

1. Approximately 15 percent of U.S. adults engage
regularly (3 times a week for at least 20 minutes)
in vigorous physical activity during leisure time.
2. Approximately 22 percent of adults engage regu-
larly (5 times a week for at least 30 minutes) in
sustained physical activity of any intensity dur-
ing leisure time.

3. About 25 percent of adults report no physical
activity at all in their leisure time.
4. Physical inactivity is more prevalent amongwomen
than men, among blacks and Hispanics than whites,
among older than younger adults, and among the
less affluent than the more affluent.

5. The most popular leisure-time physical activities
among adults are walking and gardening or yard
work.

Adolescents and Young Adults
1. Only about one-half of U.S. young people (ages
12-21 years) regularly participate in vigorous
physical activity. One-fourth report no vigorous
physical activity.

2. Approximately one-fourth of young people walk
or bicycle (i.e., engage in light to moderate activ-
ity) nearly every day.

3. About 14 percent of young people report no
recent vigorous or light-to-moderate physical
activity. This indicator of inactivity is higher
among females than males and among black
females than white females.

4. Males are more likely than females to participate
in vigorous physical activity, strengthening ac-
tivities, and walking or bicycling.
5. Participation in all types of physical activity de-
clines strikingly as age or grade in school increases.
6. Among high school students, enrollment in physi-
cal education remained unchanged during the
first half of the 1990s. However, daily attendance
in physical education declined from approxi-
mately 42 percent to 25 percent.
7. The percentage of high school students who were
enrolled in physical education and who reported
being physically active for at least 20 minutes in
physical education classes declined from approxi-
mately 81 percent to 70 percent during the first
  half of this decade.

8. Only 19 percent of all high school students report
being physically active for 20 minutes or more in
daily physical education classes.

Chapter 6: Understanding and
Promoting Physical Activity
1. Consistent influences on physical activity pat-
terns among adults and young people include
confidence in one's ability to engage in regular
physical activity (e.g., self-efficacy), enjoyment
of physical activity, support from others, positive
beliefs concerning the benefits of physical activ-
ity, and lack of perceived barriers to being physi-
cally active.
2. For adults, some interventions have been success-
ful in increasing physical activity in communities,
worksites, and health care settings, and at home.
3. Interventions targeting physical education in
elementary school can substantially increasethe
amount of time students spend being physically
active in physical education class.

8


               CHAPTER 2
HISTORICAL BACKGROUND, TERMINOLOGY,
  EVOLUTION OF RECOMMENDATIONS,
           AND MEASUREMENT

Contents

Introduction . . . . ..___..______....................._________................. 11

Western Historical Perspective  ..................................................  12
Early Promotion of Physical Activity for Health .................................. 12
Associating Physical Inactivity with Disease   ....................................  15
Health, Physical Education, and Fitness  ........................................  16
Exercise Physiology Research and Health .......................................  18

Terminology of Physical Activity, Physical Fitness, and Health . . . . . . . . . . . . . . . . . . . . . 20

Evolution of Physical Activity Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Summary of Recent Physical Activity Recommendations . , . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Measurement of Physical Activity, Fitness, and Intensity  ............................. 29
Measuring Physical Activity  ................................................. 29
  Measures Based on Self-Report  ............................................ 29
  Measures Based on Direct Monitoring  ....................................... 31
  Measuring Intensity of Physical Activity  ..................................... 32
  Measuring Physical Fitness  ............................................... 33
     Endurance  .......................................................... 33
     Muscular Fitness  ..................................................... 34
    Body Composition  ................................................... 35
  Validity of Measurements  ................................................ 35

Chaptersummary . .._._.................................................... . . 37


Contents, continued

Conclusions . . . .._.._.____.................................................. 37

References . . . . . . . . . . . . . . . . .._..._....._._...............___._............... 37

Appendix A: Healthy People 2000 Objectives _ . . . . . . . . . . . . . . . _ _ _ _ . . . . . . . . . . .-. 47

Appendix B: NIH Consensus Conference Statement  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . 50


               CHAPTER 2
HISTORICAL BACKGROUND, TERMINOLOGY,
  EVOLUTION OF RECOMMENDATIONS,

AND MEASUREMENT

Introduction

The exercise boom is notjust afad; it is a return
to `nutwrul' activity-the kind for which our
bociics are engineered and whichfacilitates the
proper/unction of our biochemistry and physi-
ology. Viewed through the perspective ofevolu-
tiotmry time, sedentary existence, possible for
grcut numbers of people only during the lust
century, represents a transient, unnatural uber-
ration. (Eaton,Shostak, Konner 1988, p. 168)

T hischapter examines the historical development
of physical activity promotion as a means to
improve health among entire populat,ions. The chap-
tcr focuses on Western (i.e., Greco-Roman) history,
bccausc of the near-linear development of physical
activity promotion across those times and cultures
Icading to current American attitudes and guidelines
regarding physical activity. These guidelines are
discussed in detail in the last half of the chapter. To
Ilcsh out this narrow focus on Western traditions, as
well as to provide a background for the promotional
emphasis of the chapter, this chapter begins by
briefly outlining both anthropological and historical
evidence of the central, "natural" role of physical
activity in prehistoric cultures. Mention is also made
of the historical prominence of physical activity in
non-Greco-Roman cultures, including those of China,
India, Africa, and precolonial America.

Xrchaeologists working in conjunction withmedi-
Cal anthropologists have established that our ances-
tors up through the beginning of the Industrial
Revolution incorporated strenuous physical activity
as a normal part of their daily lives-and not only for
the daily, subsistence requirements of their "work"
.li\cs. Investigations of preindustrial societies still

intact today confirm that physical capability was not
just a grim necessity for success at gathering food and
providing shelter and safety (Eaton, Shostak, Konner
1988). Physical activity was enjoyed throughout every-
day prehistoric life, as an integral component of
religious, social, and cultural expression. Food sup-
plies for the most part were plentiful, allowing ample
time for both rest and recreational physical endeavors.
Eaton, Shostak, and Konner (1988) describe a
"Paleolithic rhythm" (p. 32) observed among con-
temporary hunters and gatherers that seems to
mirror the medical recommendations for physical
activity in this report. This natural cycle of regu-
larly intermittent activity was likely the norm for
most of human existence. Sustenance preoccupa-
tions typically were broken into l- or 2-day periods
of intense and strenuous exertion, followed by l- or
2-day periods of rest and celebration. During these
rest days, however, less intense but still strenuous
exertion accompanied 6- to 20-mile round-trip vis-
its to other villages to see relatives and friends and
to trade with other clans or communities. There or
at home, dancing and cultural play took place.
As the neolithic Agricultural Revolution allowed
more people to live in larger group settings and
cities, and as the specialization of occupations re-
duced the amount and intensity of work-related
physical activities, various healers and philosophers
began to stress that long life and health depended on
preventing illnesses through proper diet, nutrition,
and physical activity. Such broad prescriptions for
health, including exercise recommendations, long
predate the increasingly specific guidelines of classi-
cal Greek philosophy and medicine, which are the
predominant historical focus of this chapter.


Physical Activity and Health

In ancient China as early as 3000 to 1000 B.C.,
the classic Yellow Emperor's Book ojlnternal Medicine
(Huang Ti 1949) first described the principle that
human harmony with the world was the key to
prevention and that prevention was the key to long
life (Shampo and Kyle 1989). These principles grew
into concepts that became central to the 6th century
Chinese philosophy Taoism, where longevity through
simple living attained the status of a philosophy that
has guided Chinese culture through the present day.
tai chi chuan, an exercise system that teachesgraceful
movements, began as early as 200 B.C. with Hua T'o
and has recently been shown to decrease the incidence
of falls in elderly Americans (Huard and Wong 1968;
see Chapter 4).

In India, too, proper diet and physical activity
were known to be essential principles of daily
living. The Ajur Veda, a collection of health and
medical concepts verbally transmitted as early as
3000 B.C., developed into Yoga, a philosophy that
included a comprehensively elaborated series of
stretching and flexibility postures. The principles
were first codified in 600B.C. in the Upanishads and
later in the Yoga Sutras by Patanjali sometime be-
tween 200 B.C. and 200 A.D. Yoga philosophies
also asserted that physical suppleness, proper breath-
ing, and diet were essential to control the mind and
emotions and were prerequisites for religious ex-
perience. In both India and China during this
period, the linking of exercise and health may
have led to the development of a medical subspe-
cialty that today would find its equivalent in sports
medicine (Snook 1984).

Though less directly concerned with physical
health than with social and religious attainment,
physical activity played a key role in other ancient
non-Greco-Roman cultures. In Africa, systems of
flexibility, agility, and endurance training not only
represented the essence of martial arts capability
but also served as an integral component bf reli-
gious ritual and daily life. The Sambuiu and the
Masai of Kenya still feature running as a virtue of
the greatest prowess, linked to manhood and social
stature.

Similarly, in American Indian cultures, running
was a prominent feature of all major aspects of life
(Nabokov 1981). Long before the Europeans in-
vaded, Indians ran to communicate, to fight, and to

hunt. Running was also a means for diverse Ameri-
can Indian cultures to enact their myths and thereby
construct a tangible link between themselves and
both the physical and metaphysical worlds. Among
the Indian peoples Nabokov cites are the Mesquakie
of Iowa, the Chemeheuvi of California, the Inca of
Peru, the Zuni and other Pueblo peoples of the
American Southwest, and the Iroquois of the Ameri-
can East, who also developed the precursor of mod-
ern-day lacrosse. Even today, the Tarahumarahe of
northern Mexico play a version of kickball that
involves entire villages for days at a.time (Nabokov
1981; Eaton, Shostak, Konner 1988).

Western Historical Perspective

Besides affecting the practice of preventive hygiene
(as is discussed throughout this section), the ancient
Greek ideals of exercise and health have influenced
the attitudes of modern western culture toward
physical activity. The Greeks viewed great athletic
achievement as representing both spiritual and
physical strength rivaling that of the gods (Jaeger
1965). In the classical-era Olympic Games, the Greeks
viewed the winners as men who had the character
and physical prowess to accomplish feats beyond the
capability of most mortals. Although participants in
the modern Olympic Games no longer compete with
the gods, today's athletes inspire others to be physi-
cally active and to realize their potential-an inspi-
ration as important for modern peoples as it was for
the ancient Greeks.

Early Promotion of
Physical Activity for Health
Throughout much of recorded western history, phi-
losophers, scientists, physicians, and educators have
promoted the idea that being physically active con-
tributes to better health, improved physical func-
tioning, and increased longevity. Although some of
these claims were based on personal opinions or
clinical judgment, others were the result of system-
atic observation.

Among the ancient Greeks, the recognition that
proper amounts of physical activity are necessary for
healthy living dates back to at least the 5th century
B.C. (Berryman 1992). The lessons found in the

12


Historical Background, Terminology, Evolution of Recommendations, and Measurement

..lalVs of health" taught during the ancient period
sound familiar lo us today: to breathe fresh air, eat
prc>pcr foods, drink the right beverages, take plenty
L,f cscrcise, get the proper amount of sleep, and
inciudc our emotions when analyzing our overall
\vcll-being.

\vcstern historians agree that the close connec-
tlon hctween exercise and medicine dates back to
lhrcc Greek physicians-Herodicus (ca. 480 B.C.),
Hippocrates (ca. 460-ca. 377 B.C.), and Galen
(/I.D. 129-ca. 199). The first to study therapeutic
$~ll~n:~stics--or gymnastic medicine, as it was often
caitcd-was the Greek physician and former exer-
cisc instructor, Herodicus. His dual expertise united
rhc gymnastic with the medical art, thereby prepar-
ing the way for subsequent Greek study of the health
hcncfits of physical activity.
Although Hippocrates is generally known as the
father of preventive medicine, most historians credit
I Icroclicus as the influence behind Hippocrates' in-
lcrcst in the hygienic usesofexerciseanddiet (Cyriax
1~ 1-t; Prccope 1952; Licht 1984; Olivova 1985).
K~~gimcn, the longer of Hippocrates' two works deal-
111g with hygiene, was probably written sometime
mend 400 B.C. In Book 1, he writes:

Eafing alone will not keep a man well; he must
also take exercise. Forfoodand exercise, white
posscssingoppositequalities,yet work together
IO produce health. For it is the nature ofexer-
cisc to USC up material, but offood and drink to
mokc good dejiciencies. And it is necessary, as
il clppcars, to discern the power of various
cxcrcises, both natural exercises andartificial,
to know which of them tends to increaseflesh
cold which to lessen it; and not only this, but
&o to proportion exercise to bulk offood, to
the constitution of the patient, to the age ofthe
i~ldividual, to the season of the year, to the
chclngcs in the winds, to the situation of the
region in which the patient resides, and to the
CoMilu~ion of the year. (1953 reprint, p. 229)
Hippocrates was a major influence on the career
of Claudius Galenus, or Galen, the Greek physician
lvllo wrote numerous works of great importance to
lncdical history during the second century. Of these
.\rorks, his book entitled On Hygiene contains the
lllost information on the healthfulness of exercise.

Whether by sailing, riding on horseback, or driving,
or via cradles, swings, and arms, everyone, even
infants, Galen said, needed exercise (Green 1951
trans., p. 25). He further stated:

The uses of exercise, I think, are twofold, one
for the evacuation ofthe excrements, the other
for the production ofgood condition ofthefit-m
parts oJthe body. For since vigorous motion is
exercise, it must needs be that only these three
things result from it in the exercising body-
hardness of the organs from mutual attrition,
increase of the intrinsic warmth, and acceler-
ated movement of respiration. These are fol-
lowed by all the other individual benefits which
accrue to the bodyfrom exercise;from hardness
of the organs, both insensitivity and strength
forfunction; from warmth, both strongatlrac-
tion for things to be eliminated, readier me-
tabolism, and better nutrition and diffusion of
all substances, whereby it results that solidsare
softened, liquids diluted, and ducts dilated.
And from the vigorous movement of respira-
tion the ducts must be purged and the excre-
ments evacuated. (p. 54)

The classical notion that one could improve
one's health through one's own actions-for ex-
ample, through eating right and getting enough sleep
and exercise -proved to be a powerful influence on
medical theory as it developed over the centuries.
Classical medicine had made it clear to physicians
and the lay public alike that responsibility for disease
and health was not the province of the gods. Each
person, either independently or in counsel with his
or her physician, had a moral duty to attain and
preserve health. When the Middle Ages gave way to
the Renaissance, with its individualistic perspective
and its recovery of classical humanistic influences,
this notion of personal responsibility acquired even
greater emphasis. Early vestiges of a "self-help"
movement arose in western Europe in the 16th
century. As that century progressed, "laws of bodily
health were expressed as value prescriptions" (Burns
1976, p. 208).

More specifically, "orthodox Greek hygiene,"
as Smith (1985, p. 257) called it, flourished as part
of the revival of Galenic medicine as early as the
13th century. The leading medical schools of the


Physical Activity and Health

world--Italy's Salerno, Padua, and Bologna-taught
hygiene to their students as part of general instruc-
tion in the theory and practice of medicine The
works of Hippocrates and Galen dominated a sys-
tem whereby "the ultimate goal was to be able to
practise medicine in the manner of the ancient
physicians" (Bylebyl 1979, p. 341).
Hippocrates' Regimen also became important
during the Renaissance in a literature that Gruman
(1961) identified as "prolongevity hygiene" and de-
fined as "the attempt to attain a markedly increased
longevity by means of reforms in one's way of life"
(p. 221). Central to this literature was the belief that
persons who decided to live a temperate life, espe-
cially by reforming habits of diet and exercise, could
significantly extend their longevity. Beginning with
the writings of Luigi Cornaro in 1558, the classic
Greek preventive hygiene tradition achieved increas-
ing attention from those wishing to live longer and
healthier lives.

Christobal Mendez, who received his medical
training at the University of Salamanca, was the
author of the first printed book devoted to exercise,
Book of Bodily Exercise (1553). His novel and com-
prehensive ideas preceded developments in exercise
physiology and sports medicine often thought to be
unique to the early 20th century. The book consists
of four treatises that cover such topics as the effects
of exercise on the body and on the mind. Mendez
believed, as the humoral theorists did, that the phy-
sician had to clear away excess moisture in the body.
Then, after explaining the ill effects of vomiting,
bloodletting, purging, sweating, and urination, he
noted that "exercise was invented and used to clean
the body when it was too full of harmful things. It
cleans without any of the above-mentioned inconve-
nience and is accompanied by pleasure and joy (as
we will say). If we use exercise under the conditions
which we will describe, it deserves lofty' praise as a
blessed medicine that must be kept in high esteem"
(1960 reprint, p. 22).

In 1569, Hieronymus Mercurialis' The Art of
Gymnastics Among the Ancients was published in
Venice. Mercurialis quoted Galen extensivly and
provided a descriptive compilation of ancient mate-
rial from nearly 200 works by Greek and Roman
authors. In general, Mercurialis established the fol-
lowing exercise principles: people who are ill should

not be given exercise that might aggravate existing
conditions; special exercises should be prescribed on
an individual basis for convalescent, weak, and older
patients; people who lead sedentary lives need ex-
ercise urgently; each exercise should preserve the
existing healthy state; exercise should not disturb
the harmony among the principal humors; exercise
should be suited to each part of the body; and all
healthy people should exercise regularly.
Although Galenism and the humoral theory of
medicine were displaced by new ideas, particularly
through the study of anatomy and physiology, the
Greek principles of hygiene and regimen continued
to flourish in 18th century Europe. For some 18th
century physicians, such nonintervention tactics were
practical alternatives to traditional medical therapies
that employed bloodletting and heavy dosing with
compounds of mercury and drugs-"heroic" medi-
cine (Warner 1986), in which the "cure" was often
worse than the disease.

George Cheyne's An Essay ofHealth and Long LiJe
was published in London in 1724. By 1745, it had
gone through 10 editions and various translations.
Cheyne recommended walking as the "most natural"
and "most useful" exercise but considered riding on
horseback as the "most manly" and "most healthy"
(1734 reprint, p. 94). He also advocated exercises in
the open air, such as tennis and dancing, and recom-
mended cold baths and the use of the "flesh brush"
to promote perspiration and improve circulation.
John Wesley's Primitive Physic, first published in
1747, was influenced to a large degree by George
Cheyne. In his preface, Wesley noted that "the power
of exercise, both to preserve and restore health, is
greater than can well be conceived; especially in
those who add temperance thereto" (1793 reprint,
p. iv). William Buchan's classic Domestic Medicine,
written in 1769, prescribed proper regimen for im-
proving individual and family health. The book
contained rules for the healthy and the sick and
stressed the importance ofexercise for good health in
both children and adults.

During the 19th century, both the classical Greek
tradition and the general hygiene movement were
finding their way into the United States through
American editions of western European medical
treatises or through books on hygiene written by
American physicians. The "self-help" era was also in

14


full bloom during antebellum America. Early ves-
tiges of a self-help movement had arisen in western
Europe in the 16th century. AS that century pro-
grcssed, .&laws of bodily health were expressed as
\aluc prescriptions " (Burns 1976, p. 208). Classical
Greek preventive hygiene was part of formal medical
training through the 18th century and continued on
in the American health reform literature for most of
the 19th century. During the latter period, an effort
~`as made to popularize the Greek laws of health, to
lrlilkc each person responsible for the maintenance
;lnd balance of his or her health. Individual reform
lvritcrs thus wrote about self-improvement, self-
regulation, the responsibility for personal health,
;~nd self-management (Reiser 1985). Ifpeople ate too
much, slept too long, or did not get enough exercise,
they could only blame themselves for illness. By the
3ilmt` token, they could also determine their own
good health (Cassedy 1977; Numbers 1977;
Vcrhrugge 1981; Morantz 1984).
A.F.M. Willich's Lectures on Diet and Regimen
( 1801) emphasized the necessity of exercise within
lhc hounds of moderation. He included information
OII specific exercises, the time for exercise, and the
duration of exercise. The essential advantages of
cscrcisc included increased bodily strength, improved
circulation of the blood and all other bodily fluids,
Cl in necessary secretions and excretions, help in
clearing and refining the blood, and removal of
obstructions.

John Gunn's classic Domestic Medicine, Or Poor
.HuII's Friend, was first published in 1830. His section
c*ntitlcd "Exercise" recommended temperance, exer-
cisc, and rest and valued nature's way over tradi-
lional medical treatment. He also recommended
cscrcise for women and claimed that all of the
"diseases of delicate women" like "hysterics and
hypochondria, arise from want of due exercise in the
open, mild, and pure air" (1986 reprint; p. 109).
Fill:$`, in an interesting statement fdr the 1830s if
IlOt the 199Os, Gunn recommended a training sys-
`cln for all: "The advantages of the training systems
:\rc not confined to pedestrians or walkers-or to
Pugilists or boxers alone; or to horses which are
trained for the chase and the race track; they extend
10 man in all conditions; and were training intro-
duced into the United States, and made use of by
physicians in many cases instead of medical drugs,

Historical Background, Terminology, Evolution of Recommendations, and Measurement

the beneficial consequences in the cure of many
diseases would be very great iFed" (p. 113).

Associating Physical Inactivity with Disease
Throughout history, numerous health professionals
have observed that sedentary people appear to suffer
from more maladies than active people. An early
example is found in the writings of English physician
Thomas Cogan, author of TheHavenofHealth (1584);
he recommended his book to students who, because
of their sedentary ways, were Gelieved to be most
susceptible to sickness.

In his 1713 book Diseases of Workers, Bernar-
dino Ramazzini, an Italian physician considered the
father of occupational medicine, offered his views on
the association between chronic inactivity and poor
health. In the chapter entitled "Sedentary Workers
and Their Diseases," Ramazzini noted that "those
who sit at their work and are therefore called `chair-
workers,' such as cobblers and tailors, suffer from
their own particular diseases." He concluded that
"these workers . . _ suffer from general ill-health and
an excessive accumulation of unwholesome humors
caused by their sedentary life," and he urged them to
at least exercise on holidays "so to some extent
counteract the harm done by many days of sedentary
life" (1964 trans., pp. 281-285).
Shadrach Ricketson, a New York physician, wrote
the first American text on hygiene and preventive
medicine (Rogers 1965). In his 1806 book Means of
Preserving Health and Preventing Diseases, Ricketson
explained that "a certain proportion of exercise is not
much less essential to a healthy or vigorous constitu-
tion, than drink, food, and sleep; for we see that
people, whose inclination, situation, or employ-
ment does not admit of exercise, soon become pale;
feeble, and disordered." He also noted that "exercise
promotes the circulation of the blood, assists diges-
tion, and encourages perspiiation" (pp. 152-153).
Since the 186Os, physicians and others had
been attempting to assess the longevity of runners
and rowers. From the late 1920s (Dublin 1932;
Montoye 1992) to the landmark paper by Morris
and colleagues (1953), observations that prema-
ture mortality is lower among more active persons
than sedentary persons began to emerge and were
later replicated in a variety of settings (Rook 1954;

15


Physical Activity and Health

Brown et al. 1957; Pomeroy and White 1958; Zukel
et al. 1959). The hypothesis that a sedentary lifestyle
leads to increased mortality from coronary heart
disease, as well as the later hypothesis that inactiv-
ity leads to the development of some other chronic
diseases, has been the subject of numerous studies
that provide the major source of data supporting
the health benefits of exercise (see Chapter 4).

Health, Physical Education, and Fitness
The hygiene movement found further expression in
19th century America through a new literature de-
voted to "physical education." In the early part of the
century, many physicians began using the term in
journal articles, speeches, and book titles to describe
the task of teaching children the ancient Greek "laws
of health." As Willich explained in his Lectures on Diet
and Regimen (1801), "by physical education is meant
the bodily treatment of children; the term physical
being applied in opposition to mord (p. 60). In his
section entitled "On the Physical Education of Chil-
dren," he continued to discuss stomach ailments,
bathing, fresh air, exercise, dress, and diseases of the
skin, among other topics. Physical education, then,
implied not merely exercising the body but also
becoming educated about one's body.
These authors were joined by a number of early
19th century educators. For example, an article
entitled "Progress of Physical Education" (1826),
which appeared in the first issue of American journal
of Education, declared that "the time we hope is
near, when there will be no literary institution
unprovided with the proper means to healthful
exercise and innocent recreation, and when literary
men shall cease to be distinguished by a pallid
countenance and a wasted body" (pp. 19-20). Both
William Russell, who was the journal's editor, and
Boston educator William Fowler believed that girls
as well as boys should have ample outdoor exercise.
Knowledge about one's body also was deemed cru-
cial to a well-educated and healthy individual by
several physicians who, as Whorton has suggested,
"dedicated their careers to birthing the modern
physical education movement" (p. 282).
  Charles Caldwell held a prominent position in
Lexington, Kentucky's, Transylvania University
Medical Department. Although he wrote on a variety
of medical topics, his Thoughts on Physical Education

in 1834 gained him national recognition. Caldwell
defined physical education as "that scheme of train-
ing, which contributes most effectually to the devel-
opment, health, and perfection of living matter. As
applied to man, it is that scheme which raises his
whole system to its summit of perfection. . . . Physical
education, then, in its philosophy and practice, is of
great compass. If complete, it would be tantamount
to an entire system of Hygeiene. It would embrace
every thing, that, by bearing in any way on the
human body, might injure or benefit it in its health,
vigor, and fitness for action" (pp. 28-29).
During the first half of the 19th century, systems
of gymnastic and calisthenic exercise that had been
developed abroad were brought to the United States.
The most influential were exercises advanced by Per
Henrik Ling in Sweden in the early 1800s and the
"German system" of gymnastic and apparatus exer-
cises that was based on the work of Johan Christoph
GutsMuths and Friedrich LudwigJahn. Also, Ameri-
cans like Catharine Beecher (1856) and Dioclesian
Lewis (1883) devised their own extensive systems of
calisthenic exercises intended to benefit both women
and men. By the 187Os, American physicians and
educators frequently discussed exercise and health.
For example, physical training in relation to health
was a regular topic in the Boston Medical and Surgical
Journal from the 1880s to the early 1900s.
Testing of physical fitness in physical education
began with the extensive anthropometric documen-
tation by Edward Hitchcock in 1861 at Amherst
College. By the 188Os, Dudley Sargent at Harvard
University was also recording the bodily measure-
ments of college students and promoting strength
testing (Leonard and Affleck 1947). During the early
19OOs, the focus on measuring body parts shifted to
tests of vital working capacity. These tests included
measures of blood pressure (McCurdy 1901;
McKenzie 1913), pulse rate (Foster 1914), and fa-
tigue (Storey 1903). As early as 1905, C. Ward
Crampton, former director of physical training and
hygiene in New York City, published the article "A
Test of Condition" in Medical News. Attempts to
assess physical fitness had constituted a significant
aspect of the work of turn-of-the-century physical
educators, many of whom were physicians.
  Allegations that American conscripts during
World War I were inadequately fit to serve their

16


countq helped shift the emphasis of physical educa-
tion from health-related exercise to performance out-
c`omcs. Public concern stimulated legislation to make
ph\.r;ical education a required subject in schools. But
the financial austerities of the Great Depression had a
neg;ltive effect on education in general, including
physical education (Rogers 1934). At the same time,
the combination of increased leisure time for many
;\mericans and a growing national interest in college
;md high school sports shifted the emphasis on physi-
(al education away from the earlier aim of enhancing
performance and health to a new focus on sports-
related skills and the worthy use of leisure time.
physical efficiency was a term widely used in
the literature of the 1930s. Another term, physical
condition, also found its way into research reports.
111 1936, Arthur Steinhaus published one of the
carlicst articles on "physical fitness" in thejournal
(I\- ffctrld~, Pllysical Education, and Recreation; in
1038, C. H. McCloy's article "Physical Fitness and
<;itizenship" appeared in the same journal.
  As the United States entered World War II, the
Icdcral government showed increasing interest in
physical education, especially toward physical fit-
ucss testing and preparedness. In October 1940,
President Franklin Roosevelt named John Kelly, a
lormcr Olympic rower, to the new position of
national director of physical training. The follow-
i ng year, Fiorella La Guardia, the Mayor of New
York City and the director of civilian defense for the
I'cdcral Security Agency, appointed Kelly as assis-
tant in charge of physical fitness; tennis star Alice
Marble was also chosen to promote physical fitness
among girls and women (Park 1989; Berryman
1995).

In 1943, Arthur Steinhaus chaired a committee
ilppointed by the Board of Directors of the American
Medical Association to review the nature and role of
exercise in physical fitness (Steinhaus et al. 1943),
and C. Ward Crampton chaired a committee on
Physical fitness under the direction'of the Federal
Security Agency. Crampton and his 73-member
advisory council were charged with developingphysi-
~a1 fitness in the civilian population (Crampton 1941;
Park 1989).

In 1941, Morris Fishbein, editor of theJournal of
the American Medical Association, stated that "from
the point of view on physical fitness we are a far

better nation now than we were in 1917," but he
cautioned Americans not to believe "we have at-
tained an optimum in physical fitness" (p. 54). He
realized the magnitude of the fitness problem when
he noted that the poor results of physical examina-
tions reported by the Selective Service Boards were "a
challenge to the medical profession, to the social
scientists, the physical educators, the public health
officials, and all those concerned in the United States
with the physical improvement of our population"
(p. 55). The goals most frequently cited for physical
education between 1941 and 1945 were resistance to
disease, muscular strength and endurance, cardio-
respiratory endurance, muscular growth, flexibility,
speed, agility, balance, and accuracy (Larson and
Yocom 1951).

After World War II concluded, a continuing
interest in physical fitness convinced other key mem-
bers of the medical profession and the American
Medical Association to continue studying exercise.
Much of this interest can be attributed to the pioneer-
ing work of Thomas K. Cureton, Jr., and his Physical
Fitness Research Laboratory at the University of Illinois
(Shea 1993). Cardiologists, health education special-
ists, and physicians in preventive medicine were be-
coming aware of the contributions of exercise to the
overall health and efficiency of the heart and circula-
tory system. In 1946, the American Medical
Association's Bureau of Health Education designed
and organized the Health and Fitness Program to
provide "assistance to local organizations throughout
the nation in the development of satisfactory health
education programs" (Fishbein 1947, p. 1009). The
program became an important link among physical
educators, physicians, and physiologists.
The event that attracted the most public attention
to physical fitness, including that of President Dwight
D. Eisenhower, was the publication of the article
"Muscular Fitness and Health" in the December 1953
issue of the Journal of Health, Physical Education,
and Recreation. The authors, Hans Kraus and Ruth
Hirschland of the Institute of Physical Medicine
and Rehabilitation at the New York University
Bellevue Medical Center, stated that 56.6 per-
cent of the American schoolchildren tested "failed
to meet even a minimum standard required for
health" (p. 17). When this rate was compared with
the 8.3 percent failure rate for European children, a

Historical Background, Terminology, Evolution of Recommendations, and Measurement

17


Physical Activity and Health

call for reform went out. Kraus and Hirschland
labeled the lack of sufficient exercise "a serious
deficiency comparable with vitamin deficiency" and
declared "an urgent need" for its remedy (pp. 17-19).
John Kelly, the former national director of physical
fitness during World War II, notified Pennsylvania
Senator James Duff of these startling test results.
Duff, in turn, brought the research to the attention of
President Eisenhower, who invited several athletes
and exercise experts to a meeting in 1955 to examine
this issue in more depth. A President's Conference
on Fitness of American Youth, held in June 1956,
was attended by 150 leaders from government, physi-
cal education, medical, public health, sports, civic,
and recreational organizations. This meeting even-
tually led to the establishment of the President's
Council on Youth Fitness and the President's Citizens
Advisory Committee on the Fitness of American
Youth (Hackensmith 1966; Van Dalen and Bennett
1971).

When John Kennedy became president in 1961,
one of his first actions was to call a conference on
physical fitness and young people. Iri 1963, the
President's Council on Youth Fitness was renamed
the President's Council on Physical Fitness. In 1968,
the word "sports" was added to the name, making it
the President's Council on Physical Fitness and Sports
(PCPFS). The PCPFS was charged with promoting
physical activity, fitness, and sports for Americans of
all ages.

During the 1960% a number of educational and
public health organizations published articles and
statements on the importance of fitness for children
and youths. The American Association for Health,
Physical Education, and Recreation (AAHPER) ex-
panded its physical fitness testing program to in-
clude college-aged men and women. The association
developed new norms from data collected from more
than 11,000 boys and girls lo-17 years old. The
AAHPER also joined with the President's Cduncil on
Physical Fitness to conduct the AAHPER Youth
Fitness Test, which had motivational awards. In
1966, President Lyndon Johnson's newly created
Presidential Physical Fitness Award was incorpo-
rated into the program.

In the mid-1970s, the need to promote the health-
rather than exclusively the performance-benefits of
exercise and physical fitness began to reappear. In

1975, AAHPER stated it was time to differentiate
physical fitness related to health from performance
related to athletic ability (Blair, Falls, Pate 1983).
Accordingly, AAHPER commissioned the develop-
ment of the Health Related Physical Fitness Test. This
move in youth fitness paralleled the adoption of the
aerobic concept, which promoted endurance-type
exercise among the public (Cooper 1968).

Exercise Physiology Research and Health
The study of the physiology of exercise in a modern
                             r
sense began in Paris, France, when Antoine Lavoisier
in 1777 and Lavoisier and Pierre de Laplace in 1780
developed techniques to measure oxygen uptake and
carbon dioxide production at rest and during exer-
cise. During the 18OOs, European scientists used and
advanced these procedures to study the metabolic
responses to exercise (Scharling 1843; Smith 1857;
Katzenstein 1891; Speck 1889; Allen and Pepys
1809). The first major application of this research to
humans-Edward Smith's study of the effects of
"assignment to hard labor" by prisoners in London
in 1857-was to determine if hard manual labor
negatively affected the health and welfare of the
prisoners and whether it should be considered cruel
and unusual punishment.

William Byford published "On the Physiology of
Exercise" in the American Journal of Medical Sciences
in 1855, and Edward Mussey Hartwell, a leading
physical educator, wrote a two-part article, "On the
Physiology of Exercise, " for the Boston Medical and
SurgicalJournal in 1887. The first important book on
the subject, George Kolb's Beitrage zur Physiologic
Maximaler Muskelarbeit Besondersdes ModemenSports,
was published in 1887 (trans. Physiology of Sport,
1893) (cited in Langenfeld 1988 and Park 1992). The
followingyear,FernandLagrange'sPhysiology ofBodily
Exercise was published in France.
From the early 1900s to the early 192Os, several
works on exercise physiology began to appear. George
Fitz, who had established a physiology of exercise
laboratory during the early 189Os, published his
Principles of Physiology and Hygiene in 1908. R. Tait
McKenzie's Exercise in Education and Medicine (1909)
was followed by such works as Francis Benedict and
Edward Cathcart's Muscular Work, A Metabolic Study
with Special Reference to the Efficiency of the Human
Body as a Machine (1913). The next year, a professor

18


of physiology at the University of London, F.A.
Bainbridge, published a second edition of Physiology
(,I- .tlllscular Exercise (Park 1981).
In 1923, the year Archibald Hill was appointed
]oddrell Professor of Physiology at University Col-
lege, London, the physiology of exercise acquired
ot,c of its most respected researchers and staunchest
supporters, for Hill had won the Nobel Prize in
\Iedicine and Physiology the year before. Hill's 1925
prcsidcntial address on "The Physiological Basis of
*Athletic Records" to the British Association for the
;\dvancement of Science appeared in The Lancel
( I925a) and Scientgic Monthly (1925b), and in 1926
he published his landmark book Muscular Activity.
The following year, Hill published Living Machinery,
Lvhich was based largely on his lectures before audi-
I'IICCS at the Lowell Institute in Boston and the Baker
Laboratory of Chemistry in Ithaca, New York.
  Several leading physiologists besides Hill were
Intcrcstcd in the human body's response to exercise
ant1 cnvironmcntal stressors, especially activities
involving endurance, strength, altitude, heat, and
l~~lcl. Consequently, they studied soldiers, athletes,
;rvlators, and mountain climbers as the best models
lor acquiring data. In the United States, such re-
\c;lrch was centered in the Boston area, first at the
<:arncgic Nutrition Laboratory in the 1910s and
I;trcr at the Harvard Fatigue Laboratory, which was
c.>tablishcd under the leadership of Lawrence
I Icndcrson in 1927 (Chapman and Mitchell 1965;
I)ill lY67; Horvath and Horvath 1973). That year,
I Icnclcrson and colleagues first demonstrated that
~*ntlurancc exercise training improved the efficiency
()I the cardiovascular system by increasing stroke
~~~)lutnc and decreasing heart rate at rest. Two years
I;itcr, Schneider and Ring (1929) published the
rc5ults of a 12-week endurance training program on
c)lle person, demonstratinga 24-percent increase in
"crest load of oxygen" (maximal oxygen uptake).
over the next 15 years, a limited number of exercise
training studies were published that-evaluated the
--+csponsc of maximal oxygen uptake or endurance
Vrformancc capacity to exercise training. These
I~l~luded noteworthy reports by Gemmill and col-
Ic%ues (I931), Robinson and Harmon (1941), and
Knehr. Dill, and Neufeld (1942) on endurance
lraining responses by male college students. HOW-
cVer. none of those early studies compared the

Historical Background, Terminology, Evolution of Recommendations, and Measurement

effects of different types, intensities, durations, or
frequencies of exercise on performance capacity or
health-related outcomes.

Activities surrounding World War II greatly in-
fluenced the research in exercise physiology, and
several laboratories, including the Harvard Fatigue
Laboratory, began directing their efforts toward top-
ics of importance to the military. The other national
concern that created much interest among physiolo-
gists was the fear (discussed earlier in this chapter),
that American children were less fit than their Euro-
pean counterparts. Research was directed toward the
concept of fitness in growth and development, ways
to measure fitness, and the various components of
fitness (Berryman 1995). Major advances were also
made in the 1940s and 1950s in developing the
components of physical fitness (Cureton 1947) and
in determining the effects of endurance and strength
training on measures of performance and physi-
ologic function, especially adaptations of the cardio-
vascular and metabolic systems. Also investigated
were the effects ofexercise trainingon health-related
outcomes, such as cholesterol metabolism (Taylor,
Anderson, Keys 1957; Montoye et al. 1959).
Starting in the late 1950s and continuing through
the 197Os, a rapidly increasing number of published
studies evaluated or compared different components
of endurance-oriented exercise training regimens.
For example, Reindell, Roskamm, and Gerschler
(1962) in Germany, Christensen (1960) in Denmark,
and Yakovlev and colleagues (1961) in Russia
compared-and disagreed-about the relative ben-
efits of interval versus continuous exercise train-
ing in increasing cardiac stroke volume and
endurance capacity. Other investigators began to
evaluate the effects of different modes (Sloan and
Keen 1959) and durations (Sinasalo and Juurtola
1957) of endurance-type training on physiologic
and performance measures.

Karvonen and colleagues' (1957) landmark paper
that introduced using "percent maximal heart rate
reserve" to calculate or express exercise training in-
tensity was one of the first studies designed to com-
pare the effects of two different exercise intensities on
cardiorespiratory responses during exercise. Over the
next 20 years, numerous investigators documented
the effects of different exercise training regimens on a
variety of health-related outcomes among healthy

19


Physical Activity and Health

men and women and among persons under medical
care (Bouchard, Shephard, Stephens 1994). Many of
these studies evaluated the effects of endurance or
aerobic exercise training on cardiorespiratory capac-
ity and were initially summarized by Pollock (1973).
The American College of Sports Medicine (ACSM)
(1975, 1978) and the American Heart Association
(AHA) (1975) further refined the results of this re-
search (see the section on "Evolution of Physical
Activity Recommendations," later in this chapter).
Over the past two decades, experts from numer-
ous disciplines have determined that exercise training
substantially enhances physical performance and have
begun to establish the characteristics of the exercise
required to producespecific healthbenefits (Bouchard,
Shephard, Stephens 1994). Also, behavioral scientists
have begun to evaluate what determines physical
activity habits among different segments of the popu-
lation and are developing strategies to increase physi-
calactivityamongsedentary persons (Dishman 1988).
The results of much of this research are cited in the
other chapters of this report and were the focus of the
various conferences, reports, and guidelines summa-
rized later in this chapter.

  As the literature of exercise science has matured
and recommendations have evolved, certain widely
agreed-on terms have emerged. Because a number of
these occur throughout the rest of this chapter and
report, they are presented and briefly defined in the
following section.

Terminology of Physical Activity,
Physical Fitness, and Health

This section discusses four broad terms used frequently
in this report: physical activity, exercise (or exercise
training), physical fitness, and health. Also included is
a glossary (Table 2-l) of more specific terms and
concepts crucial to understanding the material pre-
sented in later parts of this chapter and report.

Physical activity. Physical activity is defined as
bodily movement produced by the contraction of
skeletal muscle that increases energy expenditure
above the basal level. Physical activity can be cat-
egorized in various ways, including type, intensity,
and purpose.

Because muscle contraction has both mechani-
cal and metabolic properties, it can be classified by

either property. This situation has caused some
confusion. Typically, mechanical classification
stresses whether the muscle contraction produces
movement of the limb: isometric (same length) or
static exercise if there is no movement of the limb, or
isotonic (same tension) or dynamic exercise if there
is movement of the limb. Metabolic classification
involves the availability of oxygen for the contrac-
tion process and includes aerobic (oxygen available)
or anaerobic (oxygen unavailable) processes.
Whether an activity is aerobic or anaerobic depends
primarily on its intensity. Most'activities involve
both static and dynamic contractions and aerobic
and anaerobic metabolism. Thus, activities tend to
be classified according to their dominant features.
The physical activity of a person or group is
frequently categorized by the context in which it
occurs. Common categories include occupational,
household, leisure time, or transportation. Leisure-
time activity can be further subdivided into catego-
ries such as competitive sports, recreational activities
(e.g., hiking, cycling), and exercise training.
Exercise (or exercise training). Exercise and
physical activity have been used synonymously in
the past, but more recently, exercise has been used to
denote a subcategory of physical activity: "physical
activity that is planned, structured, repetitive, and
purposive in the sense that improvement or mainte-
nance of one or more components of physical fitness
is the objective" (Caspersen, Powell, Christensen
1985). Exercise training also has denoted physical
activity performed for the sole purpose of enhancing
physical fitness.

Physical fitness. Physical fitness has been de-
fined in many ways (Park 1989). A generally ac-
cepted approach is to define physical fitness as the
ability to carry out daily tasks with vigor and alert-
ness, without undue fatigue, and with ample energy
to enjoy leisure-time pursuits and to meet unfore-
seen emergencies. Physical fitness thus includes car-
diorespiratory endurance, skeletal muscular
endurance, skeletal muscular strength, skeletal mus-
cular power, speed, flexibility, agility, balance, reac-
tion time, and body composition. Because these
attributes differ in their importance to athletic
performance versus health, a distinction has been
made between performance-related fitness and
health-related fitness (Pate 1983; Caspersen, Powell,
Christensen 1985). Health-related fitness has been

20


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Table 2-1.  Glossary of terms
   ~~__

Aerobic training-Training that improves the efficiency of the
,It,r,)ljic energy-producing systems and that can improve
c ,Ir(tlorespiratory endurance.'

Agility-A skill-related component of physical fitness that relates
i,, the ,~bility to rapidly change the position of the entire body in
,ptlcc~ with speed and accuracy.+
Anaerobic training-Training that improves the efficiency of the
.,n,lerohic energy-producing systems and that can increase
n1u\cular strength and tolerance for acid-base imbalances during
hI&-Intensity effort.'

Balance-A skill-related component of physical fitness that
rctl,ltes to the maintenance of equilibrium while stationary or
mch~ln~.'

Body composition-A health-related component of physical
tltnclss that relates to the relative amounts of muscle, fat, bone,
,I~[I other vital parts of the body.+
Calorimetry-Methods used to calculate the rate and quantity
01 cbnk>rgy expenditure when the body is at rest and during
~.\orci~(~.'

Direct calorimetry-A method that gauges the body's rate
.1n(1 qu.mtity of energy production by direct measurement of
tl1(3 I~otly's heat production; the method uses a calorimeter,
\vhic:h is a chamber that measures the heat expended by the
I1ody.'

tndircct calorimetry-A method of estimating energy
c*spc,nditure by measuring respiratory gases. Given that the
.~rnount of 0, and CO1 exchanged in the lungs normally
(YI~,IIS that used and released by body tissues, caloric
c.upc.nditure can be measured by CO, production and O2
( onsumption..

Grdiorespiratory endurance (cardiorespiratory fitness)-A
tlcb.llth-related component of physical fitness that relates to the
.il~lllty oithe circulatory and respiratory systems to supply oxygen
tlurlng sustained physical activity.+
Coordination-A skill-related component of physical fitness that
rcSl.ltcs to the ability to use the senses, such as sight and hearing,
t~I<~~tl~cr with body parts in performing motor tasks smoothly
.Iml .tccurately.+

Detraining-Changes the body undergoes in response to a
rc.duc.tion or cessation of regular physical training.'
Endurance training/endurance activities-Repetitive, aerobic
art' of large muscles (e.g., walking, bicycling, swimming).*
Exercise (exercise training)-Planned, structured, and repetitive
I)(J(lily movement done to improve or maintain one or more
I omponents of physical fitness.

Flexibility-A health-related component of physical fitness that
rc'l~~tes to the range of motion available at a joint.*
Kilocalorie &cab--A measurement of energy. I kilocalorie = 1
(:dhie = 4,184 joules = 4.184 kilojoules.

Kilojoule (kjoule)-A measurement of energy. 4.184 kilojoules =
4,184 joules = 1 Calorie = 1 kilocalorie.
Maximal heart rate reserve-The difference between maximum
heart rate and resting heart rate.'
Maximal oxygen uptake (i/O, max )-The maximal capacity
for oxygen consumption by the body during maximal exertion.
It is also known as aerobic power, maximal oxygen consumption,
and cardiorespiratory endurance capacity.'
Maximal heart rate (HR max)-The highest heart rate value
attainable during an all-out effort to the point of exhaustion.'
Metabolic equivalent (MET)-A unit used to estimate the
metabolic cost (oxygen consumption) of physical activity. One
MET equals the resting metabolic rate of approximately 3.5 ml
0, o kg-l o min-I .*

Muscle fiber-An individual muscle cell.*

Muscular endurance-The ability of the muscle to continue to
perform without fatigue.'

Overtraining-The attempt to do more work than can be
physically tolerated.*

Physical activity-Bodily movement that is produced by the
contraction of skeletal muscle and that substantially increases
energy expenditure.

Physical fitness-A set of attributes that people have or achieve
that relates to the ability to perform physical activity.
Power-A skill-related component of physical fitness that relates
to the rate at which one can perform work.
Relative perceived exertion (RPE)-A person's subjective
assessment of how hard he or she is working. The Borg scale is a
numerical scale for rating perceived exertion.*
Reaction time-A skill-related component of physical fitness that
relates to the time elapsed between stimulation and the beginning
of the reaction to it.+

Resistance training-Training designed to increase strength,
power, and muscle endurance.*

Resting heart rate-The heart rate at rest, averaging 60 to 80
beats per minute.'

Retraining-Recovery of conditioning after a period of inactivity.*
Speed-A skill-related component of physical fitness that relates
to the ability to perform a movement within a short period of
time.+

Strength-The ability of the muscle to exert force.'
Training heart rate (THR)-A heart rate goal established by using
the heart rate equivalent to a selected training level (percentage
of $0, max ). For example, if a training level of 75 percent i/O,
max is desired, theGO, at 75 percent is determined and the heart
rate corresponding to this V02 is selected as the THR.'

`i rrJn' tVllm()re IH, Costill DL. Physiology ofsport and exercise. Champaign, IL: Human Kinetics. 1994.
' T'lnJ (:()rhin CB. Lindsey R. Concepts in physica/ education with /aboratories. 8th eci. Dubuque, IA: Times Mirror Higher Education Group, 1994.
' "l.!lltt'ci tr(jnl Corhin CB, Lindsey R, 1994, and Wilmore JH, Costill DL, 1994.


Physical Activity and Health

said to include cardiorespiratory fitness, muscular
strength and endurance, body composition, and flex-
ibility. The relative importance of any one attribute
depends on the particular performance or health goal.
  Health. The 1988 International Consensus Con-
ference on Physical Activity, Physical Fitness, and
Health (Bouchard et al. 1990) defined health as "a
human condition with physical, social, and psycho-
logical dimensions, each characterized on a con-
tinuum with positive and negative poles. Positive
health is associated with a capacity to enjoy life and
to withstand challenges; it is not merely the absence
of disease. Negative health is associated with mor-
bidity and, in the extreme, with premature mortal-
ity." Thus, when considering the role of physical
activity in promoting health, one must acknowledge
the importance of psychological well-being, as well
as physical health.

Evolution of Physical Activity
Recommendations

In the middle of the 20th century, recommendations
for physical activity to achieve fitness and health
benefits were based on systematic comparisons of
effects from different profiles of exercise training
(Cureton 1947; Karvonen, Kentala. Mustala 1957;
Christensen 1960; Yakolav et al. 1961; Reindell,
Roskamm, Gerschler 1962). In the 1960s and 1970s,
expert panels and committees, operating under the
auspices of health- or fitness-oriented organizations,
began to recommend specific physical activity pro-
grams or exercise prescriptions for improving physi-
cal performance capacity or health (President's
Council on Physical Fitness 1965; AHA 1972,1975;
ACSM 1975). These recommendations were based
on substantial clinical experience and on scientific
data available at that time.

Pollock's 1973 review of what type of exercise
was needed to improve aerobic power and body
composition subsequently formed the basis for a
1978 position statement by the ACSM titled "The
Recommended Quantity and Quality of Exercise for
Developing and Maintaining Fitness in Healthy
Adults." This statement outlined the exercise that
healthy adults would need to develop and maintain
cardiorespiratory fitness and healthy body composi-
tion. These guidelines recommended a frequency of

exercise training of 3-5 days per week, an intensity
of training of 60-90 percent of maximal heart rate
(equivalent to 50-85 percent of maximal oxygen
uptake or heart rate reserve), a duration of 15-60
minutes per training session, and the rhythmical and
aerobic use of large muscle groups through such
activities as running or jogging, walking or hiking,
swimming, skating, bicycling, rowing, cross-country
skiing, rope skipping, and various endurance games
or sports (Table 2-2).

Between 1978 and 1990, most exercise recom-
mendations made to the general public were based
on this 1978 position statement, even though it
addressed only cardiorespiratory fitness and body
composition. By providing clear recommendations,
these guidelines proved invaluable for promoting
cardiorespiratory endurance, although many people
overinterpreted them as guidelines for promoting
overall health. Over time, interest developed in po-
tential health benefits of more moderate forms of
physical activity, and attention began to shift to
alternativephysicalactivityregimens (HaskelllQ84;
Blair, Kohl, Gordon 1992; Blair 1993).
In 1990, the ACSM updated its 1978 position
statement by adding the development of muscular
strength and endurance as a major objective (ACSM
1990). The recommended frequency, intensity, and
mode of exercise remained similar, but the duration
was slightly increased from 15-60 minutes to 20-60
minutes per session, and moderate-intensity resis-
tance training (one set of 8-12 repetitions of 8-10
different exercises at least 2 times per week) was
suggested to develop and maintain muscular strength
and endurance (Table 2-2). These 1990 recommen-
dations also recognized that activities of moderate
intensity may have health benefits independent of
cardiorespiratory fitness:

Since the original position statement was pub-
fished in 1978, an important distinction has
been made between physical activity as it
relates to health versus fitness. It has been
pointed out that the quantity and quality of
exercise needed to obtain health-related ben-
efits may differ from what is recommended
forfitness benefits. It is now clear that lower
levels ofphysical activity than recommended
by this position statement may reduce the
riskfor certain chronic degenerative diseases


Historical Background, Terminology, Evolution of Recommendations, and Measurement

attd yet may not be of sufficient quantity or
cilia/ity to improve [maximal oxygen uptake].
~\CSM recognizes the potential health benefits
c,fr.cg[41ar exercise performed morefrequently
cl,~d,f~t- longer duration, but at lower intensi-
tics t/Ian prescribed in this position statement.

ln conjunction with a program to certify exercise
professionals at various levels of experience and
~c~Inpetence, the ACSM has published five editions
(,f G&clines for Exercise Testing and Prescription
(ACSM 1975, 1980, 1986, 1991, 1995b) that de-
scribe the components of the exercise prescription
arid explain how to initiate and complete a proper
cscrcise training program (Table 2-2). The ACSM
1~1s also published recommendations on the role
ofcxcrcise for preventing and managing hyperten-
5ion (1993) and for patients with coronary heart
discasc (1994) and has published a position stand
011 osteoporosis (1995a). For the most part, newer
rccommcndations that focus on specific health
outcomes are consistent with the ACSM's 1978
;lnrl 1990 position statements, but they generally
cspand the range of recommended activities to
include moderate-intensity exercise.
  Bctwccn the 1960s and lQQOs, other U.S. health
;~ncl fitness organizations published recommenda-
tions for physical activity. Because these organiza-
tions used the same scientific data as the ACSM, their
position statements and guidelines are similar. A
IW~I&J example is Healthy People 2000 (USDHHS
IWO), the landmark publication of the U.S. Public
I Icalth Service that lists various health objectives for
the nation. (The objectives for physical activity and
~I~UCSS, as revised in 1995 [USDHHS 19951, are
lucludcd as Appendix A of this chapter.) Other
rccommcndations include specific exercise programs
clc\*clopcd for men and women by the President's
Gjuncil on Physical Fitness (1965) and the YMCA
(%lional Council YMCA 1989). The AHA (1972,
1975, 1992, 1993, 1994, 1995) has pbblished for
lull health professionals and the public a series of
l)lWcal activity recommendations and position state-
Illcnts directed at CHD prevention and cardiac reha-
1Jilitation. In 1992, the AHA published a statement
Identifying physical inactivity as a fourth major risk
factor for CHD, along with smoking, high blood
Pressure. and high blood cholesterol (Fletcher et al.
1'192). The American Association of Cardiovascular

and Pulmonary Rehabilitation has also published
guidelines for using physical activity for cardiac
(199 1, 1995) and pulmonary (1993) rehabilitation.
Some of these recommendations provide substantial
advice to ensure that exercise programs are safe for
people at increased risk for heart disease or for
patients with established disease.
  Between the 1970s and the mid-lQQOs, exercise
training studies conducted on middle-aged and older
persons and on patients with lower functional capac-
ity demonstrated that significant.cardiorespiratory
performance and health-related benefits can be ob-
tained at more moderate levels of activity intensity
than previously realized. In addition, population-
based epidemiologic studies demonstrated dose-
response gradients between physical activity and
health outcomes. As a result of these findings, the
most recent CDC-ACSM guidelines recommend that
all adults perform 30 or more minutes of moderate-
intensity physical activity on most, and preferably
all, days--either in a single session or "accumulated"
in multiple bouts, each lasting at least 8-10 minutes
(Pate et al. 1995). This guideline thus significantly
differs from the earlier ones on three points: it
reduces the minimum starting exercise intensity
from 60 percent of maximal oxygen uptake to 50
percent in healthy adults and to 40 percent in pa-
tients or persons with very low fitness; it increases
the frequency of exercise sessions from 3 days per
week to 5-7 days per week, depending on intensity
and session duration; and it includes the option of
accumulating the minimum of 30 minutes per day in
multiple sessions lasting at least 8-10 minutes (Pate
et al. 1995). This modification in advice acknowl-
edges that people who are sedentary and who do not
enjoy, or are otherwise not able to maintain, a regi-
men of regular, vigorous activity can still derive
substantial benefit from more moderate physical
activity as long as it is done regularly.
  The NIH Consensus Development Conference
Statement on Physical Activity and Cardiovascular
Health identifies physical inactivity as a major pub-
lic health problem in the United States and issues a
call to action to increase physical activity levels
among persons in all population groups. (See Ap-
pendix B for full text of the recommendations.) The
core recommendations, similar to those jointly made
by the CDC and the ACSM (Pate et al. 1995), call for

23


Physical Activity and Health

Table 2-2. Selected physical activity recommendations in the United States (1965-1996)

Source                Objective             Type/mode
                                           General fitness

                                           Endurance
                                 Endurance, strength, flexibility
                                 Endurance, strength, flexibility

PCPF (1965)

AHA Recommendations (1972)

YMCA (1973)

ACSM Guidelines (1975)

Physical fitness
CHD prevention
General health and fitness
Cardiorespiratory fitness

AHA Recommendations (1975)

ACSM Position Statement (1978)

USDHEW-Healthy People (1979)

ACSM Guidelines (1980)

ACSM Guidelines (1986)

USDHHS-Surgeon General's Report
on Nutrition and Health (1988)

USPSTF (1989)

ACSM Position Stand (1990)

ACSM Guidelines (1991)

USHHS/USDA Dietary
Guidelines (1990)

AACVPR (1991)

DHHS-Healthy People 2000 (1991)*

AHA Position Statement (1992)

AHA Standards (1992 and 1995)

AACVPR (1993)

ACSM Position Statement (1993)

Secondary prevention in patients
with heart disease

Cardiorespiratory fitness
and body composition

Disease prevention/
health promotion
Cardiorespiratory fitness

Cardiorespiratory fitness

Weight control

Primary prevention in clinical practice
Cardiorespiratory and muscular
fitness

Cardiorespiratory fitness

Health promotion/disease prevention,
weight maintenance
Cardiac rehabilitation

Disease prevention/health promotion

CVD prevention and rehabilitation
CHD prevention and rehabilitation

Pulmonary rehabilitation

Prevention and treatment
of hypertension

Endurance

Endurance

Endurance

Endurance, strength, flexibility

Endurance, strength, flexibility

Endurance

Not specified, implied endurance
Endurance, strength

Endurance, strength, flexibility

Not specified

Endurance, strength

Endurance, strength, flexibility

Endurance

Endurance, strength

Endurance

Endurance, strength

24


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Intensity
Five levels

70-85% MHR
80% i/O, max
60-90% i/O, max
60-90% HRR

T&85% MHR

Endurance

Frequency

Duration

Resistance training

5 x week

3-7 x week

3 x week

3 x week

Approximately 30 minutes

15-20 minutes

40-45 minutes

20-30 minutes

Selected calisthenics

Not addressed

Not specified
Not specified

34 x week

20-60 minutes

Not addressed

  .
Not addressed

50-85% ifO, max
50435% HRR
60-90% MHR

Moderate/hard

3-5 x week

3 x week

5s85%\;/0, max/HRR
ho-90% MH R
io-05% i/O, max/HRR
oo-`10% MHR

Not specified

3-5 x week

3-5 x week

13 x week

AI least moderate
.50-85%i/O, max
W-85'% HRR
OO-OO'%, MHR
40-11.5'%1 00, max
5 5-OO'X, MHR
KI'E = 12-l 6

Not specified

Not specified

3-5 x week

3-5 x week

Not specified

bcrcise following ACSM
I 1 OtlO) and AHA (1983)
rcbc-ommendations
Light/moderate/vigorous

3-5 x week

3-5 x week

b- 50% i/O2 nlax
jO-60% 90, max
jO-60% HR reserve

3-4 x week

13 x week

()()":I HR reserve         3 x week
-W70"/0 i/O, max        3-5 x week

15-60 minutes

15-30 minutes

15-60 minutes

15-60 minutes

2 20 minutes

Not specified

20-60 minutes

15-60 minutes

Not specified

15-60 minutes

20-30 minutes

30-60 minutes

2 30 minutes

20-30 minutes

20-60 minutes

Not addressed

Not specified

Not specified

Not addressed

Not addressed

1 set, 8-l 2 repetitions
8-l 0 exercises
2 days x week
Not specified

Not addressed

l-3 sets, 12-l 5 repetitions
major muscle groups
2-3 days x week
Not specified

Not addressed

1 set, 1 O-l 5 repetitions
8-l 0 exercises,
2-3 days x week

Not addressed

Not specified

--

25


Physical Activity and Health

Table 2-2. Continued

Source

Obiective

Type/mode

AHA Position             CVD prevention
Statement (1993)             and rehabilitation

ACSM Position Stand (1994)

Secondary prevention in patients
with coronary heart disease

AHA Position Statement (1994)

Cardiac rehabilitation

Physical Activity Guidelines
for Adolescents (1994Y

AACVPR (I 995)

Lifetime health promotion
for adolescents

Cardiac rehabilitation

ACSM Guidelines (1995)

Cardiorespiratory fitness
and muscular fitness

ACSM Position Stand (1995)

Prevention of osteoporosis

AHCPR (1995)

Cardiac rehabilitation

AMA Guidelines for
Adolescent Preventive
Services (GAPS) (1994)

CDC/ACSM (1995)*

Health promotion/
physical fitness

Health promotion

USHHYUSDA Dietary
Guidelines (1995)

NHLBI Consensus Conference
(1996)

USPSTF (1996)

Health promotion/disease
prevention, weight maintenance
CVD prevention for adults and
children and cardiac rehabilitation

Primary prevention
in clinical practice

Moderate intensity
(i.e., brisk walking) integrated
into daily routine

Endurance, strength

Endurance and strength training
of moderate intensity following
other guidelines

Endurance

Endurance, strength

Endurance, strength

Strength, flexibility, coordination,
cardiorespiratory fitness
Endurance, strength

Endurance

Endurance

Endurance

Endurance

Endurance, strength, flexibility

26


Historical Background, Terminology, Evolution of Recommendations, and Measurement

- .~__
Intensity

Endurance

Frequency
Not specified

Duration

Resistance training

Not specified

Not specified

Not addressed

4045% 00, max
JO-85% HRR
55-90% MHR
Not specified

3 x week,
nonconsecutive days

Not specified

Moderate/vigorous

> 50% i/O, max
KPE 12-14

3 x week, vigorous
daily, moderate

3-5 x week

JO-SS%i/O, max/HRR
RPE 12-16

3-5 x week

NOI specified         Not specified

7045% MHR

3 x week

Mo(kratc

2 3 x week

2040 minutes

Not specified

2 20 minutes, vigorous
not specified, moderate

30-45 minutes, 200-300
kcal per session or
1,000-l ,500 kcal per week
12-l 5 minutes initially:
20-30 minutes for
conditioning and
maintaining
Not specified

20-40 minutes

20-30 minutes

Not specified

Not specified

Not addressed

1 set, 1 O-l 5 repetitions,
major muscle groups
2-3 days x week
1 set, 8-l 2 repetitions
8-l 0 exercises
2 days x week

Not specified

Not specified

Not addressed

Moderate/hard

All or most days

L 30 minutes per day
in bouts of at least 8-l 0
minutes

Not specified

Modcrate

All or most days

2 30 minutes per day

Not addressed

iMoclcrate/hard

All or most days

2 30 minutes per day

Not addressed

Most days

30 minutes

Not specified

     .~                                                                           --
`4f't8 :\t)twndix B for listing of objectives.  `See Sallis and Patrick, 1994.  *See Pate et al., 1995.
hIa\ 11) `lssnciations: AACVPR = American Association for Cardiovascular and Pulmonary Rehabilitation; ACSM = American College of sports
\\l.(ilc lw; AHA = American Heart Association; AHCPR = Agency for Health Care Policy and Research; CDC = Centers for Disease Control and
I'r15\~*nrmn: NtjLBI = National Heart, Lung, and Blood Institute; PCPF = President's Council on Physical Fitness; USDA = United States Department
oI ,\<rl! ulture: LJSDHEW = United States Department of Health, Education, and Welfare; USDHHS = United States Department of Health and
t tum.1n Swwces: USPSTF = United States Preventive Services Task Force; YMCA = Young Men's Christian Association.
il.\ 111 ,~hhrevialions: CHD = coronary heart disease; CVD = cardiovascular disease; HRR = heart rate reserve; MHR = maximal heart fate;
K"f = r,ltinR oi perceived exertion;i/O> max = maximal oxygen uptake.
\I" ,I(itlre\sed = not included in recommendations. Not specified = recommended but not quantified.

27


Physical Activity and Health

all children and adults to accumulate at least 30
minutes per day of moderate-intensity physical
activity. The recommendations also acknowledge
that persons already achieving this minimum could
experience greater benefits by increasing either the
duration or the intensity of activity. In addition, the
statement recommends more widespread use of car-
diac rehabilitation programs that include physical
activity.

The consensus statement from the 1993 Inter-
national Consensus Conference on Physical Activ-
ity Guidelines for Adolescents (Sallis and Patrick
1994) emphasizes that adolescents should be physi-
cally active every day as part of general lifestyle
activities and that they should engage in 3 or more
20-minute sessions of moderate to vigorous exer-
cise each week. The American Academy of Pediat-
rics has issued several statements encouraging active
play in preschool children, assessment of children's
activity levels, and evaluation of physical fitness
(1992, 1994). Both the consensus statement and
the American Academy of Pediatrics' statements
emphasize active play, parental involvement, and
generally active lifestyles rather than specific vigor-
ous exercise training. They also acknowledge the
need for appropriate school physical education
curricula.

Recognizing the important interrelationship of
nutrition and physical activity in achieving a balance
between energy consumed and energy expended, the
1988 Surgeon General's Report on Nutrition and
Health (USDHHS 1988) recommended physical ac-
tivities such as walking, jogging, and bicycling for at
least 20 minutes, 3 times per week. The 1995 Dietary
Guidclincs Jot- Americans greatly expanded physical
activity guidance to maintain and improve weight.
The bulletin recommends that all Americans engage
in 30 minutes of moderate-intensity physical activity
on all, or most, days of the week (USDA/USDHHS
1995).

The U.S. Preventive Services Task Force
(USPSTF) has recommended that health care pro-
viders counsel all patients on the importance of
incorporating physical activities into their daily
routines to prevent coronary heart disease, hyper-
tension, obesity, and diabetes (Harris et al. 1989;
USPSTF 1989, 1996). Similarly, the American

Medical Association's Guidelines for Adolescent
Preventive Services (GAPS) (AMA 1994) recom-
mends that physicians provide annual physical ac-
tivity counseling to all adolescents.

Summary of Recent Physical
Activity Recommendations
Sedentary persons can increase their physical activ-
ity in many ways. The traditional, structured ap-
proach originally described by the ACSM and others
involved rather specific recommendations regard-
ing type, frequency, intensity, and duration of ac-
tivity. Recommended activities typically included
fast walking, running, cycling, swimming, or aero-
bics classes. More recently, physical activity recom-
mendations have adopted a lifestyle approach to
increasing activity (Pate et al. 1995). This method
involves common activities, such as brisk walking,
climbing stairs (rather than taking the elevator),
doing more house and yard work, and engaging in
active recreational pursuits. Recent physical activity
recommendations thus acknowledge both the struc-
tured and lifestyle approaches to increasing physical
activity. Either approach can be beneficial for a
sedentary person, and individual interests and op-
portunities should determine which is used. The
most recent recommendations cited agree on sev-
eral points:

. All people over the age of 2 years should
accumulate at least 30 minutes of endurance-
type physical activity, of at least moderate
intensity, on most-preferably all-days of
the week.

. Additional health and functional benefits of
physical activity can be achieved by adding
more time in moderate-intensity activity, or
by substituting more vigorous activity.

. Persons with symptomatic CVD, diabetes, or
other chronic health problems who would like
to increase their physical activity should be
evaluated by a physician and provided an
exercise program appropriate for their clinical
  status.


Historical Background, Terminology, Evolution of Recommendations, and Measurement

. Previously inactive men over age 40, women
over age 50, and people at high risk for CVD
should first consult a physician before em-
barking on a program of vigorous physical
activity to which they are unaccustomed.

. Strength-developing activities (resistance train-
ing) should be performed at least twice per
week. At least 8-10 strength-developing exer-
cises that use the major muscle groups of the
legs. trunk, arms, and shoulders should be
performed at each session, with one or two sets
of 8-12 repetitions of each exercise.

Measurement of Physical Activity,
Fitness, and Intensity
~I-hc :lbitity to relate physical activity to health de-
pcnds on accurate, precise, and reproducible mea-
4~~~~~ (\Vilson et al. 1986; National Center for Health
\r;llistics 1989). Measurement techniques have
cvotvc`cl considerably over the years (Park 1989),
c.rcating a shifting pattern of strength and weakness
in I hc cvidcnce supporting the assertion that physi-
(.;I1 ;lctivity improves health (Ainsworth et al. 1994).
I'hc complexity is heightened by the different health
Implications of measuring activity, gauging inten-
YII~. ;~ntl assessing fitness. The tools currently in use
( I`;lt>lc 2-3) must be evaluated not only for their
~~lt'icacy in measuring an individual's status, but also
Ior 1 heir applicability as instruments in larger-scale
L*piclcmiologic research. These tools vary consider-
.llJI!. in the age groups to which they can be applied,
:\4 well as in their cost, in their likelihood of affecting
1 hc behavior they try to measure, and in their accept-
.\hiliry. For example, many of the tools that are
.ll>propriate for young and middle-aged persons are
1~~s so for the elderly and may have no relevance at
.kIt for children. A brief review of these approaches
Ilr(j\.idcs some insight into the current. constellation
of strengths and weaknesses on which epidemio-
I(jgic conclusions rest.

Measuring Physical Activity
Measures Based on Self-Report
l'h!sical activity is a complex set of behaviors most
c(`mmonly assessed in epidemiologic studies by ask-
In3 People to classify their level of physical activity

(LaPorte, Montoye, Caspersen 1985; Caspersen
1989). Techniques used to gather this self-reported
information include diaries, logs, recall surveys,
retrospective quantitative histories, and global self-
reports (Kannel, Wilson, Blair 1985; Wilson et al.
1986; Powell et al. 1987; Caspersen 1989). Surveys
are practical for assessing physical activity in large
populations because they are not costly, are rela-
tively easy to administer, and are generally accept-
able to study participants (Montoye andTaylor 1984;
LaPorte, Montoye, Caspersen 1985.; Caspersen 1989).
Information obtained from self-report instruments
has often been converted into estimates of energy
expenditure (i.e., kilocalories or kilojoules; meta-
bolic equivalents [METS]) or some other summary
measure that can be used to categorize or rank
persons by their physical activity level. This tech-
nique has also been used to convert job classifica-
tions into summary measures.
Diaries can detail virtually all physical activity
performed during a specified (usually short) period.
A summary index can be derived from a diary by
1) summing the total duration of time spent in a
given activity multiplied by an estimated rate of
energy expenditure for that activity, or 2) listing
accumulated time across all activities or time ac-
crued within specific classes of activities. Compari-
sons with indirect calorimetry or with caloric intake
have shown that diaries are accurate indices of daily
energy expenditure (Acheson et al. 1980). Because
diaries are commonly limited to spans of l-3 days,
they may not represent long-term physical activity
patterns (LaPorte, Montoye, Caspersen 1985). Dia-
ries require intensive effort by the participant, and
their use may itself produce changes in the physical
activities the participant does during the monitoring
period (LaPorte, Montoye, Caspersen 1985;
Caspersen 1989).

Logs are similar to diaries but provide a record of
participation in specific types of physical activity
rather than in all activites (King et al. 1991). The
time that activity was started and stopped may be
recorded, either soon after participation or at the end
of the day. Logs can be useful for recording parrici-
pation in an exercise training program. But as with
diaries, they can be inconvenient for the participant,
and their use may itself influence the participant's
behavior.


Physical Activity and Health

Table 2-3. Assessment procedures and their potential use in epidemiologic research

                   Use in           Low    Low
              large  Low Low subject subject Likely to  Accep-  Socially
Measurement   Applicable   scale $    time time   effort  influence table to accep-  Activity
tool          age groups   studies cost  cost cost    cost   behavior persons table  specific

Surveying
Task specific diary
Recall questionnaire
Quantitative history
Global self-report
Monitoring

Behavioral
observation

Job classification

Heart rate monitor

Heart rate and
motion sensor

Electronic motion

sensor

Pedometer

Gait assessment

Accelerometers

Horizontal time
monitor

Stabilometers

Direct calorimetry
indirect calorimetry
Doubly labeled

adult, elderly
adult, elderly
adult, elderly
adult, elderly

adult, elderly

adult

all

all           no

adult, elderly   yes

adult, elderly

child, adult,
elderly

all

child, adult,
elderly

infant

all

adult, elderly

child, adult,

no

yes

no

yes

no

water         elderly  -
Modified from LaPorte, Montoye, Caspersen. Public Health Reports, 1985.
Note that most tests that are applicable for adults can be used in adolescents as well. Few tests can be applied to the pediatric age groups;
among infants, only direct calorimetry, accelerometers, heart rate monitoring, and stabilometers can be used with accuracy.

yes

no

no


no


no

yes

no

yes

no

no


no

yes

no

yes

no

no


no


no


no

yes

yes

no

yes

no

yes

no

no

yes

yes

yes

yes

yes

yes

no


no


no

no


yes

no


yes

no

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no

yes

no

yes

no

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no


yes

yes

no


no


no

yes

no


no

no


no

no


no

no


no

110

yes

yes

no

?

yes

yes

k-5

?

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no


yes

?

yes

yes

yes

yes

yes

yes

yes

yes

yes

no


no


ye=

yes

yes

yes

no

yes

yes

no

no


no

no


no

no


no

no

yes

yes

no

Recall surveys are less likely toinfluence behav-
ior and generally require less effort by the respon-
dent than either diaries or logs, although some
participants have trouble remembering details of
past participation in physical activity (Baranowski
1985). Recall surveys of physical activity generally
have been used for time frames of from 1 week to a
lifetime (Kriska et al. 1988; Blair et al. 1991). They
can ascertain either precise details about physical

activity or more general estimates of usual or typical
participation. The recall survey is the method used
for the national and state-based information systems
providing data for Chapter 5 of this report.

The retrospective quantitative history-the most
comprehensive form of physical activity recall survey
-generally requires specific detail for time frames of
up to 1 year (LaPorte, Montoye, Caspersen 1985). If
the time frame is long enough, the quantitative history

30


Historical Background, Terminology, Evolution of Recommendations, and Measurement

can adequately represent year-round physical activ-
ity, For example, the Minnesota Leisure-Time Physi-
cal ,Activity Questionnaire and the Tecumseh
questionnaire obtained information on the average
[rcquency and duration of participation for a specific
list of physical activities performed over the previous
!.ci~r (Montoye and Taylor 1984; Taylor et al. 1978).
rufortunately, obtaining this abundance of data is a
hc:l\y demand on the respondent's memory, and the
complexity of the survey generates additional ex-
pcnsc (LaPorte, Montoye, Caspersen 1985).
Ghbal selJ-reports, another type of recall survey,
ask individuals to rate their physical activity rela-
live to other people's in general or to that of a
similar age and sex group. This easy-to-use ap-
proach, which was employed for the National Health
lntcrvicw Survey (NCHS, Bloom 1982>, tends to
hcst rcprcsent participation in vigorous physical
.lctivity (Washburn, Adams, Haile 1987; Caspersen
;~nd Pollard 1988; Jacobs et al. 1993). A weakness of
rhis approach is that persons reporting the same
rating may have different actual physical activity
prl~filcs (Washburn, Adams, Haile 1987; Caspersen
;lnd Pollard 1988).

Although survey approaches generally apply to
~lults, adolescents, and the elderly, survey instru-
111cnts must often be tailored to the specific demo-
graphic requirements of the group under study.
Rcccnlly, some researchers have suggested develop-
ing special survey instruments for older persons
(Voorrips et al. 1991; Dipietro et al. 1993; Washburn
1-l al. 1993) and adolescents or children (Noland et
ill. 1990; Sallis et al. 1993).

Measures Based on Direct Monitoring
fhc major alternative to surveys is to directly mea-
`urc physical activity through behavioral observa-
[Ion, mechanical or electronic devices, or
physiologic measurements (Table 2-3). Such ap-
IJroaches eliminate the problems of poor memory
.Ind biased self-reporting but are themselves lim-
ltcd by high cost and the burden on participants
~lnd staff. Consequently, these measures have been
used primarily in small-scale studies, though they
Ila\`e been used recently in some large-scale studies
' Lakka, Nyyssonen, Salonen 1994).

Behavioral observation is the straightforward
Uccss of watching and recording what a person
tl"es. Using general guidelines for caloric expenditure

associated with specific activities, a summary estimate
of caloric output can be obtained from such observa-
tion. An important subtype of this approach is the
classification ofwork based on the amount of physical
activity it requires. These approaches can be labor-
intensive (hence prohibitively expensive for large-
scale studies) but are usually well accepted by study
participants.'

In the category of mechanical or electronic mea-
surement, various instruments have been used to
monitor heart rate and thus @o.vide a continuous
recording of a physiologic process that reflects both
the duration and intensity of physical activity. Heart
rate is typically used to estimate daily energy expen-
diture (i.e., oxygen uptake) on physical activity; the
underlying assumption is that a linear relationship
exists between heart rate and oxygen uptake. A
major disadvantage of heart rate monitoring is the
need to calibrate the heart rate-energy expenditure
curve for each individual. Another limitation is that
the relationship between heart rate and energy ex-
penditure is variable for low-intensity physical ac-
tivities. Most monitors have to be worn for extended
periods by the participant, and they pose some dis-
comfort and inconvenience.

Other approaches for using heart rate to measure
physical activity include using the percentage of time
spent during daily activities in various ranges of
heart rate (Gilliam et al. 1981), using the difference
between mean daily heart rate and resting heart rate
(Sallis et al. 1990), and using the integration of the
area under a heart rate versus time curve adjusted for
resting heart rate (Freedson 1989). Heart rate alone
may not be a suitable surrogate for determining the
level of physical activity, given that other factors,
such as psychological stress or changes in body
temperature, can significantly influence heart rate
throughout the day.

A variety of sensors have been developed to
measure physical activity by detecting motion. Pe-
dometers, perhaps the earliest motion sensors, were
designed to count steps and thus measure the dis-
tance walked or run. However, not all pedometers
are reliable enough for estimating physical activity in
either laboratory or field research (Kashiwazaki et al.
1986; Washburn, Janney, Fenster 1990). Electronic
motion sensors tend to perform better than their
mechanical counterparts (Wong et al. 1981; Taylor
et al. 1982; LaPorte et al. 1983). Their output has

31


Physical Activity and Health

been significantly correlated with energy expendi-
ture assessed with indirect calorimetry in controlled
laboratory conditions using graded treadmill exer-
cise (Balogun, Amusa, Onyewadume 1988; Haskell
et al. 1993; Montoye et al. 1996), under short-term
controlled activity (e.g., walking or cycling over a
measured course) for heart rate during laboratory
and daily activities, and for observed behavior in a
controlled setting (Klesges and Klesges 1987; Rogers
et al. 1987; Freedson 1989; Sallis et al. 1990;
Washburn, Janney, Fenster 1990). Direct validation
has shown reasonable correlation with physical ac-
tivity records completed over a year (Richardson et
al. 1995). Recording simultaneously both the heart
rate and the motion from sensors on several parts of
the body and then calibrating each individual's heart
rate and motion sensor output versus oxygen uptake
for various activities can accurately estimate the
energy expended from physical activity (Haskell et
al. 1993). Several other devices (e.g., accelerometers,
stabilometers) are of lesser value for large-scale stud-
ies, and their use is limited to small physiologic
investigations.

Methods for physiologically monitoring energy
expenditure include direct calorimetry (requiring the
participant to remain in a metabolic chamber) and
indirect calorimetry (requiring the participant to wear
a mask and to carry equipment for analyzing expired
air). Both methods are too expensive and complicated
for use in large-scale studies. Another physiologic
measurement, the use of doubly labeled water, offers
researchers special opportunities to assess energy ex-
penditure. By using two stable isotopes (?H?O and
H,`"O) measured every few days or weeks in the urine,
researchers can calculate the rate of carbon dioxide
production-a reflection of the rate ofenergy produc-
tion in humans over time. According to their body
weight, study participants drink a specified amount of
these isotopes. A mass spectrometer is used to track
the amount of unmetabolized isotope in the urine.
Although this technique obtains objective data with
little effort on the part of participants, two disadvan-
tages are its relatively high cost and its inability to
distinguish between typesofactivitiesperformed. The
technique has been proven accurate when compared
withindirect calorimetry (Klein etal. 1984; Westerterp
et al. 1988; Edwards et al. 1990).

Measuring Intensity of Physical Activity
Common terms used to characterize the intensity
of physical activity include light or low, moderate
or mild, hard or vigorous, and very hard or strenu-
ous (Table 2-4). A frequent approach to classify-
ing intensity has been to express it relatively-that
is, in relation to a person's capacity for a specific
type of activity. For example, the intensity pre-
scribed for aerobic exercise training usually is ex-
pressed in relation to the p.erson's measured
cardiorespiratory fitness (ACSM 1990). Because
heart rate during aerobic exercise is highly associ-
ated with the increase in oxygen uptake, the per-
centage of maximal heart rate is often used as a
surrogate for estimating the percentage of maximal
oxygen uptake (ACSM 1990). Exercise intensity
can also be expressed in absolute terms, such as a
specific type of activity with an assigned intensity
(for example, walking at 4 miles per hour or jogging
at 6 miles per hour). Such quanta of work can also
be described in absolute terms as METS, where one
MET is about 3.5 ml 0, o kg-' o min.`, corresponding
to the body at rest. The workloads in the just-
quoted example are equivalent to 4 and 10 METS,
respectively. The number of METS associated with
a wide range of specific activities can be estimated
from aggregated laboratory and field measurements
(Ainsworth, Montoye, Leon 1994).
  The process of aging illustrates an important
relationship between absolute and specific mea-
sures. As people age, their maximal oxygen uptake
decreases. Activity of a given MET value (an abso-
lute intensity) therefore requires a greater percent-
age of their maximal oxygen uptake (a relative
intensity). The aforementioned walk at 4 miles per
hour (4 METS) may be light exercise for a 20-year-
old, moderate for a 60-year-old, and vigorous for an
80-year-old.

Most exercise training studies have used relative
intensity to evaluate specific exercise training regi-
mens. On the other hand, observational studies relat-
ing physical activity to morbidity or mortality usually
report absolute intensity or total amount of physical
activity estimated from composite measures that in-
clude intensity, frequency, and duration. It is thus
difficult to compare the intensity of activity that
improves physiologic markers with the intensity of
activity that may reduce morbidity and mortality.


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Table 2-4. Classification of physical activity intensity, based on physical activity lasting up to 60 minutes
                                            Strength-type
                    Endurance-type activity                   exercise

                          Absolute intensity (METS)         Relative
          Relative intensity         in healthy adults (age in years)      intensity*

                                                              Maximal
     90, max (`7'~)  Maximal                 Middle-        Very         voluntary
       heart rate    heart          Young   aged     Old     old            contraction
Intensity   reserve (%)   rate (%)   RPE+     (20-39)   (40-64)   (65-79)   W+)     RPE     (%)

\ 1'1\' llglll   <25         <30      <9       <3.0     <2.5     <2.0     11.25     <lO   <30


I I:*111       25-44       30-49     9-10      3.0-4.7    2.5-4.4    2.0-3.5    1.26-2.2   10-11    30-49


\\I I( I~Y,lll~    45-59       SO-69     11-12     4.8-7.1    4.5-5.9    3.6-4.7    2.3-2.95   12-13    50-69


) I.110       60-84       70-89     13-16     7.2-10.1   6.0-8.4    4.8-6.7   3.0-4.25   14-16    70-84

\;VV h,lrd   285         290      >16      210.2     28.5      26.8      24.25      17-19   >85

\\.,\llll.ll'    100         100      20       12.0      10.0     8.0      5.0      20      100
                ~-

1,)(~1~~ .' .& Imlvided courtesy of Haskell and Pollock.
`I:.I..,Y~ on 11 -1 2 repetitions for persons under age 50 years and 1 O-l 5 repetitions for persons aged 50 years and older.
*I:SIII: I.III~): oi Relative Perceived Exertion 6-20 scale (Borg 1982).
"X\.I\IIII.I~ V.IIUVS are mean values achieved during maximal exercise by healthy adults. Absolute intensity (METS) values are approximate mean
\.IIIIC+ lor ~NV. Mean values for women are approximately l-2 METS lower than those for men.

Rcccnt public health guidelines and research
rclwrts have used absolute intensity to define ap-
I)ropriatc levels of physical activity, but the term
~~;~b~,olutc" may convey a misplaced sense of preci-
GOII. For example, the CDC-ACSM guidelines (Pate
1.1 ;II. 1~5) use absolute intensity to classify brisk
\\~;tlking as moderate physical activity. In contrast,
I I~~cclllty People 2000 objective 1.3 defines brisk
\valking as "light to moderate" intensity and takes
~rlto ilccount the age- and sex-related variability in
maximal capacity (USDHHS 1990). One solution to
rhih inconsistency in terminology is to create con-
\i.ctcnt categories that equate a variety of measures
lo the same adjective (Table 2-4). Using such a
rubric, the observations of Spelman and colleagues
( 1993) that brisk walking for healthy adults aged
-- ' `-58 years demands 40-60 percent of their aerobic
I'o\\`er suggests a correspondence with 3-5 METS
.lnd a classification of moderate intensity. Those
I)rcscribing an exercise pattern for adults can use
rhc rating of perceived exertion (RPE) scale (ACSM
1 W 1). An RPE of 10-l 1 corresponds to light inten-
`11~~ 12-13 to moderate intensity, and 14-16 to
hard intensity (Table 2-4), and the approximate

physiologic equivalents can be estimated. This type
of subjective scale furnishes a convenient way to
monitor performance.

Measuring Physical Fitness

Perhaps the most highly developed measurement
area is the assessment of physical fitness, since it
rests on physiologic measurements that have good
to excellent accuracy and reliability. The major foci
of fitness measurements are endurance (or cardio-
respiratory fitness), muscular fitness, and body
composition.

Endurance

Cardiorespiratory fitness, also referred to as cardio-
respiratory capacity, aerobic power, or endurance
fitness, is largely determined by habitual physical
activity. However, other factors influence cardio-
respiratory fitness, including age, sex, heredity,
and medical status (Bouchard, Shepard, Stevens
1994).

The best criterion of cardiorespiratory fitness is
maximal oxygen uptake or aerobic power NO, max).
Measured in healthy persons during large muscle,


Physical Activity and Health

dynamic activity (e.g., walking, running, or cycling),
VO, max is primarily limited by the oxygen transport
capacity of the cardiovascular system (Mitchell and
Blomqvist 1971).VO, max is most accurately deter-
mined by measuring expired air composition and
respiratory volume during maximal exertion. This
procedure requires relatively expensive equipment,
highly trained technicians, and time and coopera-
tion from the participant, all of which usually limit
its use in large epidemiologic studies (Montoye et al.
1970; King et al. 1991).

  Because the individual variation in mechanical
and metabolic efficiency is for activities that do not
require much skill-such as walking or running on a
motor-driven treadmill, cycling on a stationary bi-
cycle ergometer, orclimbing steps-oxygen uptake
can be quite accurately estimated from the rate of
work (Siconolfi et al. 1982). Thus,VO? max can be
estimated from the peak exercise workload during a
maximal exercise test without measuring respiratory
gases. Such procedures require an accurately cah-
brated exercise device, careful adherence to a spe-
cific protocol, and good cooperation by the
participant. They have been used in numerous exer-
cise training studies for evaluating the effects of
exercise on cardiovascular risk factors and perfor-
mance, in secondary prevention trials for patients
after hospitalization for myocardial infarction, and
in some large-scale observational studies (Blair et al.
1989; Sidney et al. 1992).

Any maximal test to assess cardiorespiratory
fitness imposes a burden on both the participant
and the examiner. To reduce this burden, several
submaximal exercise testing protocols have been
developed. With these protocols, the heart rate
response to a specified workload is used to predict
theVOL max. The underlying assumption (besides
the linear relationship between heart rate and oxy-
gen uptake) is that the participant's maximal heart
rate can be estimated accurately. Both assumptions
are adequately met when a standardized protocol is
used to test a large sample of healthy adults. In some
cases, no extrapolation to maximal values is per-
formed, and an individual's cardiorespiratory fit-
ness is expressed as the heart rate at a set workload
(e.g., heart rate at 5 kilometers/hour or at 100
watts) or at the workload required to reach a spe-
cific submaximal heart rate (workload at a heart
rate of 120 beats/minute).

In another approach to assessing cardiorespi-
ratory fitness, participants usually walk, jog, or
run a specified time or distance, and their perfor-
mance is converted to an estimate of VO, max
(Cooper 1968). These procedures have been fre-
quently used to test the cardiorespiratory fitness
of children, of young adults, or of groups that have
occupation-related physical fitness requirements,
such as military and emergency service personnel.
In many cases, these tests require maximal or
near-maximal effort by the participant and thus
have not been used for older persons or those at
increased risk for CVD. The advantage is that large
numbers of participants can be tested rapidly at low
cost. However, to obtain an accurate evaluation,
participants must be willing to exert themselves
and know how to set a proper pace.

Muscular fitness

Common measures of muscular fitness are muscular
strength, muscular endurance, flexibility, and bal-
ance, agility, and coordination. Muscular strength
can be measured during performance of either static
or dynamic muscle contraction (NCHS, Wilmore
1989). Because muscular strength is specific to the
muscle group, the testing of one group does not
provide accurate information about the strength of
other muscle groups (Clarke 1973). Thus, for a
comprehensive assessment, strength testing must
involve at least several major muscle groups, includ-
ing the upper body, trunk, and lower body. Standard
tests have included the bench press, leg extension,
and biceps curl using free weights. The heaviest
weight a person can lift only one time through the
full range of motion for a particular muscle group is
considered the person's maximum strength for that
specific muscle group.

Muscular endurance is specific to each muscle
group. Most tests for use in the general population do
not distinguish between muscular endurance and
muscular strength. Tests of muscular endurance and
strength, which include sit-ups, push-ups, bent-arm
hangs, and pull-ups, must be properly administered
and may not discriminate well in some populations
(e.g., pull-ups are not a good test for many popula-
tions because a high percentage of those tested will
have 0 scores). Few laboratory tests of muscular
endurance have been developed, and such tests usu-
ally involve having the participant perform a series of

34


Historical Background, Terminology, Evolution of Recommendations, and Measurement

contractions at a set percentage of maximal strength
and at a constant rate until the person can no longer
continue at that rate. The total work performed or
the test duration is used as a measure of muscular
endurance.

Flexibility is difficult to measure accurately and
reliably. Because it is specific to the joint being
tested, no one measure provides a satisfactory index
of an individual's overall flexibility (Harris 1969).
Field testing of flexibility frequently has been lim-
ited to the sit-and&reach test, which is considered to
be a measure of lower back and hamstring flexibility.
The criterion method for measuring flexibility in the
laboratory is goniometry, which is used to measure
the angle of the joint at both extremes in the range of
motion (NCHS, Wilmore 1989).
  Balance, agility, and coordination are especially
important among older persons, who are more prone
to fall and, as a result, suffer fractures due to reduced
bone mineral density. Field methods for measuring
balance, agility, and coordination have included
various balance stands (e.g., one-foot stand with
eyes open and with eyes closed; standing on a narrow
block) and balance walks on a narrow line or rail
(Tse and Bailey 1992). In the laboratory, computer-
based technology is now being used to evaluate
balance measured on an electronic force platform or
IO analyze a videotape recording of the participant
walking (Lehmann et al. 1990). Agility or coordina-
lion are measured most frequently by using a field
IC`SI, such as an agility walk or run (Cureton 1947).
In the laboratory, coordination or reaction/move-
ment time are determined by using electronic signal-
ing and timing devices (Spirduso 1975). More
dcvclopment is needed to establish norms using
standardized tests for measuring balance, agility,
ilnd coordination, especially of older persons.

Body Composition

In most population-based studies that have provided
Information on the relationship between physical
activity and morbidity or mortality, body composi-
tion has been estimated by measuring body height
and weight and calculating body mass index (weight/
height?). The preferred method for determining
;unount of body fat and lean body mass in exercise
[raining studies has been hydrostatic or underwater
\vcighing (NCHS, Wilmore 1989); however, this

method lacks accuracy in some populations, includ-
ing older persons and children (Lohman 1986).
Anthropometric measurements (i.e., girths, diam-
eters, and skinfolds) used to calculate the percentage
of body fat have varying degrees of accuracy and
reliability (Wilmore and Behnke 1970).
Data now suggest that the distribution of body
fat, especially accumulation in the abdominal area,
and total body fat are significant risk factors for CVD
and diabetes (Bierman and Brunzell 1992; Blumberg

and Alexander 1992). Researchers have determined
the magnitude of this abdominal or central obesity
by calculating the waist-to-hip circumference ratio
or by using new electronic methods that can image
regional fat tissue. New technologies that measure
body composition include total body electrical con-
ductivity (Segal et al. 1985), bioelectrical impedance
(Lukaski et al. 1986), magnetic resonance imaging
(Lohman 1984), and dual-energy x-ray absorptio-
metry (DEXA) (Mazess et al. 1990). These new
procedures have substantial potential to provide
new information on how changes in physical activity
affect body composition and fat distribution.

Valicfity of Measurements

Health behaviors are difficult to measure, and this is
certainly true for the behavior of physical activity. Of
particular concern is how well self-reported physical
activity accurately represents a person's habitual
activity status. Factors that interfere with obtaining
accurate assessments include incomplete recall, ex-
aggeration of amount of activity, and nonrepresenta-
tive sampling of time intervals during which activity
is assessed.

One of the principal difficulties in establishing the
validity of a physical activity measure is the lack of a
suitable "gold-standard" criterion measure for com-
parison. In the absence of a true criterion measure,
cardiorespiratory fitness has often been used as a
validation standard for physical activity surveys. Al-
though habitual physical activity is a major determi-
nant of cardiorespiratory fitness, other factors, such as
genetic inheritance, also play a role. Therefore, a
perfect correlation between physical activity report-
ing and cardiorespiratory fitness would not be ex-
pected. Nonetheless, correlations of reported physical
activity with measured cardiorespiratory fitness have
been examined. Table 2-5 shows results from studies


Physical Activity and Health

Table 2-5.  Correlation of two survey instruments with physiologic measures of caloric exchange
Study             Sample     Physiologic test          Correlation coefficient

Taylor et al. (1978)

Skinner et al. (1966)

Leon et al. (1981)

DeBacker et al. (1981)

Jacobs et al. (1993)

Richardson et al. (1995)

Albanes et al. (1990)

Montoye et al. (1996)

Siconolfi et al. (1985)

Jacobs et al. (1993)

Albanes et al. (1990)

Montoye et al. (1996)

Minnesota Leisure-Time Physical Activity Questionnaire

    175 men      Treadmill endurance

    54 men      Submaximal treadmill text

    175 men      Treadmill
             Submaximal heart rate

    1,513 men    Submaximal treadmill test

    64 men    i/O, max
    & women     Submaximal heart rate

    78 men    VO, max
    & women

    21 men     Resting caloric intake

    28 men     Doubly labeled water

     College Alumni Study Survey

    36 men    i/O, max
    32 women   i/O, max

    64 men
     & women    00, max
              Submaximal heart rate

    21 men     Resting caloric intake

    28 men     Doubly labeled water
           Energy intake, 7 days

0.45

0.13 NS

0.41
0.59

0.10

0.43
0.45

0.47

0.17 NS

0.26 NS

0.29
0.46

0.52
0.52

0.32 NS

0.39
0.44

NS = nonsignificant correlation coefficient; all others were statistically significant.

in which questionnaire data from the Minnesota
Leisure-Time Physical Activity Questionnaire (Taylor
et al. 1978) and the College Alumni Study survey
(Paffenbarger et al. 1993) are compared with physi-
ological measures, in most cases cardiorespiratory
fitness. Although most correlation coefficients (e.g.,
Pearson's r) are statistically significant, they exhibit
considerable variability (range 0.10 to 0.59), and the
overall central tendency (median,. 0.41) suggests
only moderate external validity. However, in a
study of predictors of cardiorespiratory fitness
among adults (Blair et al. 1989). in all age and sex
subgroups, self-reported physical activity was the
principal contributor to the predictive models that
also included weight, resting heart rate, and current
smoking. Thus, self-reported physical activity may

not be perfectly correlated with cardiorespiratory
fitness, but it may be the predominant predictive
factor.

Because misclassification of physical activity, as
could occur by using an invalid measure, would tend
to bias studies towards finding no association, the
consistently found associations between physical.ac-
tivity and lower risk of several diseases (as is discussed
in Chapter 4) suggest that the measure has at least
some validity. Moreover, they suggest that a more
precise measure of physical activity would likely yield
even stronger associations with health. Thus, although
measurement of physical activity by currently avail-
able methods may be far from ideal, it has provided a
means to investigate and demonstrate important health
benefits of physical activity.

36


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Chapter Summary

The assertion that frequent participation in physical
activity contributes to better health has been a recur-
ring theme in medicine and education throughout
much of Western history. Early empirical observa-
tions and case studies suggesting that a sedentary life
was not healthy have been supported by rigorous
scientific investigation that has evolved over the past
century. In recent decades, a number of experimental
and clinical specialties have contributed substan-
tially to an emerging field that may accurately be
described as exercise science. This field includes
disciplines ranging from exercise physiology and
biomechanics to physical activity epidemiology, ex-
ercise psychology, clinical sports medicine, and pre-
ventive medicine.' Research findings from these
specialties provide the basis for this first Surgeon
General's report on physical activity and health.
Numerous expert panels, committees, and confer-
cnces have been convened over the years to evaluate
the evidence relating physical activity and health.
These gatherings have laid a solid foundation for the
current consensus that for optimal health, people of
all ages should be physically active. on most days.
Specific exercise recommendations have empha-
sized only vigorous activity for cardiorespiratory
fimcss until recently, when the benefits of moderate-
intensity physical activity have been- recognized
ani promoted as well.

Conclusions

1. Physical activity for better health and well-being
has been an important theme throughout much
of western history.

2. Public health recommendations have evolved
from emphasizingvigorousactivity for cardiores-
piratory fitness to including the option of moder-
ate levels of activity for numerous health benefits.

3.

4.









5.









6.

Recommendations from experts agree that for
better health, physical activity should be per-
formed regularly. The most recent recommenda-
tions advise people of all ages to include a
minimum of 30 minutes of physical activity of
moderate intensity (such as brisk walking) on
most, if not all, days of the week. It is also
acknowledged that for most people, greater health
benefits can be obtained by engaging in physical
activity of more vigorous intensity or of longer
duration.

Experts advise previously sedentary people em-
barking on a physical ac&ity program to start
with short durations of moderate-intensity activ-
ity and gradually increase the duration or inten-
sity until the goal is reached.

Experts advise consulting with a physician before
beginning a new physical activity program for
people with chronic diseases, such as CVD and
diabetes mellitus, or for those who are at high risk
for these diseases. Experts also advise men over
age 40 and women over age 50 to consult a
physician before they begin a vigorous activity
program.

Recent recommendations from experts also
suggest that cardiorespiratory endurance ac-
tivity should be supplemented with strength-
developing exercises at least twice per week
for adults, in order to improve musculoskel-
eta1 health, maintain independence in per-
forming the activities of daily life, and reduce
the risk of falling.

37


Physical Activity and Health

Appendix A: Healthy People 2000 Objectives

The nation's public health goals for the 1990s and beyond, as presented in Healthy People2000 (USDHHS 1990),
aim co increase the span of healthy life for all Americans, to reduce health disparities among Americans, and to
achieve access to preventive services for all Americans. Reproduced here are the Healthy People 2000 objectives
for physical activity and fitness as revised in 1995 (USDHHS 1995).

Duplicate objectives that appear in two or more priority areas are marked with an asterisk alongside the
objective number.

Physical Activity and Fitness
Health Status Objectives

1.1*  Reduce coronary heart disease deaths to no more than 100 per 100,000 people.
                 Special Population Target
Coronary Deaths (per IOOJIOO)                     2000 Target
l.la   Blacks                                         115
1.2*  Reduce overweight to a prevalence of no more than 20 percent among people aged 20 and older and
   no more than 15 percent among adolescents aged 12-19.

                 Special Population Target
Overweight Prevalence
1.2a  Low-income women aged 20 and older
1.2b  Black women aged 20 and older
1.2c  Hispanic women aged 20 and older
1.2d  American Indians/Alaska Natives
1.2e  People with disabilities
1.2f  Women with high blood pressure
1.2g  Men with high blood pressure
1.2h Mexican-American men

2000 Target
  25%
  30%
  25%
  30%
  25%
  41%
  35%
  25%

NOW For pcoplc aged 20 and oldcr, ovcrwcight is dcJincd as body mass index (BMI) equal to or grcatcr than 27.8Jor men and 27.3Jor women. For adolescents,
overweight is d&cd us BMI equal to or grrutcr than 23.Ojor males aged 12-14.24.31 or males ugcd 15-I 7, 25.8Jor males aged 18-19, 23.4forfemales aged
12-14.24.8~~Jemulcs aged 15-Z 7, and25.7forjcmuIcs aged 18-19. The values/or adults arc thcgender-speciJic85thpercentilevalues ofthe 1976-80 National
Hculth and Nutrition Examination Survey (NHANES II), ef
                                  r crencc population 20-29 ycurs of age For adolescents, overweight was dejned using BMI cute//S
boscd on modiJicd age- and gcndcr-spcc$c 85th pcrccntile values o/the NHANES II. BMI is calculated by dividing weight in kilograms by the square of height
in mctcrs. The cut points used to dcJinc overweight approximate the 120 percent ojdcsirable body weight dejnition used in the 1990 objectives.

Risk Reduction Objectives

1.3*  Increase to at least 30 percent the proportion of people aged 6 and older who engage regularly, preferably
  daily, in light to moderate physical activity for at least 30 minutes per day.

               Special Population Targets
Moderate Physical Activity                        2000 Target
1.3a  Hispanics aged 18 and older                          25 %
   5 or more times per week

Note: Light to modcr-utc physical activity rcquircs sustuincd, rhythtmc muscular movements. is at least equivalent to sustained walking. and is performed at less
thun 60 pet-cent ojmuximum heart ratejor age. Maximum heart rate equals roughly 220 beats per minute minus age. Examples may include walking, swimming,
cycling, dancing, gar-drning und yurdwork, various domestic and occupational activities, and games and other childhood pursuits.

38


Historical Background, Terminology, Evolution of Recommendations, and Measurement

1.4

Increase to at least 20 percent the proportion of people aged 18 and older and to at least 75 percent the
proportion of children and adolescents aged 6-17 who engage in vigorous physical activity that
promotes the development and maintenance of cardiorespiratory fitness 3 or more days per week for
20 or more minutes per occasion.

                  Special Population Targets
Vigorous Physical Activity
1 .Sa  Lower-income people aged 18 and older
   (annual family income <$20,000)
1.4b  Blacks aged 18 years and older
1.4c  Hispanics aged 18 years and older

2000 Target
  12%


  17%
  17%

Nofc: Vigorous physical activities are rhythmic, rcpetitivc physical activities that USC large muscle groups at 60 percent or more ojmarimum hurt ratcjor ugc.
Art cxcrcisc ruts ~$60 percent oJ maximum heart ratcjor agr is about 50 pcrccnt o~maximal cardiorcspiratory capacity und is suJJicicntfor cardiorcspll-ator:\~
C-omlltiotlitlg. Muximum heart rate equals roughly 220 beats per minute minus age.

1.5  Reduce to,no more than 15 percent the proportion of people aged 6 and older who engage in no leisure-
   time physical activity.

                   Special Population Targets
No Leisure-Time Physical Activity
1.5a  People aged 65 and older
1.5b  People with disabilities
1.5c  Lower-income people (annual family
   income <$20,000)
1.5d  Blacks aged 18 and older
1.5c  Hispanics aged 18 and older
1.5f  American Indians/Alaska Natives aged 18 and older

2000 Target
  22%
  20%
  17%


  20%
  25%
  21%

NOIC For this objcctivc. pcoplc with disabilitirs arc pcoplc who report any limitation in activity due to chronic conditions.

I .6  Increase to at least 40 percent the proportion of people aged 6 and older who regularly perform physical
  activities that enhance and maintain muscular strength, muscular endurance, and flexibility.
I .7"  Increase to at least 50 percent the proportion of overweight people aged 12 and older who have adopted
  sound dietary practices combined with regular physical activity to attain an appropriate body weight.

Moption of Weight-Loss Practices
1.7a  Overweight Hispanic males
   aged 18 and older
1.71,  Overweight Hispanic females
   aged 18 and older

Special Population Targets

2000 Target
  24%


  22%

So-vices and Protection Objectives

I .H  Increase to at least 50 percent the proportion of children and adolescents in lst-12th grade who
   participate in daily school physical education.
1 .c)  Increase to at least 50 percent the proportion of school physical education class time that students spend
  being physically active, preferably engaged in lifetime physical activities.

39


Physical Activity and Health

Note: Lifetimeactivitiesareactivities that may be readily carried intoadulthoodbecnuse they generally need only oneortwopeople. Examples include swimming,
bicycling, jogging, and racquet sports. Also counted as lijetime activities are vigorous social activities such as dancing. Competitive group sports and activities
typically played only by young children such as group games are excluded.

1.10  Increase the proportion of worksites offering employer-sponsored physical activity and fitness
   programs as follows:

Worhsite Size                              2000 Target
50-99 employees                                      20%
loo-249 employees                                     35%
250-749 employees                                    50%
1750 employees                                       80%

1.11  Increase community availability and accessibility of physical activity and fitness facilities as follows:

Facility
Hiking, biking, and fitness trail miles
Public swimming pools
Acres of park and recreation open space

    2000 Target
  1 per 10,000 people
  1 per 25,000 people
  4 per 1,000 people
(250 people per managed acre>

1.12  Increase to at least 50 percent the proportion of primary care providers who routinely assess and counsel
  their patients regarding the frequency, duration, type, and intensity of each patient's physical activity
   practices.

Health Status Objective

1.13*  Reduce to no more than 90 per 1,000 people the proportion of all people aged 65 and older who have
   difficulty in performing two or more personal care activities thereby preserving independence.

Difficulty Performing
Self Care (per 1,000)
1.13a  People aged 85 and older
1.13b Blacks aged 65 and older

Special Population Targets

2000 Target
  325
  98

Note: Personal care activities are bathing. dressing, using the toilet, getting in and out ofbed or chair, and eating

40


Historical Background, Terminology, Evolution of Recommendations, and Measurement

Appendix B: NI H Consensus

Conference Statement
III Press (3/I8/96)
Sational Institutes of Health
Consensus Development Conference Statement
Physical Activity and Cardiovascular Health
Dcccmber 18-20, I995

31~ Consensus Statements are prepared by a
r,nnadvocatc, non-Federal panel ofexperts, based on
( l J presentations by investigators working in areas
rclcvant to the consensus questions during a 2-day
public session; (2) questions and statements from
~.~~llfcrcncc attendees, during open discussion peri-
& that arc part of the public session; and (3) closed
deliberations by the panel during the remainder of
rllr second day and morning qf the third. This
\I;ltcmcnt is an independent report of the panel and
I, Ilot a policy statement of the NIH or the Federal
(;~,vcrnmcnt.

Alxtract

( )/Jjt.c.li\fc*. To provide physicians and the general
I"ll)lic with a responsible assessment of the relation-
\llilJ hctwccn physical activity and cardiovascular
11lx1t11.

f'clrficipmls. A non-Federal, nonadvocate, 13-
~~~c~uhcr panel representing the fields of cardiology,
1)~~~chology, exercise physiology, nutrition, pediat-
rlc'h. public health, andepidemiology. Inaddition, 27
cspcrts in cardiology, psychology, epidemiology,
c*scrcisc physiology, geriatrics, nutrition, pediatrics,
Wlic health, and sports medicine presented data to
[ hc panel and a conference audience of 600.

~~~YICC. The literature was searched through
xlcdlinc and an extensive bibliography of references
\\`;ls provided to the panel and the conference audi-
c~c. Experts prepared abstracts with relevant cita-
[i~)ns from the literature. Scientific evidence was
.W'C~I precedence over clinical anecdot'al experience.

CO~ISCmUS Process. The panel, answering pre-
defined questions, developed their conclusions
hascd on the scientific evidence presented in open
lorl~m and the scientific literature. The panel com-
I'"scd a draft statement that was read in its entirety
bind circulated to the experts and the audience for

comment. Thereafter, the panel resolved conflict-
ing recommendations and released a revised state-
ment at the end of the conference. The panel
finalized the revisions within a few weeks after the
conference.

Conclusions. All Americans should engage in
regular physical activity at a level appropriate to
their capacity, needs, and interest. Children and
adults alike should set a goal of accumulating at
least 30 minutes of moderate-intensity physical
activity on most, and preferably, all days of the
week. Most Americans have little or no physical
activity in their daily lives, and accumulating evi-
dence indicates that physical inactivity is a major
risk factor for cardiovascular disease. However,
moderate levels of physical activity confer signifi-
cant health benefits. Even those who currently
meet these daily standards may derive additional
health and fitness benefits by becoming more physi-
cally active or including more vigorous activity. For
those with known cardiovascular disease, cardiac
rehabilitation programs that combine physical ac-
tivity with reduction in other risk factors should be
more widely used.

Introduction

Over the past 25 years, the United States has experi-
enced a steady decline in the age- adjusted death toll
from cardiovascular disease (CVD), primarily in
mortality caused by coronary heart disease and stroke.
Despite this decline, coronary heart disease remains
the leading cause of death and stroke the third
leading cause of death. Lifestyle improvements by
the American public and better control of the risk
factors for heart disease and stroke have been major
factors in this decline.

Coronary heart disease and stroke have many
causes. Modifiable risk factors include smoking,
high blood pressure, blood lipid levels, obesity, dia-
betes, and physical inac.tivity. In contrast to the
positive national trendsobserved with cigarette smok-
ing, high blood pressure, and high blood cholesterol,
obesity and physical inactivity in the United States
have not improved. Indeed automation and other
technologies have contributed greatly to lessening
physical activity at work and home.

41


Physical Activity and Health

The purpose of this conference was to examine
the accumulating evidence on the role of physical
activity in the prevention and treatment of CVD and
its risk factors.

Physical activity in this statement is defined as
"bodily movement produced by skeletal muscles
that requires energy expenditure" and produces
healthy benefits. Exercise, a type of physical activity,
is defined as "a planned, structured, and repetitive
bodily movement done to improve or maintain one
or more components of physical fitness." Physical
inactivity denotes a level of activity less than that
needed to maintain good health.
Physical inactivity characterizes most Ameri-
cans. Exertion has been systematically engineered
out of most occupations and lifestyles. In 1991, 54
percent of adults reported little orno regular leisure
physical activity. Data from the 1990 Youth Risk
Behavior Survey show that most teenagers in grades
9-12 are not performing regular vigorous activity.
About 50 percent of high school students reported
they are not enrolled in physical education classes.
Physical activity protects against the develop-
ment of CVD and also favorably modifies other CVD
risk factors, including high blood pressure, blood
lipid levels, insulin resistance, and obesity. The type,
frequency, and intensity of physical activity that are
needed to accomplish these goals remain poorly
defined and controversial.

Physical activity is also important in the treat-
ment of patients with CVD or those who are at
increased risk for developing CVD, including pa-
tients who have hypertension, stable angina, or pe-
ripheral vascular disease, or who have had a prior
myocardial infarction or heart failure. Physical activ-
ity is an important component of cardiac rehabilita-
tion, and people with CVD can benefit from
participation. However, some questions remain re-
garding benefits, risks, and costs associated with
becoming physically active.         *
Many factors influence adopting and maintaining

a physically active lifestyle, such as socioeconomic
status, cultural influences, age, and health status.
Understanding is needed on how such variables in-
fluence the adoption of this behavior at the individual
level. Intervention strategies for encouraging indi-
viduals from different backgrounds to adopt and
adhere to a physically active lifestyle need to be

developed and tested. Different environments such
as schools, worksites, health care settings, and the
home can play a role in promoting physical activity.
These community-level factors also need to be better
understood.

  To address these and related issues, the NIH's
National Heart, Lung, and Blood Institute and Office
of Medical Applications of Research convened a
Consensus Development Conference on Physical
Activity and Cardiovascular Health. The conference
was cosponsored by the NIH's National Institute of
Child Health and Human Development, National
Institute on Aging, National Institute of Arthritis and
Musculoskeletal and Skin Diseases, National Insti-
tute of Diabetes and Digestive and Kidney Diseases,
National Institute of Nursing Research, Office of
Research on Women's Health, and Office of Disease
Prevention, as well as the Centers for Disease Con-
trol and Prevention and the President's Council on
Physical Fitness and Sports.

The conference brought together specialists in
medicine, exercise physiology, health behavior, epi-
demiology, nutrition, physical therapy, and nursing
as well as representatives from the public. After a day
and a half of presentations and audience discussion,
an independent, non-Federal consensus panel
weighed the scientific evidence and developed a
draft statement that addressed the following five
questions.

o What is the health burden of a sedentary lifetyle
on the population?

o What type, what intensity, and what quantity of
physical activity are important to prevent car-
diovascular disease?

o What are the benefits and risks of different
types of physical activity for people with car-
diovascular disease?

o What are the successful approaches to adopting
and maintaining a physically active lifestyle?
o What are the important questions for future
research?

1. What Is the Health Burden of a Sedentary
Lifestyle on the Population?

Physical inactivity among the U.S. population is now
widespread. National surveillance programs have
documented that about one in four adults (more


Historical Background, Terminology, Evolution of Recommendations, and Measurement

,,.omen than men) currently have sedentary lifestyles
\vitii no leisure time physical activity. An additional
one-third of adults are insufficiently active to achieve
health benefits. The prevalence of inactivity varies by
gctrder, age, ethnicity, health status, and geographic
region but is common to all demographic groups.
cll;lngc in physical exertion associated with occupa-
lioti has declined markedly in this century.
Girls become less active than do boys as they grow
older. Children become far less active as they move
through adolescence. Obesity is increasing among
cliildrcn, at least in part related to physical inactivity.
I>;it;t indicate that obese children and adolescents
llnvc a high risk of becoming obese adults, and obesity
iti adulthood is related to coronary artery disease,
liyI"rtcnsion, and diabetes. Thus, the prevention of
childhood obesity has the potential of preventing
(:\lD in adults. At age 12,70 percent of children report
I';trticipation in vigorous physical activity; by age 21
lllis activity falls to 42 percent for men and 30 percent
lor lvomcn. Furthermore, as adults age, their physical
;lc.tivity lcvcls continue to decline.
Although knowledge about physical inactivity as
;I risk factor for CVD has come mainly from investiga-
11ons of middle-aged, white men, more limited evi-
tlcncc from studies in women minority groups and the
c.ltlcrly suggests that the findings are similar in these
;J'OLIIX. On the basis of current knowledge, we must
I~OIC that physical inactivity occurs disproportion-
.t~cly among Americans who are not well educated and
wlro ;II-c socially or economically disadvantaged.
  Physical activity is directly related to physical
Iitucss. Although the means of measuring physical
.rctivity have varied between studies (i.e., there is no
~t:iildardization of measures), evidence indicates that
l'li?sical inactivity and lack of physical fitness are
tlirecrly associated with increased mortality from
(Ii'D. The increase in mortality is not entirely ex-
iJl;tined by the association with elevated blood pres-
`tire. smoking, and blood lipid levels. '
  There is an inverse relationship between mea-
`tires of physical activity and indices of obesity in
rll~`st U.S. population studies. Only a few studies
hive examined the relationship between physical
Jctivity and body fat distribution, and these suggest
~`1 inverse relationship between levels of physical
CIctivitv and visceral fat. There is evidence that in-
< re~isco physical activity facilitates weight loss and

that the addition of physical activity to dietary en-
ergy restriction can increase and help to maintain
loss of body weight and body fat mass.
Middle-aged and older men and women who
engage in regular physical activity have significantly
higher high-density lipoprotein (HDL) cholesterol
levels than do those who are sedentary. When exercise
training has extended to at least 12 weeks, beneficial
HDL cholesterol level changes have been reported.
  Most studies of endurance exercise training of
individuals with normal blood pressure and those
with hypertension have shown decreases in systolic
and diastolic blood pressure. Insulin sensitivity is
also improved with endurance exercise.
  A number of factors that affect thrombotic
function-including hematocrit, fibrinogen, plate-
let function, and fibrinolysis-are related to the risk
of CVD. Regular endurance exercise lowers the risk
related to these factors.

The burden of CVD rests most heavily on the
least active. In addition to its powerful impact on the
cardiovascular system, physical inactivity is also
associated with other adverse health effects, includ-
ing osteoporosis, diabetes, and some cancers.

2. What Type, What Intensity, and What
Quantity of Physical Activity Are Important
to Prevent Cardiovascular Disease?

Activity that reduces CVD risk factors and confers
many other health benefits does not require a struc-
tured or vigorous exercise program. The majority of
benefits of physical activity can be gained by per-
forming moderate-intensity activities. The amount
or type of physical activity needed for health benefits
or optimal health is a concern due to limited time and
competing activities for most Americans. The amount
and types of physical activity that are needed to
prevent disease and promote health must, therefore,
be clearly communicated, and effective strategies
must be developed to promote physical activity to
the public.

The quantitative relationship between level of
activity or fitness and magnitude of cardiovascular
benefit may extend across the full range of activity. A
moderate level of physical activity confers health
benefits. However, physical activity must be per-
formed regularly to maintain these effects.

43


Physical Activity and Health

Moderate=intensity activity performed by previously
sedentary individuals results in significant improve-
ment in many health-related outcomes. These mod-
erate intensity activities are more likely to be
continued than are-high-intensity activities.
We recommend that all people in the United
States increase their regular physical activity to a
level appropriate to their capacities, needs, and inter-
est. We recommend that all children and adults
should set a long-term goal to accumulate at least 30
minutes or more of moderate-intensity physical ac-
tivity on most, or preferably all, days of the week.
Intermittent or shorter bouts of activity (at least 10
minutes), includingoccupaiional, nonoccupational,
or tasks of daily living, also have similar cardiovascu-
lar and health benefits if performed at a level of
moderate intensity (such as brisk walking, cycling,
swimming, home repair, and yardwork) with an
accumulated duration of at least 30 minutes per day.
People who currently meet the recommended mini-
mal standards may derive additional health and
fitness benefits from becoming more physically ac-
tive or including more vigorous activity.
  Some evidence suggests lowered mortality with
more vigorous activity, but further research is needed
to more specifically define safe and effective levels.
The most active individuals have lower cardiovascu-
lar morbidity and mortality rates than do those who
are least active; however, much of the benefit appears
to be accounted for by comparing the least active
individuals to those who are moderately active. Fur-
ther increases in the intensity or amount of activity
produce further benefits in some, but not all, param-
eters of risk. High-intensity activity is also associated
with an increased risk of injury, discontinuation of
activity, or acute cardiac events during the activity.
Current low rates of regular activity in Americans
may be partially due to the mis-perception of many
that vigorous, continuous exercise is necessary to
reap health benefits. Many people, for example, fail
to appreciate walking as "exercise" or to recognize
the substantial benefits of short bouts (at least 10
minutes) of moderate-level activity.
  The frequency, intensity, and duration of activ-
ity are interrelated. The number of episodes of
activity recommended for health depends on the
intensity and/or duration of the activity: higher

intensity or longer duration activity could be per-
formed approximately three times weekly and
achieve cardiovascular benefits, but low-intensity
or shorter duration activities should be performed
more often to achieve cardiovascular benefits.
The appropriate type of activity is best deter-
mined by the individual's preferences and what will
be sustained. Exercise, or a structured program of
activity, is a subset of activity that may encourage
.interest and allow for more vigorous activity. People
who perform more formal exercise (i.e., structured
or planned exercise programs) can accumulate this
daily total through a variety of recreational or sports
activities. People who are currently sedentary or
minimally active should gradually build up to the
recommended goal of 30 minutes of moderate activ-
ity daily by adding a few minutes each day until
reaching their personal goal to reduce the risk asso-
ciated with suddenly increasing the amount or inten-
sity of exercise. (The defined levels of effort depend
on individual characteristics such as baseline fitness
and health status.)

Developing muscular strength and joint flexibil-
ity is also important for an overall activity program to
improve one's ability to perform tasks and to reduce
the potential for injury. Upper extremity and resis-
tance (or strength) training can improve muscular
function, and evidence suggests that there may be
cardiovascular benefits, especially in older patients
or those with underlying CVD, but further research
and guidelines are needed. Older people or those
who have been deconditioned from recent inactivity
or illness may particularly benefit from resistance
training due to improved ability in accomplishing
tasks of daily living. Resistance training may contrib-
ute to better balance, coordination, and agility that
may help prevent falls in the elderly.

Physical activity carries risks as well as benefits.
The most common adverse effects of activity relate to
musculoskeletal injury and are usually mild and self-
limited. The risk of injury increases with increased
intensity, frequency, and duration of activity and
also depends on the type of activity. Exercise-related
injuries can be reduced by moderating these param-
eters. A more serious but rare complication of activ-
ity is myocardial infarction or sudden cardiac death.
Although persons who engage in vigorous physical

33


Historical Background, Terminology, Evolution of Recommendations, and Measurement

.lcti\.ity have a slight increase in risk of sudden
c.lrdiac death during activity, the health benefits
c,,lttvcigh this risk because of the large overall risk
reduction.

In children and young adults, exertion-related
dcarhs are uncommon and are generally related to
cangcnital heart defects (e.g., hypertrophic cardi-
,,mvopathy, Marfan's syndrome, severe aortic valve
,lc1I()sis. prolonged QT syndromes, cardiac conduc-
lloll abnormalities) or to acquired myocarditis. It is
rcc(>mmcnded that patients with those conditions
rclnGlin ilctive but not participate in vigorous or
c.~~lllpctitivc athletics.

BKWSC the risks of physical activity are very low
c.(,lnp;lrcd with the health benefits, most adults do
[lot uccd medical consultation or pretesting before
\r;lrtirig a moderate-intensity physical activity pro-
,<r;lln. However, those with known CVD and men
,)~cr :tgc -to and women over age 50 with multiple
I ;lrdiovascular risk factors who contemplate a pro-
c:r-am of vigorous activity should have a medical
t.\..lIu;ltion prior to initiating such a program.

3. What Are the Benefits and Risks of
Different Types of Physical Activity for
People with Cardiovascular Disease?

Xlorc than 10 million Americans are afflicted with
( lillically significant CVD, including myocardial in-
I.lrction, angina pectoris, peripheral vascular dis-
(`:Iw. and congestive heart failure. In addition, more
I~KU~ 300,000 patients per year are currently sub-
~.tccl to coronary artery bypass surgery and a similar
~~~~mbcr to percutaneous transluminal coronary
.+$@asty. Increased physical activity appears to
h~ncfit each of these groups. Benefits include reduc-
ll(~n in cardiovascular mortality, reduction of symp-
l~~lll~, improvement in exercise tolerance and
Illnctional capacity, and improvement in psycho-
I~)gicul well-being and quality of life.
jcw-al studies have shown that exercise training

IJWran= significantly reduce overall mortality, as
~~11 as death caused by myocardial infarction. The
Vl~rtcd reductions in mortality have been highest-
Wroximately 25 percent-in cardiac rehabilitation
19Wms that have included control of other cardio-
\`ascular risk factors. Rehabilitation programs using
`~(~111 moderate and vigorous physical activity have

been associated with reductions in fatal cardiac events,
although the minimal or optimal level and duration
of exercise required to achieve beneficial effects
remains uncertain. Data are inadequate to determine
whether stroke incidence is affected by physical
activity or exercise training.

The risk of death during medically supervised
cardiac exercise training programs is very low. How-
ever, those who exercise infrequently and have poor
functional capacity at baseline may be at somewhat
higher risk during exercise. training. All patients
with CVD should have a medical evaluation prior to
participation in a vigorous exercise program.
Appropriately prescribed and conducted exer-
cise training programs improve exercise tolerance
and physical fitness in patients with coronary heart
disease. Moderate as well as vigorous exercise train-
ing regimens are of value. Patients with low basal
levels of exercise capacity experience the most func-
tional benefits, even at relatively modest levels of
physical activity. Patients with angina pectoris typi-
cally experience improvement in angina in associa-
tion with a reduction in effort-induced myocardial
ischemia, presumably as a result of decreased myo-
cardial oxygen demand and increased work capacity.
Patients with congestive heart failure also appear
to show improvement in symptoms, exercise capac-
ity, and functional well-being in response to exercise
training, even though left ventricular systolic func-
tion appears to be unaffected. The exercise program
should be tailored to the needs of these patients and
supervised closely in view of the marked predisposi-
tion of these patients to ischemic events and
arrhythmias.

Cardiac rehabilitation exercise training often
improves skeletal muscle strength and oxidative
capacity and, when combined with appropriate nu-
tritional changes, may result in weight loss. In addi-
tion, such training generally results in improvement
in measures of psychological status, social adjust-
ment, and functional capacity. However, cardiac
rehabilitation exercise training has less influence on
rates of return to work than many nonexercise vari-
ables, including employer attitudes, prior employ-
ment status, and economic incentives. Multifactorial
intervention programs, including nutritional changes
and medication plus exercise, are needed to improve
health status and reduce cardiovascular disease risk.

45


Physical Activity and Health

Cardiac rehabilitation programs have tradition-
ally been institutional-based and group-centered (e.g.,
hospitals, clinics, community centers>. Referral and
enrollment rates have been relatively low, generally
ranging from 10 to 25 percent of patients with CHD.
Referral rates are lower for women than for men and
lower for non-whites than for whites. Home-based
programs have the potential to provide rehabilitative
services to a wider population. Home-based pro-
grams incorporating limited hospital visits with regu-
lar mail or telephone followup by a nurse case
manager have demonstrated significant increases in
functional capacity, smokingcessation, and improve-
ment in blood lipid levels. A range of options exists
in cardiac rehabilitation including site, number of
visits, monitoring, and other services.
  There are clear medical and economic reasons
for carrying out cardiac rehabilitation programs.
Optimal outcomes are achieved when exercise train-
ing is combined with educational messages and
feedback about changing lifestyle. Patients who par-
ticipate in cardiac rehabilitation programs show a
lower incidence of rehospitalization and lower
charges per hospitalization. Cardiac rehabilitation is
a cost-efficient therapeutic modality that should be
used more frequently.

4. What Are the Successful Approaches to
Adopting and Maintaining a Physically
Active Lifestyle?
The cardiovascular benefits from and physiological
reactions to physical activity appear to be similar
amongdiverse populationsubgroupsdefined by age,
sex, income, region of residence, ethnic background,
and health status. However, the behavioral and atti-
tudinal factors that influence the motivation for and
ability to sustain physical activity are strongly deter-
mined by social experiences, cultural background,
and physical disability and health status. .For ex-
ample, perceptions of appropriate physical activity
differ by gender, age, weight, marital status, family
roles and responsibilities, disability, and social class.
Thus, the following general guidelines will need to
be further refined when one is planning with or
prescribing for specific individuals and population
groups, but generally physical activity is more likely
to be initiated and maintained if the individual

.


.


.


.


.


.


.




.






.




.

Perceives a net benefit.

Chooses an enjoyable activity.
Feels competent doing the activity.
Feels safe doing the activity.
Can easily access the activity on a regular basis.
Can fit the activity into the daily schedule.
Feels that the activity does not generate financial
or social costs that he or she is unwilling to bear.
Experiences a minimum of negative conse-
quences such as injury, loss of time, negative
peer pressure, and problems with self-identity.
Is able to successfully address issues of compet-
ing time demands.

Recognizes the need to balance the use of labor-
saving devices (e.g., power lawn mowers, golf
carts,automobiles) andsedentaryactivities (e.g.,
watching television, use of computers) with
activities that involve a higher level of physical
exertion.

Other people in the individual's social environ-
ment can influence the adoption and maintenance of
physical activity. Health care providers have a key
role in promoting smoking cessation and other risk-
reduction behaviors. Preliminary evidence suggests
that this also applies to physical activity. It is highly
probable that people will be more likely to increase
their physical activity if their health care provider
counsels them to do so. Providers can do this effec-
tively by learning to recognize stages of behavior
change, to communicate the need for increased ac-
tivity, to assist the patient in initiating activity, and
by following up appropriately.
Family and friends can also be important sources
of support for behavior change. For example, spouses
or friends can serve as "buddies," joining in the
physical activity; or a spouse could offer to take on a
household task, giving his or her mate time to engage
in physical activity. Parents can support their
children's activity by providing transportation, praise,
and encouragement, and by participating in activi-
ties with their children.

Worksites have the potential to encourage in-
creased physical activity by offering opportunities,
reminders, and rewards for doing so. For example,
an appropriate indoor area can be set aside to enable
walking during lunch hours. Signs placed near

46


Historical Background, Terminology, Evolution of Recommendations, and Measurement

clcvators can encourage the use of the stairs instead.
Discounts on parking fees can be offered to employ-
ccs who elect to park in remote lots and walk.

Schools are a major community resource for
increasing physical activity, particularly given the
nrgent need to develop strategies that affect children
;rnd adolescents. As noted previously, there is now
cfcar evidence that U.S. children and adolescents
bavc become more obese. There is also evidence that
c,besc children and adolescents exercise less than
their leaner peers. All schools should provide oppor-
tunities for physical activities that

Arc appropriate and enjoyable for children of
all skill levels and are not limited to competitive
sports or physical education classes.
Appeal to girls as well as to boys, and to children
from diverse backgrounds.
Can serve as a foundation for activities through-
out life.

Arc offered on a daily basis.
5uccessful approaches may involve mass educa-

INHI strategies or changes in institutional policies or
c.ommunity variables. In some environments (e.g.,
s~.h~~ols, worksites, community centers), policy-level
llrtcrventions may be necessary to enable people to
;rl.tlicvc and maintain an adequate level of activity.
~`cbltcy changes that increase opportunities for physi-
I .rI irctivity can facilitate activity maintenance for
Illotivatcd individuals and increase readiness to
c II;III~C' among the less motivated. As in other areas
01 health promotion, mass communication strate-
~1~s should be used to promote physical activity.
I Ircsc strategies should include a variety of main-
\trc:nn channels and techniques to reach diverse
.~nclicnccs that acquire information through differ-
(`rlt media (e.g., TV, newspaper, radio, Internet).

5. What Are the Important Considerations
for Future Research?
\\`hilc much has been learned about the role of
I~h!.~ical activity in cardiovascular health, there are
rrr~~rrv unanswered questions.
  o Maintain surveillance of physical activity levels
in the U.S. population by age, sex, geographic,
  and socioeconomic measures.

Develop better methods for analysis and quan-
tification of activity. These methods should be
applicable to both work and leisure time mea-
surements and provide direct quantitative esti-
mates of activity.

Conduct physiologic, biochemical, and genetic
research necessary to define the mechanisms
by which activity affects CVD including changes
in metabolism as well as cardiac and vascular
effects. This will provide new insights into
cardiovascular biology that may have broader
implications than for other clinical outcomes.
Examine the effects of physical activity and
cardiac rehabilitation programs on morbidity
and mortality in elderly individuals.

Conduct research on the social and psychologi-
cal factors that influence adoption of a more
active lifestyle and the maintenance of that
behavior change throughout life.

Carry out controlled randomized clinical trials
among children and adolescents to test the
effects of increased physical activity on CVD
risk factor levels including obesity. The effects
of intensity, frequency, and duration of in-
creased physical activity should be examined in
such studies.

Conclusions

Accumulatingscientific evidence indicates that physi-
cal inactivity is a major risk factor for CVD. Moderate
levels of regular physical activity confer significant
health benefits. Unfortunately, most Americans have
little or no physical activity in their daily lives.

All Americans should engage in regular physical
activity at a level appropriate to their capacities,
needs, and interests. All children and adults should
set and reach a goal of accumulating at least 30
minutes of moderate-intensity physical activity on
most, and preferably all, days of the week. Those who
currently meet these standards may derive additional
health and fitness benefits by becoming more physi-
cally active or including more vigorous activity.

Cardiac rehabilitation programs that combine
physical activity with reduction in other risk factors
should be more widely applied to those with known
CVD. Well-designed rehabilitation programs have

47


Physical Activity and Health

benefits that are lost because of these programs'
limited use.

  Individuals with CVD and men over 40 or women
over 50 years of age with multiple cardiovascular risk
factors should have a medical evaluation prior to
embarking on a vigorous exercise program.
Recognizing the importance of individual and
societal factors in initiating and sustaining regular
physical activity, the panel recommends the following:
o Development of programs for health care pro-
  viders to communicate to patients the impor-
  tance of regular physical activity.
o Community support of regular physical activ-
  ity with environmental and policy changes at
  schools, worksites, community centers, and
   other sites.

o Initiation of a coordinated national campaign
involving a consortium of collaborating health
organizations to encourage regular physical
activity.

o The implementation of the recommendations
in this statement has considerable potential to
improve the health and well-being of American
citizens.

About the NIH Consensus
Development Program
NIH Consensus Development Conferences are con-
vened to evaluate available scientific information
and resolve safety and efficacy issues related to a
biomedical technology. The resultant NIH Consen-
sus Statements are intended to advance understand-
ing of the technology or issue in question and to be
useful to health professionals and the public.

48


Historical Background, Terminology, Evolution of Recommendations, and Measurement

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57


               CHAPTER 3
PHYSIOLOGIC RESPONSES AND LONG-TERM
       ADAPTATIONS TO EXERCISE

Contents

111trocluction . .`_ . . . . . . . . _ . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  61

I`ll\,\iologic Responses to Episodes of Exercise  ....................................  61
<:ardiovascular and Respiratory Systems  ......................................  61
  Cardiovascular Responses to Exercise  .......................................  62
    CardiacOutput  .....................................................  62

     BloodFlow  ........................................................  63

     Blood Pressure  ......................................................  63

    Oxygen Extraction  ..................................................  63
    Coronary Circulation  ................................................  63

   Respiratory Responses to Exercise  .........................................  64

    Resistance Exercise  ....................................................  65

  skclctal Muscle  ..........................................................  65
hkcictd Muscle Energy Metabolism  ..........................................  65
   Energy Systems  .......................................................  65

    McrabolicRate  ........................................................  66
   Maximal Oxygen Uptake  ................................................  66

   LactateThreshold ......................................................  66
t IlJrmonal Responses to Exercise  ............................................  66
Immune Responses to Exercise  ..............................................  67

1 i)tlg-Terrn Adaptations to Exercise Training  .....................................  67
:\daptations of Skeletal Muscle and Bone  ......................................  67
Jletaholic Adaptations  .....................................................  69
Cardiovascular and Respiratory Adaptations  ...................................  71
  Long-Term Cardiovascular Adaptations  ....................................  71
  Respiratory Adaptations  .................................................  71


Physical Activity and Health

Contents, continued

Maintenance, Detraining, and Prolonged Inactivity  ................................  7 1
Maintaining Fitness and Muscular Strength  ....................................  72
Detraining  ..............................................................  72
Prolonged Inactivity  ......................................................  72

Special Considerations  .......................................................  73
Disability  ........................................................ . ......  73

Environmental Conditions  .................................................  73
EffectsofAge  ............................................................  75
DifferencesbySex  ........................................................  76

Conclusions  ...............................................................  77

Research Needs  ........ . .................................................  77

References . . . . . . . . . . . . . . ..__...................._............._............  77

60


              CHAPTER 3
PHYSIOLOGIC RESPONSES AND LONG-TERM
       ADAPTATIONS TO EXERCISE

Introduction

W hen challenged with any physical task, the
  human body responds through a series of
integrated changes in function that involve most, if
not all, of its physiologic systems. Movement re-
quires activation and control of the musculoskeletal
system; the cardiovascular and respiratory systems
provide the ability to sustain this movement over
extended periods. When the body engages in exer-
cise training several times a week or more frequently,
each of these physiologic systems undergoes specific
adaptations that increase the body's efficiency and
capacity. The magnitude of these changes depends
largely on the intensity and duration of the training
sessions, the force or load used in training, and the
body's initial level of fitness. Removal of the train-
ing stimulus, however, will result in loss of the
efficiency and capacity that was gained through
these training-induced adaptations; this loss is a
process called detraining.

This chapter provides an overview of how the
body responds to an episode of exercise and adapts
to exercise training and detraining. The discussion
focuses on aerobic or cardiorespiratory endurance
exercise (e.g., walking, jogging, running, cycling,
swimming, dancing, and in-line skating) and resis-
tance exercise (e.g., strength-developing exercises).
It does not address training for speed, agility, and
flexibility. In discussing the multiple effects of
exercise, this overview will orient the reader to the
physiologic basis for the relationship of physical
activity and health. Physiologic information perti-
nent to specific diseases is presented in the next
-chapter. For additional information, the reader is
referred to the selected textbooks shown in the
sidebar.

Selected Textbooks on Exercise Physiology
Astrand PO, Rodahl K. Texibook of work physiology.
3rd edition. New York: McGraw-Hill Book Company,
1986.

Brooks GA, Fahey TD, White TP. Exercise physiology:
human bioenergetics and its applications. 2nd edition.
Mountain View, CA: Mayfield Publishing Company,
1996.

Fox E, Bowers R, Foss M. The physiological basis for
exercise and sport. 5th edition. Madison, WI: Brown
and Benchmark, 1993.

McArdle WD, Katch FI, Katch VL. Essentials of
exercise physiology. Philadelphia, PA: Lea and
Febiger, 1994.

Powers SK, Howley ET. Exercise physiology: theory
and application tojitness and performance. Dubuque,
IA: William C. Brown, 1990.

Wilmore JH, Costill DL. Physiology of sport and
exercise. Champaign, IL: Human Kinetics, 1994.

Physiologic
of Exercise

Responses to Episodes

The body's physiologic responses to episodes of
aerobic and resistance exercise occur in the muscu-
loskeletal, cardiovascular, respiratory, endocrine,
and immune systems. These responses have been
studied in controlled laboratory settings, where ex-
ercise stress can be precisely regulated and physi-
ologic responses carefully observed.

Cardiovascular and Respiratory Systems
The primary functions of the cardiovascular and
respiratory systems are to provide the body with


Physical Activity and Health

oxygen (0,) and nutrients, to rid the body of carbon
dioxide (CO,) and metabolic waste products, to
maintain body temperature and acid-base balance,
and to transport hormones from the endocrine
glands to their target organs (Wilmore and Costill
1994). To be effective and efficient, the cardiovascu-
lar system should be able to respond to increased
skeletal muscle activity. Low rates of work, such as
walking at 4 kilometers per hour (2.5 miles per
hour), place relatively small demands on the cardio-
vascular and respiratory systems. However, as the
rate of muscular work increases, these two systems
will eventually reach their maximum capacities and
will no longer be able to meet the body's demands.

Cardiovascular Responses to Exercise
The cardiovascular system, composed of the heart,
blood vessels, and blood, responds predictably to
the increased demands of exercise. With few excep-
tions, the cardiovascular response to exercise is
directly proportional to the skeletal muscle oxygen
demands for any given rate of work, and oxygen
uptake (VOJ increases linearly with increasing rates
of work.

Cardiac Output

Cardiac output (Q) is the total volume of blood
pumped by the left ventricle of the heart per minute.
It is the product of heart rate (HR, number of beats
per minute) and stroke volume (SV, volume of blood
pumped per beat). The arterial-mixed venous oxygen
(A-TO,) difference is the difference between the oxy-
gen content of the arterial and mixed venous blood. A
person's maximum oxygen uptake NO, max) is a
function of cardiac output (Q) multiplied by the
A40,difference. Cardiac output thus plays an im-
portant role in meeting the oxygen demands for
work. As the rate of work increases, the cardiac
output increases in a nearly linear manner to meet
the increasing oxygen demand, but only up to the
point where it reaches its maximal capacity (Q max).
To visualize how cardiac output, heart rate, and
stroke volume change with increasing rates of work,
consider a person exercising on a cycle ergometer,
starting at 50 watts and increasing 50 watts every 2
minutes up to a maximal rate of work (Figure 3-l A,
B, and C). In this scenario, cardiac output and heart
rate increase over the entire range of work, whereas
stroke volume only increases up to approximately 40

Figure 3-1. Changes in cardiac output (A), heart rate
     (B), and stroke volume (C) with increasing
     rates of work on the cycle ergometer

(A)
221

6 t     I     I      I     I     I      I      I
25   50   75   100  125  150  175  200
          Power (watts)

(B)

200 1

X180-
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>160-
z
:140-
:120-
z
IlOO-

80 1     I      I     I     I      I      I      8
25   50   75   100  125  150  175  200
           Power (watts)

60-
25 50 75  100 125 150 175 200
           Power (watts)

62


Physiologic Responses and Long-Term Adaptations to Exercise

to 60 percent of the person's maximal oxygen uptake
(i'Oz max), after which it reaches a plateau. Recent
studies have suggested that stroke volume in highly
trained persons can continue to increase up to near
maximal rates of work (Scruggs et al. 1991; Gledhill,
Cox, Jamnik 1994).

Blood Flow

The pattern of blood flow changes dramatically when
a person goes from resting to exercising. At rest, the
skin and skeletal muscles receive about 20 percent of
the cardiac output. During exercise, more blood is
sent to the active skeletal muscles, and, as body
temperature increases, more blood is sent to the skin.
This process is accomplished both by the increase in
cardiac output and by the redistribution of blood flow
away from areas of low demand, such as the splanch-
nit organs. This process allows abou t 80 percent of the
cardiac output to go to active skeletal muscles and
skin at maximal rates of work (Rowe11 1986). With
exercise of longer duration, particularly in a hot and
humid environment, progressively more of the car-
diac output will be redistributed to the skin to counter
the increasing body temperature, thus limiting both
the amount going to skeletal muscle and the exercise
endurance (Rowe11 1986).

Blood Pressure

Mean arterial blood pressure increases in response to
dynamic exercise, largely owing to an increase in
systolic blood pressure, because diastolic blood pres-
sure remains at near-resting levels. Systolic blood
pressure increases linearly with increasing rates of
work, reaching peak values of between 200 and 240
millimeters of mercury in normotensive persons. Be-
cause mean arterial pressure is equal to cardiac output
times total peripheral resistance, the observed increase
in mean arterial pressure results from an increase in
cardiac output that outweighs a concomitant decrease
in total peripheral resistance. This increase in mean
arterial pressure is a normal and desirable response, the
result of a resetting of the arterial baroreflex to a higher
pressure. Without such a resetting, the body would
experience severe arterial hypotension during intense
activity (Rowe11 1993). Hypertensive patients typically
reach much higher systolic blood pressures for a given
rate of work, and they can also experience increases in
diastolic blood pressure. Thus, mean arterial pressure

is generally much higher in these patients, likely owing
to a lesser reduction in total peripheral resistance.
For the first 2 to 3 hours following exercise,
blood pressure drops below preexercise resting lev-
els, a phenomenon referred to as postexercise hy-
potension (Isea et al. 1994). The specific mechanisms
underlying this response have not been established.
The acute changes in blood pressure after an episode,
of exercise may be an important aspect of the role of
physical activity in helping control blood pressure in
hypertensive patients.

Oxygen Extraction

The A-TO, difference increases with increasing rates
of work (Figure 3-2) and results from increased
oxygen extraction from arterial blood as it passes
through exercising muscle. At rest, the A10, differ-
ence is approximately 4 to 5 ml of 0, for every 100 ml
of blood (ml/100 ml); as the rate of work approaches
maximal levels, the A-CO, difference reaches 15 to 16
ml/l00 ml of blood.

Coronary Circulation

The coronary arteries supply the myocardium with
blood and nutrients. The right and left coronary
arteries curve around the external surface of the heart,
then branch and penetrate the myocardial muscle
bed, dividing and subdividing like branches of a tree
to form a dense vascular and capillary network to
supply each myocardial muscle fiber. Generally one
capillary supplies each myocardial fiber in adult hu-
mans and animals; however, evidence suggests that
the capillary density of the ventricular myocardium
can be increased by endurance exercise training.

At rest and during exercise, myocardial oxygen
demand and coronary blood flow are closely linked.
This coupling is necessary because the myocardium
depends almost completely on aerobic metabolism
and therefore requires a constant oxygen supply.
Even at rest, the myocardium's oxygen use is high
relative to the blood flow. About 70 to 80 percent of
the oxygen is extracted from each unit of blood
crossing the myocardial capillaries; by comparison,
only about 25 percent is extracted from each unit
crossing skeletal muscle at rest. In the healthy heart,
a linear relationship exists between myocardial oxy-
gen demands, consumption, and coronary blood
flow, and adjustments are made on a beat-to-beat

63


Physical Activity and Health

Figure 3-2. Changes in arterial and mixed venous oxygen content with increasing rates of work on the
     cycle ergometer

18

A

arterial oxygen content

25

I         I
50      75

I
100

I         I         I         I         I         I       I
125     150     175     200     225     250     275

Power (watts)

basis. The three major determinants of myocardial
oxygen consumption are heart rate, myocardial
contractility, and wall stress (Marcus 1983;
Jorgensen et al. 1977). Acute increases in arterial
pressure increase left ventricular pressure and wall
stress. As a result, the rate of myocardial metabolism
increases, necessitating an increased coronary blood
flow. A very high correlation exists between both
myocardial oxygen consumption and coronary blood
flow and the product of heart rate and systolic blood
pressure (SBP) (Jorgensen et al. 1977). This so-
called double product (HR o SBP) is generally used
to estimate myocardial oxygen and coronary blood
flow requirements. During vigorous exercise, all
three major determinants of myocardial oxygen re-
quirements increase above their resting levels.

The increase in coronary blood flow during exer-
cise results from an increase in perfusion pressure of
the coronary artery and from coronary vasodilation.
`Most important, an increase in sympathetic nervous
system stimulation leads to an increase in circulating
catecholamines. This response triggers metabolic pro-
cesses that increase both perfusion pressure of the

64

coronary artery and coronary vasodilation to meet the
increased need for blood flow required by the increase
in myocardial oxygen use.

Respiratory Responses to Exercise

The respiratory system also responds when chal-
lenged with the stress of exercise. Pulmonary ven-
tilation increases almost immediately, largely
through stimulation, of the respiratory centers in
the brain stem from the motor cortex and through
feedback from the proprioceptors in the muscles
and joints of the active limbs. During prolonged
exercise, or at higher rates of work, increases in CO,
production, hydrogen ions (H'), and body and
blood temperatures stimulate further increases in
pulmonary ventilation. At low work intensities, the
increase in ventilation is mostly the result of in-
creases in tidal volume. At higher intensities, the
respiratory rate also increases. In normal-sized,
untrained adults, pulmonary ventilation rates can
vary from about 10 liters per minute at rest to more
than 100 liters per minute at maximal rates ofwork;
in large, highly trained male athletes, pulmonary


ventilation rates can reach more than 200 liters per
minute at maximal rates of work.

Resistance Exercise

The cardiovascular and respiratory responses to
episodes of resistance exercise are mostly similar to
those associated with endurance exercise. One no-
table exception is the exaggerated blood pressure
response that occurs during resistance exercise. Part
of this response can be explained by the fact that
resistance exercise usually involves muscle mass
that develops considerable force. Such high, isolated
force leads to compression of the smaller arteries and
results in substantial increases in total peripheral
resistance (Coyle 1991). Although high-intensity
resistance training poses a potential risk to hyperten-
sive patients and to those with cardiovascular dis-
ease, research data suggest that the risk is relatively
low (Gordon et al. 1995.) and that hypertensive
persons may benefit from resistance training (Tipton
1991; American College of Sports Medicine 1993).

Skeletal Muscle

The primary purpose of the musculoskeletal system is
to define and move the body. To provide efficient and
effective force, muscle adapts to demands. In response
to demand, it changes its ability to extract oxygen,
choose energy sources, and rid itself of waste prod-
ucts. The body contains three types of muscle tissue:
skeletal (voluntary) muscle, cardiac muscle or myo-
cardium, and smooth (autonomic) muscle. This sec-
tion focuses solely on skeletal muscle.

Skeletal muscle is composed of two basic types of
muscle fibers distinguished by their speed of con-
traction-slow-twitch and fast-twitch-a character-
istic that is largely dictated by different forms of the
enzyme myosin adenosinetriphosphatase (ATPase).
Slow-twitch fibers, which have relatively slow con-
tractile speed, have high oxidative capacity and fa-
tigue resistance, low glycolytic capacity, relatively
high blood flow capacity, high capiilary density, and
high mitochondrial content (Terjung 1995). Fast-
twitch muscle fibers have fast contractile speed and
are classified into two subtypes, fast-twitch type "a"
(FT,) and fast-twitch type "b" (FT,). FT, fibers have
moderately high oxidative capacity, are relatively
fatigue resistant, and have high glycolytic capacity,
relatively high blood flow capacity, high capillary

Physiologic Responses and Long-Term Adaptations to Exercise

, density, and high mitochondrial content (Terjung
1995). FT, fibers have low oxidative capacity, low
fatigue resistance, high glycolytic capacity, and fast
contractile speed. Further, they have relatively low
blood flow capacity, capillary density, and mito-
chondrial content (Terjung 1995).
There is a direct relationship between predomi-
nant fiber type and performance in certain sports.
For example, in most marathon runners, slow-twitch
fibers account for up to or more than 90 percent of
the total fibers in the leg muscles. On the other hand,
the leg muscles in sprinters are often more than 80
percent composed of fast-twitch fibers. Although the
issue is not totally resolved, muscle fiber type ap-
pears to be genetically determined; researchers have
shown that several years of either high-intensity
sprint training or high-intensity endurance training
do not significantly alter the percentage of the two
major types of fibers (folesz and Sreter 1981).

Skeletal Muscle Energy Metabolism
Metabolic processes are responsible for generating
adenosine triphosphate (ATP), the body's energy
source for all muscle action. ATP is generated by three
basic energy systems: the ATP-phosphocreatine
(ATP-PCr) system, the glycolytic system, and the
oxidative system. Each system contributes to energy
production in nearly every type of exercise. The
relative contribution of each will depend on factors
such as the intensity of work rate at the onset of
exercise and the availability of oxygen in the muscle.

Energy Systems

The ATP-PCr system provides energy from the ATP
stored in all of the body's cells. PCr, also found in all
cells, is a high-energy phosphate molecule that stores
energy. As ATP concentrations in the cell are reduced
by the breakdown of ATP to adenosine diphosphate
(ADP) to release energy for muscle contraction, PCr is
broken down to release both energy and a phosphate
to allow reconstitution of ATP from ADP. This process
describes the primary energy system for short, high-
intensity exercise, such as a 40- to 200-meter sprint;
during such exercise, the system can produce energy
at very high rates, and ATP and PCr stores, which are
depleted in lo-20 seconds, will last just long enough
to complete the exercise.

65


Physical Activity and Health

At high rates of work, the active muscle cells
oxygen demand exceeds its supply. The cell must
then rely on the glycolytic energy system to produce
ATP in the absence of oxygen (i.e., anaerobically).
This system can only use glucose, available in the
blood plasma and stored in both muscle and the liver as
glycogen. The glycolytic energy system is the primary
energy system for all-out bouts of exercise lasting
from 30 seconds to 2 minutes, such as an 800-meter
run. The major limitation of this energy system is
that it produces lactate, which lowers the pH of both
the muscle and blood. Once the pH drops below a
value of 6.4 to 6.6, enzymes critical for producing
energy are no longer able to function, and ATP
production stops (Wilmore and Costill 1994).
The oxidative' energy system uses oxygen to
produce ATP within the mitochondria, which are
special cell organelles within muscle. This process
cannot generate ATP at a high enough rate to sustain
an all-out sprint, but it is highly effective at lower
rates of work (e.g., long distance running). ATP can
also be produced from fat and protein metabolism
through the oxidative energy system. Typically, car-
bohydrate and fat provide most of the ATP; under
most conditions, protein contributes only 5 to 10
percent at rest and during exercise.

Metabolic Rate

The rate at which the body uses energy is known as
the metabolic rate. When measured while a person is
at rest, the resulting value represents the lowest (i.e.,
basal) rate of energy expenditure necessary to main-
tain basic body functions. Resting metabolic rate is
measured under highly controlled resting condi-
tions following a 12-hour fast and a good night's
sleep (Turley, McBride, Wilmore 1993). To quantify
the rate of energy expenditure during exercise, the
metabolic rate at rest is defined as 1 metabolic
equivalent (MET); a 4 MET activity thus represents
an activity that requires four times the resting meta-
bolic rate. The use of METS to quantify physical
activity intensity is the basis of the absolute intensity
scale. (See Chapter 2 for further information.)

Maximal Oxygen Uptake

During exercise,\iO, increases in direct proportion to
the rate of work. The point at which a person's 30, is
no longer able to increase is defined as the maximal

oxygen uptake (\iO,max) (Figure 3-3). A person's
VO,max is in part genetically determined; it can be
increased through training until the point that the
genetically possible maximum is reached.\iO,max is
considered the best estimate of a person's cardio-
respiratory fitness or aerobic power (Jorgensen et al.
1977).

f acta te Threshold
Lactate is the primary by-product of the anaerobic
glycolytic energy system. At lower exercise intensi-
ties, when the cardiorespiratory system can meet the
oxygen demands of active muscles, blood lactate
levels remain close to those observed at rest, because
some lactate is used aerobically by muscle and is
removed as fast as it enters the blood from the
muscle. As the intensity of exercise is increased,
however, the rate of lactate entry into the blood from
muscle eventually exceeds its rate of removal from
the blood, and blood lactate concentrations increase
above resting levels. From this point on, lactate
levels continue to increase as the rate of work in-
creases, until the point of exhaustion. The point at
which the concentration of lactate in the blood
begins to increase above resting levels is referred to
as the lactate threshold (Figure 3-3).
Lactate threshold is an important marker for endur-
ance performance, because distance runners set their
race pace at or slightly above the lactate threshold
(Farrell et al. 1979). Further, the lactate thresholds
of highly trained endurance athletes occur at a much
higher percentage of their VO,max, and thus at higher
relative workloads, than do the thresholds of un-
trained persons. This key difference is what allows
endurance athletes to perform at a faster pace.

Hormonal Responses to Exercise
The endocrine system, like the nervous system,
integrates physiologic responses and plays an im-
portant role in maintaining homeostatic conditions
at rest and during exercise. This system controls the
release of hormones from specialized glands through-
out the body, and these hormones exert their actions
on targeted organs and cells. In response to an
episode of exercise, many hormones, such as cat-
echolamines, are secreted at an increased rate, though
insulin is secreted at a decreased rate (Table 3-l).
The actions of some of these hormones, as well as

66


Physiologic Responses and Long-Term Adaptations to Exercise

Figure 3-3. Changes in oxygen uptake and blood lactate concentrations with increasing rates of work on the
     cycle ergometer*

  55



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Ti
2

30



25

VO,max
t

                      oxygen uptake (00, max) are indicated.

I        I        I        I        I        I        I        I        I

50

75

100

                         t
125    150    175    200    225    250    275
  Power (watts)

25

their specific responses to exercise, are discussed in
more detail in Chapter 4.

Immune Responses to Exercise
The immune system is a complex adaptive system
that provides surveillance against foreign proteins,
viruses, and bacteria by using the unique functions of
cells produced by the bone marrow and the thymus
gland. By interacting with neural and endocrine
factors, the immune system influences the body's
overall response to exercise (Reichlin 1992). A grow-
ing body of literature indicates that the incidence of
some infections may be influenced by the exercise
history of the individual (Nieman 1994; Hoffman-
Goetz and Pedersen 1994).

  Moderate exercise has been shotin to bolster the
function of certain components of the human immune
system- such as natural killer cells, circulatingl- and
B-lymphocytes, and cells of the monocyte-macroph-
age system -thereby possibly decreasing the inci-
dence of some infections (Keast, Cameron, Morton
1988; Pedersen and Ullum 1994; Woods and Davis
1994) and perhaps of certain types of cancer (Shephard
and Shek 1995).

Exercise of high intensity and long duration or
exercise that involves excessive training may have
adverse effects on immune function. In general, a
high-intensity, single episode of exercise results in a
marked decline in the functioning of all major cells of
the immune system (Newsholme and Parry-Billings
1994; Shephard and Shek 1995). In addition, over-
training may reduce the response of T-lymphocytes to
mutagenic stimulation, decrease antibody synthesis
and plasma level of immunogiobins and complement,
and impair macrophage phagocytosis. The reduced
plasma glutamine levels that occur with high-intensity
exercise or excessive training are postulated to con-
tribute to these adverse effects on the immune system
(Newsholme and Parry-Billings 1994).

Long-Term Adaptations to
Exercise Training

Adaptations of Skeletal Muscle and Bone
Skeletal muscle adapts to endurance training chiefly
through a small increase in the cross-sectional area
of slow-twitch fibers, because low- to moderate-

67


Physical Activity and Health

Table 3-1. A summary of hormonal changes during an episode of exercise

Hormone

Exercise
resoonse  Soecial relationshios         Probable imoortance

Catecholamines

Growth hormone (GH)

Adrenocorticotropic
hormone (ACTH)-cortisol

Thyroid-stimulating
hormone (TSH)-thyroxine

Luteinizing hormone (LH)

Testosterone

Estradiol-progesterone

Insulin

Glucagon

Renin-angiotensin-
aldosterone

Antidiuretic hormone
(ADI-

Parathormone
(PTH)-calcitonin

Erythropoietin

Prostaglandins

Increases  Greater increase with intense
     exercise; norepinephrine >
     epinephrine; increases less after
     training

Increases  Increases more in untrained
     persons; declines faster in trained
       persons

Increases  Greater increase with intense
      exercise; increases less
     after training with
      submaximal exercise

Increases  Increased thyroxine turnover
     with training but no toxic effects
      are evident

No change None
increases   None

Increases  Increases during luteal phase
     of the menstrual cycle

Decreases  Decreases less after training

Increases  Increases less after training

Increases  Same increase after training
       in rats

Expected   None
increase

Unknown None

Unknown None

May    May increase in response to
increase  sustained isometric contractions;
     may need ischemic stress

Increased blood glucose;
increased skeletal muscle and
liver glycogenolysis; increased
lipolysis

Unknown

Increased gluconeogenesis in
liver; increased mobilization of
fatty acids

Unknown

None

Unknown

Unknown

Decreased stimulus to use blood
glucose
Increased blood glucose via
glycogenolysis and
gluconeogenesis
Sodium retention to maintain
plasma volume

Water retention to maintain
plasma volume
Needed to establish proper
bone development
Would be important to increase
erythropoiesis
May be local vasodilators

Adapted from Wilmore JH, Costill DL. Physiplogy of sport and exercise. Champaign, IL: Human Kinetics, 1994, p. 136.

68


Physiologic Responses and Long-Term Adaptations to Exercise

intensity aerobic activity primarily recruits these
fibers (Abernethy, Thayer, Taylor 1990). Prolonged
endurance training (i.e., months to years) can lead to
a transition of FT, fibers to FTa fibers, which have a
higher oxidative capacity (Abernethy, Thayer, Taylor
1990). No substantive evidence indicates that fast-
twitch fibers will convert to slow-twitch fibers under
normal training conditions (lolesz and Sreter 1981).
Endurance training also increases the number of
capillaries in trained skeletal muscle, thereby allow-
ing a greater capacity for blood flow in the active
muscle (Terjung 1995).

  Resistance-trained skeletal muscle exerts con-
siderably more force because ofboth increased muscle
size (hypertrophy) and increased muscle fiber re-
cruitment. Fiber hypertrophy is the result of in-
creases in both the size and number of myofibrils in
both fast-twitch and slow-twitch muscle fibers
(Kannus et al. 1992). Hyperplasia, or increased fiber
number, has been reported in animal studies, where
the number of individual muscle fibers can be counted
(Gonyea et al. 1986), and has been indirectly demon-
strated during autopsies on humans by using direct
fiber counts to compare dominant and nondominant
paired muscles (Sjostrom et al. 1991).
During both aerobic and resistance exercise,
active muscles can undergo changes that lead to
muscle soreness. Some soreness is felt immediately
after exercise, and some can even occur during exer-
cise. This muscle soreness is generally not physically
limiting and dissipates rapidly. A more limiting sore-
ness, however, may occur 24 to 48 hours following
exercise. This delayed-onset muscle soreness is pri-
marily associated with eccentric-type muscle action,
during which the muscle exerts force while lengthen-
ing, as can happen when a person runs down a steep
hill or lowers a weight from a fully flexed to a fully
extended position (e.g., the two-arm curl). Delayed-
onset muscle soreness is the result of structural dam-
age to the muscle; in its most severe form, this damage
may include rupture of the cell membrane and disrup-
tion of the contractile elements of individual muscle
fibers (Armstrong, Warren, Warren 1991). Such dam-
age appears to result in an inflammatory response
(MacIntyre, Reid, McKenzie 1995).
Total inactivity results in,muscle atrophy and
loss of bone mineral and mass. Persons who are
sedentary generally have less bone mass than those
who exercise. but the increases in bone mineral and

mass that result from either endurance or resistance
training are relatively small (Chesnut 1993). The
role of resistance training in increasing or maintain-
ing bone mass is not well characterized. Endurance
training has little demonstrated positive effect on
bone mineral and mass. Nonetheless, even small
increases in bone mass gained from endurance or
resistance training can help prevent or delay the
process of osteoporosis (Drinkwater 1994). (See
Chapter 4 for further information on the effects of
exercise on bone.)

Themusculoskeletalsystemcannotfunctionwith-
out connective tissue linking bones to bones (liga-
ments) and muscles to bones (tendons). Extensive
animal studies indicate that ligaments and tendons
become stronger with prolonged and high-intensity
exercise. This effect is the result of an increase in the
strength of insertion sites between ligaments, ten-
dons, and bones, as well as an increase in the cross-
sectional areas of ligaments and tendons. These
structures also become weaker and smaller with sev-
eral weeks of immobilization (Tipton andvailas 1990),
which can have important implications for muscu-
loskeletal performance and risk of injury.

Metabolic Adaptations

Significant metabolic adaptations occur in skeletal
muscle in response to endurance training. First, both
the size and number of mitochondria increase sub-
stantially, as does the activity of oxidative enzymes.
Myoglobin content in the muscle can also be aug-
mented, increasing the amount of oxygen stored in
individual muscle fibers (Hickson 1981), but this
effect is variable (Svedenhag, Henriksson, Sylven
1983). Such adaptations, combined with the increase
in capillaries and muscle blood flow in the trained
muscles (noted in a previous section), greatly enhance
the oxidative capacity of the endurance-trained muscle.

Endurance training also increases the capacity of
skeletal muscle to store glycogen (Kiens et al. 1993).
The ability of trained muscles to use fat as an energy
source is also improved, and this greater reliance on
fat spares glycogen stores (Kiens et al. 1993). The
increased capacity to use fat following endurance
training results from an enhanced ability to mobilize
free-fatty acids from fat depots and an improved
capacity to oxidize fat consequent to the increase in
the muscle enzymes responsible for fat oxidation
(Wilmore and Costill 1994).

69


Physical Activity and Health

These changes in muscle and in cardiorespi-
ratory function are responsible for increases in
both \iO,max and lactate threshold. The endurance-
trained person can thus perform at considerably higher
rates of work than the untrained person. Increases in
30,max generally range from 15 to 20 percent follow-
ing a 6-month training period (Wilmore and Costill
1994). However, individual variations in this response
are considerable. In one study of 60- to 71-year-old
men and women who endurance trained for 9 to 12
months, the improvement in 30,max varied from 0
to 43 percent; the mean increase was 24 percent

(Kohrt et al. 1991). This variation in response may
be due in part to genetic factors and to initial levels
of fitness. To illustrate the changes that can be
expected with endurance training, a hypothetical
sedentary man's pretraining values have been com-
pared with his values after a 6-month period of
endurance training and with the values of a typical
elite endurance runner (Table 3-2).

Responses to endurance training are similar for
men and women. At all ages, women and men show
similar gains in strength from resistance training

(Rogers and Evans 1993; Holloway and Baechle 1990)

Table 3-2.  A hypothetical example of alterations in selected physiological variables consequent to a C-month
    endurance training program in a previously sedentary man compared with those of a typical elite
       endurance runner

Sedentary man

Variable              Pretraining

Posttraining

Runner

Cardiovascular
HR at rest (beats o min-`1
HR max (beats o min-`1
SV rest (ml)

SV max (ml)

Q rest (L o min.`)
Q max (L o min.`)
Heart volume (ml)
Blood volume (L)
Systolic BP rest (mmHg)
Systolic BP max (mmHg)
Diastolic BP rest (mmHg)
Diastolic BP max (mmHg)

71                   59                36
185                  183                 174
65                  80                125
120                   140                200
4.6                   4.7                4.5
22.2                 25.6               32.5
750                  820            1,200
4.7                  5.1                 6.0
135                  130                120
210                  205                210
78                  76                 65
82                   80                 65

Respiratory
vE rest (L o min.`)
V, rest (L o min-`1
TV rest (L)
TV max (L)
RR rest (breaths o min-`1
RR max (breaths o min-`1

Metabolic
A-CO, diff rest (ml o 100 ml-`)
A-CO, diff max (ml o 100 ml-`)
i.`O, rest (ml o kg-' o min-`1
90, max (ml o kg-' o min-`1
Blood lactate rest (mmol o L-7
Blood lactate max (mmol o L-`)

7                    6                  6
110                  135                195
0.5                  0.5               0.5
2.75                 3.0                3.9
14                   12                 12
40                  45                50



6.0                  6.0                6.0
34.5                 15.0               16.0
3.5                  3.5                3.5
40.5                 49.8               76.5
1 .o                  1 .o                1 .o

7.5

8.5

9.0

Adapted from Wilmore JH, Costill DL. Physiology ofsport and exercise. Champaign, IL: Human Kinetics, 1994, p. 230.
HR = heart rate; max = maximal; SV = stroke volume; 0 = cardiac output; BP = blood pressure;i/, = ventilatory volume; TV = tidal volume;
RR = respiration rate; A-60, diff = arterial-mixed venous oxygen difference;\jO, = oxygen consumption.

70


and similar gains in \iO,max from aerobic'endurance
training (Kohrt et al. 1991; Mitchell et al. 1992).

Cardiovascular and Respiratory Adaptations
Endurance training leads to significant cardiovascu-
lar and respiratory changes at rest and during steady-
state exercise at both submaximal and maximal rates
of work. The magnitude of these adaptations largely
depends on the person's initial fitness level; on mode,
intensity, duration, and frequency of exercise; and
on the length of training (e.g., weeks, months, years).

Long-Term Cardiovascular Adaptations
Cardiac output at rest and during submaximal exer-
cise is essentially unchanged following an endur-
ance training program. At or near maximal rates of
work, however, cardiac output is increased sub-
stantially, up to 30 percent or more (Saltin and
Rowe11 1980). There are important differences in
the responses of stroke volume and heart rate to
training. After training, stroke volume is increased
at rest, during submaximal exercise, and during
maximal exercise; conversely, posttraining heart
rate is decreased at rest and during submaximal
exercise and is usually unchanged at maximal rates
of work. The increase in stroke volume appears to
be the dominant change and explains most of the
changes observed in cardiac output.
  Several factors contribute to the increase in
stroke volume from endurance training. Endurance
training increases plasma volume by approximately
the same percentage that it increases stroke volume
(Green, Jones, Painter 1990). An increased plasma
volume increases the volume of blood available to
return to the right heart and, subsequently, to the
left ventricle. There is also an increase in the end-
diastolic volume (the volume of blood in the heart
at the end of the diastolic filling period) because of
increased amount of blood and increased return of
blood to the ventricle during exercise (Seals et al.
1994). This acute increase in, the'left ventricle's
end-diastolic volume stretches its walls, resulting
in a more elastic recoil.

Endurance training also results in long-term
changes in the structure of the heart that augment
stroke volume. Short-term adaptive responses in-
clude ventricular dilatation; this increase in the vol-
ume of the ventricles allows end-diastolic volume to

Physiologic Responses and Long-Term Adaptations to Exercise

increase without excessive stress on the ventricular
walls. Long-term adaptive responses include hyper-
trophy of the cardiac muscle fibers (i.e., increases in
the size of each fiber). This hypertrophy increases
the muscle mass of the ventricles, permitting greater
force to be exerted with each beat of the heart.
Increases in the thickness of the posterior and septal
walls of the left ventricle can lead to a more forceful
contraction of the left ventricle, thus emptying more
of the blood from the left ventricle (George, Wolfe,
Burggraf 1991).

Endurance training increases the number of cap-
illaries in trained skeletal muscle, thereby allowing a
greater capacity for blood flow in the active muscle
(Terjung 1995). This enhanced capacity for blood
flow is associated with a reduction in total peripheral
resistance; thus, the left ventricle can exert a more
forceful contraction against a lower resistance to
flow out of the ventricle (Blomqvist and Saltin 1983).
Arterial blood pressure at rest, blood pressure
during submaximal exercise, and peak blood pres-
sure all show a slight decline as a result of endurance
training in normotensive individuals (Fagard and
Tipton 1994). However, decreases are greater in
persons with high blood pressure. After endurance
training, resting blood pressure (systolic/diastolic)
will decrease on average -3/-3 mmHg in persons with
normal blood pressure; in borderline hypertensive
persons, the decrease will be -6/-7 mmHg; and in
hypertensive persons, the decrease will be -lo/-8
mmHg (Fagard and Tipton 1994). (See Chapter 4 for
further information.)

Respiratory Adaptations

The major changes in the respiratory system from en-
durance training are an increase in the maximal rate of
pulmonary ventilation, which is the result of increases
in both tidal volume and respiration rate, and an
increase in pulmonary diffusion at maximal rates of
work, primarily due to increases in pulmonary blood
flow, particularly to the upper regions of the lung.

Maintenance, Detraining, and
Prolonged Inactivity
Most adaptations that result from both endurance
and resistance training will be reversed if a person
stops or reduces training. The greatest deterioration

71


Physical Activity and Health

in physiologic function occurs during prolonged bed
rest and immobilization by casts. A basic mainte-
nance training program is necessary to prevent these
losses in function.

Maintaining Fitness and Muscular Strength
Muscle strength and cardiorespiratory capacity are
dependent on separate aspects of exercise. After a per-
son has obtained gains in VO,max by performing
cardiorespiratory exercise six times per week, two
to four times per week.is the optimal frequency of
training to maintain those gains (Hickson and
Rosenkoetter 1981). Further, a substantial part of
the gain can be retained when the duration of each
session is reduced by as much as two-thirds, but
only if the intensity during these abbreviated ses-
sions is maintained at 270 percent of VO,max
(Hickson et al. 1985). If training intensity is reduced
by as little as one-third, however, a substantial
reduction in \iO,max can be expected over the next
15 weeks (Hickson et al. 1985).
In previously untrained persons, gains in mus-
cular strength can be sustained by as little as a single
session per week of resistance training, but only if
the intensity is not reduced (Graves et al. 1988).

Detraining

With complete cessation of exercise training, a sig-
nificant reduction in iTO,max and a decrease in
plasma volume occur within 2 weeks; all prior func-
tional gains are dissipated within 2 to 8 months, even
if routine low- to moderate-intensity physical activ-
ity has taken the place of training (Shephard 1994).
Muscular strength and power are reduced at a much
slower rate than \iO,max, particularly during the
first few months after an athlete discontinues resis-
tance training (Fleck and Kraemer 1987). In fact, no
decrement in either strength or power may occur for
the first 4 to 6 weeks after training ends (Neufer et al.
1987). After 12 months, almost half of the strength
gained might still be retained if the athlete remains
moderately active (Wilmore and Costil! 1994).

Prolonged Inactivity

The effects of prolonged inactivity have been studied
by placing healthy young male athletes and sedentary
volunteers in bed for up to 3 weeks after a control
period during which baseline measurements were

made. The'resulting detrimental changes in physi-
ologic function and performance are similar to those
resulting from reduced gravitational forces during
space flight and are more dramatic than those result-
ing from detraining studies in which routine daily
activities in the upright position (e.g., walking, stair
climbing, lifting, and carrying) are not restricted.
Results of bed rest studies show numerous physi-
ologic changes, such as profound decrements in
cardiorespiratory function proportional to the dura-
tion of bed rest (Shephard 1994; Saltin et al. 1968).
Metabolic disturbances evident within a few days of
bed rest include reversible glucose intolerance and
hyperinsulinemia in response to a standard glucose
load, reflecting cell insulin resistance (Lipman et al.
1972); reduced total energy expenditure; negative
nitrogen balance, reflecting loss of muscle protein;
and negative calcium balance, reflecting loss of bone
mass (Bloomfield and Coyle 1993). There is also a
substantial decrease in plasma volume, which affects
aerobic power.

From one study, a decline in VO,max of 15 per-
cent was evident within 10 days of bed rest and
progressed to 27 percent in 3 weeks; the rate of loss was
approximately 0.8 percent per day of bed rest
(Bloomfieldand Coyle 1993). The decrement inVO,max
from bed rest and reduced activity results from a
decrease in maximal cardiac output, consequent to a
reduced stroke volume. This, in turn, reflects the
decrease in end-diastolic volume resulting from a
reduction in total blood and plasma volume, and
probably also from a decrease in myocardial contrac-
tility (Bloomfield and Coyle 1993). Maximal heart
rate and A-TO, difference remain unchanged
(Bloomfield and Coyle 1993). Resting heart rate
remains essentially unchanged or is slightly in-
creased, whereas resting stroke volume and cardiac
output remain unchanged or are slightly decreased.
However, the heart rate for submaximal exertion is
generally increased to compensate for the sizable
reduction in stroke volume.

Physical inactivity associated with bed rest or
prolonged weightlessness also results in a progres-
sive decrement in skeletal muscle mass (disuse
atrophy) and strength, as well as an associated
reduction in bone mineral density that is approxi-
mately proportional to the duration of immobiliza-
tion or weightlessness (Bloomfield and Coyle 1993).
The loss of muscle mass is not as great as that which

77


Physiologic Responses and Long-Term Adaptations to Exercise

~,c~~~rs \vith immobilization of a limb by a plaster
ilaSt. but it exceeds that associated with cessation of
rcsist;lnce exercise training. The muscle groups
n,05t affected by prolonged immobilization are the
.,ntlgravity postural muscles of the lower extremi-
t,cs (Bloomfield and Coyle 1993). The loss of nor-
m&,1 mechanical strain patterns from contraction of
,hcsc muscles results in a corresponding loss of
Llcllsit\ in the bones of the lower extremity, particu-
1.~~1~ the heel and the spine (Bloomfield and Coyle
IQQJ). Muscles atrophy faster than bones lose their
Llcn%ity. For example, 1 month of bed rest by healthy
VoIIII$ men resulted in a 10 to 20 percent decrease
,,, Inl~sclc fiber cross-sectional areaand a 21 percent
, L~d~~ction in peak isokinetic torque of knee exten-
sc,~~ (Bloomfield and Coyle 1993), whereas a simi-
I,\r period of bed rest resulted in a reduction in bone
InlncraI density of only 0.3 to 3 percent for the
I~lmhar spine and 1.5 percent for the heel.
c!Llantitative histologic examination of muscle
I,lc,ljsics of the vastus lateralis of the leg following
~~llmobilization shows reduced cross-sectional area
1,)~ hot11 slow-twitch and fast-twitch fibers, actual
~~c~.rolic` changes in affected fibers., loss of capillary
clwsily. and a decline in aerobic enzyme activity,
L I MI Ininc phosphate, and glycogen stores (Bloomfield
.IIKI (:oylc 1993). On resuming normal activity,
I c.\,cr\il,iliry of these decrements in cardiorespiratory,
In~*r.tholic. and muscle function is fairly rapid (within
~I.I\.\ to weeks) (Bloomfield and Coyle 1993). By
h ~~IILI'A~~, the reversal of the decrement of bone min-
~.KII clcnsity requires weeks to months.

Special Considerations

111~ l~hysiologic responses to exercise and physi-
olo::ic adaptations to training and detraining, re-
\ I~.\\uI in the preceding sections, can be influenced
!I\ J Ill~ml~cr of factors, including physical disability,
~`ll\`lronmcntal conditions, age, and sex.

Disability

.\l~ll~~ugh there is a paucity of information about
Ptl!~~i~~logic responses to exercise among persons
`A Ith disabilities, existing information supports the
:l~ill~ln that the capacity of these persons to adapt to
"`( rcascd levels of physical activity is similar to that
"I I'crsons without disabilities. Many of the acute

effects of physical activity on the cardiovascular,
respiratory, endocrine, and musculoskeletal systems
have been demonstrated to be similar among persons
with disabilities, depending on the specific nature of
the disability. For example, physiologic responses to
exercise have been studied among persons with
paraplegia (Davis 1993), quadriplegia (Figoni 1993),
mental retardation (Fernhall 1993), multiple sclero-
sis (Ponichtera-Mulcare 1993), and postpolio syn-
drome (Birk 1993).

Environmental Conditions

The basic physiologic respbnses to an episode of
exercise vary considerably with changes in environ-
mental conditions. As environmental temperature
and humidity increase, the body is challenged to
maintain its core temperature. Generally, as the
body's core temperature increases during exercise,
blood vessels in the skin begin to dilate, diverting
more blood to the body's surface, where body heat
can be passed on to the environment (unless envi-
ronmental temperature exceeds body temperature).
Evaporation of water from the skin's surface signifi-
cantly aids in heat loss; however, as humidity in-
creases, evaporation becomes limited.
These methods for cooling can compromise car-
diovascular function during exercise. Increasing
blood flow to the skin creates competition with the
active muscles for a large percentage of the cardiac
output. When a person is exercising for prolonged
periods in the heat, stroke volume will generally
decline over time consequent to dehydration and
increased blood flow in the skin (Rowe11 1993;
Montain and Coyle 1992). Heart rate increases sub-
stantially to try to maintain cardiac output to com-
pensate for the reduced stroke volume.
High air temperature is not the only factor that
stresses the body's ability to cool itself in the heat.
High humidity, low air velocity, and the radiant heat
from the sun and reflective surfaces also contribute
to the total effect. For example, exercising under
conditions of 32oC (90oF) air temperature, 20 per-
cent relative humidity, 3.0 kilometers per hour (4.8
miles per hour) air velocity, and cloud cover is much
more comfortable and less stressful to the body than
the same exercise under conditions of 24oC (75oF)
air temperature, 90 percent relative humidity, no air
movement, and direct exposure to the sun.

73


Physical Activity and Health

Children respond differently to heat than adults
do. Children have a higher body surface area to body
mass ratio (surface area/mass), which facilitates heat
loss when environmental temperatures are below
skin temperature. When environmental tempera-
ture exceeds skin temperature, children are at an
even greater disadvantage because these mecha-
nisms then become avenues of heat gain. Children
also have a lower rate of sweat production; even
though they have more heat-activated sweat glands,
each gland produces considerably less sweat than
that of an adult (Bar-Or 1983).
The inability to maintain core temperature can
lead to heat-related injuries. Heat cramps, character-
ized by severe cramping of the active skeletal muscles,
is the least severe of three primary heat disorders.
Heat exhaustion results when the demand for blood
exceeds what is available, leading to competition for
the body's limited blood supply. Heat exhaustion is
accompanied by symptoms including extreme fa-
tigue, breathlessness, dizziness, vomiting, fainting,
cold and clammy or hot and dry skin, hypotension,
and a weak, rapid pulse (Wilmore and Costill 1994).
Heatstroke, the most extreme of the three heat disor-
ders, is characterized by a core temperature of 40oC
(104oF) or higher, cessation of sweating, hot and dry
skin, rapid pulse and respiration, hypertension, and
confusion or unconsciousness. If left untreated, heat-
stroke can lead to coma, then death. People experi-
encing symptoms of heat-related injury should be
taken to a shady area, cooled with by whatever means
available, and if conscious given nonalcoholic bever-
ages to drink. Medical assistance should be sought.
To reduce the risk of developing heat disorders, a
person should drink enough fluid to try to match
that which is lost through sweating, avoid extreme
heat, and reduce the intensity of activity in hot
weather. Because children are less resistant to the
adverse effects of heat during exercise, special atten-
tion should be given to protect them when they
exercise in the heat and to provide them with'extra
fluids to drink.

Stresses associated with exercising in the ex-
treme cold are generally less severe. For most situa-
tions, the problems associated with cold stress can be
eliminated by adequate clothing. Still, cold stress can
induce a number of changes in the physiologic re-
sponse to exercise (Doubt 1991; Jacobs, Martineau,

Vallerand 1994; Shephard 1993). These include the
increased generation of body heat by vigorous activ-
ity and shivering, increased production of catechola-
mines, vasoconstriction in both the cutaneous and
nonactive skeletal muscle beds to provide insulation
for the body's core, increased lactate production, and
a higher oxygen uptake for the same work (Doubt
1991). For the same absolute temperature, exposure
to cold water is substantially more stressful than
exposure to cold air because the heat transfer in
water is about 25 times greater than in air (Toner and
McArdle 1988). Because the ratio of surface area to
mass is higher in children than in adults, children
lose heat at a faster rate when exposed to the same
cold stress. The elderly tend to have a reduced
response of generating body heat and are thus more
susceptible to cold stress.

Altitude also affects the body's physiologic re-
sponses to exercise. As altitude increases, barometric
pressure decreases, and the partial pressure of inhaled
oxygen is decreased proportionally. A decreased par-
tial pressure of oxygen reduces the driving force to
unload oxygen from the air to the blood and from the
blood to the muscle, thereby compromising oxygen
delivery (Fulco and Cymerman 1988). VO,max is
significantly reduced at altitudes greater than 1,500
meters. This effect impairs the performance of endur-
ance activities. The body makes both short-term and
long-term adaptations to altitude exposure that en-
able it to at least partially adapt to this imposed stress.
Because oxygen delivery is the primary concern, the
initial adaptation that occurs within the first 24 hours
of exposure to altitude is an increased cardiac output
both at rest and during submaximal exercise. Ventila-
tory volumes are also increased. An ensuing reduction
in plasma volume increases the concentration of red
blood cells (hemoconcentration), thus providing more
oxygen molecules per unit of blood (Grover, Weil,
Reeves 1986). Over several weeks, the red blood cell
mass is increased through stimulation of the bone
marrow by the hormone erythropoietin.
Exercising vigorously outdoors when air qual-
ity is poor can also produce adverse physiologic
responses. In addition to decreased tolerance for
exercise, direct respiratory effects include increased
airway reactivity and potential exposure to harmful
vapors and airborne dusts, toxins, and pollens
(Wilmore and Costill 1994).

74


Physiologic Responses and Long-Term Adaptations to Exercise

Effects of Age

When absolute values are scaled to account for
differences in body size, most differences in physi-
ologic function between children and adults dis-
appear. The exceptions are notable. For the same
absolute rate of work on a cycle ergometer, chil-
dren will have approximately the same metabolic
cost, orVO,demands, but they meet those demands
differently. Because children have smaller hearts,
their stroke volume is lower than that for adults for
the same rate of work. Heart rate is increased to
compensate for the lower stroke volume; but be-
cause this increase is generally inadequate, cardiac
output is slightly lower (Bar-Or 1983). The A-GO,
difference is therefore increased to compensate for
the lower cardiac output to achieve the sameV0,.
The iTO,max, expressed in liters per minute, in-
creases during the ages of 6-18 years for boys and
6-14 years for girls (Figure 3-4) before it reaches a
plateau (Krahenbuhl, Skinner, Kohrt 1985). When
expressed relative to body weight (milliliters per
kilogram per minute),VO,max remains fairly stable
for boys from 6-18 years of age but decreases

steadily for girls during those years (Figure 3-4)
(Krahenbuhl, Skinner, Kohrt 1985). Most likely,
different patterns of physical activity contribute to
this variation because the difference in aerobic
capacity between elite female endurance athletes
and elite male endurance athletes is substantially
less than the difference between boys and girls in
general (e.g., 10 percent vs. 25 percent) (Wilmore
and Costill 1994).

The deterioration of physiologic function with
aging is almost identical to the change in function
that generally accompanies inactivity. Maximal heart
rate and maximal stroke volume are decreased in
older adults; maximal cardiac output is thus de-
creased, which results in a VO,max lower than that
of a young adult (Raven and Mitchell 1980). The
decline inVOzmax approximates 0.40 to 0.50 milli-
liters per kilogram per minute per year in men,
according to data from cross-sectional studies; this
rate of decline is less in women (Buskirk and
Hodgson 1987). Through training, both older men
and women can increase their30,max values by
approximately the same percentage as those seen

Figure 3-4. Changes in CiO, max with increasing age from 6 to 18 years of age in boys and girls*

4.0 1

r 60

E 3.5
.-
E
p 3.0
al
.=
=
2 2.5
m
FL
3 2.0
5
$
;: 1.5

-5
E  1.0
.-
::
2 0.5

60~s. ml/kg                -- c- 4

              II ."            @`-
H-50 t
    Girls, ml/kg ,R'               x.

                         .                 3

       /-- 0'                 40 ;
          HH

  *CM- --- -0-- @@(Boys, L/min          2
                                          30 =
                              _--- __---______      -D
ed c-            ---- -7-c                         G
                                                            k

             c- /-- o-            _---     Girls, I h-tin
   /j/A- /----- -cc-

s--- -- &Z--

1     ?D
20 zj
     -
$

`Values are expressed in both liters per minute and  t 10 g.
relative to body weight (milliliters Per kilogram PP~ minlltej

0.0 I       I       I       I       I       I       I       I       I       I       I       I   1 0
   6     7     8     9    IO    11    12    13    14    15    16    17    18
                     Age (years)

Data were taken from Krahenbuhl GS, Skinner IS, Kohrt WM 198S and Bar-Or 0 1983

75


Physical Activity and Health

in younger adults (Kohrt et al. 1991). The inter-
relationships of age, \i02max, and training status
are evident when the loss inVO,max with age is
compared for active and sedentary individuals
(Figure 3-5).

When the cardiorespiratory responses of an older
adult are coinpared with those of a young or middle-
aged adult at the same absolute submaximal rate of
work, stroke volume for an older person is generally
lower and heart rate is higher from the attempt to
maintain cardiac output. Because this attempt is
generally insufficient, the A-+0, difference must
increase to provide the same submaximal oxygen
uptake (Raven and Mitchell 1980; Thompson and
Dorsey 1986). Some researchers have shown, how-
ever, that cardiac output can be maintained at both
submaximal and maximal rates of work through a
higher stroke volume in older adults (Rodeheffer et
al. 1984).

The deterioration in physiological function nor-
mally associated with aging is, in fact, caused by a
combination of reduced physical activity and the

aging process itself. By maintaining an active
lifestyle, or by increasing levels of physical activ-
ity if previously sedentary, older persons can
maintain relatively high levels of cardiovascular
and metabolic function, including irO,max (Kohrt
et al. 199 1)) and of skeletal muscle function (Rogers
and Evans 1993). For example, Fiatarone and col-
leagues (1994) found an increase of 113 percent in
the strength of elderly men and women (mean age of
87.1 years) following a lo-week training program of
progressive resistance exercise. Cross-sectional thigh
muscle area was increased, as was stair-climbing
power, gait velocity, and level of spontaneous activ-
ity. Increasing endurance and strength in the elderly
contributes to their ability to live independently.

Differences by Sex

For the most part, women and men who participate
in exercise training have similar responses in car-
diovascular, respiratory, and metabolic function
(providing that size and activity level are normal-
iced). Relative increases in\jO,max are equivalent

Figure 3-5. Changes in 00, max with aging, comparing an active population and sedentary population (the
    figure also illustrates the expected increase in VO, max when a previously sedentary person begins
     an exercise program)

A-  Active adults

R&&on in
activity plus
weight gain

Sedentary adults

0 (              I              I              I
    20         30          40          50
                        Age (years)
Adapted, by permission, from Buskirk ER, Hodgson JL. Federation Proceedings 1987.

I              I              I
60          70          80

76


Physiologic Responses and Long-Term Adaptations to Exercise

for women and men (Kohrt et al. 1991; Mitchell et
al. 1992). Some evidence suggests that older women
accomplish this increase inVO,max mainly through
an increase in the AGO, difference, whereas younger
women and men have substantial increases in stroke
volume, which increases maximal cardiac output
(Spina et al. 1993). With resistance training, women
experience equivalent increases in strength (Rogers
and Evans 1993; Holloway and Baechle 1990),
although they gain less fat-free mass due to less
muscle hypertrophy.

  Several sex differences have been noted in the
acute response to exercise. At the same absolute
rate of exercise, women have a higher heart rate
response than men, primarily because of a lower
stroke volume. This lower stroke volume is a func-
tion of smaller heart size and smaller blood volume.
In addition, women have less potential to increase
the A-CO, difference because of lower hemoglobin
content. Those differences, in addition to greater
fat mass, result in a lower V02max in women, even
when normalized for size and level of training
(Lewis, Kamon, Hodgson 1986).

Conclusions

1. Physical activity has numerous beneficial physi-
ologic effects. Most widely appreciated are its
effects on the cardiovascular and musculo-
skeletal systems, but benefits on the functioning
of metabolic, endocrine, and immune systems
are also considerable.

2. Many of the beneficial effects of exercise train-
ing-from both endurance and resistance ac-
tivities-diminish within 2 weeks if physical
activity is substantially reduced, and effects
disappear within 2 to 8 months if physical
activity is not resumed.

3. People of all ages, both male and female, undergo
beneficial physiologic adaptations to physical
activity.

Research Needs
1. Explore individual variations in response to
exercise.

2.





3.







4.



5.

Better characterize mechanisms through which
the musculoskeletal system responds differen-
tially to endurance and resistance exercise.
Better characterize the mechanisms by which
physical activity reduces the risk of cardiovascular
disease, hypertension, and non-insulin-
dependent diabetes mellitus.
Determine the minimal and optimal amount of
exercise for disease prevention.

Better characterize beneficial activity profiles for
people with disabilities.

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80


             CHAPTER 4
THE EFFECTS OF PHYSICAL ACTIVITY ON
        HEALTH AND DISEASE

Contents

Introduction  .......................


Overall Mortality  ...................
Conclusions  .....................


Cardiovascular Diseases  ..............

. .

.

.

.....................................  85




.....................................  85

.....................................  87




.....................................  87

                                  . .
Cardiovascular Diseases Combined  ..........................................  87
Coronary Heart Disease  ...................................................  87

CVD Risk Factors in Children  ..............................................  91

Stroke   ................................................................ 102
HighBloodPressure  ......... . ............................................ 103
Biologic Plausibility  ...................................................... 110

Atherosclerosis  ........................................................ 110
Plasma Lipid/Lipoprotein Profile  .......................................... 111

BloodPressure   ........................................................ 111

lschemia  ............................................................. 111

Thrombosis  ........................................................... 112
Arrhythmia  ........................................................... 112

Conclusions  ............................................................ 112

Cancer  ................................................................... 112

Colorectal Cancer  ......................................................... 113

  Colon Cancer  ......................................................... 113

  RectalCancer  ......................................................... 116
Hormone-Dependent Cancers in Women  ..................................... 116

  BreastCancer  ......................................................... 117
  Other Hormone-Dependent Cancers in Women  .......................... 1 ... 120


Contents, continued

Cancers in Men . . . . . . . . .

Prostate Cancer . . . . . . .
Testicular Cancer . . . . .
Other Site-Specific Cancers
Biologic Plausibility . . . .
Conclusions . . _ . . . . . . . .

.......

.......

.......

.......

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

.............................. 121


.............................. 124


.............................. 124


..............................  124


.......................... . ... 124

Non-Insulin-Dependent Diabetes Melhtus  ...................................... 125
Physical Activity and NIDDM  .............................................. 125
Biologic Plausibility  ...................................................... 128

Conclusions  ............................................................ 129

Osteoarthritis  ............................................................. 129
Physical Activity in Persons with Arthritis ..................................... 129
Biologic Plausibility  ......................................................  130

Conclusions  ............... . ............................................ 130

Osteoporosis  .............................................................. 130
Biologic Plausibility  ...................................................... 13 1
Physical Activity and the Prevention of Fractures and Falling  .....................  132
Conclusions  ............................................................ 132

Obesity  .................................................................. 133
Physical Activity and Obesity  ............................................... 133
Biologic Plausibility  ...................................................... 134

Conclusions  ............................................................ 135

MentalHealth  ............................................................. 135
Physical Activity and Mental Health  ......................................... 136
Biologic Plausibility  ...................................................... 141

Conclusions  ............................................................. 141

Health-Related Quality of Life  ................................................ 141
Conclusions  ............................................................ 142


Contents, continued

Adverse Effects of Physical Activity  ............................................. 142
Types of Adverse Effects  .................................................... 142
  Musculoskeletal Injuries  .................................................. 142

  Metabolic Abnormalities .................................................. 143
  Hematologic and Body Organ Abnormalities  .................................. 143

  Hazards ........................................................ . .... ..14 3
  Infectious, Allergic, and Inflammatory Conditions  ............................. 143

  Cardiac Events  ......................................................... 143

Occurrence of Adverse Effects  ............................................... 144

Conclusions  ........................................................... ..14 4

Nature of the Activity/Health Relationship  ....................................... 144
Causality  ................................................................ 144
Population Burden of Sedentary Living  ........................................ 145

Dose  ................................................................... 146

Conclusions  ............................................................. 148

ChapterSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._..... 149

Conclusions  ............................................................. ..14 9

ResearchNeeds  ........................................................... 150

References . . . . . . . . .._........................._............................ 151


             CHAPTER 4
THE EFFECTS OF PHYSICAL ACTIVITV ON
        HEALTH AND DISEASE

Introduction

T his chapter examines the relationship of physi-
cal activity and cardiorespiratory fitness to a
variety of health problems. The primary focus is on
diseases and conditions for which sufficient data exist
to evaluate an association with physical activity, the
strength of such relationships, and their potential
biologic mechanisms. Because most of the research to
date has addressed the health effects of endurance-
type physical activity (involving repetitive use of
large muscle groups, such as in walking and bicy-
cling), this chapter focuses on that type of activity.
Unless otherwise specified, the term physical activity
should be understood to refer to endurance-type
physical activity. Less well studied are the health
effects of resistance-type physical activity (i.e., that
which develops muscular strength); when this type
of physical activity is discussed, it is specified as
such. Much of the research summarized is based on
studies having only white men as participants; it
remains to be clarified whether the relationships
described here are the same for women, racial and
ethnic minority groups, and people with disabilities.
Physical activity is difficult to measure directly.
Three types of physical activity measures have been
used in observational studies over the last 40 years.
Most studies have relied on self-reported level of
physical activity, as recalled by people prompted by
a questionnaire or interview. A more objectively
measured characteristic is cardiorespiratory fitness
(also referred to as cardiorespiratory endurance)
which is measured by aerobic power (see Chapter 2
for more information on measurement issues). Some
studies have relied on occupation to classify people
according to how likely they were to be physically
active at work.

Epidemiologic studies of physical activity and
health have compared the activity levels of people
who have or develop diseases and those who do not.
Cohort studies follow populations forward in time to
observe how physical activity habits affect disease
occurrence or death. In case-control studies, groups
of persons who have disease and separate groups of
people who do not have disease are asked to recall
their previous physical activity. Cross-sectional stud-
ies assess the association between physical activity
and disease at the same point in time. Clinical trials,
on the other hand, attempt to alter physical activity
patterns and then assess whether disease occurrence
is modified as a result.

Results from epidemiologic studies can be used
to estimate the relative magnitude or strength of an
association between physical activity and a health
outcome. Two such measures used in this chapter
are risk ratio (RR) and odds ratio (OR). For these
measures, an estimate of 1 .O indicates no association,
when the risk of disease is equivalent in the two
groups being compared. RR or OR estimates greater
than 1.0 indicate an increase in risk; those less than
1.0 indicate a decreased risk. Confidence intervals
(CI) reported with estimates of association indicate
the precision of the estimate, as well as its statistical
significance. When the CI range includes 1.0, the
effect is considered likely to have occurred by chance;
therefore the estimate of association is not consid-
ered statistically significantly different from the null
value of 1.0.

Overall Mortality

Persons with moderate to high levels of physical
activity or cardiorespiratory fitness have a lower
mortality rate than those with sedentary habits or


Physical Activity and Health

low cardiorespiratory fitness. For example, com-
pared with people who are most active, sedentary
people experience between a 1.2-fold to a 2-fold
increased risk of dying during the follow-up interval
(Slattery and Jacobs 1988; Slattery, Jacobs, Nichaman
1989; Leon and Connett 1991; Stender et al. 1993;
Sandvik et al. 1993; Chang-Claude and Frentzel-
Beyme 1993; Kaplan et al. 1987; Arraiz, Wigle, Mao
1992; Paffenbarger et al. 1993).
Associations are generally stronger for measured
cardiorespiratory fitness than for reported physical
activity (Blair, Kohl, Paffenbarger 1989). Blair, Kohl,
and Barlow (1993) showed that low levels of cardio-
respiratory fitness were strongly associated with
overall mortality for both women (RR = 5.35; 95%
CI, 2.44-11.73) and men (RR= 3.16; 95% CI, 1.92-
5.20). The association with physical inactivity was
weaker for men (RR = 1.70; 95% CI, 1.06-2.74), and
there was no association for women (RR = 0.95; 95%
CI, 0.54-1.70).

Though cardiorespiratory fitness may be the
better indicator of regular physical activity, the level
of reported physical activity has been associated with
reduced all-cause mortality. Paffenbarger, Lee, and
Leung (1994) evaluated several types of recalled
activity (walking, stair climbing, all sports, moderate-
level sports, and total energy expended in activity per
week) as predictors of all-cause mortality among
male Harvard alumni. Among these men, the relative
risk of death within the follow-up period was reduced
to 0.67 with walking 15 or more kilometers per week
(reference group, < 5 kilometers/week), to 0.75 with
climbing 55 or more flights of stairs per week (refer-
ence group, < 20 flights/week), to 0.63 with involve-
ment in moderate -sports (reference group, no
involvement), and to 0.47 with 3 or more hours of
moderate sports activities per week (reference group,
< 1 hour/week). Most importantly, there was a signifi-
cant trend of decreasing risk of death across increas-
ing categories of distance walked, flights of stairs
climbed, and degree of intensity of sports play.
Researchers have also examined age.-specific ef-
fects of different levels of physical activity on all-
cause mortality. Kaplan and colleagues (1987) have
shown that physical activity level has an effect on
death rates among both older and younger persons.
Data from a study of 9,484 Seventh-Day Adventist
men aged 30 years or older in 1958 who were

followed through 1985 indicated that both moderate
and intense levels of activity reduced overall risk of
death even late in life (Lindsted, Tonstad, Kuzma
1991). Both moderate and vigorous levels of activity
were equally protective at age 50 years. The protec-
tive effect of high levels of activity lasted only until
age 70, but the protective effect for moderate activity
lasted beyond age 80.

The studies cited thus far in this section assessed
physical activity or cardiorespiratory fitness at
baseline only and then followed up for mortality. A
stronger test for a causal relationship is to examine
the effect that changing from lower to higher levels
of physical activity or cardiorespiratory fitness has
on subsequent mortality. Two large studies provide
such evidence. Among middle-aged Harvard male
alumni who were sedentary in 1962 or 1966, those
who took up moderately intense sports activity dur-
ing the study's 11 years of follow-up had a 23 percent
lower death rate (RR= 0.77; 95% CI, 0.58-0.96) than
those who remained sedentary (Paffenbarger et al.
1993). (By comparison, men who quit smoking
during the interval had a 41 percent decrease in
death rate [RR = 0.59; 95% CI, 0.43-0.801.) Men
45-84 years of age who took up moderately intense
sports extended their longevity on average by 0.72
years; added years of life were observed in all
age groups, including men 75-84 years of age
(Paffenbarger et al. 1993).

  Similar reductions in death rates with increases
in cardiorespiratory fitness were reported for men in
the Aerobics Center Longitudinal Study. Blair and
colleagues (1995) reported a reduction in death rates
among healthy men (aged 20-82 years) who im-
proved their initially low levels of cardiorespiratory
fitness. The men performed two maximal exercise
tests an average of 4.8 years apart; follow-up for
mortality after the second test occurred an average of
4.7 years later. Among men in the bottom fifth of the
cardiorespiratory fitness distribution, those who
improved to at least a moderate fitness level had a 44
percent lower death rate than their peers who re-
mained in the bottom fifth (RR = 0.56; 95% CI, 0.41-
0.75). After multivariate adjustment, those who
became fit had a significant 64 percent reduction in
their relative mortality rate. In comparison, men
who stopped smoking reduced their adjusted RR by
about 50 percent.

86


Conclusions

The data reviewed here suggest that regular physical
activity and higher cardiorespiratory fitness decrease
overall mortality rates in a dose-response fashion.
Whereas most studies of physical activity and health
address specific diseases and health conditions, the
studies in this chapter provide more insight into the
biologic mechanisms by which mortality rate reduc-
tion occurs.

Cardiovascular Diseases

Despite a progressive decline since the late 196Os,
cardiovascular diseases (CVDs), including coronary
heart disease (CHD) andstroke, remain major causes
of death, disability, and health care expenditures in
the United States (NCHS 1994; Gillum 1994). In
1992, more than 860,000 deaths in the United States
were attributed to heart disease and stroke (DHHS
1994). High blood pressure, a major risk factor for
CVD, affects about 50 million Americans (National
Institutes of Health [NIH] 1993), including an esti-
mated 2.8 million children and adolescents 6-17
years of age (Task Force on Blood Pressure Control
in Children 1987). The prevalence of CVD increases
with age and is higher among African Americans than
whites. The majority of population-based research in
the area of physical activity and health has focused on
some aspect of CVD.

Cardiovascular Diseases Combined
Most of the reported studies relating physical activity
to CVD have reported CVD mortality as an endpoint;
two also reported on nonfatal disease, and one re-
ported on CVD hospitalization (Table 4-l). Seven
cohort studies evaluated the association between
level of physical activity and the risk of total CVD
(Kannel and Sorlie 1979; Paffenbarger et al. 1984;
Kannel et al. 1986; Lindsted, Tonstad, Kuzma 1991;
Arraiz, Wigle, Mao 1992; Shermanet al. 1994; LaCroix
et al. 1996). All relied on a single point-in-time
estimate of physical activity, in some cases assessed
as long as 26 years before the end of the observational
period, and four had follow-up periods of 114 years.
Four of the seven studies found both an inverse
association and a dose-response gradient between
level of physical activity and risk of CVD outcome
(Kannel and Sorlie 1979; Paffenbarger et al. 1984;

Kannel et al. 1986; LaCroix et al. 1996). One study
among men found an inverse association among the
moderately active group but less of an effect in the
vigorously active group (Lindsted, Tonstad, Kuzma
199 1). One study of women 50-74 years of age found
no relationship of physical activity with CVD mor-
tality (Sherman et al. 1994).

Five large cohort studies have related cardiores-
piratory fitness to the risk of CVD mortality (Arraiz,
Wigle, Mao 1992; Ekelund et al. 1988; Blair, Kohl,
Paffenbarger 1989; Sandvik et al. 1993; Blair et al.
1995), but only one provided a separate analysis for
women (Blair, Kohl, Paffenbarger 1989). Each of
these studies demonstrated an inverse dose-response
relationship between level of cardiorespiratory fit-
ness and CVD mortality. Three of the five studies
relied on a maximal or near-maximal exercise test to
estimate cardiorespiratory fitness. One study (Blair
et al. 1995) demonstrated that men with low cardio-
respiratory fitness who became fit had a lower risk of
CVD mortality than men who remained unfit.
Taken together, these major cohort studies indi-
cate that low levels of physical activity or cardiores-
piratory fitness increase risk of CVD mortality.
Findings seem to be more consistent for studies of
cardiorespiratory fitness, perhaps because of its
greater precision of measurement, than for those of
reported physical activity. The demonstrated dose-
response relationship indicates that the benefit de-
rived from physical activity occurs at moderate levels
of physical activity or cardiorespiratory fitness and
increases with increasing levels of physical activity
or higher levels of fitness.

Coronary Heart Disease

Numerous studies have examined the relationship
between physical activity and CHD as a specific CVD
outcome. Reviews of the epidemiologic literature
(Powell et al. 1987; Berlin and Colditz 1990; Blair
1994) have concluded that physical activity is strongly
and inversely related to CHD risk. Although physical
exertion may transiently increase the risk of an acute
coronary event among persons with advanced coro-
nary atherosclerosis, particularly among those who
do not exercise regularly (Mittleman et al. 1993;
Willich et al. 1993; Siscovick et al. 1984), physically
active people have a substantially lower overall risk
for major coronary events.

The Effects of Physical Activity on Health and Disease

87


Physical Activity and Health

Table 4-1. Population-based studies of association of physical activity or cardiorespiratory fitness with total
      cardiovascular diseases

Study
Physical activity
Kannel and
Sorlie (1979)

Paffenbarger et al.
(1984)

Kannel et al.
(1986)

Lindsted, Tonstad,
Kuzma
(1991)

Arraiz, Wigle,
Mao (1992)

Sherman et al
(1994)

LaCroix et al.
(1996)

Population

Definition of physical activity     Definition of
or cardiorespiratory fitness       cardiovascular disease

1,909 Framingham (MA)
men and 2,311 women
aged 35-64 years at
14-year follow-up

16,936 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962-l 978

1 ,166 Framingham (MA)
men aged 45-64 years;
24-year follow-up

9,484 Seventh-Day
Adventist men aged
2 30 years; 26-year
follow-up

Stratified probability
sample of Canadians
aged 30-69 years,
conducted in 1978-
1979; 7-year follow-up

1,404 Framingham (MA)
women aged 50-74
years; 16-year
follow-up

1,645 HMO members
age 2 65 years; 4.2-year
average follow-up

Cardiorespiratory fitness
Ekelund et al.     3,106 North American
(1988)        men aged 30-69
          years; 8.5-year
          average follow-up

Blair et al.
(1989)

10,244 men and 3,120
women aged 2 20 years;
8.1 -year average
follow-up

Physical activity index based
on hours per day spent at
activity-specific intensity

Physical activity index estimated
from reports of stairs climbed,
city blocks walked, and sports
played each week

Physical activity index based on
hours per day at activity-specific
intensity; occupational physical
activity classified by physical
demand of work

Self-report to single physical
activity question

Physical activity index
summarizing frequency, intensity,
and duration of leisure-time
activity and household chores

Physical activity index based on
hours per day spent at activity-
specific intensity

Hours of walking per week

Submaximal aerobic capacity
estimated from exercise test

Maximal aerobic capacity
estimated by exercise test

CVD fatal and nonfatal
in men (n = 140 deaths,
n = 435 total cases) and
women (n = 101 deaths)

Death due to CVD
(n = 640)

Death due to CVD
(n = 325)

Death due to CVD
(ICD-8 41 O-458)
(n = 410)

Death due to CVD
(n = 256)

CVD incidence (n = 994)
and mortality (n = 303)

CVD hospitalization
(ICD-9 390-448)
(n = 359)

Death due to CVD
(KID-8 390-458)
(n = 45)

Death due to CVD
(ICD-9 390-448)
in men (n = 66)
and women (n = 7)

88


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
resDonse*    and other comments

Inverse association between physical activity
index and CVD mortality for both men
and women

Inverse association; relative to highest
category (2,000+ kcal/week), relative risk
estimates were 1.28 and 1.84, respectively

Inverse association; for physical activity
index, age-adjusted RR relative to high
activity category = 1.62 for low activity,
I .30 for moderate; for occupational activity,
age-adjusted RR relative to heavy physical
demand category = 1.34 for sedentary, 1.26
for light, 1.09 for medium

Inverse association relative to inactive group;
moderately active RR = 0.79
(95% Cl, 0.58-l .07), highly active RR = 1.02
(95% Cl,O.66-1.58)

Null association across categories of physical
activity index

Null association across quartiles of physical
activity index

Inverse association; compared with walking
4 hrs/week, RR = 0.90 (95% Cl 0.69-l .17)
for walking l-4 hrs/week; RR = 0.73
(95% Cl 0.55-0.96) for walking > 4 hrs/week

Inverse association; adjusted risk estimate of
2.7-fold increased risk of CVD death for a
35 beat/min increase in heart rate for stage II
of exercise test

Inverse association; for men, age-adjusted RR
for lowest 20% compared with upper 40% =
7.9; for middle 40% = 2.5; for women, 9.2
and 3.6

Yes

Control for several confounding variables;
statistical significance only for men after
multivariate adjustment

Yes

Significant dose-response after adjusting for age,
smoking, and hypertension prevalence

Yes

Inverse association constant across all analyses;
inverse association maintained after multivariate
analyses

No

No statistical significance after controlling for
sociodemographic variables, BMI, and dietary
pattern

No

Point estimates adjusted for age, BMI, sex, and
smoking

No

No statistical significance after controlling for
several clinical and sociodemographic
confounding variables

Yes

Multivariate analysis adjusted for age, sex,
functional status, BMI, smoking, chronic
illnesses, and alcohol

Yes

Extensive control for clinical and
sociodemographic confounding influences

Yes

Significant linear dose-response association;
adjusted for age

89


Physical Activity and Health

Table 4-1. Continued

Study
Arraiz, Wigle,
Mao (1992)

Population
Stratified probability
sample of Canadians
aged 30-69 years,
conducted in 1978-
1979; 7-year follow-up

Definition of physical activity     Definition of
or cardiorespiratory fitness       cardiovascular disease

Submaximal aerobic capacity      Death due to CVD
estimated from home step test     (n = 37)

Sandvik et al.
(1993)

1,960 Norwegian men
aged 40-59 years;
average 16-year
follow-up

Maximal aerobic capacity
estimated by exercise test

Death due to CVD
(n = 144)

Blair et al.
(1995)

9,777 US men aged
20-82 years with 2
evaluations; 5.1 -year
average follow-up

Maximal aerobic capacity
estimated by exercise test

Death due to CVD
(ICD-9 390-449.9)
(n = 87)

Thirty-six studies examining the relationship of
physical activity level to risk of CHD have been
published since 1953 (Table 4-2). Studies published
before 1978 predominantly classified physical activ-
ity level byjob title or occupational activities. Studies
thereafter usually defined activity level by recall of
leisure-time activity or by such activity combined
with occupational activity. These later studies were
also able to control statistically for many potentially
confounding variables in addition to age. Most of
these studies focused on men in the age ranges
associated with increasingriskof CHD (30-75 years);
only four included women. Although in several stud-
ies, CHD mortality was the sole outcome variable,
most included both fatal and nonfatal disease. All but
one (Morris et al. 1973) were cohort studies; lengths
of follow-up from baseline assessment ranged from 4
to 25 years. All studies related a single baseline
estimate of physical activity level to risk of CHD
during the follow-up period.

Some study populations have had more than one
follow-up assessment for CHD. For example, three
follow-up assessments (at 10,12, and 23 years) have
been reported for men in the Honolulu Heart Pro-
gram (Yano, Reed, McGee 1984; Donahue et al. 1988;
Rodriguez et al. 1994). Each represented follow-up
further removed from the original determination of
physical activity. Thus, the diminishing effect seen
over time might indicate changing patterns of physical

activity- and thereby a lessening of validity of the
original physical activity classification (Table 4-2).
Oddly, in the 12-year follow-up, the reduction in
CHD risk observed among both active middle-aged
men (RR = 0.7) and active older men (RR = 0.4)
when compared with their least active counterparts
was not diminished by bivariate adjustment for
serum cholesterol, body mass index (BMI), or blood
pressure (Donahue et al. 1988). In the 23-year
follow-up, however, the reduction in CHD risk
among active men (RR = 0.8) was greatly diminished
by simultaneous adjustment for serum cholesterol,
BMI, blood pressure, and diabetes, (RR = 0.95),
leading the authors to conclude that the beneficial
effect of physical activity on CHD risk is likely
mediated by the beneficial effect of physical activity
on these other factors (Rodriguez et al. 1994). These
reports thus illustrate not only the problem of lengthy
follow-up without repeated assessments of physical
activity but also the problem of lack of uniformity in
adjustment for potential confounding factors, as well
as the underlying, thorny problem of adjustment for
multiple factors that may be in the causal pathway
between physical activity and disease. Studies have
in fact varied greatly in the extent to which they have
controlled for potential confounding and in the
factors selected for adjustment.
  Although early studies were not designed to dem-
onstrate a dose-response gradient between physical

90


The Effects of Physical Activity on Health and Disease

Main findings
Inverse association; relative to highest fitness
level, persons in "moderate" and "low"
categories had risks of 0.8 (95% Cl, 0.1-7.6)
and 5.4 (95% Cl, 1.9-l 5.9), respectively

Dose
response*

No

Adjustment for confounders
and other comments
Point estimates adjusted for age, BMI, sex, and
smoking

Inverse association; relative to men in lowest
fitness quartile, multivariate adjusted RR in
quartiles 2, 3, and 4 were 0.59, 0.45, and
0.41, respectively

Yes      Extensive control for confounding influences

Inverse association; relative to men who
remained unfit (lowest 20% of distribution),
those who improved had an age-adjusted RR

Yes

For each minute of improvement in exercise test
time, adjusted CVD mortality risk was reduced
8.6%

of 0.48 (95% Cl,`O.3 l-0.74)

Abbreviations: BMI = body mass index (wt [kg] /ht [ml2 ); CVD = cardiovascular disease: Cl = confidence interval; HMO = health
maintenance organization; ICD = International Classification of Diseases (8 and 9 refer to editions); RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison: "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

activity level and CHD, most found an inverse asso-
ciation: more active persons were found to be at
lower risk of CHD than their more sedentary coun-
terparts. Of the 17 recent studies that found an
inverse relationship and were able to examine dose-
response relationships, 13 (76 percent) demonstrated
an inverse dose-response gradient between level of
physical activity and risk of CHD, whereas 2 showed
a dose-response gradient only for some subgroups.
The relationship between cardiorespiratory fit-
ness and risk of CHD was examined in seven cohort
studies (follow-up range, 4-20 years). All but two
(Lie, Mundal, Erikssen 1985; Erikssen 1986) used
estimates of aerobic power based on submaximal
exercise testing. None of these studies included
women. Similar to the studies of physical activity
and CHD, these all related a single baseline assess-
ment of cardiorespiratory fitness to risk of CHD
during the follow-up period. Most controlled statis-
tically for possible confounding variables. All seven
studies showed an inverse association between
cardiorespiratory fitness and CHD. Of the six
studies that had more than two categories of cardio-
respiratory fitness, all demonstrated an inverse
dose-response gradient.

Two recent meta-analyses of studies of physical
activity and CHD have included independent scoring
for the quality of the methods used in each study
(Powell et al. 1987; Berlin and Colditz 1990). Both
concluded that studies with higher-quality scores
tended to show higher relative risk estimates than
those with lower-quality scores. In the Berlin and
Colditz quantitative meta-analysis, the pooled rela-
tive risk for CHD-comparingrisk for the lowest level
of physical activity with risk for the highest level-
was 1.8 among the studies judged to be of higher
quality. In contrast, the pooled relative risk for the
studies with low-quality scores was in the null range.

CVD Risk Factors in Children

Because CHD is rare in children, the cardiovascular
effects of physical activity in children are assessed
through the relationship of physical activity with
CHD risk factors such as elevated low-density lipo-
protein cholesterol (LDL-C), lowered high-density
lipoprotein cholesterol (HDL-C), and elevated blood
pressure. The presence of CHD risk factors in chil-
dren is of concern because of evidence that athero-
sclerosis begins in childhood (Star-y 1989), that
presence of CHD in adults is related to elevated blood

91


Physical Activity and Health

Table 4-2.  Population-based studies of association of physical activity or cardiorespiratory fitness with coronary
       heart disease

Study

Population

Definition of physical activity
or cardiorespiratory fitness

Definition of coronary
heart disease

Kahn (1963)

Morris et al.
(1966)

Cassel et al.
(1971)

Physical activity

Morris et al.
(1953)

31,000 male employees
of London Transport
Executive aged 35-64
years

Morris and
Crawford (1958)

3,731 case necropsy
studies (decedents aged
45-70 years) conducted
in Scotland, England,
and Wales

Taylor et al.
(1962)

191,609 US white male
railroad industry
employees aged 40-64
years

2,240 Postal Service
employees in the
Washington, D.C., Post
Office between 1906
and 1940; followed
through December 1961

667 London bus
conductors and drivers
aged 30-69 years;
5-year follow-up

3,009 male residents
of Evans County,
Georgia, aged over 40
years in 1960-l 962;
7.25-year average
follow-up

Morris et al.
(1973)

British male executive
grade civil servants
aged 40-60 years;
232 heart attack case-
patients and 428
matched controls .

Brunner et al.
(1974)

5,288 male and 5,229
female residents of 58
Israeli kibbutzim aged
40-69 years; 15-year
follow-up

Occupational classification of job
duties: sedentary drivers and
active conductors

Physical activity at work defined
by coding of last known job title
before death (light, active, heavy)

Physical activity at work defined
by job title for clerks, switchmen,
and section men

Physical activity at work defined
by job title for clerks and carriers

Occupational classification of job
duties as sedentary drivers
and active conductors

Incidence of CHD
(n = 47)

Occupational classification of job   Incidence of CHD
duties as active or sedentary      (n = 337)

48-hour recall of leisure-time
physical activities; activities
defined as capable of reaching
7.5 kcal/min were defined as
vigorous

Work types classified as sedentary
or nonsedentary

First clinical episode of
CHD

Necropsy evaluation of
IMF among persons
dying from
noncoronary causes

Death due to
arteriosclerotic disease
(ICD 420, 422)
in 1955-l 956

Death due to CHD

First CHD attack
(fatal and nonfatal)

Fatal and nonfatal CHD,
males (n = 281) and
females (n = 70)

92


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*   and other comments

Inverse association; relative to men whose
main job responsibility was driving buses,
conductors had an age-adjusted risk of first
coronary episode of 0.70

Inverse association; RR for IMF for persons
in light occupations was 1.97 relative to
heavy group; active group rate was
intermediate

Inverse association; RR for arteriosclerotic
disease among clerks was 2.03 relative to
that for section men; risk estimate for
switchmen was 1.46

Inverse and null associations; among
employees classified by their original
occupational category, the age-adjusted risk
for CHD death for clerks relative to carriers
was 1.26

Inverse association; age-adjusted risk of CHD
incidence among drivers was 1.8 relative to
that for conductors

Inverse association; age-adjusted risk of CHD
among sedentary, nonfarm occupations
relative to that for active nonfarm
occupations was 1.8

Inverse association; RR estimate for first
attack among vigorous group = 0.33
compared with nonvigorous group

Inverse association; risk for CHD incidence
among those engaged in sedentary work
compared with that for nonsedentary peers
was 2.52 for men and 3.28 for women

NA

No control for confounding; results were
similar in subgroup of men who died of
CHD-associated conditions

Yes

No control for confounding; one of few
pathology studies

Yes

NA

NA

NA

NA

No control for confounding; specific analyses
were consistent with overall results

No control for confounding; extensive efforts
made to consider and evaluate job transfers

Medical evaluation data used to control
for confounding variables

Data also available on black residents;
comparisons between sedentary and active
occupations not possible

Only study to analyze 48-hour recall
of leisure-time physical activity
(5-minute intervals)

NA

No differences in serum cholesterol
and body weight between groups

93


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study       Population       or cardiorespiratory fitness      heart disease

Paffenbarger and
Hale (1975)

Paffenbarger et al.
(1977)

Rosenman, Bawol,
Oscherwitz
(1977)

Chave et al.
(1978)

Paffenbarger,
Wing, Hyde
(1978)

Morris et al.
(1980)

Salonen et al.
(1982)

Pomrehn et al.
(1982)

6,351 San Francisco
Bay Area longshoremen
aged 35-74 years;
followed for 22 years,
from 1951 to death
or to age 75

3,686 San Francisco
Bay Area longshoremen
aged 35-74 years;
followed for 22 years,
from 195 1 to death
or to age 75

2,065 white male San
Francisco Bay Area
federal employees aged
35-59 years; 4-year
follow-up

3,591 British male
executive-grade civil
servants aged 40-64
years; 8.5-year average
follow-up from
1968 to 1970

16,936 Harvard male
alumni aged 35-74
years; followed up for
6-l 0 years

17,944 British male
executive grade civil
servants aged 40-64
years; 8.5-year average
follow-up from
1968 to 1970

3,829 women and
4,110 men aged 30-59
years from Eastern
Finland; 7-year
follow-up

61,922 deaths from
1964-l 978 among
Iowa men aged 20 to
64 years

Work-years according to
required energy output: heavy
(5.2-7.5 kcal/min), moderate
(2.4-5.0 kcal/min), and light
(1.5-2.0 kcal/min)

Work-years according to
required energy output: high
(5.2-7.5 kcal/min), intermediate
(2.4-5.0 kcaI/min), and light
(1.5-2.0 kcal/min)

Occupational physical activity;,
estimated caloric expenditure for
work and nonwork activity

48-hour leisure-time physical
activity recall; activities capable
of reaching 7.5 kcal/min defined
as vigorous

Physical activity index based on
self-report of stairs climbed, blocks
walked, and strenuous sports play

48-hour recall of leisure-time
physical activities; activities
defined as capable of reaching
7.5 kcal/min were defined as
vigorous

Dichotomous assessment of
occupational and leisure-time
physical activity (low/high)

Occupational classification;
farmers vs. nonfarmers

CHD death (ICD-7 420)
(n = 598)

CHD death ([CD-7 420)
(n = 395)
     i

Fatal and nonfatal CHD
(n = 65)

Fatal and nonfatal first
CHD attack (n = 268)

Fatal and nonfatal first
heart attack (n = 572)

Fatal and nonfatal first
heart attack (n =l ,138)

Fatal acute ischemic heart
disease (ICD-8, 410-412)
(n = 89 men and 14 women)
and acute myocardial
infarction (ICD-8,41 O-41 1)
(n = 210 men and 63 women)

Death from ischemic
heart disease

94


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
resuonse'   and other comments

Inverse association; relative to heavy
category, age-adjusted RR of CHD death was
1.70 in moderate and 1.80 in light categories

Yes

No control for confounding variables; efforts
made to evaluate job changes in the cohort
over time

Inverse association overall, inverse for
younger birth cohorts and null for older
cohorts; relative to high category,
age-adjusted RRs of CHD death were 1.8
in intermediate and 1.60 in light categories

No/Yes

Dose response noted in age-adjusted rates
only for two younger groups; two older
groups exhibited no association

Null association

No

Relatively short-term follow-up

Inverse association; risk of CHD attack
among men reporting nonvigorous exercise
relative to men reporting vigorous exercise
was 2.2

NA

Inverse association; age-adjusted RR of first     Yes
heart attack for men who expended fewer than
2,000 kcal/week was 1.64 compared with
men who expended 2,000 or more kcal/week

Inverse association; age-adjusted risk
of CHD attack among men reporting
nonvigorous exercise relative to those
reporting vigorous exercise was 2.2

NA

Inverse association; RR of acute
myocardial infarction for men and women
with low levels of physical activity at work =
1.5 (90% Cl, 1.2-2.0) for men and 2.4
(90% Cl, 1.5-3.7) for women

NA

Preliminary report of further data of
Morris et al. 1980

History of athleticism not associated with
lower risk unless there was also current
energy expenditure

Increased risk similar for fatal and
nonfatal attacks

No associations with leisure-time physical
activity; extensive adjustment for
confounding

Farm men had significantly less mortality than   NA      No adjustment for confounding
expected from the experience in the general
Population of Iowa men (SMR = 0.89)

95


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study        Population       or cardiorespiratory fitness       heart disease

Garcia-Palmieri
et al. (1982)

Paffenbarger et al.
(1984)

Yano, Reed,
McGee (1984)

Menotti and
Seccareccia
(1985)

Kannel et al.
(1986)

Lapidus and
Bengtsson (1986)

Leon et al.
(1987)

Pekkanen et al.
(1987)

Sobolski et al.
(1987)

8,793 Puerto Rican
men aged 45-64 years;
followed for up to 8.25
years

16,936 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962 to 1978

7,705 Hawaiian men of
Japanese ancestry aged
45-68 years with no
history of heart disease;
1 O-year follow-up

99,029 Italian male
railroad employees
aged 40-59 years;
S-year follow-up

1 ,166 Framingham (MA)
men aged 45-64 years.;
24-year follow-up

1,462 Swedish women
aged 38-60 years;
follow-up between
1968 and 1981

12,138 North American  Leisure-time physical activity
men at high risk for    index; energy expenditure
CHD, aged 35-57 years;  (minutes/week)

Usual 24hour physical activity
index based on hours/day at
specific intensity

Physical activity index estimated
from reports of stairs climbed,
city blocks walked, and sports
played each week

Self-report of 24hour habitual
physical activity in 1965-l 968

Occupational physical activity
(heavy, moderate, sedentary)

Physical activity index based on
hours per day at activity-specific
intensity; occupational physical
activity classified by physical
demand of work

Physical activity at work and
during leisure hours, lifetime, and
during previous years

7-year average follow-up

636 apparently healthy  Occupational and transport/
Finnish men aged     recreational physical activity
45-64 years, followed  (high or low)
for 20 years from   .
1964 baseline

2,109 Belgian men
aged 40-55 years in
1976-l 978; 5-year
follow-up

Occupational and leisure-time
physical activity (4 categories
each)

CHD incidence other than
angina pectoris (n = 335)

Death due to CHD
(n = 441)

Incident cases of fatal and
nonfatal CHD (n = 511)

Fatal myocardial infarction
(n = 614)

Death due to CHD
(n = 220)

Nonfatal myocardial
infarction and angina
pectoris

Fatal and nonfatal CHD
(n = 781; 368 fatal)

Death due to CHD
(n = 106)

Incident cases of fatal and
nonfatal myocardial
infarction and sudden
death (n = 36)

96


The Effects of Physical Activity on Health and Disease

                              Dose
Main findings                response'
Inverse association; physical activity index     Yes
was significantly related to lower risk of CHD
in urban as well as rural men

Inverse association; relative to highest
category of index (2,000+ kcal/week),
risk estimates in next two lower categories
were 1.28 and 1.84, respectively

Yes

Inverse association; significant only for all
CHD; no significant association for various
subtypes

NA

Inverse association; relative to sedentary,
men in moderate and heavy occupational
activity had RRs of 0.97 and 0.64,
respectively

Yes

Inverse association; age-adjusted RR (relative   Yes
to high category) = 1.38 (low), 1.21 (moderate);
for occupational activity, age-adjusted RR
(relative to heavy category) = 1.27 (sedentary),
1.22 (light), 0.99 (medium)

Inverse association only for leisure-time
physical activity; RR = 2.8 (95% Cl, 1.2-
6.5) comparing low leisure-time physical
activity with all other categories

NA      Adjusted for age

Inverse association; multivariate adjusted
risk estimate (relative to low activity tertile)
was 0.90 (95% Cl, 0.76-l .06) for more
active and 0.83 (95% Cl, 0.70-0.99) for
most active

Yes

Inverse association; adjusted RR for men
in low physical activity group was 1.30
fp = 0.17)

NA

Null association for both leisure-time and
occupational physical activity

No

Adjustment for confounders
and other comments

Significant inverse relationship for CHD
after multivariate adjustment

Significant dose-response after adjusting for
age, smoking, and hypertension prevalence

Adjusted for age, blood pressure, cholesterol,
BMI, serum glucose, vital capacity, etc.

Adjusted for age

Inverse association constant across all
analyses and maintained after controlling
for multivariate confounding

Dose response for fatal and nonfatal cases
combined but not for CHD death or sudden
death separately

Association limited to second half
of follow-up period

One of two studies to simultaneously
evaluate associations of physical activity,
fitness, and CHD

97


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study       Population       or cardiorespiratory fitness      heart disease

Donahue et al.
(1988)

Salonen et al.
(1988)

lohansson et al.
(1988)

Slattery, Jacobs,
Nichaman
(1989)

Morris et al.
(1990)

Lindsted,
Tonstad,
Kuzma
(19911

Shaper and
Wannamethee
(1991)

Seccareccia and
Menotti (1992)

Hein,
Suadicani,
Gyntelberg
(1992)

7,644 Hawaiian men of
Japanese ancestry aged
45-64 years with no
history of heart disease;
12-year follow-up

15,088 Eastern Finnish
men and women aged
30-59 years; 6-year
follow-up

7,495 Goteburg men
aged 47-55 years at
entry; 11.8-year
average follow-up

3,043 US male
railroad employees;
followed for
17-20 years

9,376 British male
middle grade
executives aged 45-64
years; 9.3-year
average follow-up

9,484 Seventh-Day
Adventist men aged
2 30 years; 26-year
follow-up

7,735 British men aged
40-59 years; 8.5-year
follow-up

1,712 men from
Northern and Central
Italy, aged 40-59 years,
initially examined in
1960; 25-year follow-up

4,999 Copenhagen
men aged 40-59 years;
17-year follow-up

Self-report of 24hour habitual
physical activity in 1965-l 968;
3-point scale defined by tertiles
of distribution

Self-reported leisure-time and
occupational physical activity
(4 levels collapsed into 2
categories each)

Physical activity at work and
physical activity during leisure
time (4-point scale for each)

Leisure-time physical activity
index (kcal/week)

Leisure-time physical activity
reported over previous 4 weeks;
energy expenditure values
ascribed to reported activities

Self-report to single physical
activity question

Self-report of physical activity at
baseline; 6-point scale

Occupational physical activity
(self-report): sedentary,
moderate, and heavy

Leisure-time physical activity
(4-point scale)

Incident cases of fatal
and nonfatal CHD
(n = 444)

Death due to CHD

(ICD-8 41 O-41 4)
(n=102
90 men, 12 women)

Incident cases of fatal
and nonfatal CHD

Death due to CHD
(ICD-8 41 o-41 4)

Fatal and nonfatal CHD
(ICD-8 41 o-41 4)
(n = 474)

lschemic heart disease
mortality
(ICD-8 410-414)
(n = 1,351)

Fatal and nonfatal heart
attack (n = 488)

Death due to CHD

Fatal myocardial
infarction
(ICD-8 41 o-41 4)
(n = 266)

from 1970/l 971

98


The Effects of Physical Activity on Health and Disease

Dose     Adjustment for confounders

Main findings

response*

and other comments

Inverse association; RR among active men
relative to sedentary men was 0.69 (95% Cl,
0.53-0.88) for men aged 45-64 and 0.43
(95% Cl, 0.1 g-0.99) for older men aged 65-74

Inverse association; occupational: adjusted
RR among inactive was 1.3 (95% Cl,
1.1-1.6) relative to active; adjusted RR of
CHD among leisure-time active was 1.2
(95% Cl, 1.0-l .5)

Null association between physical activity at
work and CHD risk; inverse association (not
statistically significant) between leisure-time
physical activity and CHD

Inverse association; adjusted risk estimate
(relative to highest physical activity category)
was 1.28 for sedentary group (not statistically
significant)

Inverse association; age-adjusted RR for
3 episodes per week of vigorous physical
activity relative to sedentary group was 0.36

Null association; risk estimates of CHD
death exhibited a U-shaped relationship
with increasing physical activity levels

Inverse association only for 2 activity levels;
RR compared with sedentary for increasing
physical activity levels: occasional 0.9
(95%CI, 0.5-l .3), light 0.9 (95% Cl, 0.6-l .4),
moderate 0.5 (95% Cl, 0.2-0.8), moderately
vigorous 0.5 (95% Cl, 0.3-0.9), and
vigorous 0.9 (95% Cl, 0.5-l .8)
Inverse association; age-adjusted RRfor
moderate and heavy categories compared
with that for sedentary group was 0.69 and
0.58, respectively

Inverse association; relative to more active
men (categories 2-4 of index), least active
men had an adjusted RR of CHD of 1.59
(95% Cl, 1.14-2.21)

Yes

Adjusted for age, alcohol use, and smoking;
bivariate adjustment for cholesterol, BMI,
and blood pressure did not alter findings;
follow-up to Yano, Reed, McGee (1984)

NA

Point estimate for low leisure-time physical
activity was adjusted toward the null after
consideration of other CHD risk factors

No

Extensive control for confounding variables;
ancillary analysis on postinfarction patients
also yielded null association

Yes

Adjusted for age, smoking, cholesterol,
and blood pressure

Yes

No adjustment for confounding; association
only noted for vigorous physical activity

No

No

Yes

Possible protective association among
moderate activity group

No clear linear trend

Inverse association remained statistically
significant after adjustment for confounding

No

One of two studies to simultaneously
evaluate activity and fitness in relation
to CHD mortality

99


Physical Activity and Health

Table 4-2. Continued
                   Definition of physical activity    Definition of coronary
Study       Population       or cardiorespiratory fitness      heart disease

Shaper,
Wannamethee,
Walker (1994)

5,694 British men aged
40-59 years; 9.5-year
follow-up

Rodriguez et al.
(1994)

7,074 Hawaiian men
of Japanese ancestry
aged 45-68 years;
23-year follow-up

Cardiorespiratory fitness
Peters et al.
(1983)

2,779 male Los Angeles
County public safety
employees aged
< 55 years; 4.8-year
average follow-up

Lie, Mundal,
Erikssen
(1985)

Erikssen (1986)

Sobolski et al.
(1987)

Ekelund et al.
(1988)

Slattery et al.
(1988)

2,431 US male railroad
employees; 17- through
20-year follow-up

Hein,        4,999 Copenhagen
Suadicani,      men aged 40-59 years;
Gyntelberg     17-year follow-up
(1992)         from 1970/l 971

2,014 Norwegian
employed men aged
40-59 years; 7-year
follow-up

1,832 Norwegian
men aged 40-59 years;
-/-year average
follow-up

2,109 Belgian men
aged 40-55 years in
1976-l 978; 5-year
follow-up

3,106 North American
men aged 30-69 years;
8.5-year average
follow-up

Self-report of physical activity at
baseline; 6-point scale data
analyzed by hypertensive status

Self-report of 24hour habitual
physical activity in 1965-l 968

Submaximal aerobic capacity
estimated from cycle ergometer
test; age-specific median split used
to determine low/high fitness

Near maximal cycle ergometer
exercise test; total work in
quartiles

Near maximal cycle ergometer
exercise test; total work in
quartiles

Submaximal aerobic capacity
estimated from cycle ergometry
test

Submaximal aerobic capacity
estimated from exercise test

Submaximal exercise heart rate on
standard (3 min) treadmill test
evaluation

Submaximal aerobic capacity
estimated from cycle ergometer
exercise test

Fatal and nonfatal heart
attack (n = 311; 165
normotensive, 146
hypertensive)
Incident cases of fatal
and nonfatal CHD
(n = 340)

Incident cases of fatal
and nonfatal myocardial
infarction (n = 36)

Incident cases of fatal
and nonfatal CHD

Incident cases of fatal
and nonfatal myocardial
infarction and CHD death

Incident cases of fatal
and nonfatal myocardial
infarction and sudden
death (n = 36)

Death due to CHD
(ICD-8 41 o-41 4)

Death due to CHD
(ICD-8 41 o-41 4)

Fatal myocardial infarction
(ICD-8 41 o-41 4)
(n = 266)

100


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*    and other comments

Inverse association; statistically significant
trend among nonhypertensive participants,
U-shaped association among hypertensive
participants

Inverse association when adjusted only for
age; null association when adjusted for
cholesterol, blood pressure, BMI, diabetes,
etc.

inverse association; RR for CHD incidence in
low fitness group was 2.2 (95% Cl, 1.1-4.7)
compared with high fitness

Inverse association; point estimates and
significance not reported

Inverse association; point estimates and
significance not reported

Inverse association; RR for myocardial
infarction and sudden death in low fit
group was 1.6 relative to high fit

Inverse association; adjusted risk estimate of
3.2-fold increased risk of CHD death for a
35 beat/min increase in heart rate for stage II
of exercise test

Inverse association; adjusted risk estimate for
highest heart rate response group relative to
lowest was 1.20 (95% Cl, 1 .l O-l .26)

Inverse association; relative to more fit men,
least fit men had an adjusted risk of 1.46
(95% Cl, 0.94-2.26)

Yes/No

In hypertensive men, the protective
effect of physical activity was eliminated
with vigorous activity

No

Follow-up report to that of Yano, Reed,
McGee (1984) and Donahue et al. (1988)

NA

Yes

Yes

Similar results seen when men with
electrocardiogram evidence of heart
disease were excluded

No adjustment for confounding variables

No adjustment for confounding variables

Yes

One of two studies to simultaneously
evaluate associations of activity, fitness,
and CHD

Yes

Extensive control for confounding
influences

Yes

Risk estimate attenuated substantially after
adjustment for other CHD risk factors

Yes

One of two studies to simultaneously
evaluate activity and fitness in relation
to CHD mortality

Abbreviations: BMI = Body mass index (wt [kg/ /ht [ml2 ); CHD = coronary heart disease; Cl = confidence interval; ICD = International
Classification of Diseases (8 and 9 refer to editions); IMF = ischemic myocardial fibrosis; RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only
2 levels of comparison; "No" means that there were more than 2 levels but no dose-response gradient was found: "Yes" means
that there were more than 2 levels and a dose-response gradient was found.

101


Physical Activity and Health

lipids in children (Lee, Lauer, Clarke 1986), and that
CHD risk factor patterns persist from childhood to
adulthood (Webber et al. 1991; Mahoney et al. 1991).
Recently, Armstrong and Simons-Morton (1994)
reviewed the research literature on physical activity
and blood lipids in children and adolescents, includ-
ing over 20 observational and 8 intervention studies.
They concluded that the cross-sectional observa-
tional studies did not demonstrate a relationship
between physical activity level or cardiorespiratory
fitness and total cholesterol, LDL-C, or HDL-C,
especially when differences in body weight or fat
were taken into account, suggesting that activity and
body fat are not independently related to serum
lipids. However, highly physically active or fit chil-
dren and adolescents tended to have higher HDL-C
than their inactive or unfit peers. The intervention
studies generally showed favorable effects of exer-
cise on LDL-C or HDL-C -only in children and
adolescents who were at high risk for CHD because
of obesity, insulin-dependent diabetes mellitus, or
having a parent with three or more CHD risk factors.
  Alpert and Wilmore (1994) recently reviewed
the research literature on physical activity and blood
pressure in children and adolescents; including 18
observational and 11 intervention studies. These
authors found evidence in studies of normotensive
children and adolescents that higher levels of physi-
cal activity tended to be related to lower blood
pressure. The associations were generally reduced in
magnitude in those studies that adjusted for BMI,
suggesting that lower body far mass may at least
partly explain why physical activity is related to
lower blood pressure. Intervention studies tended to
show that training programs lowered blood pressure
by 1-6 mm Hg in normotensive children and adoles-
cents, although the effects were inconsistent for boys
and girls and for systolic and diastolic blood pres-
sure. In hypertensive childrenand adolescents, physi-
cal activity interventions lowered blood pressure to
a greater degree than in their normotensive peers
(by approximately 10 mm Hg), although statistical
significance was not always achieved because of
small sample sizes.

Interpreting these studies on lipids and blood
pressure in children and adolescents is hindered by
several factors. Studies used a variety of physical
activity categorizations, and the interventions cov-
ered a wide range of frequency, type, duration, and

intensity, which were not all specified. The difficul-
ties of assessing physical activity by self-report in
children and adolescents, together with the highly
self-selected population in the observational studies,
may account for the less consistent findings on lipids
and physical activity that were reported for children
and adolescents than for adults. The relationship
between dose of physical activity and amount of
effect on blood pressure or serum lipids in children
has not been adequately addressed.
Nonetheless, there appears to be some evidence,
although not strong, of a direct relationship between
physical activity and HDL-C. level in children and
adolescents. There is also evidence that increased
physical activity can favorably influence the lipid
profile in children and adolescents who are at high
risk of CHD. Similarly, the evidence suggests that
physical activity can lower blood pressure in chil-
dren and adolescents, particularly in those who have
elevated blood pressure.

Stroke

A major cardiovascular problem in developed coun-
tries, stroke (ischemic stroke and hemorrhagic stroke)
is the third leading cause of death in the United States
(NCHS 1994). Atherosclerosis of the extracranial
and intracranial arteries, which triggers thrombosis,
is thought to be the underlying pathologic basis of
ischemic stroke. Cigarette smoking and high blood
pressure are major risk factors for ischemic stroke,
whereas high blood pressure is the major determi-
nant of hemorrhagic stroke. The studies cited in this
section examined the association between reported
level of physical activity and stroke. No published
studies have examined the association between car-
diorespiratory fitness and stroke.
Fourteen population-based studies (four that
include women) relate physical activity to risk of all
types of stroke; these closely parallel the study
designs and populations previously cited for CVD
and CHD (Table 4-3). Thirteen of the studies were
cohort studies (follow-up range, 5-26 years). Only
eight found an inverse association. As with the
earlier studies on CHD, the earlier studies of stroke
did not permit a dose-response evaluation. Among
later studies that could do so by virtue of design,
half did not find a gradient. This outcome, coupled
with some suggestion of a "U-shaped" association

102


in two studies (Menotti and Seccareccia 1985;
Lindsted, Tonstad, Kuzma 199 l), casts doubt on the
nature of the association between physical activity
and risk of both types of strokes combined.
Because of their different pathophysiologies,
physical activity may not affect ischemic and hemor-
rhagic stroke in the same way; this issue requires
more research. Only one study distinguished be-
tween ischemic and hemorrhagic stroke (Abbott et
al. 1994). In this study, inactive men were more likely
than active men to have a hemorrhagic stroke; physi-
cal activity was also associated with a lower risk of
ischemic stroke in smokers but not in nonsmokers.
Thus the existing data do not unequivocally
support an association between physical activity and
risk of stroke..

High Blood Pressure

High blood pressure is a major underlying cause of
cardiovascular complications and mortality. Organ
damage and complications related to elevated blood
pressure include left ventricular hypertrophy (which
can eventually lead to left ventricular dysfunction
and congestive heart failure), hemorrhagic stroke,
aortic aneurysms and dissections, renal failure, and
retinopathy. Atherosclerotic complications of high
blood pressure include CHD, ischemic stroke, and
peripheral vascular disease. Although rates of hyper-
tension have been declining in the United States
since 1960, nearly one in four Americans can be
classified as being hypertensive (DHHS 1995).

Prospective observational studies relating physi-
cal activity level or cardiorespiratory fitness to risk
of hypertension are summarized in Table 4-4.
Several cohort studies have followed male college
alumni after graduation. One found later develop-
ment of hypertension to be inversely related to the
reported number of hours per week of participation
in sports or exercise while in college (Paffenbarger,
Thorne, Wing 1968). In a later follow-up of the
same cohort, using information'on physical ac-
tivity during mid-life, vigorous sports were asso-
ciated with a 19-30 percent reduction in risk of
developing hypertension over the 14-year period
(Paffenbarger et al. 1991). Follow-up of a different
cohort of male college alumni similarly showed the
least active men to have a 30 percent increased risk
of developing hypertension (Paffenbarger et al.

The Effects of Physical Activity on Health and Disease

1983). In a study of 55- through 69-year-old women
followed for 2 years, the most active women were
found to have a 30 percent reduced risk of develop-
ing hypertension (Folsom et al. 1990).
One randomized trial for the primary prevention
of hypertension has been conducted. A 5-year trial of
a nutrition and physical activity intervention showed
that the incidence of hypertension for the interven-
tion group was less than half that of the control group
(Stamler et al. 1989). Participants in the intervention
group lost more weight than those in the control
group, reduced more of their sodium and alcohol
intake, and were more likely to become more physi-
cally active. Although the effects of the nutritional
and physical activity components of this interven-
tion cannot be separated, the study does show that
the risk for developing hypertension among persons
who are at high risk for the disease can be lowered by
weight loss and improvements in dietary and physi-
cal activity practices.

Like physical inactivity, low cardiorespiratory
fitness in middle age is associated with increased risk
for high blood pressure. After adjustment for sex,
age, baseline blood pressure, and body mass index,
persons with low cardiorespiratory fitness had a 52
percent higher risk of later developing high blood
pressure than their fit peers (Blair et al. 1984).
Taken together, the cohort studies show that
physical inactivity is associated with an increased
risk of later developing hypertension among both
men and women. Three of the studies had more than
two categories of physical activity for comparison,
and each demonstrated a dose-response gradient
between amount of activity and degree of protection
from hypertension. Point estimates for quantifica-
tion of risk suggest that those least physically active
have a 30 percent greater risk of developing hyper-
tension than their most active counterparts. Unfor-
tunately, none of these studies was conducted in
minority populations, which have a disproportion-
ate burden of hypertensive disease (DHHS 1995).
  Several randomized controlled trials have been
conducted to determine the effects of exercise on
blood pressure in people with elevated blood pres-
sure levels. The reduction of elevated blood pressure
is important for preventing stroke and CHD, for
which high blood pressure is a risk factor with a
dose-response relationship (NIH 1992). Thirteen

103


Physical Activity and Health

Table 4-3.  Population-based studies of association of physical activity with stroke (CVA)
                        Definition of              Definition of
Study       Population       physical activity            stroke

Paffenbarger and
Williams (1967)

Paffenbarger
(1972)

Kannel and
Sorlie (1979)

Salonen et al.
(1982)

Herman et al.
(1983)

Paffenbarger et al
(1984)

Menotti and
Seccareccia
(1985)

Lapidus and
Bengtsson
(1986)

Menotti et ai.

(1990)

> 50,000 US male
college alumni
aged 30-70years

3,991 US longshoremen
aged 35 years and older;
18.5-year follow-up
from 1951

1,909 Framingham (MA)
men aged 35-64 at
4th biennial examina-
tion; 14-year follow-up

3,829 women and
4,110 men aged 30-59
years from Eastern
Finland; 7-year
follow-up

132 hospitalized Dutch
stroke case-patients and
239 age- and sex-.
matched controls; men
and women aged
40-74 years

16,936 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962-l 978

99,029 Italian males
railroad employees
aged 40-59 years;
5-year follow-up

1,462 Swedish women
aged 38-60; follow-up
between 1968 and 1981

8,287 men aged 40-59
years in six of seven
countries from Seven
Countries Study;
20-year follow-up

Participation in college varsity
athletics (yes/no)

Occupational activity (cargo
handler or not)

Physical activity index based on
hours per day spent at activity-
specific intensity

Dichotomous assessment of
occupational physical activity
(low/high)

Leisure-time physical activity
(greatest portion of one's lifetime)
ranging from little to regular-heavy

Physical activity index estimated
from reports of stairs climbed, city
blocks walked, and sports played
each week

Classification of occupational
physical activity (heavy, moderate,
sedentary)

Work and leisure physical activity
assessed via 4-scales for lifetime
and for the time before 1968
baseline

Classification of occupational
physical activity (heavy, moderate,
sedentary)

Hemorrhagic and
ischemic stroke death
(n = 171)

Hemorrhagic and
ischemic stroke death
(n = 132)

Cerebrovascular accident
(n = 87)

Cerebral stroke
(ICD-8 430-437) morbidity
and mortality among men
(n = 71) and women
(n = 56)

Rapidly developed clinical
signs of focal or global
disturbance of cerebral
function lasting more
than 24 hours or leading
to death with no apparent
cause other than
vascular origin

Death due to stroke
(n = 103)

Fatal stroke (n = 187)

Fatal and nonfatal stroke
(n = 13)

Fatal stroke
(cohort analysis)

104


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*    and other comments

Inverse association; nondecedents were 2.2
times as likely to have participated in varsity
sports than were decedents; hemorrhagic
strokes = 2.1, occlusive strokes = 2.5

Noncargo handlers were 1.11 times as likely
as cargo handlers to die from stroke

Inverse association between physical activity
index and 14-year incidence of stroke

Inverse association with statistically significant
RRs for men and women with low levels of
physical activity at work were-l.5 (95% Cl,
1.2-2.0) for men and 2.4 (95% Cl, 1.5-3.7)
for women

Inverse association; relative to lowest
physical activity category, risk estimates were
0.72 (95% Cl, 0.37-l .42) for moderate and
0.41 (95% Cl, 0.21-0.84) for high categories

Inverse association; relative to highest
category of index (2,000+ kcal/week), risk
estimates in next two lower categories were
1.25 and 2.71, respectively

Nonlinear "U" shape association; relative to
sedentary category, men in moderate and
heavy occupational activity categories had
risks of 0.65 and 1 .O, respectively

Inverse association; women with low physical
activity at work were 7.8 times as likely as
others to have stroke (95% Cl, 2.7-23.0);
womenwith low physical activity leisure were
10.1 times as likely as others to have stroke
(95% Cl, 3.8-27.1)

Null association

NA

Results adjusted for age only

NA

Results adjusted for age only

Yes

No statistical significance ,after controlling
for several confounding variables

NA

Evidence for inverse association for low
activity during leisure time, but no statistical
significance after adjustment for other factors

Yes

Adjusted for a variety of potential
confounding influences

Yes

No

Significant dose-response trend after adjusting
for differences in age, cigarette smoking, and
hypertension prevalence

Age-adjusted only

NA

Age-adjusted only

No

No association after statistical adjustment
for risk factors

10.5


Physical Activity and Health

Table 4-3. Continued

                          Definition of              Definition of
Study       Population       physical activity             stroke

Harmsen et al.
(1990)

Lindsted,
Tonstad,
Kuzma,
(1991)

Wannamethee
and Shaper
(1992)

Abbott et al.
(1994) j

Kiely et al.
(1994)

7,495 Swedish men
aged 47-55 years at
baseline examination;
11.8-year average
follow-up

9,484 male Seventh-
Day Adventists aged
2 30 years; 26year
follow-up

7,735 British men aged
40-59 years; 8.5-year
follow-up

7,530 Hawaiian men of
Japanese ancestry aged
45-68 years; 22-year
follow-up

Four cohorts of
Framingham (MA) men
and women: cohort I-
1,897 men aged 35-69
years; cohort II-2,299
women aged 35-68
years; cohort Ill-men
aged 49-83 years;
cohort IV-women
aged 49-83 years;
follow-up for cohorts I
and II up to 32 years,
for cohorts III and IV
up to 18 years

Physical activity at work and
leisure hours (low, high)

Self-report of physical activity
level in 1960 (highly active,
moderately active, low activity)

Self-report of physical activity at
baseline; 6-point scale defined on
the basis of type and frequency
of activity

Self-report of 24hour habitual
physical activity in 1965-l 968
(inactive, partially active, active)

Self-report of daily activity level;
composite score formulated from
index and categorized into high,
medium, and low physical activity

Fatal stroke
(all and subtypes)
(n = 230)

Fatal stroke (n = 410)

Fatal and nonfatal stroke
(n = 128)

Fatal and nonfatal
neurologic deficit
with sudden
occurrence and remaining
present for at least 2 weeks
or until death (subtypes)
(n = 537)

Fatal and nonfatal
first occurrence of
atherothrombotic brain
infarction, cerebral
embolism, or other stroke
(cohort I, n = 195;
cohort II, n = 232;
cohort III, n = 113;
cohort IV, n = 140)

106


The Effects of Physical Activity on Health and Disease

Main findings

Dose     Adjustment for confounders
response*    and other comments

Null association; relative to low physical
activity category, slightly elevated estimates
were observed for all strokes and subtypes
for high activity group

Nonlinear "U" shape association; relative to
low activity level, risk estimates were 0.78
(95% Cl, 0.61-l .OO) for moderate activity
and 1.08 (95% Cl, 0.58-2.01) for high activity

Inverse association; statistically significant
linear trend of lower risk of stroke with higher
physical activity scale

Null association seen for all strokes and all
subtypes for men aged 45-54 years

Inverse association seen for all strokes and
subtypes for men aged 55-68 years

Risk estimate relative to low
physical activity group:
cohort l-nonsignificant inverse association
for medium group = 0.90 (0.62-l .31)
and for high group = 0.84 (0.59-l .18);
cohort II-nonsignificant nonlinear association
for medium group = 1.21 (0.89-l .63)
and for high group = 0.89 (0.60-l .3 1);
cohort Ill-significant inverse association
for medium group = 0.41 (0.24-0.69)
and for high group = 0.53 (0.34-0.84);
cohort IV-nonsignificant nonlinear association
for medium group = 0.97 (0.64-l .47)

and for high group = 1.21

Abbreviations: BMI = body mass index (wt [kg] /ht [ml2 ); CVA = cerebrovascular accident; Cl = confidence interval; ICD = International
Classification of Diseases (8 and 9 refer to editions); RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradieht was found.

No

No

Yes

Yes, in
older

No in
younger

Yes, C I
Yes, C I

No, C II
No, C II
Yes, C III

No, C IV

No association after statistical adjustment
for risk factors

Adjusted for sociodemographic factors, BMI,
and dietary pattern

Linear trend observed in men both with and
without existing ischemic heart disease

No association of physical activity to risk
of stroke in older smokers

Control for many confounding factors;
nonlinear association in women only
(cohorts III and IV); suggestion of threshold
relationship (cohort III)

107


Physical Activity and Health

Table 4-4. Population-based cohort studies of association of physical activity with hypertension
                        Definition of              Definition of
study -    Population       physical activity         hypertension

Paffenbarger,
Thorne,
Wing
(1968)

7,685 men who
attended the University
of Pennsylvania
between 193 1 and
1940 and who
responded to a
questionnaire in 1962

Reported hours per week of
participation in sports or exercise
in college

Self-reported incidence of
physician-diagnosed
hypertension from mail-
back health questionnaire
(n = 671 I

Paffenbarger et al.
(1983)

Blair et al.
(1984)

Stamler et al.
(1989)

Folsom et al.
(1990)

Paffenbarger et al
(1991)

14,998 US male college
alumni who entered
college between 1916
and 1950; followed
from 1962-l 972
(for 6-l 0 years)

Physical activity index (kcal/week)
estimated from reports of stairs
climbed, city blocks walked, and
sports played each week, assessed
by mail-back questionnaire in
1962 or 1966

4,820 US men and     Maximal aerobic capacity
1,219 US women     estimated by exercise tests,
patients of a preventive  categorized into "high" fitness
medical clinic aged    (2 85th percentile) and "low"
20-65 years at baseline   fitness

201 US men and women  Self-report of moderate physical
with diastolic blood    activity
pressure 85-89 mm Hg
or 80-84 mm Hg (if
overweight) were
randomly assigned to
control or nutritional/
hygienic intervention
(including exercise)

41,837 Iowa women   Self-reported frequency of
aged 55-69 years;    leisure-time physical activity from
2-year follow-up      mail-back survey

5,463 male college
alumni from the
University of
Pennsylvania

Self-report of physical activity from
mail-back questionnaire in 1962

Self-reported incidence of
physician-diagnosed
hypertensjon from mail-
back health questionnaire
(n = 681)

Self-reported incidence
of physician-diagnosed
hypertension (n = 240)

Initiation of hypertensive
therapy or sustained
elevation of diastolic
blood pressure
>90mm Hg

Self-reported incidence of
physician-diagnosed
hypertension

Self-reported incidence of
physician-diagnosed
hypertension from mail-
back questionnaire

in 1976 (n = 739)

108


The Effects of Physical Activity on Health and Disease

Main findings

Dose      Adjustment for confounders
response*    and other comments

Inverse association; respondents who
reported participation in sports or exercise
fewer than 5 hours per week had a
significantly increased age- and interval-
adjusted risk of physician-diagnosed
hypertension (RR = 1.30, p < 0.01)

Inverse association; alumni with
c 2,000 kcal/week of energy expenditure
had RR of 1.30 (95% Cl, 1.09-l .55)
of developing hypertension relative
to others

Patients in low fitness category were 1.52
times as likely (95% Cl, 1.08-2.15) to
develop hypertension as those in high
fitness category

Control group RR = 2.4 (90% Cl, 1.2-4.8)
of developing hypertension when compared
with the intervention group

Inverse association; relative to women
at low levels of physical activity, women
at high and moderate levels had 30% and
10% lower age-adjusted risks of developing
hypertension (RR high = 0.70, 95% Cl,
0.6-0.9; RR moderate = 0.90, 95% Cl,
0.7-l .l)

Vigorous sports play in 1962 was associated
with a 30% reduced risk of developing
hypertension

NA

Adjustments for age and follow-up
had little effect

Yes,
especially
in
heavier

men

Increased risk observed for less active alumni
with stratification of student blood pressure,
alumnus BMI, increase'in BMI since college,
and family history of hypertension

NA

Extensive control for confounding variables;
no sex-specific analyses

NA

Yes

Intervention was combined nutritional,
weight loss, and physical activity

Adjustment for BMI, waist-to-hip ratio,
cigarette smoking, and age eliminated
the association with physical activity

Yes

Adjusted for age, BMI, weight gain
since college, and parental history of
hypertension

Abbreviations: BMI = body mass index (wt [kg] /ht [ml2 ); Cl = confidence interval; RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only
2 levels of comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means
that there were more than 2 levels and a dose-response gradient was found.

109


Physical Activity and Health

controlled trials of habitual activity and blood pres-
sure were analyzed in a meta-analysis by Arroll and
Beaglehole (1992), and nine randomized controlled
trials of aerobic exercise using the lower extremities
(e.g., walking, jogging, cycling) and blood pressure
were analyzed in a meta-analysis by Kelley and
McClellan (1994). The two meta-analyses indepen-
dently concluded that aerobic exercise decreases
both systolic and diastolic blood pressure by ap-
proximately 6-7 mm Hg. Some of the studies were
conducted with persons with defined hypertension
(> 140/90 mm Hg), and others were conducted with
persons with high normal blood pressure. Most of
the studies tested aerobic training of 60-70 percent
maximum oxygen uptake, 3-4 times/week, 30-60
minutes per session,

Three trials have specifically examined the effect
of different intensities of exercise on blood pressure.
Hagberg et al. (1989) randomly assigned 33 hyper-
tensive participants to a nonexercising control group
and to two groups participating in different intensi-
ties of exercise (53 percent and 73 percent of VO,
max) for 9 months. Both exercise groups had compa-
rable decreases in diastolic blood pr,essure (11-12
mm Hg), and the lower-intensity group had a greater
decrease in systolic blood pressure than the higher-
intensity group (20 mm Hg vs. 8 mm Hg). All the
decreases were statistically significant when com-
pared with the control group's blood pressure level,
except the 8 mm Hg decrease in systolic blood
pressure in the higher-intensity group. Matsusaki
and colleagues (1992) randomly assigned 26 mildly
hypertensive participants to two exercise intensities
(50 percent VOLmaxand 75 percent VO,max) for 10
weeks. The pretest-to-posttest decreases in systolic
and diastolic blood pressure in the lower-workload
group were significant (9 mm Hg/6 mm Hg), but
those in the higher-intensity group were not (3 mm
Hg/S mm Hg). Marceau and colleagues (1993) used
a randomized crossover design to compare intensi-
ties of 50 percent and 70 percent `?O,max training on
24-hour ambulatory blood pressure in persons with
hypertension. A similar reduction in 24-hour blood
pressure was observed for both training intensities
(5 mm Hg decrease), but diurnal patterns of reduc-
tion were different.

These trials provide some evidence that moderate-
intensity activity may achieve a similar, or an even

greater, blood-pressure-lowericg effect than
vigorous-intensity activity. Because few studies have
directly addressed the intensity question, however,
the research base is not strong enough to draw a firm
conclusion about the role of activity intensity in
lowering blood pressure. It is not clear, for example,
how the findings could have been affected by several
issues, such as use of antihypertensive medications,
changes in body weight, lack of direct intervention-
control comparisons, dropout rates, and total caloric
expenditure.

Biologic Plausibility

Multiple physiological mechanisms may contribute
to the protective effects of physical activity against
CVDs. Postulated mechanisms involve advantageous
effects on atherosclerosis, plasma lipid/lipoprotein
profile, blood pressure, availability of oxygenated
blood for heart muscle needs (ischemia), blood clot-
ting (thrombosis), and heart rhythm disturbances
(arrhythmias) (Haskell 1995; Leon 1991a; Gordon
and Scott 1991).

Other effects of activity that may be associated
with modifications of CVD risk include reduced
incidence of obesity, healthier distribution of
body fat, and reduced incidence of non-insulin-
dependent diabetes. These other effects are dis-
cussed in later sections of this chapter.

Atherosclerosis

Atherosclerosis begins when cholesterol is trans-
ported from the blood into the artery wall by lipopro-
teins, particularly LDL (Getz 1990; Yanowitz 1992).
The formation of atherosclerotic plaques is increased
at sites where the blood vessel lining is injured,
which may occur in areas where blood flow is uneven
(e.g., near the origin or branching of major vessels).
An inflammatory reaction leads to the formation of
atherosclerotic plaques in the wall of the artery.
In animal studies, exercise has been seen to
protect against the effects of excess cholesterol and
other contributors to the development of athero-
sclerosis (Kramsch et al. 1981). In addition, longi-
tudinal studies of men with coronary artery disease
have shown that endurance training, together with a
cholesterol-lowering diet and interventions for other
CVD risk factors, can help prevent the progression or
reduce the severity ofatherosclerosis in the coronary

110


arteries (Ornish et al. 1990; Schuler et al. 1992;
Hambrecht et al. 1993; Haskell et al. 1994). There is
also an inverse relationship between cardiorespira-
tory fitness and ultrasound-measured severity of
atherosclerosis in neck arteries to the head (carotid
arteries) (Rauramaa et al. 1995).

Plasma Lipid/Lipoprotein Profile
The relationships of physical activity to blood lipid
and lipoprotein levels in men and women have been
reviewed extensively (Leon 1991a; Krummel et al.
1993; Superko 1991; Durstine and Haskell 1994;
Stefanick and Wood 1994). Of more than 60 studies
of men and women, about half found that exercise
training is associated with an increase in HDL. HDL,
a lipid scavenger, helps protect against atherosclero-
sis by transporting cholesterol to the liver for elimi-
nation in the bile (Tall 1990). Cross-sectional studies
show a dose-response relationship between the
amount of regular physical activity and plasma levels
of HDL (Leon 1991c). In these studies, the HDL
levels of endurance-trained male and female athletes
were generally 20 to 30 percent higher than those of
healthy, age-matched, sedentary persons.
Moderate-intensity exercise training appears to
be less likely to increase HDL levels in young to
middle-aged women than men in the same age range
(Leon 1991a; Kummel et al. 1993; Durstine and
Haskelll994). Moderate-intensity exercise was seen
to increase HDL as much as more vigorous exercise
in one randomized controlled trial of women
(Duncan, Gordon, Scott 1991).
  Studies have found that even a single episode of
physical activity can result in an improved blood
lipid profile that persists for several days (Tsopanakis
et al. 1989; Durstine and Haskell 1994). Evidence
also shows that exercise training increases lipopro-
tein lipase activity, an enzyme that removes choles-
terol and fatty acids from the blood (Stefanick and
Wood 1994). Exercise training also reduces elevated
levels of triglycerides (Leon 1991c;. Durstine and
Haskell 1994), another blood lipid associated with
heart disease.

Blood Pressure

The mechanisms by which physical activity low-
ers blood pressure are complicated (Leon 1991a;
American College of Sports Medicine [ACSM]

1993; Fagard et al. 1990) and are mentioned only
briefly here (see also Chapter 3). Blood pressure is
directly proportional to cardiac output and total
resistance in the peripheral blood vessels. An epi-
sode of physical activity has the immediate and
temporary effect of lowering blood pressure through
dilating the peripheral blood vessels, and exercise
training has the ongoing effect of lowering blood
pressure by attenuating sympathetic nervous system
activity (Leon 1991a; ACSM 1993; Fagard et al.
1990). The reduced sympathetic activity may reduce
renin-angiotensin system activity, reset barorecep-
tars: and promote arterial vasodilatation-all of which
help control blood pressure: Improved insulin sensi-
tivity and the associated reduction in circulating
insulin levels may also contribute to blood pressure
reduction by decreasing insulin-mediated sodium
reabsorption by the kidney (Tipton 1984).

lschemia

Clinical symptoms of atherosclerotic CHD occur
when the heart muscle (myocardium) needs more
oxygen than can be supplied from blood flowing
through narrowed coronary arteries. This oxygen
shortage leads to ischemia in the heart muscle-that
is, to inadequate oxygenated blood for myocardial
demand. Adaptations to a gradual reduction in blood
flow may reduce the likelihood of myocardial is-
chemia. For example, new bloodvessels may develop
from other coronary arteries to provide an auxiliary
blood supply (Cohen 1985). A person with advanced
atherosclerotic CHD may remain free of symptoms at
rest but may develop ischemic chest pain (angina
pectoris) or electrocardiographic changes during
physical exertion, which generally result from too
high a myocardial oxygen demand for the blood
supply available through partially occluded coronary
arteries and collateral vessels (Smith and Leon 1992).
Less commonly, angina pectoris may result from
transient constriction (spasm) of a large coronary
artery, generally at the site of an atherosclerotic
plaque, or from spasm of small arterial vessels that
have no evidence of plaque formation.

A recent review has summarized adaptations in
the coronary circulation that are induced by endur-
ance exercise training and that can decrease the
likelihood of ischemia (Laughlin 1994). Data ob-
tained primarily from research on animals have

The Effects of Physical Activity on Health and Disease

111


Physical Activity and Health

demonstrated that exercise leads to a greater capacity
to increase coronary blood flow and an improved
efficiency of oxygen exchange between blood in the
capillaries and the heart muscle cells. These func-
tional changes are the result of a remodeled vascular
structure, improved control of blood flow dynamics,
and promotion of biochemical pathways for oxygen
transfer.

The first and most consistent structural adapta-
tion to exercise is an increase in the interior diameter
of the major coronary arteries and an associated
increase in maximal coronary blood flow (Leon and
Bloor 1968, 1976; Scheuer 1982; Laughlin 1994).
The second vascular adaptation is the formation of
new myocardial blood vessels (capillaries and coro-
nary arterioles) (Tomanek 1994; Leon and Bloor
1968). Animal studies also have shown that exercise
training alters coronary vascular reactivity and
thereby improves control of blood flow and distribu-
tion (Overholser, Laughlin, Bhatte 1994; Underwood,
Laughlin, Sturek 1994). This adaptation may reduce
the incidence of spasms in the proximal coronary
arteries and arterioles (Laughlin 1994). In addition,
exercise training results in a reduced workload on the
heart due to both an increase in compliance of the
heart and a relative reduction in peripheral resistance;
together, these reduce myocardial oxygen demand
(Jorgensen et al. 1977).

Thrombosis

An acute coronary event is usually initiated by dis-
ruption of an atherosclerotic plaque within an artery
(Smith and Leon 1992). Platelet accumulation at the
injury site initiates a cascade of processes leading to
clot formation (thrombosis), which further reduces
or completely obstructs coronary flow. A major
obstruction of flow in a coronary artery may lead to
the death of heart muscle (myocardial infarction) in
the area served by that artery. These obstructions can,
in addition, trigger potentially lethal. disturbances
in the rhythm of the heart (cardiac arrhythmia).

Thrombosis, usually occurring at the site of
rupture or fissuring of an atherosclerotic plaque, is
the precipitating event in the transition of silent or
stable coronary artery disease to acute ischemic
events, such as unstable angina, acute myocardial
infarction, or sudden cardiac death, and in the occur-
rence of ischemic stroke (Davies and Thomas 1985;

Falk 1985). Endurance training reduces thrombosis
by enhancing the enzymatic breakdown of blood
clots (fibrinolysis) and by decreasing platelet adhe-
siveness and aggregation (which helps prevent clot
formation) (Kramsch et al. 1981; Leon 1991b).

Arrhythmia

Although persons with coronary artery disease have
an increased risk of ventricular fibrillation (a life-
threatening heart rhythm disturbance) during acute
physical activity, persons with a healthy cardiovas-
cular system do not incur this elevated risk (Siscovick
et al. 1984; Mittleman et al. 1993; Willich et al. 1993;
Thompson and Mitchell 1984; Thompson, Funk, et
al. 1982; Haskelll995; Dawson, Leon, Taylor 1979).
Exercise training may reduce the risk of ventricular
fibrillation in healthy persons and in cardiac patients
by improving myocardial oxygen supply and de-
mand and by reducing sympathetic nervous system
activity (Leon 199 lc). Evidence from epidemiologic
studies shows that a physically active lifestyle re-
duces the risk of sudden cardiac death (Leon et al.
1987). A meta-analysis of studies that examined use
of physical activity for cardiac rehabilitation showed
that endurance exercise training reduced the overall
risk of sudden cardiac death even among persons
with advanced coronary atherosclerosis (O'Connor
et al. 1989).

Conclusions

The epidemiologic literature supports an inverse
association and a dose-response gradient between
physical activity level or cardiorespiratory fitness
and both CVD in general and CHD in particular. A
smaller body of research supports similar findings
for hypertension. The biological mechanisms for
these effects are plausible and supported by a wealth
of clinical and observational studies. It is unclear
whether physical activity plays a protective role
against stroke.

Cancer

Cancer, the second leading cause of death in the
United States, accounts for about 25 percent of all
deaths, and this percentage is increasing (NCHS
1996; American Cancer Society [ACS] 1996). The
ACS has estimated that 1,359,150 new cases of

112


The Effects of Physical Activity on Health and Disease

cancer and 554,740 cancer-related deaths will occur
amongAmericansduring 1996 (ACS 1996). Physical
inactivity has been examined as an etiologic factor
for some cancers.

Colorectal Cancer

Colorectal cancer has been the most thoroughly
investigated cancer in epidemiologic studies of physi-
cal activity. To date, nearly 30 published studies have
examined the association between physical activity
and risk of developing colon cancer alone.
  Studies that combined colon and rectal cancers
as a single endpoint-colorectal cancer-are only
briefly reviewed here because current research, sum-
marized in this section, suggests that the relation-
ship between physical activity and risk of colon
cancer may be different from that for rectal cancer.
Among nine studies that have examined the relation-
ship between physical activity and colorectal cancer,
one reported an inverse relationship (Wu et al.
1987), and three reported positive associations that
were not statistically significant (Garfinkel and
Stellman 1988; Paffenbarger, Hyde, Wing 1987 [for
analysis of two cohorts] ). One (Kune, Kune, Watson
1990) reported no significant associations, and in
the four other studies (Albanes, Blair, Taylor 1989;
Ballard-Barbash et al. 1990; Markowitz et al. 1992;
Peters et al. 1989), the associations lacked consis-
tency in subpopulations within the study, anatomic
subsites of the large bowel, or measures of physical
activity. Colorectal adenomas are generally thought
to be precursors to colorectal cancers. A single study
of colorectal adenomatous polyps has reported an
inverse relationship between risk of adenomas and
level of total physical activity (Sandler, Pritchard,
Bangdiwala 1995). Another study of colorectal ad-
enomas also found an inverse association, but only
for running or bicycling, and only with one of two
different comparison groups (Little et al. 1993).

Colon Cancer

Of the 29 studies of colon cancer,.18 used job title as
the only measure of physical activity and thus ad-
dressed only occupational physical activity. These
studies are a mix of mortality and incidence studies,
and few have evaluated possible confounding by
socioeconomic status, diet, and other possible risk
factors for colon cancer. Nonetheless, findings from

these 18 studies have been remarkably consistent: 14
studies (Brownson et al. 1989; Brownson et al. 1991;
Chow et al. 1993; Dosemeci et al. 1993; Fraser and
Pearce 1993; Fredriksson, Bengtsson, Hardelll989;
Garabrant et al. 1984; Gerhardsson et al. 1986; Kato,
Tominaga, Ikari 1990; Lynge and Thygesen 1988;
Marti and Minder 1989; Peters et al. 1989; Vena et al.
1985; Vena et al. 1987) reported a statistically sig-
nificant inverse relationship between estimated oc-
cupational physical activity and risk of colon cancer.
Four studies (Arbman et al. 1993; Vetter et al. 1992;
Vlajinac, Jarebinski, Adanja 1987; Vineis, Ciccone,
Magnino 1993) found no significant relationship
between occupational physical activity and risk of
colon cancer. The 18 studies were conducted in a
variety of study populations in China, Denmark,
Japan, New Zealand, Sweden, Switzerland, Turkey,
and the United States.

  Eleven studies assessed the association be-
tween leisure-time or total physical activity and
colon cancer risk in 13 different study populations
(Table 4-5). These studies either measured physical
activity and tracked participants over time to ascer-
tain colon cancer outcomes or compared recalled
histories of physical activity among colon cancer
patients with those among controls. In eight study
populations, an inverse association was reported
between physical activity and risk of colon cancer,
and results were generally consistent for men and
women. The three studies that examined the effect of
physical activity during early adulthood (Polednak
1976; Paffenbarger, Hyde, Wing 1987; Marcus,
Newcomb, Storer 1994) found no effect, which could
indicate that the earlier activity did not affect risk of
colon cancer later in life. In studies that used more
than two categories of physical activity, 10 potential
dose-response relationships between level of physi-
cal activity or cardiorespiratory fitness and colon
cancer risk were evaluated. Five of these showed a
statistically significant inverse dose-response gradi-
ent, one showed an inverse dose-response gradient
that was not statistically significant, three showed no
gradient, and one showed a positive relationship that
was not statistically significant.

Two studies of colon adenomas (Giovannucci
et al. 1995; Kono et al. 1991) reported an inverse
relationship between leisure-time physical activity
and risk of colon adenomas.

113


Physical Activity and Health

Table 4-5.  Epidemiologic studies of leisure-time or leisure-time plus occupational physical activity*
       and colon cancer

Study

Population

Definition of
physical activity

Definition of

cancer

Polednak       Cohort of 8,393 former
(1976)        US college men

Paffenbarger,
Hyde, Wing
(1987)

Cohort of 51,977 male,
4,706 female former US
college students

Gerhardsson,
Floderus,
Norell
(1988)

Slattery et al.
(1988)

Severson et al.
(1989)

Gerhardsson
et al.
(1990)

Whittemore et al.
(1990)

Lee,
Paffenbarger,
Hsieh
(1991)

Cohort of 16,936 male
US college alumni
aged 35-74 years

Cohort of 16,477
Swedish men and
women twins aged
43-82 years
Cohort of Utah men
(110 cases and
180 controls) and
women (119 cases
and 204 controls)
aged 40-79 years

Cohort of 7,925
Japanese men
aged 46-65 years

Swedish men (163
cases) and women
(189 cases) and 5 12
controls; all ages

North American
Chinese men
(179 cases and 698
controls) and women
(114 cases and 494
controls) aged
2 20 years

Asian Chinese men
(95 cases and 678 *
controls) and women
(78 cases and 618
controls) aged
20-79 years

Cohort of 7,148 male
male US college alumni
aged 30-79 years

College athletic status; major,
minor, and nonathlete
Sports play in college

Physical activity index (kcal/week)

Categories of occupational and
leisure-time activity

Occupational and leisure-time
activity were both assessed by
total energy expended

Physical activity index from
Framingham study and heart rate

Categories of occupational and
leisure-time activity

Time per day spent sleeping/
reclining, sitting, in light or
moderate activity, and in
vigorous activity

Time per day spent sleeping
reclining, sitting, in light or
moderate activity, and in
vigorous activity

Index of energy expenditure based
on stair climbing, walking, and
sports/recreation, assessed 2 times

Colon cancer mortality
(n = 107)

Colon cancer incidence
(n = 201)

Colon cancer mortality
(n = 44) ,

Colon cancer incidence

Colon cancer incidence

Colon cancer incidence
(n = 172)

Colon cancer incidence

Colon cancer incidence

Colon cancer incidence

Colon cancer incidence

> 11 years apart

114


The Effects of Physical Activity on Health and Disease

Main findings

Dose    Adjustment for confounders
response+  and other comments

No differences in mortality                No

Sports play 15 hrs/week relative to
< 5 hrs/week: RR = 0.91; p = 0.60

NA

Risk increased with physical activity index:
p for trend = 0.45

No

Least active relative to most active for work
and leisure: RR = 3.6 (95% Cl, 1.3-9.8)

NA

High activity quartile relative to low
activity quartile; men: OR total 0.70
(90% Cl, 0.38-l .29); women: OR total 0.48
(90% Cl, 0.27-0.87)

High activity tertile relative to low activity
tertile: RR 0.71 (95% Cl, 0.51-0.99); high
heart rate relative to low: RR 1.37
(95% Cl, 0.97-l .93)

Low activity relative to high: work and leisure,
RR = 1.8 (95% Cl, 1 .O-3.4)

Sedentary relative to active:
RR = 1.6 (95% Cl, 1 .l-2.4) for men,
RR = 2.0(95% Cl, 1.2-3.3) for women

Sedentary relative to active:
RR = 0.85 (95% Cl, 0.39-l .V) for men,
RR = 2.5 (95% Cl, 1 .O-6.3) for wemen

Highly active relative to inactive:
RR = 0.85 (90% Cl, 0.6-l .l);
high lifetime activity:
RR = 0.5 (90% Cl, 0.3-0.9)

Yes

No

Yes

Yes

NA

NA

No

None

Adjusted for age (2 levels of activity)

Adjusted for age, BMI, and smoking

Adjusted for age and sex (2 levels of lag ttvity);
adjustments for possible confounders 5,1t,t
to not change results

Adjusted for age, BMI, dietary fiber, allIt total
energyintake; greater effect with inten\,;
activity; population-based

Adjusted for age, BMI

Adjusted for age, sex, BMI, dietary int.ll.,,
of total energy, protein, fat, fiber, and
browned meat surface; population-b,r>,.,t

Adjusted for age (2 levels of activity);
population-based; adjustment for diet l,.,d little
effect on findings

Adjusted for age (2 levels of activity);
population-based; no effect of physic -11
activity after adjustment for diet

Adjusted for age

115


Physical Activity and Health

Table 4-5. Continued

                          Definition of              Definition of
Study       Population       physical activity                  cancer

Marcus,         Wisconsin women    Total strenuous physical activity    Colon cancer incidence
Newcomb,     aged up to 74 years,    during ages 14-22 years
Storer          536 cases and
(1994)        2,315 controls

Giovannucci et al.  47,723 US male health   Weekly recreational physical     Colon cancer incidence
(1995)        professionals aged     activity index based on 8        (n = 201)
           40-75 years       categories of moderate and
                      vigorous activities
Longnecker et al.   US men aged > 30    Leisure-time vigorous physical    Right-Gded colon cancer
(1995)        years, 163 cases      activity                   incidence
            703 controls

Dietary factors may confound or modify the
association between physical activity and colon
cancer risk (Willett et al. 1990). Five of the studies
in Table 4-5 controlled for dietary components in
analyses and continued to observe a significant
inverse association (Gerhardsson, Floderus, Norell
1988; Slattery et al. 1988; Gerhardsson et al. 1990;
Giovannucci et al. 1995; Longnecker et al. 1995),
and in one study (Whittemore et a1.1990), adjust-
ment for dietary intakes altered findings in one
study population but not in the other.
Together, the research on occupational and
leisure-time or total physical activity strongly sug-
gests that physical activity has a protective effect
against the risk of developing colon cancer.

Rectal Cancer

Many of the studies on physical activity and colon
cancer risk also studied rectal cancer as a separate
outcome. Of 13 studies that investigated occupa-
tional physical activity alone, 10 reported no statis-
tically significant association with rectal cancer risk
(Garabrant et al. 1984; Vena et al: 1985, 1987;
Gerhardsson et al. 1986; Jarebinski, Adanja, Vlajinac
1988; Lynge and Thygesen 1988; Brownson et al.
1991; Marti and Minder 1989; Peters et al. 1989;
Dosemeci et al. 1993), two reported significant in-
verse associations (Kate, Tominaga, Ikari 1990; Fraser
and Pearce 1993), and one reported a significant

direct association (i.e., increasing risk with increas-
ing physical activity) (Arbman et al. 1993).
Six of the studies that investigated the associa-
tion between leisure-time or total physical activity
and the risk of developing rectal cancer failed to
find a significant association (Gerhardsson,
Floderus, Norell 1988; Severson et al. 1989;
Gerhardsson et al. 1990; Kune, Kune, Watson 1990;
Lee, Paffenbarger, Hsieh 1991; Longnecker et al.
1995). In another study, Whittemore and colleagues
(1990) observed a statistically significant inverse
association in one study population and no effect in
the other. Paffenbarger, Hyde, and Wing (1987)
found an inverse relationship in one cohort and a
direct relationship in the other.
Taken together, study results on both occupa-
tional and leisure-time or total physical activity
suggest that risk of rectal cancer is unrelated to
physical activity.

Hormone-Dependent Cancers in Women
Of the epidemiologic studies examining the relation-
ship between physical activity and hormone-
dependent cancers in women, 13 have investigated
the risk associated with breast cancer, two with
ovarian cancer, four with uterine corpus cancer
(mostly endometrial), and one with a combination of
cancers. It should be noted that studies of physical
activity in women have been especially prone to
misclassification problems because they did not

116


The Effects of Physical Activity on Health and Disease

Main findings
Any strenuous activity relative to none:
RR = 1 .O (95% Cl, 0.8-l .3)

Dose    Adjustment for confounders
response+   and other comments

No     Adjusted for age, family history, screening
     sigmoidoscopy, BMI; population based

Most active quintile compared with least
active quintile, RR = 0.53 (95% Cl,
0.32-0.88) p for trend = 0.03

Yes

Adjusted for age, BMI, parental history of
colorectal cancer, history of endoscopic
screening or polyp diagnosis, smoking,
aspirin use, and diet

Vigorous activity > 2 hours/week relative
to none: RR = 0.6 (95% Cl, 0.4-l .O)

Yes

Adjusted for BMI, fahily history, income,
race, smoking, and intakes of alcohol, energy,
fat, fiber, and calcium

Abbreviations: BMI = body mass index (wt [kg] /ht [ml' ); Cl = confidence interval; OR = odds ratio; RR = relative risk.
`Excludes studies where only occupational physical activity was measured.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

include household work and child care in their
assessment. Studies of leisure-time or total physical
activity and hormone-dependent cancers in women
are summarized in Table 4-6.

Breast Cancer

Four of the 13 breast cancer studies considered only
occupational physical activity. Two of those studies
described significant inverse associations (Vena et
al. 1987; Zheng et al. 1993), and two others reported
no significant association (Dosemeci et al. 1993;
Pukkala etal. 1993). Only two (Dosemecietal. 1993;
Pukkala et al. 1993) adjusted for socioeconomic
status, and none gathered information about repro-
ductive factors and thus could not control for those
potential confounding variables.

The epidemiologic studies of leisure-time or
total physical activity and breast cancer risk have
yielded inconsistent results (Table 4:6). Of these 10
studies, two reported a significant inverse associa-
tion (Bernstein et al. 1994; Mittendorf et al. 1995),
three reported an inverse association that was not
statistically significant (Frisch et al. 1985,1987;
Friedenreich and Rohan 1995), three reported no
relationship (Paffenbarger, Hyde, Wing 1987;
Albanes, Blair, Taylor 1989; Taioli, Barone, Wynder
1995). The other two reported a direct association,

although in one this did not reach statistical signifi-
cance (Dorgan et al. 1994), and in the other it
remained statistically significant (after adjustment
for confounding) only for physical activity at age 30-
39 years (Sternfeld et al. 1993).

Even among the studies that controlled for po-
tential confounding by reproductive factors, find-
ings were inconsistent (Bernstein et al. 1994; Dorgan
et al. 1994; Sternfeld et al. 1993; Friedenreich and
Rohan 1995; Mittendorf et al. 1995; Taioli, Barone,
Wynder 1995). Results were inconsistent as well
among studies that included primarily postmeno-
pausal women (i.e., all but the study by Bernstein and
colleagues [ 19941).

Nonetheless, it is possible that physical activ-
ity during adolescence and young adulthood may
protect against later development of breast cancer.
Five of the studies cited here have examined this
possibility. Among these five studies, two found a
strong and statistically significant reduction in
risk (Bernstein et al. 1994 [RR = 0.421; Mittendorf
et al. 1995 [RR = 0.5]), one found a nonsignificant
reduction in risk (Frisch et al. 1985 [RR = 0.54]),
and two found a null association (Paffenbarger,
Hyde, Wing 1987; Taioli, Barone, Wynder 1995).
These studies thus lend limited support to the hy-
pothesis that physical activity during adolescence

117


Physical Activity and Health

Table 4-6.  Epidemiologic studies of leisure-time or leisure-time plus occupational physical activity*
     and hormone-dependent cancers in women

                           Definition of              Definition of

Study

Population

physical activity

cancer

Breast cancer

Frisch et al.
(1985 and 1987)

Paffenbarger,
Hyde, Wing
(1987)
Albanes, Blair,
Taylor (1989)

Sternfeld et al.
(1993)

Bernstein et al.
(1994)

Dorgan et al.
(1994)

Friedenreich and
Rohan (1995)

Mittendorf et al.
(1995)

Taioli, Barone,    All ages in US; 617
Wynder (1995)    cases; 531 controls

Ovarian cancers

Mink et al. (1996)

Iowa Women's
Health Study; cohort
of 3 1,396 postmeno-
pausal women

Cohort of former US
college athletes and
nonathletes; 5,398
women aged 2 l-80
years

Cohort of former US
college students,
4,706 women

NHANES cohort: 7,413
women aged 25-74
years, in US

254 cases and 201
controls in an HMO

Women 2 40 years; 545
cases and 545 controls
in California, US

Framingham Study
cohort: 2,307 women
aged 35-68 years,
Massachusetts, US

Australian women
aged 20-74 years;
451 cases and 451
controls (matched)

US women aged
17-74 years; 6,888
cases and 9,539
controls

Athletic status during college

Sports play during college

One question on nonrecreational
activity, one on recreational
activity

Age-specific recreational activity
levels

Participation in several leisure-
time activities after menarche

Physical activity index

Recreational physical activity
index

Strenuous physical activity at
ages 14-22 years

Leisure-time physical activity at
ages 15-22 years

Categories of physical activity

Breast cancer prevalence
(n = 69)

Breast cancer incidence
and mortality

Breast cancer incidence
(n = 122)

Breast cancer incidence

Breast cancer incidence
in situ and invasive

Breast cancer incidence
(n = 117)

Breast cancer incidence

Breast cancer incidence

Breast cancer incidence

Ovarian cancer incidence
(n = 97)

118


The Effects of Physical Activity on Health and Disease

Main findings

Dose
response+

Adjustment for confounders
and other comments

Nonathletes vs. athletes:
RR = 1.86 (95% Cl, 1 .O-3.47)

Sports play of 2 5 relative to < 5 hours/week
RR = 0.96 (p value = 0.92)

Sedentary relative to most active: RR = 1 .l
(95% Cl, 0.6-2.0) for nonrecreational;
RR = 1 .O (95% Cl, 0.6-l .6) for recreational

For activity from age 30-39, high activity
quartile vs. low activity quartile, postmeno-
pausal OR = 2.3 (95% Cl, 1.03-5.04); pre-
menopausal OR = 2.8 (95% Cl, 0.98-5.18)

2 3.8 hours/week relative to 0 hours
of leisure-time activity, RR = 0.42
(95% Cl, 0.27-0.64)

High activity quartile relative to low activity
quartile: RR = 1.6 (95% Cl, 0.9-2.9)

> 4,000 kcal/week in physical activity
relative to none: RR = 0.73
(95% Cl, 0.51-l .05)

1 daily strenuous activity relative
to none: RR = 0.5 (95% Cl, 0.4-0.7)

> 1,750 kcal/week relative to none:
RR = 1.1 (95% Cl, 0.5-2.6)     .

Most active relative to least active:
RR = 1.97 (95% Cl, 1.22-3.19)

NA

Adjusted for age, family history of cancer,
age at menarche, number of pregnancies,
oral contraceptive use, smoking,
use of estrogen, leanness

NA      Adjusted for age

No

Adjusted for age; adjustment for confounders
had little effect on results; suggestive of variable
effects by menopausal status

Yes
(opposite
direction)

Adjusted for age, menopausal status, and
potential confounders

Yes

Adjusted for age, race, neighborhood, age at
menarche, age at first full-term pregnancy,
number of full-term pregnancies, oral
contraceptive use, lactation, family history of
breast cancer, Quetelet index; population-based

Yes
(opposite
direction)

Adjusted for age, menopausal status, age at
first pregnancy, parity, education, occupation,
and alcohol

Yes

Adjusted for BMI and energy intake;
effects observed for premenopausal and
postmenopausal cancer and for light and
vigorous activity; population-based

Yes

Adjusted for age, parity, age at first birth, family
history, BMI, prior breast disease, age at
menopause, menopausal status, alcohol use,
and menopausal status x BMI; population-based

No

Adjusted for age, education, BMI, age at
menarche, and prior pregnancy; hospital-based

Yes
(opposite
direction)

Adjusted for age, smoking, education, live births,
hysterectomy, and family history

119


Physical Activity and Health

Table 4-6. Confirmed

                           Definition of              Definition of
Study        Population       physical activity                   cancer

Endometrial cancers

Levi et al.
(1993)

Shu et al.
(1993)

Sturgeon et al.
(1993)

Combined set

Frisch et al.
(1985 and 1987)

Switzerland/Northern   Categories of leisure-time and
Italy; 274 cases and 572  occupational activity
controls aged 31-75

Women in Shanghai,
China aged 18-74
years, 268 cases
and 268 controls

Occupational and nonoccupa-     Endometrial cancer
tional physical activity index      incidence

US women aged
20-74 years;
405 cases
and 297 controls

Recreational and nonrecreational
activity categories

Cohort of former US
college athletes and
nonathletes; 5,398
women aged 2 l-80
years

Athletic status during college

Endometrial cancer
incidence

Endometrial cancer
incidence

Cervix, uterus, ovary,
vagina cancer prevalence
(n = 37)

and young adulthood may be protective against later
development of breast cancer.

Other Hormone-Dependent Cancers in Women
Too little information is available to evaluate the
possible effect of physical activity on risk of ovarian
cancer. Zheng and colleagues (1993) found no sig-
nificant associations between occupational physical
activity and risk of ovarian cancer. On the other
hand, data from the Iowa Women's Health Study
showed that risk of ovarian cancer among women
who were most active was twice the risk among
sedentary women (Mink et al. 1996).   '
Findings are limited for uterine corpus cancers as

well. Zheng et al. (1993) found no relationship
between physical activity and risk of cancer of the
uterine corpus. Among the endometrial cancer stud-
ies, one (Levi et al: 1993) found a decreased risk
associated with nonoccupational activity, and one
(Sturgeon et al. 1993) found combined recreational

and nonrecreational activity to be protective. An-
other study (Shu et al. 1993) found no protective
effect of nonoccupational activity in any age group
and a possible protective effect of occupational activ-
ity among younger women but not among older
women.

In Frisch and colleagues' (1985) study of the
combined prevalence of cancers of the ovary, uterus,
cervix, and vagina, nonathletes were 2.5 times more
likely than former college athletes to have these
forms of cancer at follow-up. Because these cancers
have different etiologies, however, the import of this
finding is difficult to determine.

Thus the data are either too limited or too
inconsistent to firmly establish relationships be-
tween physical activity and hormone-dependent can-
cers in women. The suggestive finding that physical
activity in adolescence and early adulthood may
protect against later development of breast cancer
deserves further study.

120


The Effects of Physical Activity on Health and Disease

Main findings

Dose
response+  Adjustment for confounders
       and other comments

Sedentary relative to active for total activity:
RR = 2.4 (95% Cl, 1 .O-5.8) to RR = 8.4
(95% Cl, 3.0-25.3) for different ages

LOW average adult activity quartile relative
to high quartile: occupational age I 55 years
RR = 2.5 (95% Cl, 0.9-6.3), age > 55 years
RR = 0.6 (no Cl given); nonoccupational
RR = 0.8 (95% Cl, 0.5-l .3)

Sustained (lifetime) activity, inactive
relative to active: recreational RR = 1.5
(95% Cl, 0.7-3.2) nonrecreational RR = 1.6
(95% Cl, 0.7-3.3)

Nonathletes vs. athletes:
RR = 2.53 (95% Cl, 1 .17-5.47)

Yes

Adjusted for age, education, parity,
menopausal status, oral contraceptive use,
estrogen replacement, BMI, and caloric intake;
hospital-based

No

Adjusted for age, number of pregnancies,
BMI, and caloric intake; possible modification
of occupational activity by age;
population-based *

No

Adjusted for age, study area, education, parity,
oral contraceptive use, hormone replacement
use, cigarette smoking, BMI, and other type of
activity; recent activity also protective;
population-based

N/A

Adjusted for age, family history of cancer,
age at menarche, number of pregnancies,
oral contraceptive use, smoking, use of
estrogen, leanness

Abbreviations: BMI = body mass index (wt [kg]/ht [ml> ); Cl = confidence interval; HMO = health maintenance organization;
NHANES = National Health and Examination Survey; OR = odds ratio; RR = relative risk.
`Excludes studies where only occupational physical activity was measured.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

Cancers in Men

Prostate Cancer

Among epidemiologic studies of physical activity
and cancer, prostate cancer is the second most com-
monly studied, after colorectal cancer. Results of
these studies are inconsistent. Seven studies have
investigated the association between occupational
physical activity and prostate cancer risk or mortal-
ity. Two described significant inverse dose-response
relationships (Vena et al. 1987; Brownson et al.
199 1). Two showed a nonsignificant decreased risk
with heavy occupational activity (Dosemeci et al.
1993; Thune and Lund 1994). In one publication
that presented data from two cohorts, there was no
effect in either (Paffenbarger, Hyde, Wing 1987).

The remaining study (Le Marchand, Kolonel,
Yoshizawa 1991) reported inconsistent findings by
age: increasing risk with increasing activity among
men aged 70 years or older and no relationship
among men younger than age 70.
The 10 studies of leisure-time physical activity,
or total physical activity, or cardiorespiratory fitness
and risk of prostate cancer have also produced
inconsistent results (Table 4-7). Two of the studies
described significant inverse relationships (Lee,
Paffenbarger, Hsieh 1992; Oliveria et al. 1996),
although one of these (Lee, Paffenbarger, Hsieh
1992) observed this relationship only among men
aged 70 years or older. Four studies found inverse
relationships (Albanes, Blair, Taylor 1989; Severson
et al. 1989; Yu, Harris, Wynder 1988; Thune and

121


Physical Activity and Health

Table 4-7. Epidemiologic studies of leisure-time or total physical activity or cardiorespiratory fitness and
     prostate cancer
                   Definition of physical activity     Definition of
Study       Population       or cardiorespiratory fitness          cancer

Physical activity
Polednak (1976)

Paffenbarger,
Hyde, Wing
(1987)

Yu, Harris,
Wynder
(1988)

Albanes, Blair,
Taylor (1989)

Severson et al.
(1989)

West et al. (1991)

Lee, Paffenbarger,
Hsieh (1992)

Thune and Lund
(1994)

Cohort of 8,393 former
US college men

Cohort of 51,977
US male former
college students
16,936 US male alumni
aged 35-74 years

US men, all ages,
1,162 cases and
3,124 controls

NHANES cohort of
5,141 US men aged
25-74 years

Cohort of 7,925
Japanese men
in Hawaii aged
46-65 years

Utah men aged 45-74
years, 358 cases
and 679 controls

Cohort of US college
alumni, 17,719 men
aged 30-79 years

Cohort of Norwegian
43,685 men

Cardiorespiratory Fitness
Oliveria et al.     Cohort of 12,975
(1996)         Texas men
         aged 20-80 years

Cohort of 7,570
Texas men

College athletic status, major,
minor, and nonathletes
Sports play

Physical activity index

Categories of leisure-time
aerobic exercise

Categories of recreational and
nonrecreational activity

Physical activity index from
Framingham study and heart rate

Categories of energy expended

Physical activity index based on
stair climbing, walking, playing
sports

Recreational and occupational
activity based on questionnaire;
categories of occupational and
leisure-time activity

Maximal exercise test

Categories of weekly energy
expenditure in leisure time

Prostate cancer incidence
(n = 124)

Prostate cancer incidence
and mortality (n = 154 1

Prostate cancer mortality
(n = 36) '
Prostate cancer incidence

Prostate cancer incidence

Prostate cancer incidence

Prostate cancer incidence

Prostate cancer incidence
(n = 221)

Prostate cancer incidence
(n = 220)

Prostate cancer incidence
or mortality (n = 94)

Prostate cancer incidence
or mortality (n = 44)

122


The Effects of Physical Activity on Health and Disease

Main findings

Dose    Adjustment for confounders
response*  and other comments
    -

Major athletes relative to nonathletes,
RR = 1.64 (p < 0.05)
Sports play 2 5 relative to < 5 hours/week,
RR = 1.66; (p < 0.05)

No

None

NA

Adjusted for age (2 levels of activity)

Comparing 2 2,000 with < 500 kcal/week,
RR = 0.57; p = 0.33

No

Adjusted for age, BMI, and smoking

Most sedentary relative to most active
menduring leisure time,
RR = 1.3 (95% Cl, 1.0-l .6) for whites,
RR = 1.4 (95% Cl, 0.8-2.6) for blacks

Yes

Adjusted for age; in multivariate analysis,
findings no longer significant for whites;
hospital based

Least active relative to most               Adjusted for age; further adjustment for
active individuals,                      confounders said to not affect results

RR = 1.3 (95% Cl, 0.7-2.4);
for nonrecreational
RR = 1.8 (95% Cl, 1 .O-3.3);
for recreational

RR = 1.8 (95% Cl, 1 .O-3.3)
Most active relative to least active men,
RR = 1.05 (95% Cl, 0.73-l .51);
for occupation,
RR = 0.77 (95% Cl, 0.58-l .Ol );
high heart rate relative to low,
RR = 0.97 (95% Cl, 0.69-l .36)

Overall no association found

No


Ye5


No

Adjusted for age, BMI

NA


No


NA

Men aged 2 70 years: comparing > 4,000
with c 1,000 kcal/week; RR = 0.53
(95% Cl, 0.29-0.95); men aged < 70 years,
RR = 1.21 (95% Cl, 0.8-0.18)

No

For agressive tumors, physical activity was
associated with increased risk, but this was
not statistically significant
Adjusted for age; no effect of activity at
2,500 kcal, the level found protective
for colon cancer

Heavy occupational activity relative to
sedentary, RR = 0.81 (95% Cl, 0.50-l .30);
regular training in leisure time relative to
sedentary, RR = 0.87 (95% Cl, 0.57-l .34)

No

Adjusted for age, BMI, and geographic region

Among men < 60 years, most fit relative to
least fit, RR = 0.26 (95% Cl, 0.1 o-0.63);
among men > 60 years, no effect, RR not given

13,000 kcal/week relative to < 1,000
kcal/week, RR = 0.37 (95% Cl, 0.14-0.98)

Yes

No


No

Adjusted for age, BMI, and smoking

Adjusted for age, BMI, and smoking

Adjusted for age, BMI, and smoking

Abbreviations: BMI = body mass index (wt (kg]/ht [ml* ); Cl = confidence interval; RR = relative risk.
`A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were more
than 2 levels and a dose-response gradient was found.

123


Physical Activity and Health

Lund 1994), but these were not statistically signifi-
cant, and one of the four (Thune and Lund 1994)
showed this relationship only for those aged 60 years
or older. Two studies found that men who had been
athletically active in college had significantly in-
creased risks of later developing prostate cancer
(Polednak 1976; Paffenbarger, Hyde, Wing 1987).
One study found no overall association between
physical activity and prostate cancer risk but found
a higher risk (although not statistically significant)
of more aggressive prostate cancer (West et al. 1991).

The two studies of the association of cardiorespi-
ratory fitness with prostate cancer incidence were
also inconsistent. Severson and colleagues (1989)
found no association between resting pulse rate and
subsequent risk of prostate cancer. Oliveria and col-
leagues (1996) found a strong inverse dose-response
relationship between fitness assessed by time on a
treadmill and subsequent risk of prostate cancer.

Thus the body of research conducted to date
shows no consistent relationship between prostate
cancer and physical activity.

Testicular Cancer

Two studies investigated physical activity and risk of
developing testicular cancer; again, results are in-
consistent. A case-control study in England found
that men who spent at least 15 hours per week in
recreational physical activity had approximately half
the risk of sedentary men, and a significant trend was
reported over six categories of total time spent exer-
cising (United Kingdom Testicular Cancer Study
Group 1994). A cohort study in Norway (Thune and
Lund 1994) was limited by few cases. It showed no
association between leisure-time physical activity
and risk of testicular cancer, but heavy manual
occupational activity was associated with an ap-
proximately twofold increase in risk, although this
result was not statistically significant. Thus no mean-
ingful conclusions about a relationship between
physical activity and testicular cancer can be drawn.

Other Site-Specific Cancers
Few.epidemiologic studies have examined the asso-
ciation of physical activity with other site-specific
cancers (Lee 1994). The totality of evidence provides
little basis for a suggestion of a relationship.

Biologic Plausibility

Because the data presented in this section demon-
strate a clear association only between physical ac-
tivity and colon cancer, the biologic plausibility of
this relationship is the focus of this section. The
alteration of local prostaglandin synthesis may serve
as a mechanism through which physical activity may
confer protection against colon cancer (Shephard et
al. 1991; Lee 1994; Cordain, Latin, Beanke 1986).
Strenuous physical activity increases prostaglandin
F, alpha, which strongly increases intestinal motil-
ity, and may suppress prostaglandin E,, which re-
duces intestinal motility and, released in greater
quantities by colon tumor cells than normal cells,
accelerates the rate of colon cell proliferation (Thor
et al. 1985; Tutton and Barkla 1980). It has been
hypothesized that physical activity decreases gas-
trointestinal transit time, which in turn decreases
the length of contact between the colon mucosa and
potential carcinogens, cocarcinogens, or promoters
contained in the fecal stream (Shephard 1993; Lee
1994). This hypothesis could partly explain why
physical activity has been associated with reduced
cancer risk in the colon but not in the rectum.
Physical activity may shorten transit time within
segments of the colon without affecting transit time
in the rectum. Further, the rectum is only intermit-
tently filled with fecal material before evacuation.
Despite these hypothetical mechanisms, studies on
the effects of physical activity on gastrointestinal
transit time in humans have yielded inconsistent
results (Shephard 1993; Lee 1994).

Conclusions

The relative consistency of findings in epidemio-
logic studies indicates that physical activity is asso-
ciated with a reduced risk of colon cancer, and
biologically plausible mechanisms underlying this
association have been described. The data consis-
tently show no association between physical activ-
ity and rectal cancer. Data regarding a relationship
between physical activity and breast, endometrial,
ovarian, prostate, and testicular cancers are too
limited or too inconsistent to support any firm
conclusions. The suggestion that physical activity
in adolescence and early adulthood may protect
against later development of breast cancer clearly
deserves further study.

124


The Effects of Physical Activity on Health and Disease

Non-Insulin-Dependent
Diabetes Mellitus

An estimated 8 million Americans (about 3 percent of
the U.S. population) have been diagnosed with diabe-
tes mellitus, and it is estimated that twice that many
have diabetes but do not know it (Harris 1995). More
than 169,000 deaths per year are attributed to diabetes
as the underlying cause, making it the seventh leading
cause of mortality in the United States (NCHS 1994).
This figure, however, underestimates the actual death
toll: in 1993, more than twice this number of deaths
occurred among persons for whom diabetes was listed
as a secondary diagnosis on the death certificate.
Many of these deaths were the result of complications
of diabetes, particularly CVDs, including CHD, stroke,
peripheral vascular disease, and congestive heart fail-
ure. Diabetes accounts for at least 10 percent of all
acute hospital days and in 1992 accounted for an
estimated $92 billion in direct and indirect medical
costs (Rubin et al. 1993). In addition, by age 65 years,
about 40 percent of the general population has im-
paired glucose tolerance, which increases the risk of
CVD (Harris et al. 1987).

Diabetes is a heterogeneous group of metabolic
disorders that have in common elevated blood glucose
and associated metabolic derangements. Insulin-
dependent diabetes mellitus (IDDM, or type I) is
characterized by an absolute deficiency of circulat-
ing insulin caused by destruction of pancreatic beta
islet cells, thought to have occurred by an auto-
immune process. Non-insulin-dependent diabetes
mellitus (NIDDM, or type II) is characterized either
by elevated insulin levels that are ineffective in
normalizing blood glucose levels because of insulin
resistance (decreased sensitivity to insulin), largely
in skeletal muscle, or by impaired insulin secretion.
More than 90 percent of persons with diabetes have
NIDDM (Krall and Beaser 1989).

Nonmodifiable biologic factors implicated in the
etiology of NIDDM include a strong genetic influence
and advanced age, but the development of insulin
resistance, hyperinsulinemia, and glucose intoler-
ance are related to a modifiable factor: weight gain in
adults, particularly in those persons in whom fat
accumulates around the waist, abdomen, and upper
body and within the abdominal cavity (this is also
called the android or central distribution pattern)
(Harris et al. 1987).

Physical Activity and NIDDM
Considerable evidence supports a relationship be-
tween physical inactivity and NIDDM (Kriska, Blair,
Pereira 1994; Zimmet 1992; King and Kriska 1992;
Kriska and Bennett 1992). Early suggestions of a
relationship emerged from the observation that soci-
eties that had discontinued their traditional lifestyles
(which presumably included large amounts of regu-
lar physical activity) experienced major increases in
the prevalence of NIDDM (West 1978). Additional
evidence for the importance of lifestyle was provided
by comparison studies demonstrating that groups of
people who migrated to a more technologically ad-
vanced environment had higher prevalences of
NIDDM than their ethnic counterpartswho remained
in their native land (Hara et al. 1983; Kawate et al.
1979; Ravussin et al. 1994) and that rural dwellers
had a lower prevalence of diabetes than their urban
counterparts (Cruz-Vidal et al. 1979; Zimmet 1981;
Taylor et al. 1983; King, Taylor, Zimmet, et al. 1984).
Many cross-sectional studies have found physi-
cal inactivity to be significantly associated with
NIDDM (Taylor et al. 1983; Taylor et al. 1984; King,
Taylor, Zimmet, et al. 1984; Dowse et al. 1991;
Ramaiya et al. 1991; Kriska, Gregg, et al. 1993; Chen
and Lowenstein 1986; Frish et al. 1986; Holbrook,
Barrett-Connor, Wingard 1989). Cross-sectional
studies that have examined the relationship between
physical activity and glucose intolerance in persons
without diabetes have generally found that after a
meal, glucose levels (Lindgarde and Saltin 1981;
Cederholm and Wibell 1985; Wang et al. 1989;
Schranz et al. 1991; Dowse et al. 1991; Kriska,
LaPorte, et al. 1993) and insulin values (Lindgarde
and Saltin 1981; Wang et al. 1989; McKeigue et al.
1992; Feskens, Loeber, Kromhout 1994; Regensteiner
et al. 1995) were significantly higher in less active
than in more active persons. However, some cross-
sectional studies did not find that physical inactivity
was consistently associated with NIDDM in either
the entire population or in all subgroups (King,
Taylor, Zimmet, et al. 1984; Dowse et al. 1991;
Kriska, Gregg, et al. 1993; Montoye et al. 1977;
Taylor et al. 1983; Fisch et al. 1987; Jarrett, Shipley,
Hunt 1986; Levitt et al. 1993; Harris 1991). For
example, the Second National Health and Nutrition
Examination Survey and the Hispanic Health and
Nutrition Examination Survey found that higher

125


Physical Activity and Health

levels of occupational physical activity among
Mexican Americans were associated with less NIDDM
(Harris 199 1). However, in contrast to findings from
the First National Health and Nutrition Examination
Survey (Chen and Lewenstein 1986), this associa-
tion was not found for either occupational or leisure-
time physical activity among blacks or whites.

Two case-control studies have found physical
inactivity to be significantly associated with NIDDM
(Kaye et al. 1991; Uusitupa et al. 1985). One was a
population-basednestedcase-controlstudy, inwhich
women aged 55-69 years who had high levels of
physical activity were found to be half as likely to
develop NIDDM as were same-aged women with low
levels of physical activity (age-adjusted OR = 0.5;
95% Cl, 0.4-0.7) (Kaye et al. 1991). Moderately
active women had an intermediate risk (OR = 0.7;
95% Cl, 0.5-0.9).

Prospective cohort studies of college alumni,
female registered nurses, and male-physicians have
demonstrated that physical activity protects against
the development of NIDDM (Table 4-8). A study of

male university alumni (Helmrich et al. 1991) dem-
onstrated that physical activity was inversely related
to the incidence of NIDDM, a relationship that was
particularly evident in men at high risk for develop-
ing diabetes (defined as those with a high BMI, a
history of high blood pressure, or a parental history
of diabetes). Each 500 kilocalories of additional
leisure-time physical activity per week was associ-
ated with a 6 percent decrease in risk (adjusted for
age, BMI, history of high blood pressure, and paren-
tal history of diabetes) of developing NIDDM. This
study showed a more pronounced benefit from vig-
orous sports than from stair climbing or walking. In
a study of female registered nurses aged 34-59 years,
women who reported engaging in vigorous physical
activity at least once a week had a 16 percent lower
adjusted relative risk of self-reported NIDDM during
the 8 years of follow-up than women who reported
no vigorous physical activity (Manson et al. 1991).
Similar findings were observed between physical
activity and incidence of NIDDM in a S-year pro-
spective study of male physicians 40-84 years of age

Table 4-8.  Cohort studies of association of physical activity with non-insulin-dependent diabetes mellitus
       (NIDDM)

Definition of              Definition of

study

Population

physical activity

NIDDM

Helmrich et al.
(1991)

Male college alumni

Leisure-time physical activity
(walking, stair climbing, and
sports)

Self-reported physician-
diagnosed diabetes

Manson et al.
(1991)

Female nurses

Single questions regarding number  Self-reported diagnosed
of times per week of vigorous     diabetes, confirmed by
activity              classic symptoms plus
                fasting plasma glucose
               L 140 mg/dl; two elevated
                plasma glucose levels on
                   two different occasions;
                 hypoglycemic medication
                               use

Manson et al.
(1992)

Male phystcrans

Single questions regarding number  Self-reported physician-
of times per week of vigorous     diagnosed diabetes
activity

126


The Effects of Physical Activity on Health and Disease

(Manson et al. 1992). Although the incidence of
diabetes was self-reported in these cohorts, concerns
about accuracy are somewhat mitigated by the fact
that these were studies of health professionals and
college-educated persons. In these three cohort stud-
ies, two found an inverse dose-response gradient of
physical activity and the development of NIDDM
(Helmrich et al. 1991; Manson et al. 1992).

In a feasibility study in Malmo, Sweden, physical
activity was included as part of an intervention
strategy to prevent diabetes among persons with
impaired glucose tolerance (Eriksson and Lindgarde
1991). At the end of 5 years of follow-up, twice as
many in the control group as in the intervention
group had developed diabetes. The lack of random
assignment of participants, however, limits the
generalizability,of this finding. A study conducted in
Daqing, China, also included physical activity as an
intervention to prevent diabetes among persons with
impaired glucose tolerance (Pan, Li, Hu 1995). After
6 years of follow-up, 8.3 cases per 100 person-years
occurred in the exercise intervention group and 15.7
cases per 100 person-years in the control group.

It has been recommended that an appropriate
exercise program may be added to diet or drug
therapy to improve blood glucose control and re-
duce certain cardiovascular risk factors among per-
sons with diabetes (American Diabetes Association
1990). Diet and exercise have been found to be most
effective for controlling NIDDM in persons who
have mild disease and are not taking medications
(Barnard, Jung, Inkeles 1994). However, excessive
physical activity can sometimes cause persons with
diabetes (particularly those who take insulin for
blood glucose control) to experience detrimental
effects, such as worsening of hyperglycemia and keto-
sis from poorly controlled diabetes, hypoglycemia
(insulin-reaction) either during vigorous physical
activity or-more commonly-several hours after
prolonged physical activity, complications from pro-
liferative retinopathy (e.g., detached retina), compli-
cations from superficial foot injuries, and a risk of
myocardial infarction and sudden death, particularly
among older people with NIDDM and advanced, but
silent, coronary atherosclerosis. These risks can be
minimized by a preexercise medical evaluation and
by taking proper precautions (Leon 1989, 1992). To

Main findings
0.94 (95% Cl, 0.90-0.98) or 6% decrease in
NIDDM for each 500 kcal increment

Dose
response*

Yes

Adjustment for confounder
and other comments
Adjusted for age, BMI, hypertension
history, parental history of diabetes

0.84 (95% Cl, 0.75-0.94) for 2 1 time
per week vs. < 1 time per week
vigorous activity

No

Adjusted for age, BMI, family history
of diabetes, smoking, alcohol consumption,
hypertension history, cholesterol history,
family of history coronary heart disease

0.71 (95% Cl, 0.54-0.94) for 2 1 .time per
week vs. < 1 time per week vigorous
activity

Yes

Adjusted for age, BMI, smoking, alcohol
consumption, reported blood pressure,
hypertension history, cholesterol history,
parental history of myocardial infarction

Abbreviations: BMI = body mass index (wt [kg]/ht [ml2 ); Cl = confidence interval.
*A dose-response relationship requires more than 2 levels of comparison. In this column, "NA" means that there were only 2 levels of
comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means that there were
more than 2 levels and a dose-response gradient was found.

127


Physical Activity and Health

reduce risk of hypoglycemic episodes, persons with
diabetes who take insulin or oral hypoglycemic drugs
must closely monitor their blood glucose levels and
make appropriate adjustments in insulin or oral hy-
poglycemic drug dosage, food intake, and timing of
physical activity sessions.

Biologic Plausibility

Numerous reviews of the short- and long-term
effects of physical activity on carbohydrate metabo-
lism and glucose tolerance describe the physiologi-
cal basis for a relationship (Bjiirntorp and Krotkiewski
1985; Koivisto, Yki-Jarvinen, DeFronzo 1986;
Lampman and Schteingart 1991; Horton 1991;
Wallberg-Henriksson 1992; Leon 1992; Richter,
Ruderman, Schneider 1981; Harris et al. 1987).
During a single prolonged session of physical activ-
ity, contracting skeletal muscle appears to have a
synergistic effect with insulin in enhancing glucose
uptake into the cells. This effect appears to be related
to both increased blood Bow in the muscle and
enhanced glucose transport into the muscle cell.
This enhancement persists for 24 hours or more as
glycogen levels in the muscle are being replenished.
Such observations suggest that many of the effects of
regular physical activity are due to the overlapping
effects of individual physical activity sessions and
are thus independent of long-term adaptations to
exercise training or changes in body composition
(Harris et al. 1987).

In general, studies of exercise training have
suggested that physical activity helps prevent NIDDM
by increasing sensitivity to insulin (Saltin et al. 1979;
Lindgarde, Malmquist, Balke 1983; Krotkiewski
1983; Trovati et al. 1984; Schneider et al. 1984;
Ronnemaa et al. 1986). These studies suggest that
physical activity is more likely to improve abnormal
glucose tolerance when the abnormality is primarily
caused by insulin resistance than when it is caused
by deficient amounts of circulating insulin (Holloszy
et al. 1986). Thus, physical activity is likely to be
most beneficial in preventing the progression of
NIDDM during the earlier stages of the disease
process, before insulin therapy is required. Evidence
supporting this theory includes intervention pro-
grams that promote physical activity together with a
low-fat diet high in complex carbohydrates (Barnard,
Jung, Inkeles 1994) or programs that promote diet

alone (Nagulesparan et al. 1981). Thesestudies have
shown that diet and physical activity interventions
are much less beneficial for persons with NIDDM
who require insulin therapy than for those who do
not yet take any medication or those who take only
oral medications for blood glucose control.
  Cross-sectional studies also show that, com-
pared with their sedentary counterparts, endurance
athletes and exercise-trained animals have greater
insulin sensitivity, as evidenced by a lower plasma
insulin concentration at a similar plasma glucose
concentration, and increased `z*I-insulin binding to
white blood cells and adipocytes ,(Koivisto et al.
1979). Insulin sensitivity and rate of glucose dis-
posal are related to cardiorespiratory fitness even in
older persons (Hollenbeck et al. 1984). Resistance or
strength-training exercise has also been reported to
have beneficial effects on glucose-insulin dynamics
in some, but not all, studies involving persons who
do not have diabetes (Goldberg 1989; Kokkinos et
al. 1988). Much of the effect of physical activity
appears to be due to the metabolic adaptation of
skeletal muscle. However, exercise training may
contribute to improved glucose disposal and glucose-
insulin dynamics in both adipose tissue and the
working skeletal muscles (Leon 1989,1992; Gudat,
Berger, Lefebvre 1994; Horton 1991).
In addition, exercise training may reduce other
risk factors for atherosclerosis (e.g., blood lipid
abnormalities and elevated blood pressure levels), as
discussed previously in this chapter, and thereby
decrease the risk of macrovascular or atherosclerotic
complications of diabetes (Leon 1991a).
Lastly, physical activity may prevent or delay the
onset of NIDDM by reducing total body fat or specifi-
cally intra-abdominal fat, a known risk factor for
insulin resistance. As discussed later in this chapter,
physical activity is inversely associated with obesity
and intra-abdominal fat distribution, and recent
studies have demonstrated that physical training can
reduce these body fat stores (Bjdrntorp, Sjdstrom,
Sullivan 1979;BrownellandStunkard 1980; Despres
et al. 1988; Krotkiewski 1988).

Conclusions

The epidemiologic literature strongly supports a
protective effect of physical activity on the likeli-
hood of developing NIDDM in the populations

128


studied. Several plausible biologic mechanisms exist
to explain this effect. Physical activity may also
reduce the risk of developing NIDDM in groups of
people with impaired glucose tolerance, but this
topic needs further study.

Osteoarthritis

Osteoarthritis, the most common form of arthritis, is
characterized by both degeneration of cartilage and
new growth of bone around the joint. Because its
prevalence increases with age, osteoarthritis is the
leading cause of activity limitation among older
persons. The etiology of osteoarthritis is unknown,
and the risk factors and pathogenesis of osteoarthri-
tis differ for each joint group.

Whether an active lifestyle offers protection
against the development of osteoarthritis is not
known, but studies have examined the risk of devel-
oping it in relation to specific athletic pursuits.
Cross-sectional studies have associated competitive-
as opposed to recreational-running at high levels
and for long periods with the development of os-
teoarthritis seen on x-rays (Marti and Minder 1989;
Kujala, Kaprio, Sarna 1994; Kujala et al. 1995). On
the other hand, both cross-sectional and cohort
studies have suggested that persons who engage in
recreational running over long periods of time have
no more risk of developing osteoarthritis of the knee
or hip than sedentary persons (Lane 1995; Lane et al.
1986,1993; Panush et al. 1995; Panush et al. 1986;
Panush and Lane 1994). There is also currently no
evidence that persons with normal joints increase
their risk of osteoarthritis by walking.
Studies of competitive athletes suggest that
some sports-specifically soccer, football, and
weight lifting-are associated with developing os-
teoarthritis of the joints of the lower extremity
(Kujala, Kaprio, Sarna 1994; Kujala et al. 1995;
Rall, McElroy, Keats 1964; Vincelette, Laurin,
Levesque 1972; Lindberg, Roos, G&sell 1993).
Other competitive sports activities in which spe-
cific joints are used excessively have also been
associated with the development of osteoarthritis.
For example, baseball pitchers are reported to have
an increased prevalence of osteoarthritis in the
elbow and shoulder joint (Adams 1965; Bennett
1941). These studies are limited because they

involve small sample sizes. Further confounding
these studies is the high incidence of fractures,
ligamentous and cartilage injuries, and other inju-
ries to joints that occur with greater-than-average
frequency among competitive participants in these
sports. Because joint injury is a strong risk factor for
the development of osteoarthritis, it may not be the
physical activity but rather the associated injuries
that cause osteoarthritis in these competitive ath-
letes. In a study by Roos and colleagues (1994),
soccer players who had not suffered knee injuries
had no greater prevalence of osteoarthritis than did
sedentary controls. Regular noncompetitive physi-
cal activity of the amount and intensity recom-
mended for improving health thus does not appear
harmful to joints that have no existing injury.

Physical Activity in Persons with Arthritis
Given the high prevalence of osteoarthritis among
older people, it is important to determine whether
persons with arthritis can safely exercise and be
physically active. Experimental work with animals
shows that use of injured joints inhibits tissue repair
(Buckwalter 1995). More specifically, several stud-
ies have indicated that running accelerates joint
damage in animal models where osteoarthritis has
beenexperimentallyinduced (Armstronget al. 1993).
In contrast, several short-term studies of human
subjects *have indicated that regular moderate-
exercise programs, whether including aerobic or
resistance training, relieve symptoms and improve
function among people with both osteoarthritis and
rheumatoid arthritis (Ettinger and Afable 1994;
Allegrante et al. 1993; Fisher et al. 1991; Fisher et al.
1994; Fisher and Pendergast 1994; Puett and Griffin
1994). For example, it has been shown that after
regular physical activity, persons with arthritis have
a significant reduction in joint swelling (Minor et al.
1988). In other studies of persons with osteoarthri-
tis, increased levels of physical activity were associ-
ated with improved psychosocial status, functional
status, and physical fitness (Minor 1991; Minor and
Brown 1993). Furthermore, regular physical activ-
ity of moderate intensity has been found to raise the
pain threshold, improve energy level, and improve
self-efficacy among persons with osteoarthritis
(Minor et al. 1989; Chow et al. 1986; Holman,
Mazonson, Lorig 1989).

The Effects of Physical Activity on Health and Disease

129


Physical Activity and Health

Biologic Plausibility

The biologic effects of physical activity on the
health and function of joints have not been exten-
sively investigated, but some level of physical activ-
ity is necessary to preserve joint function. Because
hyaline cartilage has no blood vessels or nerves,
mature cartilage cells (chondrocytes) receive nour-
ishment only from the diffusion of substances
through the cartilage matrix from joint fluid. Physi-
cal activity enhances this process. In the laboratory,
putting pressure on cartilage deforms the tissue,
creating pressure gradients that cause fluid to flow
and alter osmotic pressures within the cartilage
matrix (Hall, Urban, Gehll991). The effect of such
loading on the metabolism of chondrocytes is not
well described, but when loading is performed
within the physiologic range, chondrocytes increase
proteoglycan synthesis (Grodzinsky 1993). In con-
trast, high-intensity loading and -repetitive high-
impact loads disrupt the cartilage matrix and inhibit
proteoglycan synthesis (Lammi 1993).
  The role of normal loading is confirmed by the
effect of inactivity on articular cartilage..lmmobility
leads to decreased cartilage proteoglycan synthesis,
increased water content, and decreased cartilage
stiffness and thickness. Disuse may make the carti-
lage more vulnerable to injury, and prolonged disuse
causes loss of normal joint function as the joint
cavity is obliterated by fibrous tissue.
  Studies of running on joint function in dogs with
normal joints have confirmed that running does
affect the proteoglycan and water content of cartilage
and does not lead to degeneration of articular sur-
faces or to degenerative joint disease (Arokoski et al.
1993). In contrast, in dogs with injured joints, run-
ning has been shown to cause arthritis (Buckwalter
1995).

Conclusions

Physical activity is essential for maintaining the
health of joints and appears to be beneficial for
control of symptoms among people with osteoar-
thritis. Although there is no evidence that physical
activity itself causes osteoarthritis, injuries sus-
tained during competitive sports have been shown
to increase the risk of developing osteoarthritis.

Osteoporosis

Osteoporosis is characterized by decreased bone
mass and structural deterioration of bone tissue,
leading to bone fragility and increased susceptibility
to fractures. Because bone mass and strength pro-
gressively decline with advancing age, this disease
primarily affects older persons (Cummings et al.
1985). Osteoporosis is more common among women
than among men, for at least three reasons: women
have lower peak bone mass than men, women lose
bone mass at an accelerated rate after menopause
when estrogen levels decline, and women have a
                             '
longer life span than men.

The most common potential fracture sites are
vertebrae of the chest and lower back, the distal
radius (or wrist), the hips, and the proximal hu-
merus (NIH 1984). Vertebral fractures can occur
spontaneously or with minimal trauma (e.g., bend-
ing forward or coughing); once deformed, the verte-
brae never return to their normal shape. These
fractures may be asymptomatic and discovered only
incidentally on a chest or spine x-ray. Accumulation
of such vertebral fractures causes a bent-over or
hunchbacked posture that is generally associated
with chronic back pain and often with gastrointesti-
nal and abdominal problems related to a lowering of
the rib cage.

In the United States, fractures of the hip account
for 250,000 of the 1.5 million fractures that are
attributed each year to osteoporosis. Hip fractures
are associated with more deaths (a 15-20 percent
l-year mortality rate), permanent disability, and
medical and institutional care costs than all other
osteoporotic fractures combined (Cummings et al.
1985; Rankin 1993). By age 90, about one-third of
women and about one-sixth of men will have sus-
tained a hip fracture.

In both men and women, the development of
osteoporosis may be related to three factors: a defi-
cient level of peak bone mass at physical maturity,
failure to maintain this peak bone mass during the
third and fourth decades of life, and the bone loss
that begins during the fourth or fifth decade of life.
Physical activity may positively affect all three of
these factors.

Physical activity may play a substantial role in
the development of bone mass during childhood and
adolescence and in the maintenance of skeletal mass

130


as a young adult. This inference is partly based on
findings that athletic young adults have a higher
density of bone mineral than sedentary young adults
(Kirchner, Lewis, O'Connor 1996; Grimston, Willows,
Hanley 1993; Conroy et al. 1993; Nichols et al. 1994;
Rubin et al. 1993), on reports that athletes have a
differential density of bones according to the sport
they train for (Robinson et al. 1995; Heinonen et al.
1995), and on evidence that increase in bone mass in
university students is related to higher levels of
physical activity (Reeker et al. 1992).
Beyond this hypothesized function in youth,
physical activity plays a well-established role
throughout the life span in maintaining the normal
structure and functional strength of bone. Pro-
longed bed rest or immobility causes rapid and
marked reduction in bone mineral density (Krolner
et al. 1983; Chesnut 1993; Donaldson et al. 1970).
Of particular public health interest is the degree to
which physical activity can prevent or slow the
bone loss that begins occurring in women as a
normal process after menopause. Cross-sectional
studies of postmenopausal women have shown that
bone mineral density is correlated with muscle
strength (Sinaki et al. 1986; Sinaki and Offord
1988), physical activity (Sinaki and Offord 1988;
Shimegi et al 1994; Jacobson et al. 1984; Talmage et
al. 1986), and cardiorespiratory fitness (Pocock et
al. 1986; Chow et al. 1986). Longitudinal studies of
postmenopausal women have attributed increases
in both cardiorespiratory fitness and bone mass to
physical activity (Chow et al. 1987; Dalsky et al.
1988). There is some evidence that through physi-
cal activity, osteoporotic women can minimize bone
loss or facilitate some gain in bone mineral content
(Krslner et al. 1983; Kohrt et al. 1995). However,
other studies have failed to show such benefits
(Nelson et al. 1991; Sandler et al. 1989; Cavanaugh
and Cann 1988). The intensity of the physical
activity and the degree to which it stresses the bones
may be crucial factors in determiningwhether bone
mass is maintained. Thus it is likely that resistance
exercise may have more pronounced effects than
endurance exercise, although this has not yet been
unequivocally established.

Several investigators have found that the posi-
tive effect of physical activity on the bones of both
premenopausal and postmenopausal women depends

The Effects of Physical Activity on Health and Disease

on the presence of estrogen. In postmenopausal
women, greater gain in bone density accrues when
physical activity and estrogen replacement therapy
occur simultaneously (Prince et al. 1991; Kohrt et al.
1995). In young, premenopausal women, however,
excessive amounts of vigorous training may lead to
a low estrogen level and secondary amenorrhea, with
subsequent decreased bone mass and increased risk
of stress fractures (Marcus et al. 1985; Drinkwater et
al. 1984; Allen 1994).

The exercise-associated changes in bone mineral
density observed over time among both premeno-
pausal and postmenopausal women are much less
pronounced than those differences observed cross-
sectionally between active and sedentary persons
(Drinkwater 1993). Cross-sectional studies demon-
strate differences of lo-15 percent in bone mineral
density at various sites (Aloia et al. 1988; Lane et al.
1986; Michel, Bloch, Fries 1989; Reeker et al. 1992),
whereas intervention studies show smaller gains of
l-5 percent (Krslner et al. 1983; Dalsky et al. 1988;
Nelson et al. 1991; Pruitt et al. 1992; Drinkwater
1993). These differences may be due to differences in
comparison groups, to follow-up duration insuffi-
cient to show large changes in bone mineral density,
or to measurement at different skeletal sites. Still to
be conducted are well-designed randomized clinical
trials that are of sufficient size and duration to
determine definitively the longitudinal effects of
physical activity change or the differential effects
of resistance and endurance activity on bone mineral
density.

Biologic Plausibility

Bone is a dynamic tissue that is constantly remod-
eling its structure by resorption and formation.
Physical activity, through its load-bearing effect on
the skeleton, is likely the single most important
influence on bone density and architecture (Lanyon
1996). Bone cells respond to mechanical loading by
improving the balance between bone formation and
bone resorption, which in turn builds greater bone
mass (Lanyon 1987,1993). The higher the load, the
greater the bone mass; conversely, when the skel-
eton is unloaded (as with inactivity), bone mass
declines. Glucose-6-phosphate, prostaglandins, and
nitric oxide play a role in mediating the mechanical

131


Physical Activity and Health

loading effect on bone (Pitsillides et al. 1995; Turner
et al. 1995; Tang et al. 1995). Because it is muscle
that exerts the largest forces on bone during physi-
cal activity, the role.of muscle mass and strength in
maintaining skeletal integrity should be explored
more fully.

Nonmechanical factors, such as age, hormonal
milieu, nutritional intake, and medications, are in-
creasingly being recognized as important determi-
nants of the bone's response to mechanical loading
(Lanyon 1996). The relative contributions of each of
these factors are currently under study and are not
yet clearly delineated.  Animal studies confirm a
difference in bone response to mechanical loading
with age and by estrogen status (Turner, Takano,
Owan 1995). The potential clinical relevance of this
research is to better define the optimal amount and
type of exercise for maintaining or increasing bone
mass, particularly with aging or in the absence of
estrogen replacement therapy after menopause.

Physical Activity and the

Prevention of Fractures and Falling
Studies of physical activity in relation to hip frac-
ture in women have generally found a lower risk of
hip fracture among those who were more active.
Three cohort studies have reported such a protec-
tive effect. One showed a statistically significant
protective effect among those reporting the most
recreational activity at baseline (Farmer et al. 1989),
one showed inverse but not statistically significant
associations for both work and leisure-time physi-
cal activity (Meyer, Tverdal, Falch 1993), and one
showed a significant protective effect of walking for
exercise (Cummings et al. 1995). Case-control stud-
ies have been more equivocal. One such study
found a significant protective effect for two levels of
past activity, but for recent activity only moderate
amounts of activity showed a significant protective
effect (Jaglal, Kreiger, Darlington 1993):Another
case-control study showed inconsistent effects
across a variety of physical activity classifications
(Cumming and Klineberg 1994).
  Nonskeletal factors that increase the risk of
fractures due to falls include limitations in activi-
ties of daily living (e.g., dressing and feeding one-
self); compromised gait, balance, reaction time,

and muscle strength; impaired vision; medication
use; and environmental hazards (Dunn et al. 1992;
Gilligan, Checovich, Smith 1993; Tinetti, Speechley,
Ginter 1988; Cummings et al. 1995). Various exer-
cises may help prevent falls by improving muscle
strength, functional capacity, gait, balance, and
reaction time. Tinetti and colleagues (1994) showed
a significant decrease in falls in the elderly concomi-
tant with an improvement in balance and gait achieved
through exercise. Province and colleagues (1995)
demonstrated a protective effect against falls through
general exercise and exercises designed to improve
balance. Moreover, Fiatarone and colleagues (1994)
have shown that even frail elderly persons who have
multiple chronic diseases benefit substantially from
resistance training. This well-controlled random-
ized trial demonstrated the importance of strength
training in improving stair-climbing power, gait,
and other measures of physical function. Moderate
exercise-training techniques, such as tai chi chuan,
have also been shown to decrease falling and to
improve function in older adults by increasing or
maintaining aerobic power, strength, and balance
(Lai et al. 1995; Wolf et al. 1996; Wolfson et al.
1996).

Conclusions

Physical activity appears to build greater bone mass
in childhood and early adolescence and to help
maintain peak bone mass in adulthood. Among
women after menopause, physical activity may pro-
tect against the rapid decline in bone mass, but
findings are inconsistent in this regard, and it is
unclear whether muscle-strengthening (resistance)
activity may be more effective than endurance activ-
ity for this purpose. Estrogen replacement therapy
has been shown conclusively to decrease bone loss
after menopause, and there is evidence that this
effect is enhanced with physical activity. However, it
is not clear whether physical activity alone, in the
absence of estrogen replacement therapy, can pre-
vent bone loss.

Physical activity, including muscle-strengthen-
ing (resistance) exercise, appears to be protective
against falling and fractures among the elderly, prob-
ably by increasing muscle strength and balance.

132


Obesity

Obesity, a major public health problem in the United
States, plays a central role in the development of
diabetes mellitus (West 1978) and confers an in-
creased risk for CHD, high blood pressure, osteoar-
thritis, dyslipoproteinemia, various cancers, and
all-cause mortality (Hubert et al. 1983; Bray 1985;
Albanes 1987; Lee et al. 1993; Manson et al. 1995).
The progressive weight gain often observed between
the third and sixth,decades of life may be partly
explained by age-related changes: although energy
intake tends to decline after the second decade of life,
this decrease is insufficient to offset the greater
decline in the amount of energy that most people
expend throughout their adult years (Bray 1983;
Federation of American Societies for Experimental
Biology 1995). In addition to these age trends, popu-
lation surveys indicate that the age-adjusted preva-
lence of overweight among adults in the United
States has increased from about 25 percent in the
1970s to 33 percent in 1988-1991 (Kuczmarski et al.
1994). The increase is evident for all race and sex
groups. This phenomenon is believed to be due to
high rates of inactivity combined with easy access to
energy-dense food (Blackburn and Prineas 1983).
Obesity, defined as an excess of adipose tissue,
is difficult to measure in population-based studies.
Most investigations have therefore either used a
relative weight index, such as percent desirable
weight (Metropolitan Life Insurance Company
1959>, or have used BMI (defined by a ratio of
weight to height) as a surrogate measure. Quetelet's
index (weight [kg1/height[m]2> has been the most
frequently used BMI. Although these weight-height
indices are strongly correlated with more direct
measures of adiposity, such as underwater weighing,
they have limitations: fatty tissue cannot be distin-
guished from muscle mass or edema, and associa-
tions between weight-height indices and adiposity
may be nonlinear or may differ by age or ethnic group
(Harrison et al. 1985; Garn, Leonard, Hawthorne
1986; Lillioja and Bogardus 1988). Despite these
limitations, BMI has shown a monotonic association
with mortality in several recent cohort studies (Lee
et al. 1993; Manson et al. 1995; Willett et al. 1995).
  Using nationally representative data, the CDC
has defined overweight as a Quetelet's index at or
above the 85th percentile for 20- to 29-year-olds

(2 27.3 kg/m2 for women, 1 27.8 kg/m2 for men>,
corresponding to 120-125 percent ofdesirable weight
(NIH 1985; Kuczmarkski 1992; Kuczmarkski et al.
1994). The 95th percentile of Quetelet's index (32.3
kg/ml for women, 31.1 kg/m2 for men), equivalent to
a relative weight of approximately 145 percent, has
been used to classify persons as severely overweight.
Between 1976 and 1991, the mean weight of U.S.
adults increased by 3.6 kg (almost 8 pounds), and 58
million American adults (33 percent) are now con-
sidered to be overweight (Kuczmarski et al. 1994).
Because substantial weight loss in adults is diffi-
cult to achieve and maintain (Dyer 1994), childhood
obesity and its prevention have received increased
attention. Overweight children are likely to remain
overweight asadolescentsandadults (Johnston 1985)
and are subsequently at increased risk for high blood
pressure, diabetes, CHD, and all-cause mortality
(Abraham, Collins, Nordsieck 1971; Nieto, Szklo,
Comstock 1992; Must et al. 1992). Moreover, paral-
leling the trend seen among adults, the prevalence of
overweight amongU.S. children and adolescents has
increased substantially over the past decade (Shear et
al. 1988; Troiano et al. 1995).

Physical Activity and Obesity
It is commonly believed that physically active people
are less likely to gain weight over the course of their
lives and are thus more likely to have a lower preva-
lence of obesity than inactive people; accordingly, it
is also commonly believed that low levels of physical
activity are a cause of obesity. Few data, however,
exist to evaluate the truth of these suppositions.
Several cross-sectional studies report lower
weight, BMI, or skinfold measures among people
with higher levels of self-reported physical activity
or fitness (DiPietro 1995; Ching et al. 1996;
Williamson et al. 1993; French et al. 1994; Folsom et
al. 1985; Dannenberg et al. 1989; Slattery et al. 1992;
Gibbons et al. 1983; Voorrips et al. 1992). Prospec-
tive studies have shown less consistent results.
French and colleagues (1994) reported an inverse
association between leisure-time physical activity
(either walking or engaging in high-intensity activ-
ity) and later weight gain, and Ching and colleagues
(1996) found that physical activity was inversely
related to the risk of becoming overweight. Klesges
and colleagues (1992) reported that weight gain was

The Effects of Physical Activity on Health and Disease

133


Physical Activity and Health

inversely associated with leisure-time physical activ-
ity among women but not among men. Williamson
and colleagues (1993), however, found no associa-
tion between physicalactivityandsubsequent weight
change. Williamson and colleagues (1993) and
Voorrips and colleagues (1992) proposed that de-
creases in physical activity may be both a cause and
a consequence of weight gain over a lifetime and that
multiple measurements over time may be necessary
to characterize the interrelationship. One cohort
study that assessed changes in physical activity
reported that among women, decreased physical
activity performed as work was related to weight
gain; no associations were found among men
(Klesges et al. 1992).

The relationship between physical activity and
obesity in children is still under investigation. Some
studies comparing obese and nonobese children
have shown higher physical activity levels in
nonobese children (Johnson, Burke, Mayer 1956;
Bullen, Reed, Mayer 1964); others have shown little
or no relationship (Stefanik, Heald, Mayer 1959;
Bradfield, Paulos, Grossman 1971). Somewhat in-
consistent results have also been seen in cross-
sectional studies, with several finding lower BMIs or
skinfold measuresamongchildren with higher levels
of physical activity or fitness (Wolf et al. 1993;
Obarzanek et al. 1994; Strazzullo et al. 1988; Tell and
Vellar 1988) and some smaller studies finding no
association (Sallis et al. 1988; LaPorte et al. 1982).
More recently, two longitudinal studies have re-
ported inverse relationships between physical activ-
ity and triceps skinfold measures (Moore et al. 1995)
and BMI (Klesges et al. 1995) in young children. A
third longitudinal study (Ku et al. 1981) found a
significant negative association between physical
activity and percentage of body fat in boys but not
in girls. Additional longitudinal studies of children,
including measurement of changes in physical ac-
tivity, will help clarify whether physical activity
prevents the development of obesity. I
  Over the past two decades, several comprehen-
sive review articles (Oscai 1973; Stefanick 1993;
Thompson, Jarvie, et al. 1982; Wilmore 1983), as
well as two meta-analyses (Ballor and Keesey 1991;
Epstein and Wing 1980), have examined the impact
of exercise training on body weight and obesity.
These reviews conclude that 1) physical activity

generally affects body composition and weight fa-
vorably by promoting fat loss while preserving or
increasing lean mass; 2) the rate of weight loss is
positively related, in a dose-response manner, to the
frequency and duration of the physical activity ses-
sion, as well as to the duration (e.g., months, years)
of the physical activity program; and 3) although the
rate of weight loss resulting from increased physical
activity without caloric restriction is relatively slow,
the combination of increased physical activity and
dieting appears to be more effective for long-term
weight regulation than is dieting alone (Brownell
and Stunkard 1980; Kayman, Bruvbld, Stern 1990).
Independent of its effect on body weight and
total adiposity, physical activity may favorably af-
fect fat distribution. Several large cross-sectional
studies in Europe (Seidell et al. 1991), Canada
(Tremblay et al. 1990), and the United States (Kaye
et al. 1990; Slattery et al. 1992; Troisi et al. 1991;
Wing et al. 1991) report an inverse association
between energy expenditure from physical activity
and several indicators of central body fat distribu-
tion, such as the waist-to-hip ratio or the waist-to-
thigh-circumference ratio.

Biologic Plausibility

Increase in fat mass and the development of obesity
occur when energy intake exceeds total daily energy
expenditure for a prolonged period (Bray 1983;
Leibel, Rosenbaum, Hirsch 1995). Total energy ex-
penditure represents the sum of 1) resting energy
expenditure for maintaining basic body functions
(approximately 60 percent of total energy require-
ments); 2) the thermic effect of eating for digestion,
absorption, transport, and deposition of nutrients
(about 10 percent); and 3) nonrestingenergy expen-
diture, primarily in the form of physical activity
(about 30 percent) (Leibel, Rosenbaum, Hirsch
1995). This third component, nonresting energy
expenditure, is the most variable. Energy balance
tilts to weight gain when disproportionately more
energy is taken in; theoretically, about one pound
(or 0.45 kg) of fat energy is stored for each 3,500
kilocalories of excess energy intake. By increasing
nonresting energy expenditure, regular physical ac-
tivity contributes to weight maintenance and weight
reduction. Evidence supports the metabolic and

134


The Effects of Physical Activity on Health and Disease

physiological benefits of incorporating physical ac-
tivity into programs that prevent or manage obesity
(pi-Sunyer 1988; Leon 1989; Bouchard, Despr&,
Tremblay 1993; DiPietro 1995; Ewbank, Darga,
Lucas 1995).

Controversy exists over whether physical activ-
ity following a meal increases the thermic effect of
food ingestion and whether physical activity before
a meal reduces appetite. The evidence suggests that
physical activity programs do not necessarily pro-
duce a compensatory increase in food intake in obese
individuals (Woo, Garrow, Pi-Sunyer 1982a, 1982b).
Moreover, daily physical activity may further assist
in weight loss by partially reducing the decline in
resting energy expenditure that occurs during diet-
ing and associated weight loss (Lennon et al. 1985).
This effect is plausible because endurance exercise
and strength training may help preserve, to some
degree, metabolically active, lean body mass, whereas
caloric restriction does not (Hill, Drougas, Peters
1994; Ballor and Keesy 1991).
Because abdominal fat is more responsive than
glureal or lower-body fat to epinephrine stimula-
rion (Wahrenberg, Bolinder, Arner 1991), physical
activity may result in a more beneficial redistribu-
Zion of body fat in both sexes (Bouchard, Despres,
Trcmblay 1993). Further investigation, however,
is needed to clarify the associations between go-
&al hormone levels, baseline regional fat distri-
hution, and exercise-related changes in weight and
body fat distribution.

Conclusions

Physical activity is important for weight control. By
using energy and maintaining muscle mass, physical
ilctivity is a useful and effective adjunct to dietary
Inanagement for avoiding weight gain or losing
weight. Physical activity appears to favorably affect
distribution of body fat.

Mental Health

Mental disorders pose a significant public health
burden in the United States. Some disorders, such as
depression, are associated with suicide, which is
currently the ninth leading cause of death among
;imericans (NCHS 1996). A major cause of hospital-
ization and disability, mental disorders cost $148

billion per year, about half of which is due to severe
mental illness (National Advisory Mental Health
Council 1993).

The annual prevalence of mental disorders in the
United States population is high. Nearly three out of
10 persons 15-54 years ofage who live in households
report having had a mental disorder during the
previous year (Regier et al. 1993; Kessler et al. 1994).
The most frequently reported disorders are affective
(mood) and anxiety disorders. More than one out of
10 adults suffers from a depressive disorder in any
given year; between 13 and 17 percent suffer from an
anxiety disorder. Women report a higher prevalence
of affective and anxiety disorders than do men. Most
people with mental disorders do not obtain any
professional treatment; only one in five people with
a disorder during the previous year has received help
from a health service provider.
  Mental disorders, mental illnesses, mental
health, and psychological well-being relate to such
factors as mood or affect, personality, cognition,
and perception. Psychological constructs about
these factors are interrelated with a person's physi-
cal health status and quality of life. In studies of the
effects of physical activity on mental health, the
most frequently studied outcomes include mood
(anxiety, depression, negative affect, and to a lesser
extent, positive affect), self-esteem, self-efficacy,
and cognitive functioning. The general hypothesis
is that people who are physically active or have
higher levels of cardiorespiratory fitness have en-
hanced mood (less negative and greater positive
affect), higher self-esteem, greater confidence in
their ability to perform tasks requiring physical
activity (i.e., greater self-efficacy), and better cog-
nitive functioning than sedentary persons or those
who are less physically fit. One National Institutes
of Mental Health workshop (Morgan and Goldston
1987) and numerous recent reviews have been
devoted to this literature (Brown 1990; LaFontaine
et al. 1992; Landers and Petruzzello 1994; Martinsen
and Stephens 1994; McAuley 1994; McDonald and
Hodgdon 1991; Morgan 1994; North, McCullagh,
Tran 1990; Plante and Rodin 1990; Raglin 1990; Sime
1990). The effects of physical activity on most mental
disorders-including sleep and eating disorders,
schizophrenia, dementia, personality disorders, and
substance-related disorders-are not as well studied

135


Physical Activity and Health

(Dishman 1986; Taylor, Sallis, Needle 1985;
Martinsen and Stephens 1994).
This section focuses primarily on the association
of physical activity with anxiety and depression.
Evidence related to other psychological factors, such
as positive affect, self-esteem, self-efficacy, and cog-
nitive functioning, is discussed later in this chapter
in the "Health-Related Quality of Life" section.

Physical Activity and Mental Health
Epidemiologic research among men and women
suggests that physical activity may be associated
with reduced symptoms of depression (Ross and
Hayes 1988; Stephens 1988; Stephens and Craig
1990; Farmer et al. 1988; Camacho et al. 1991),
clinical depression (Weyerer 1992>, symptoms of
anxiety (Ross and Hayes 1988; Stephens 1988), and
improvements in positive affect (Stephens 1988;
Stephens and Craig 1990) and general well-being
(Stephens 1988). In general, persons who are inactive
are twice as likely to have symptoms of depression
than are more active persons.

Most epidemiologic and intervention studies on
the relationship of physical activity and mental health
have used self-report questionnaires to assess symp-
toms of anxiety and depression among persons from
the general population, although some studies have
focused on patients diagnosed by clinicians. These
questionnaires are useful for identifying persons
experiencing mental distress (i.e., symptoms of
anxiety or depression), but such identifications do
not necessarily correspond to diagnoses of anxiety or
depression by clinicians using standard interview
criteria (Fechner-Bates, Coyne, Schwenk 1994).

The literature suggests that physical activity helps
improve the mental health of both clinical and
nonclinical populations. Physical activity interven-
tions have benefited persons from the general popu-
lation who report mood disturbance (Simons and
Birkimer 1988; Wilfley and Kunce 1986), including
symptoms of anxiety (Steptoe et al. 1989) and de-
pression (Morgan et al. 1970), as well as patients
who have been diagnosed with nonbipolar,
nonpsychotic depression (Doyne et al. 1987; Klein et
al. 1985; Martinsen, Medhus, Sandvik 1985). These
findings are supported by a limited number of inter-
vention studies conducted in community and labo-
ratorysettings (Brown 1990; Landers and Petruzzello

1994; Martinsen and Stephens 1994; McAuley 1994;
Morgan 1994; Plante and Rodin 1990; Sime 1990).
Intervention studies have primarily evaluated the
effects of aerobic physical activities, such as brisk
walking and running, on mental health; how other
forms of physical activity, such as strength training,
affect mental health requires further study.
The psychological benefits of regular physical
activity for persons who have relatively good physi-
cal and mental health are less clear. Some interven-
tion studies have found that physical activity
provides mental health benefits to persons recruited
from the community who are without serious psy-
chological problems. These benefits included in-
creases in general well-being (Cramer, Nieman, Lee
1991) and reductions in tension, confusion (Moses
et al. 1989), and perceived stress and anxiety (King,
Taylor, Haskelll993). Other researchers have found
that few (Brown et al. 1995; Blumenthal et al. 1989;
King, Taylor, Haskell 1989) or no mental health
benefits (Hughes, Casal, Leon 1986; Lennox, Bedell,
Stone 1990) occurred among people without men-
tal disorders who participated in physical activity
interventions.

Most of these studies involved relatively small
sample sizes. Furthermore, the participants had little
opportunity to show improvement on objective and
standardized mental health measures, since their
baseline scores were already in the normal range or
lower on measures of negative affect and were in the
normal range or higher for positive affect. Evenwhen
no change was observed on objective measures, in
some of these studies, participants reported feeling a
subjective sensation of improved physical, psycho-
logical, or social well-being after participating in
regular physical activity (Blumenthal et al. 1989;
King, Taylor, Haskell 1993).

Psychological assessments that have been used
in physical activity research have included state and
trait measures. State measures, which reflect how a
person feels "right now," are particularly useful in
assessing changes in mood that occur before and
after an intervention, such as a single episode of
physical activity. Trait measures, which evaluate
how a person "generally" feels, focus on personality
characteristics that tend to be stable or sustained
across the life span. Although physical activity train-
ing programs can result in sustained psychological

136


benefits, many people after a single session of physi-
cal activity report improvements in transient moods,
such as reduced anxiety (Morgan 1979a; Roth 1989),
and have temporary reductions in muscular tension
(DeVries 1981; DeVries and Adams 1972). The re-
duction in anxiety may persist for 2 to 6 hours
following a session of physical activity (Landers and
Petruzzello 1994; Raglin and Morgan 1987). Regular
daily physical activity is required to experience this
calming effect on an ongoing basis. Some researchers
have thus proposed, that the episodic mental health
benefits associated with physical activity may act as
an important preventive measure that could lead to
the maintenance of mental health over time (Morgan
1981; Morgan et al. 1980; Raglin 1990).
A number of epidemiologic studies of noninsti-
tutionalized populations have evaluated the associa-
tions between self-reported levels of physical activity
and mental health. These studies typically assessed
retrospective self-reports of leisure-time physical
activity during the previous several weeks or more.
How these assessments relate to changes in cardio-
respiratory fitness is unknown. The available evi-
dence indicates, however, that increases in
cardiorespiratory fitness are not necessary for psy-
chological benefits to occur (Brown and Wang 1992;
King, Taylor, Haskelll989; Landers and Petruzzello
1994; Martinsen and Stephens 1994).
  Cross-sectional epidemiologic or community
population studies support an association between
physical activity and psychological well-being in
the general population. For example, in one cross-
sectional study using data generated from a state
telephone survey, researchers determined that adults
(n = 401) who spent more time participating in
regular exercise, sports, or other physical activities
had fewer symptoms of depression and anxiety than
persons reporting no physical activity or low levels of
participation (Ross and Hayes 1988). These associa-
tions were similar for men and women and for older
and younger adults. The cause-and-effect relation-
ship, however, cannot be determined because physi-
cal activity and mood were measured at the same
time.

Inanothercross-sectionalstudy (Stephens 1988),
secondary analyses of two Canadian surveys (n =
23,791 and 22,250 young people and adults) and two
U.S. surveys (n = 3,025 and 6,913 adults) conducted

between 1971 and 1981 associated physical activity
with fewer symptoms of anxiety and depression and
with higher positive mood and general well-being.
These associations were observed in all four surveys,
even though they used different measures of physical
activity and mental health, and were strongest among
women and among persons aged 40 years or older.
However, one of the Canadian surveys found that
women manifested higher positive affect when their
energy expenditure scores were based on recre-
ational activities only, rather than on a combination
of recreational and household activities. Hence,
mental health outcomes may depend on the type of
physical activities being performed and perhaps on
the setting in which they occur. This finding is
important in that investigators have typically evalu-
ated the mental health effects of recreational aerobic
activities, such as running, rather than occupational
and household activities.

A subsequent nationwide Canadian survey
(Stephens and Craig 1990) of approximately 4,000
respondents aged 10 years and older found that
persons who reported higher levels of total daily
leisure-time energy expenditure had a more positive
mood than persons reporting lower levels of expen-
diture. Persons aged 25 years and older demon-
strated an inverse relationship between physical
activity and symptoms of depression.
Although many cross-sectional studies suggest a
positive association between physical activity and
mental health, they do not necessarily indicate a
cause-and-effect relationship. Persons who have good
mental health may simply be more likely to be active.
Another possibility is that physical activity and men-
tal health vary together, in which case a third vari-
able, such as chronic health conditions, would
mediate this relationship.

Cohort studies provide additional insights into
whether physical activity contributes to the primary
prevention of mental health problems (Table 4-9).
In one cohort study of 1,900 U.S. adults, a cross-
sectional analysis of the baseline data revealed an
association between depressive symptoms and little
or no involvement in physical activity (Farmer et al.
1988). At 8-year follow-up, little or no recreational
physical activity was found to be a significant predic-
tor of increased depressive symptoms among white
women who had reported few depressive symptoms

The Effects of Physical Activity on Health and Disease

137


Physical Activity and Health

Table 4-9. longitudinal population-based studies of physical activity as related to depressive symptoms
                          Definition of             Definition of
Study       Population       physical activity                   cancer

Farmer et al.
(1988)

NHANES I
Follow-up Study
participants,
white adults,
aged 25-77 years,
1975 baseline

Camacho et al.    Alameda County, CA
(1991)        population study
         participants aged L 20
             years; or ever
married, 1965 baseline

Weyerer (1992)

German population    Regular, occasional, or no      Psychiatric interview
study participants      exercise at baseline based on     assessed depression at
aged 116 years at    single question: How often do you  follow-up (1980-l 984)
1975-l 979 baseline    currently exercise for sports?

Little or no exercise done for
recreation at baseline

Depressive symptoms
scores of (a) < 16 and
(b) z 16 at baseline

Self-reported frequency of
involvement in active sports,
swimming or walking, daily
exercise, and gardening;
(low = O-4, moderate = 5-8,
high = 9-14)

Depressive symptoms at
1974 follow-up
     .

Paffenbarger,
Lee, Leung
(1994)

Harvard alumni
study participants,
men aged 35-74 years,
1962 or 1966 baseline

(a) I 1 hour, l-2 hours, 3+      Physician-diagnosed
hours of sports play/week at    depression at 1988
baseline             follow-up

(b) < 1,000 kcal, 1 ,OOO-2,499 kcal,
or 2,500+ kcal/week at baseline

138


The Effects of Physical Activity on Health and Disease

Main findings

Dose    Adjustment for confounders
response*   and other comments

(a) Men: 1.3 (95% Cl, 0.5-3.1)
Women: 1.9 (95% Cl, 1 .l-3.2)
(b) Men: 12.9 (95% Cl, 1.7-98.9)
Women: 2.0 (95% Cl, 0.8-l 4.5)

Relative to high active,
low active men:
1.76 (95% Cl, 1.06-2.92)
moderate active men:
1.46 (95% Cl, 0.91-2.34)
low active women:
1.70 (95O/o Cl, 1.06-2.70)
moderate active women:
1 .OO (95% Cl, 0.63-l .59)

Relative to regular exercise,
men/no exercise:
1.15 (95% Cl, 0.30-4.36)
men/occasional exercise:
0.27 (95% Cl, 0.03-2.35)
women/no exercise:
0.70 (95% Cl, 0.30-l .62)
women/occasional exercise:
0.65 (95% Cl, 0.26-l .61)
Total/no exercise:
0.88 (9570 Cl, 0.44-l .77)
Total/occasional exercise:
0.70 (95% Cl, 0.30-l .50)

Relative to I 1 hour of sports play/week,
RR for l-2 hours = 0.96,
RR for 3+ hours = 0.73

Relative to < 1,000 kcal/week,
RR for 1 ,OOO-2,499 kcal/week = 0.83

NA

Yes

No

NA

NA

NA

No

NA

No

NA

No

Yes

Yes

Odds ratio adjusted for age, education,
chronic conditions, employment status,
household income, physical activity apart
from recreation at baseline, length of follow-up

Odds ratio adjusted for age, income, race,
smoking status, alcohol cbnsumption,
relative weight for height, education, chronic
conditions, physical symptoms/disability,
stress events, isolation, feelings of anomie

Odds ratio adjusted for age, social class,
and physical health

Adjusted for age

RR for 2,500 kcal/week = 0.72

Abbreviations: CI = confidence interval; NA = not available; NHANES = National Health and Nutrition Examination Survey; RR = relative risk.
`A dose-response relationship requires mbre than 2 levels of comparison. In this column. "NA" means that there were only
2 levels of comparison; "No" means that there were more than 2 levels but no dose-response gradient was found; "Yes" means
that there were more than 2 levels and a dose-response gradient was found.

139


Physical Activity and Health

at baseline. Among white men who had excessive
depressive symptoms at baseline, low levels of rec-
reational activity predicted continued depressive
symptoms at follow-up.

A cross-sectional analysis (Camacho et al. 1991)
of 1965 baseline data on 6,928 U.S. residents re-
vealed an inverse association between physical activ-
ity (low, moderate, and high levels of participation in
active sports, swimming or walking, doing exercises,
or gardening) and depressive symptoms. Follow-up
study of the men and women who had few depressive
symptoms in 1965 showed that those who had low
levels of physical activity were at greater risk than
their highly active counterparts for having a high
number of depressive symptoms in 1974.
A 23- through 27-year follow-up study of
10,201 Harvard alumni men revealed that level of
physical activity reported at an initial interview
in 1962 or 1966 was inversely related to self-
reported physician-diagnosed depression in 1988
(Paffenbarger, Lee, Leung 1994). Physical activity
in 1962 and 1966 was defined as the number of hours
per week spent doing physical activities (e.g., golf,
gardening, carpentry, tennis, swimming, brisk walk-
ing, jogging, or running); from this information, a
physical activity index was computed as kilocalories
of energy expended per week. In 1988, respondents
were asked whether they had ever been told by a
physician that they had health problems (e.g., CHD,
emphysema), including depression, and to list the
year of onset. Incidence of depression was deter-
mined by an attack first experienced (at a known age
of the respondent) during the follow-up period. This
study was unique in that the relationship between
physical activity and deaths due to suicides was also
evaluated. The incidence of suicide (as identified on
death certificates) was largely unrelated to the 1962
or 1966 physical activity history of the college alumni.
However, the relative risk of depression was 27
percent lower for men who had reported playing3 or
more hours of sports each week than for men who
had reported playing none. In addition,' men who
had expended 1,000 to 2,499 kilocalories per week
and those who had expended 2,500 kilocalories or
more per week were at 17 percent and 28 percent less
risk for depression, respectively, than men who had
expended fewer, than 1,000 kilocalories per week.

In a study of rural Europeans (n = 1,536), a
cross-sectional association was observed between
inactivity (no physical exercise or sports participa-
tion) and depression (diagnosed by research psy-
chiatrists) (Weyerer 1992). However, low levels of
physical activity at baseline were not a risk factor for
depression at 5-year follow-up for men or women in
this study.

Two of the epidemiologic studies reviewed above
examined a possible dose-response relationship. In
one study (Camacho et al. 199 l), the baseline preva-
lence of symptoms of depression was higher for per-
sons reporting low levels of physical activity than for
highly active persons; the risk was intermediate for
the moderately active group. At follow-up, the inci-
dence of depressive symptoms revealed a significant
difference only between persons in the lowest and
highest activity groups. In the second study
(Paffenbarger, Lee, Leung 1994), an inverse dose-
response gradient was found between the baseline
self-reported amount of physical activity calculated as
kilocalories per week (< 1,000,1,000-2,499,2 2,500)
and the follow-up incidence of physician-diagnosed
depression. Men who at baseline had reported no
hours of sports play per week had a similar follow-up
incidence of depression as men who reported 1 to 2
hours of weekly play; but men who had participated
in 3 or more hours of weekly play had a 27 percent
lower risk for developing depression than the least
active group.

The findings from these two studies provide
limited support for a dose-response relationship
between levels of physical activity and measures of
depressive symptoms or depression. However, among
some endurance athletes, mood disturbances (de-
creased vigor and increased fatigue, anxiety, and
symptoms of depression) have been observed with
overtraining; mood improved after training was ta-
pered (Morgan et al. 1987). It is therefore conceiv-
able that for the general population, too strenuous a
physical activity regimen may lead to deleterious
effectson mental health (Morgan 1979b, 1994; Polivy
1994; Raglin 1990). To date, research has not iden-
tified a threshold or an optimal frequency, duration,
or intensity of physical activity necessary to improve
mental health status.

140


Biologic Plausibility

Some researchers have proposed that exercise-
induced changes in brain neuroreceptor concentra-
tions of monoamines (norepinephrine, dopamine,
or serotonin) (Ransford 1982) or endogenous opi-
ates (endorphins and enkephalins) (Moore 1982)
may help to favorably alter mood. The increased core
body temperature that occurs from physical activity
may also decrease muscle tension (DeVries 1981).
Other hypothalamic, metabolic, hormonal, or car-
diorespiratory changes that result from training may
eventually be linked to enhanced mental health.
Psychosocial aspects of physical activity, such as
having the opportunity for social interaction and
support (Hughes, Casal, Leon 1986), experiencing
increased feelings ,of self-mastery and self-efficacy
(Simons et al. 1985; Hughes, Casal, Leon 1986), and
experiencing relief from daily stressors (Bahrke and
Morgan 1978), may improve mental health status in
some people.

Conclusions

The literature reported here supports a beneficial
effect of physical activity on relieving symptoms of
depression and anxiety and on improving mood.
There is some evidence that physical activity may
protect against the development of depression, al-
though further research is needed to confirm these
findings.

Health-Related Quality of Life
For several decades, it has been recognized that
health should not be defined simply as the absence of
disease and disability; rather, health is now concep-
tualized by the World Health Organization as a
positive state of physical, mental, and social well-
being (World Health Organization 1947). This rec-
ognition has resulted in an increasing clinical,
scientific, and public interest in the assessment and
promotion of health-related quality of life (HRQL).
Kaplan and Bush (1982) introduced the term
HRQL to capture the influence that health status and
health care have on the quality of day-to-day life.
Viewed as a multidimensional construct that repre-
sents a person's overall satisfaction with life, HRQL
includes the following dimensions: cognitive, so-
cial, physical, and emotional functioning; personal

The Effects of Physical Activity on Health and Disease

productivity; and intimacy (Shumaker, Anderson,
Czajkowski 1990). Rejeski, Brawley, and Shumaker
(1996) have shown that physical activity has signifi-
cant potential to influence HRQL. The most direct
effects are likely in the areas of psychological well-
being (e.g., self-concept, self-esteem, mood, and
affect), perceived physical function (e.g., perceived
ability to perform activities of daily living), physical
well-being (e.g., perceived symptoms and perceived
physical states, such as dyspnea, pain, fatigue, and
energy), and, to a limited extent, cognitive function.
In a recent review, McAuley (1994) concluded
that a positive association exists between physical
activity habits and self-esteem in both young adults
and children. The strength of this relationship in-
creases when physical activity is personally valued
and when measures of psychological well-being are
specific rather than general. Among nonclinical and
clinical samples of men and women, this association
is observed both with the long-term effects of exer-
cise training and with the immediate, short-term
effects of a single episode of activity.
  In a review of studies of middle-aged participants
(mean age, 56.7 years), McAuley and Rudolph (1995)
found correlations between involvement in physical
activity and psychological well-being that were simi-
lar to those patterns observed among younger per-
sons. Further, the strength of these relationships was
directly related to the length of time that the partici-
pants had been involved in physical activity programs.
This moderating effect requires cautious interpreta-
tion because of the possibility of selective adherence.
There was little evidence that the relationship be-
tween physical activity and psychological well-being
was affected by either sex or age. Finally, although a
number of studies noted improvements in both the
cardiorespiratory fitness and the psychological well-
being of older adults, these improvements were not
necessarily correlated (McAuley and Rudolph 1995).
Involvement in physical activity may thus increase the
psychological well-being of older adults indepen-
dently of cardiorespiratory fitness (Brown and Wang
1992; King, Taylor, Haskell 1989; Landers and
Petruzzello 1994; Martinsen and Stephens 1994;
McAuley and Rudolph 1995).

Other data suggest that physical activity is re-
lated to perceived improvement in physical function
in activities of daily living. However, there is a limit

141


Physical Activity and Health

to this effect, since sedentary people can usually do
their daily tasks. Most research on this aspect of
HRQL is thus confined to populations of people who,
because of health problems, have restrictions in their
activities of daily living. The growing body of litera-
ture on this topic indicates that patients whose
physical function is compromised by heart disease
(Ewart 1989) or arthritis (Fisher et al. 1993) expe-
rience improved daily function from increases in
physical activity.

HRQL requires a number of different types of
measurements; however, few studies on physical
activity have used a multidimensional measure-
ment scheme. Exceptions include a randomized
clinical trial involving healthy elderly persons
(Stewart, King, Haskell 1993) and a 2-year obser-
vational study of persons with chronic disease
(Stewart et al. 1994). In the clinical trial, healthy
persons who were assigned to endurance exercise
had better self-reported ratings of their physical
functioning and health (e.g., physical and role func-
tion, experiencing of pain, perception of health
status) than control participants, yet endurance
training brought no changes in self-reported en-
ergy/fatigue, psychological distress, or psychologi-
cal well-being. By contrast, among persons with
chronic diseases, physical activity was associated
with improvement in both psychological well-be-
ing and physical function; however, the magnitude
of these effects was highly dependent on the status
of the patient's chronic disease. Participants who
have lower levels of mental or physical health may
have the most to gain from physical activity (Lennox,
Bedell, Stone 1990; Morgan et al. 1970; Simons and
Birkimer 1988; Rejeski et al. 1995), since they have
more room to improve their health status than
people already possessing good health.
  A relatively small number of cross-sectional stud-
ies have shown a strong positive association be-
tween regular physical activity and cognitive and
neuropsychological performance on tasks such as
math, acuity, and reaction time (Dustman,
Emmerson, Shearer 1994; Thomas et al. 1994).
However, longer-term training studies (2 or more
years) are required to confirm whether aerobic
exercise has a pronounced effect on cognitive func-
tion. Also unclear are whether the effects of low-
-intensity physical activity are similar to those of

aerobic exercise and whether objective measures of
cognitive function can elucidate the perceived cog-
nitive function of participants (Dustman, Emmerson,
Shearer 1994).

Conclusions

Physical activity appears to improve psychological
well-being. Among people compromised by ill health,
physical activity appears to improve their ability to
perform activities of daily living.

Adverse Effects of Physical Activity

Although physical activity has numerous health ben-
efits, its potential adverse effects must also be consid-
ered. Listing the potential risks associated with
physical activity is a straightforward matter. It is
much more difficult to determine how commonly
they occur among people who are physically active.

Types of Adverse Effects
Musculoskeletal Injuries

Acute stress from sudden forceful movement can
cause strains, tears, and even fractures. For example,
a vigorous swing of a baseball bat can lead to a
dislocated shoulder. An attempt to accelerate for-
ward in tennis can tear an Achilles tendon. Bending
to retrieve an object can rupture an intervertebral
disc. Injuries like these can result from any activity,
exercise, or sport that features sudden movements,
such as those that can occur in professional or
amateur track and field, racquet sports, basketball,
baseball, football, soccer, and golf. Collisions with
equipment, other participants, and surfaces can also
produce severe injury. Children and adolescents
with developing bodies are at special risk of perma-
nent physical damage if injury occurs to the growth
plates of long bones or to other bone or connective
tissue structures.

Activities that involve repetitive motions, some-
times with traumatic contact with a ground surface
or ball, are associated with other musculoskeletal
injuries. An extensive literature describes injuries
related to jogging and running (Hoeberigs 1992;
Rolf 1995; Van Mechelen 1992). Lower-extremity
injuries appear to be the most common; of these,

142


The Effects of Physical .Activity on Health and Disease

the knee, ankle, and foot have the highest propor-
tions of injuries (e.g., torn cartilage, tendinitis,
plantar fasciitis, neuromas, and shinsplints). Inju-
ries are also seen in excessive bicycling (e.g., ulnar
nerve palsies, ischial bursitis [Cohen 1993; Mellion
1991; PfeifferandKronisch 1995]), swimming(e.g.,
shoulder pain [Allegrucci, Whitney, Irrgang 1994;
Johnson, Sim, Scott 1987]), racquet sports (e.g.,
epicondylitis [Kamien 19901)) aerobic dancing (e.g.,
shin painand plantar fasciitis [Richie, Kelso, Bellucci
1985]), and rowing (e.g., back and knee injuries
[Howell 19841).

Metabolic Abnormalities

Severe exertion, particularly of prolonged duration
and under hot or humid conditions, can lead to
hyperthermia, electrolyte imbalance, and dehydra-
tion (Englandet al. 1982; Frizzell et al. 1986; Surgenor
and Uphold 1994). Timely fluid intake and replace-
ment, with proper electrolyte and caloric composi-
tion, can prevent or ameliorate such metabolic upsets.
Hypothermia is a risk in many water sports and for
any activities undertaken in cold weather (or even
cool weather if inadequate clothing is worn). Ex-
treme endurance training regimens can lead to endo-
crine system alterations, sometimes resulting in
anovulation and amenorrhea in females, in associa-
tion with a decrease in body weight below a critical
lean mass, as well as with a decrease in bone mass
(Shangold 1984). Hypoglycemia can occur in people
with diabetes if they do not develop a routine of
regular activity in conjunction with regular monitor-
ing of their blood sugar (and adjustment of their
medication accordingly).

Hematologic and Body Organ Abnormalities
Anemia is reported in athletes vigorously engaged in
sports such as long-distance running; hemoglobin-
uria can occur secondary to breakage of red blood
cells during the repetitive impact of distance run-
ning, and hematuria can occur when distance run-
ning traumatizes the bladder 0; other structures in
the genitourinarysystem. Rhabdomyolysis, the leak-
age of contents of muscle cells, can occur as a result
of strenuous activity, such as weight lifting or mili-
tary basic training, and can lead to renal failure
(Kuipers 1994; Sinert et al. 1994).

Hazards

Cyclists, runners, and walkers often face risks asso-
ciated with travel on roadways-collisions with motor
vehicles, injuries from falls secondary to uneven
surfaces, and attacks by animals or humans. Skiers
and skaters must contend with falls at high veloci-
ties. Baseball players may be.struck by a thrown or
batted ball or injured by a spike-soled shoe. Basket-
ball and soccer entail collisions with other players
and frequent falls to hard surfaces. Football, hockey,
and boxing, by their very nature, are sports where
sanctioned and moderately controlled interpersonal
violence often leads to contusions, lacerations, mus-
culoskeletal injury, and fractures, as well as to
concussions and chronic disability (Kraus and
Conroy 1984).

Infectious, Allergic, and
Intlammatory Conditions

Swimming increases the risk of otitis externa
("swimmer's ear"). Overtrained athletes may have an
increased risk of infections from immunosuppres-
sion (Newsholme and Parry-Billings 1994). Exer-
tion may provoke asthmatic attacks, usually occurring
after exercise in susceptible individuals (Anderson,
Daviskas, Smith 1989).

Cardiac Events

As was discussed earlier in this chapter, regular
physical activity improves cardiorespiratory fitness
and reduces the risk of CVD mortality over the long
term, although it can acutely increase risk for un-
toward cardiac events in the short term. Persons with
compromised coronary circulation may develop an-
gina or acute myocardial infarction during vigorous
activity (Mittleman et al. 1993; Willich et al. 1993).
Arrythmias may be precipitated by a combination of
exertion and underlying heart disease, and some can
lead to sudden death (Kohl et al. 1992; Koplan 1979;
Siscovick et al. 1984; Thompson, Funk, et al. 1982).
Compared with sedentary people who suddenly
begin exercising vigorously, persons who exercise
regularly have a lower risk of exercise-related sud-
den death, although even this group has a transient
elevation of risk during and immediately after vig-
orous exercise (Kohl et al. 1992; Siscovick et al.
1984). Nonetheless, the net effect of regular physi-
cal activity is to decrease the risk of cardiac death.

143


Physical Activity and Health

Occurrence of Adverse Effects
Determining the incidence or prevalence of adverse
effects of physical activity, or factors that influence
the likelihood of their occurrence, is hampered by
not knowing how many people have similar physical
activity patterns and are thus similarly at risk of an
adverse event, or how many inactive people sustain
similar injuries. Nevertheless, a few studies have
provided some insight into the occurrence of adverse
events. Of the activities that are common in the
United States, including jogging/running, walking,
gardening, bicycling, swimming, aerobic dance, and
softball, running has received the most attention by
researchers.

Injuries among runners are common, ranging
from 25 through 65 percent (Jones, Cowan, Knapik
1994). Most running-related injuries involve the
leg and foot and are usually self-correcting in a
relatively short time. Studies of such injuries have
generally shown that occurrence of musculoskel-
eta1 injury is directly related to mileage run (Blair,
Kohl, Goodyear 1987; Hoeberigs 1992; Koplan et
al. 1982; Macera 1992; Macera et al. 1989; Marti
1988; Marti et al. 1988; Walter et al. 1989) or to
frequency or duration of running (Pollock et al.
1977). Previous injury appears to be a risk factor for
subsequent injury. In one small study of people
aged 70-79 years, the injury rate was lower for
walking than jogging (5 percent vs. 57 percent)
(Pollock et al. 1991). Whether this finding is true
only among the elderly or is characteristic of these
activities at all ages remains to be determined.

Although few studies of aerobic dance have been
conducted, the injury rate appears to be higher
among those taking more than 4 classes per week
(Richie, Kelso, Bellucci 1985).

Conclusions

A wide spectrum of adverse events can occur with
physical activity, ranging from those that cause mi-
nor inconvenience to those that are life-threatening.
At least some of the musculoskeletat injuries are
likely to be preventable if people gradually work up
to a physical activity goal and avoid excessive amounts
of physical activity or excessively high levels of
intensity. Although adverse cardiac events are more
likely to occur with physical exertion, the net effect

of regular physical activity is a lower CVD mortality
rate among active than inactive people (see earlier
sections of this chapter).

People should be advised not to undertake physi-
cal activities well beyond their normal level of exer-
tion. Inactive people wishing to begin a new program
of moderate activity should begin with short dura-
tions and gradually lengthen them toward their
target. Men over age 40 and women over age 50 who
wish to begin a new program involving vigorous-
intensityactivity,peoplewho have preexisting health
problems, and people who are at high risk of CVD
should consult a physician before embarking on a
program of physical activity to' which they are
unaccustomed (ACSM 1991).

Nature of the
Activity/Health Relationship
Causality

The studies reviewed in this chapter indicate that
physical activity is associated with a reduction in risk
of all-cause mortality, all CVDs combined, CHD,
hypertension, colon cancer, and NIDDM. To evalu-
ate whether the information presented is sufficient to
infer that these associations are causal in nature, it is
useful to review the evidence according to Hill's
classic criteria for causality (Hill 1965; Paffenbarger
1988).

Strength ofAssociation. The numerous estimated
measures of association for cardiovascular outcomes
presented in this chapter generally fall within the
range of a 1.5- to 2.0-fold increase in risk of adverse
health outcomes associated with inactivity. This
range represents a moderately strong association,
similar in magnitude to the relationship between
CHD and smoking, hypertension, or elevated cho-
lesterol. The associations with NIDDM, hyperten-
sion, and colon cancer have been somewhat smaller
in magnitude. The difficulty in measuring physical
activity may lead to substantial misclassification,
which in turn would bias studies toward finding less
of an effect of activity than may actually exist. On the
other hand, not controlling for all potential con-
founders could bias studies toward finding more of
an effect than may actually exist. Efforts to stratify
studies of physical activity and CHD by the quality of

144


measurement have found that the methodologically
better studies showed larger associations than those
with lower quality scores (Powell et al. 1987; Berlin
and Colditz 1990). In addition, cardiorespiratory
fitness, which is more objectively and precisely mea-
sured than the reported level of physical activity,
often is also more strongly related to CVD and
mortality. Measures of association between physical
activity and health outcomes thus might be stronger if
physical activity measurements were more accurate.
Consistency ofFindings. Although the epidemio-
logic studies of physical activity have varied greatly
in methodology, in ways of classifying physical activ-
ity, and in populations studied, the findings have
been remarkably consistent in supporting a reduc-
tion in risk as a function of greater amounts of
physical activity, or conversely, an increase in risk as
a function of inactivity.

Temporality. For most of the health conditions
included in this chapter (all-cause mortality, CVD,
CHD, hypertension, NIDDM), longitudinal data from
cohort studies have been available and have con-
firmed a temporal sequence in which physical activ-
ity patterns are determined prior to development of
disease. For obesity and mental health, fewer longi-
tudinal studies have been conducted, and findings
have been more equivocal. Perhaps the strongest
evidence for temporality comes from two studies of
the effect of changes in activity or fitness level. Men
who became more active or more fit had a lower
mortality rate during follow-up than men who re-
mained inactive or unfit (Paffenbarger et al. 1993;
Blair et al. 1995).

Biological Gradient. Studies of all-cause mortal-
ity, CVD, CHD, and NIDDM have shown a gradient
of greater benefit associated with higher amounts of
physical activity. Most studies that included more
than two categories of amount of physical activity
and were therefore able to evaluate a dose-response
relationship found a gradient of decreasing risk of
disease with increasing amounts of physical activity
(see Tables 4-l through 4-S).   .
Biofogic Plausibility. Evidence that physiologic

effects of physical activity have beneficial conse-
quences for CHD, NIDDM, and obesity is abundant
(see Chapter 3, as well as the biologic plausibility
sections of this chapter). Such evidence includes
beneficial effects on physiologic risk factors for

The Effects of Physical Activity on Health and Disease

disease, such as high blood pressure and blood
lipoproteins, as well as beneficial effects on circula-
tory system functioning, blood-clotting mecha-
nisms, insulin production and glucose handling,
and caloric balance.

Experimental Evidence. Controlled clinical trials
have not been conducted for the outcomes of mor-
tality, CVD, cancer, obesity, or NIDDM. However,
randomized clinical trials have determined that
physical activity improves these diseases' risk fac-
tors, such as blood pressure, lipoprotein profile,
insulin sensitivity, and body fat.
The information revieyed in this chapter shows
that the inverse association between physical activity
and several diseases is moderate in magnitude, con-
sistent across studies that differed substantially in
methods and populations, and biologically plau-
sible. A dose-response gradient has been observed in
most studies that examined more than two levels of
activity. For most of the diseases found to be in-
versely related to physical activity, the temporal
sequence of exposure preceding disease has been
demonstrated. Although controlled clinical trials
have not been conducted (and are not likely to be
conducted) for morbidity and mortality related to
the diseases of interest, controlled trials have shown
that activity can improve physiologic risk factors for
these diseases. From this large body of consistent
information, it is reasonable to conclude that physi-
cal activity is causally related to the health outcomes
reported here.

Population Burden of Sedentary living
Given that the relationship between activity and
several diseases is likely to be causal, it follows that
a large number of Americans unnecessarily become
ill or die each year because of an inactive way of life.
Published estimates of the number of lives lost in a
year because of inactivity have ranged from 200,000
for inactivity alone to 300,000 for inactivity and poor
diet combined (Hahn et al. 1990; Powell and Blair
1994; McGinnis and Foege 1993). Such estimates are
generally derived by calculating the population at-
tributable risk (PAR), which is based on both the
relative mortality rate associated with inactivity and
the prevalence of inactivity in the population. Such
estimates are inherently uncertain because they do

145


Physical Activity and Health

not take into account the reality that some people
have more than one risk factor for a disease; for these
people, the elimination of a single risk factor (e.g., by
becoming physically active) may not reduce mortal-
ity risk to the level attainable for people who initially
have only that one risk factor. PAR methods thus
overestimate the proportion of deaths avoidable by
eliminating one modifiable risk factor, in this case
physical inactivity. On the other hand, PAR esti-
mates of avoidable mortality do not address other
important aspects of the population burden of sed-
entary living. The benefits of reducing the occur-
rence of CHD, colon cancer, and diabetes greatly
surpass the benefits of reducing premature mortal-
ity, yet the reductions in avoidable disease, disabil-
ity, suffering, and health care costs have not been
calculated. Similarly, the health benefits ofimproved
mood, quality of life, and functional capacity have
not been quantified. Although the total population
burden of physical inactivity in the United States has
not been quantified, sedentary living habits clearly
constitute a major public health problem.

Dose

Using the epidemiologic literature to derive recom-
mendations for how much and what kind of physical
activity a person should obtain is problematic, in
part because the methods for measuring and classi-
fying physical activity in epidemiologic studies are
not standardized. Measurement of physical activity
generally relies on self-reported information in re-
sponse to questionnaires, although some studies use
occupation to categorize a person's presumed level
of physical activity at work. Responses to questions
or occupational activity categories are usually trans-
formed, using a variety of methods, into estimates of
calories expended per week, minutes of activity per
week, categories of total activity, or other types of
composite scores.

Numerous studies have used this type of infor-
mation to estimate total amount of activity, and
many have been able to explore dose-response rela-
tionships across categories of activity amount. For
the most part, these studies demonstrate that amount
of benefit is directly related to amount of physical
activity (see Tables 4-l through 4-S), rather than
showing a threshold level of activity necessary before
health benefits accrue. Such studies are less helpful,

however, in assessing the relationship of health
benefits to intensity of physical activity (i.e., how
hard one must work during the activity itself) be-
cause few studies have separately measured or ana-
lyzed levels of intensity while taking into account the
other dimensions of activity (e.g., frequency, dura-
tion, total caloric expenditure). As described earlier,
however, for some health benefits (e.g., blood pres-
sure lowering), clinical trials of exercise intensity
suggest similar, if not greater, benefit from moderate-
as from vigorous-intensity exercise.
It is often asked how little physical activity a
person can obtain and still derive health benefit.
Although the dose-response relationship appears
not to have a lower threshold, thereby indicating
that any activity is better than none, some
quantitation of a target "dose" of activity is helpful
for many people. It has been shown that total
amount of physical activity (a combination of in-
tensity, frequency, and duration) is related to health
outcomes in a dose-response fashion, but the abso-
lute difference in amount of physical activity in
kilocalories of energy expended between exposure
categories has not been estimated routinely. Several
studies, however, have estimated average caloric
expenditure for the activity categories studied and
thus allow quantitation of amount of physical activ-
ity associated with improved health outcomes.
Paffenbarger and colleagues (1986) found that com-
pared with the least active group in the study, those
who expended 71-143 kilocalories of energy per
day had a 22 percent reduction in overall mortality,
and those who expended 143-214 kilocalories per
day had a 27 percent reduction. Leon and col-
leagues (1987) showed that a difference of about 30
minutes per day of activity (light, moderate, and
vigorous activity combined), equivalent to an aver-
age difference of about 150 kilocalories of energy
expended per day, was associated with a 36 percent
lower risk of CHD mortality and a 27 percent lower
risk of all-cause death, after the analysis adjusted
for other factors that can effect CHD and total
mortality. Slattery and colleagues (1989) found
that a daily average of 73 more kilocalories of total
activity than were expended among the least active
group was associated with a 16 percent reduction in
CHD mortality and a 14 percent reduction in all-cause
mortality. Furthermore, in the majority (62 percent)

146


The Effects of Physical Activity on Health and Disease

of that study population, no vigorous activity was
reported. In that group, a daily average of 150
kilocalories greater expenditure in light-to-moderate
activity was associated with a 27 percent lower
CHD mortality and a 19 percent lower total mortal-
ity. The effects of light-to-moderate activity on
CHD death remained significant after the analysis
adjusted for potential confounders. Similarly, in a
study of NIDDM (Helmrich et al. 199 1) that showed
a significant inverse trend between kilocalories
expended in activity and development of NIDDM,
total activity of 140-215 kilocalories per day was
associated with a 21 percent reduction in NIDDM
onset. In the group that obtained this level of
energy expenditure without any vigorous sports
participation, the reduction in NIDDM onset was
13 percent.

Based on these studies, it is reasonable to con-
clude that activity leading to an increase in daily
expenditure of approximately 150 kilocalories/day
(equivalent to about 1,000 kilocalories/week) is as-
sociated with substantial health benefits and that the
activity does not need to be vigorous to achieve
benefit. It should be emphasized that this is an
estimate based on few studies, atid that further re-
search will be required to refine it. For example, it is
not clear whether it is the total amount of caloric
expenditure or the amount of caloric expenditure
per unit of body weight that is important. Nonethe-
less, this amount of physical activity can be obtained
in a variety of ways and can vary from day to day to
meet the needs and interests of the individual. An
average expenditure of 150 kilocalories/day (or 1,000
kilocalories/week) could be achieved by walking
briskly for 30 minutes per day, or by a shorter
duration of more vigorous activity (e.g., 15 minutes
of running at 10 minutes per mile), or by a longer
duration of more vigorous activity less frequently
(e.g., running at 10 minutes per mile for about 35
minutes 3 times per week). Other sample activities
are provided in Table 4-10.

In addition to the health effects'associated with
a moderate amount of physical activity, the dose-
response relationships show that further increases in
activity confer additional health benefits. Thus people
who are already meeting the moderate activity rec-
ommendation can expect to derive additional benefit
by increasing their activity. Since amount of activity

is a function of intensity, frequency, and duration,
increasing the amount of activity can be accom-
plished by increasing any, or all, of those dimensions.
There is evidence that increasing physical activ-
ity, even after years of inactivity, improves health.
Studies of the health effects of increasing physical
activity or fitness (Paffenbarger et al. 1993; Blair et al.
1995) have shown a reduced mortality rate in men
who become more active or more fit compared with
those who remain sedentary. This benefit was appar-
ent even for men who became physically active after
the age of 60.

Most importantly, a regular pattern of physical
activity must be maintaintd to sustain the physi-
ologic changes that are assumed responsible for the
health benefits (see Chapter 3). Thus it is crucial for
each person to select physical activities that are
sustainable over the course of his or her life. For
some people, a vigorous workout at a health club is
the most sustainable choice; for others, activities
integrated into daily life (e.g., walking to work,
gardening and household chores, walking after din-
ner) may be a more sustainable option. Periodic
reevaluation may be necessary to meet changing
needs across the life span.

A related issue of pattern of physical activity
(frequency and duration in the course of a day) has
recently come under review. Three studies have held
constant both total amount of activity and intensity of
activity while daily pattern was varied (one long
session versus shorter, more frequent sessions). Two
studies showed equivalent increases in cardiorespira-
tory fitness (Jakicic et al. 1995; Ebisu 1985). One
study showed gains in cardiorespiratory fitness for
both the "short bout" and "long bout" groups, al-
though on one of three measures (maximal oxygen
uptake versus treadmill test duration and heart rate at
submaximal exercise), the gain in fitness was signifi-
cantly greater in the long bout group (DeBusk et al.
1990). These observations give rise to the notion that
intermittent episodes of activity accumulated in the
course of a day may have cardiorespiratory fitness
benefits comparable to one longer continuous epi-
sode. Whether this assumption holds true for the
outcomes of disease occurrence and death remains to
be determined. Nevertheless, some previous observa-
tional studies have shown lower rates of CHD, CVD,
and all-cause mortality among people with an active

147


Physical Activity and Health

Table 4-l 0. Duration of various activities to expend 150 kilocalories for an average 70 kg adult

                                       Metabolic       Approximate
                             equivalents          duration
Intensity       Activity                       METS'          in minutes+


Moderate       Volleyball, noncompetitive               3.0               43

Moderate      Walking, moderate pace (3 mph,
           20 min/mile)                       3.5               37

Moderate       Walking, brisk (4 mph, 15
                       pace       min/mile)       4.0              32

Moderate        Table tennis                         4.0               32

Moderate       Raking leaves                       4.5               32

Moderate       Social dancing                        4.5               29

Moderate       Lawn mowing (powered push mower)         4.5               29

Hard        Jogging (5 mph, 12 min/mile)               7.0               18

Hard         Field hockey                        8.0               16

Very hard      Running (6 mph, 10 min/mile)             10.0               13

`Based on average METS in Ainsworth et al. 1993.
+Formula:  150 kcal x 60 min/hour = minutes
      METS (kcal/k@hr) x kg

lifestyle that included activities such as walking, stair
climbing, household or yard work, and gardening-
activities that are often performed intermittently (Leon
et al. 1987; Paffenbarger et al. 1986). This informa-
tion, together with evidence that some people may
adhere better to an exercise recommendation that
allows for accumulating short episodes of activity as
an alternative to one longer episode per day (lakicic
et al. 1995), supports the notion that accumulation of
physical activity throughout the day is a reasonable
alternative to setting aside an uninterrupted period of
time for physical activity each day. Although more
research is clearly needed to better define the differ-
ential effects of various patterns of activity, experts
have agreed that intermittent episodes of activity are
more beneficial than remaining sedentary. This con-
sensus is reflected in recent physica activity recom-
mendations from the CDC and the ACSM (Pate et al.
1995) and from the NIH Consensus Development
Panel on Physical Activity and Cardiovascular Dis-
ease (see Chapter 2, Appendix B).

Conclusions

The findings reviewed in this chapter form the basis
for concluding that moderate amounts of activity
can protect against several diseases. A greater de-
gree of protection can be achieved by increasing the
amount of activity, which can be accomplished by
increasing intensity, frequency, or duration. None-
theless, modest increases in physical activity are
likely to be more achievable and sustainable for
sedentary people than are more drastic changes, and
it is sedentary people who are at greatest risk for
poor health related to inactivity. Thus the public
health emphasis should be on encouraging those
who are inactive to become moderately active. These
conclusions are consistent with the recent CDC-
ACSM recommendations for physical activity (Pate
et al. 1995) and the NIH Consensus Development
Conference Statement on Physical Activity and Car-
diovascular Health (see Chapter 2, Appendix B),
which emphasize the importance of obtainingphysi-
cal activity of at least moderate amount on a regular
basis. The recommendations also encourage those

148


The Effects of Physical Activity on Health and Disease

who are already moderately active to become more
active to achieve additional health benefits, by
increasing the intensity, duration, or frequency of
physical activity. Further study is needed to deter-
mine which combinations of these interrelated fac-
tors are most important for specific health benefits.
Most important, however, is the recognition that
physical activity recommendations should be tai-
lored to an individual's needs and preferences.
Encouraging sedentary people to become moder-
ately active is likely to reduce the burden of unnec-
essary suffering and death only if the activity can be
sustained on a daily basis for many years.

Chapter Summary

Despite the variety of methods used to measure
and classify physical activity, the imprecision of
these measures, and the considerable variation in
study designs and analytic sophistication, several
findings consistently emerge from the epidemio-
logic literature on physical activity and health.
Physical activity of the type that improves cardio-
respiratory endurance reduces the risk of develop-
ing or dying from CVD (CHD in particular),
hypertension, colon cancer, and NIDDM and im-
proves mental health. Findings are highly sugges-
tive that endurance-type physical activity may
reduce the risk of developing obesity, osteoporo-
sis, and depression and may improve psychologi-
cal well-being and quality of life. There is promising
evidence that muscle strengthening (resistance)
exercise reduces the risk of falling and fractures
among the elderly. Furthermore, there appears to
be a dose-response relationship between physical
activity and disease prevention: higher levels of
activity appear to have the most benefit, but lower
levels have demonstrable benefits for some dis-
eases as well. For the U.S. population, in which the
majority of people are sedentary or only minimally
active, achievable increases in physical activity of
a moderate amount, including some resistance
exercise to strengthen muscle, are likely to sub-
stantially improve the health and quality of life of
many people.

Conclusions

Overall Mortality
1. Higher levels of regular physical activity are asso-
ciated with lower mortality rates for both older
and younger adults.

2. Even those who are moderately active on a regu-
lar basis have lower mortality rates than those
who are least active.

Cardiovascular Diseases

1.









2.







3

Regular physical activity or cardiorespiratory fit-
ness decreases the risk of cardiovascular disease
mortality in general and of coronary heart disease
(CHD) mortality in particular. Existing data are
not conclusive regarding a relationship between
physical activity and stroke.

The level of decreased risk of CHD attributable
to regular physical activity is similar to that of
other lifestyle factors, such as keeping free from
cigarette smoking.

Regular physical activity prevents or delays the
development of high blood pressure, and exer-
cise reduces blood pressure in people with
hypertension.

Regular physical activity is associated with a
decreased risk of colon cancer.

Cancer
1.



2.








3.

There is no association between physical activity
and rectal cancer. Data are too sparse to draw
conclusions regarding a relationship between
physical activity and endometrial, ovarian, or
testicular cancers.

Despite numerous studies on the subject, exist-
ing data are inconsistent regarding an association
between physical activity and breast or prostate
cancers.

Non-/mu/in-Dependent Diabetes Mellitus
1. Regular physical activity lowers the risk of
developing non-insulin-dependent diabetes
mellitus.

149


Physical Activity and Health

Osteoarthritis

1. Regular physical activity is necessary for main-
taining normal muscle strength, joint structure,
and joint function. In the range recommended for
health, physical activity is not associated with
joint damage or development of osteoarthritis
and may be beneficial for many people with
arthritis.

2. Competitive athletics may be associated with the
development of osteoarthritis later in life, but
sports-related injuries are the likely cause.

Osteoporosis

1. Weight-bearing physical activity is essential for
normal skeletal development during childhood
and adolescence and for achieving and main-
taining peak bone mass in young adults.
2. It is unclear whether resistance- or endurance-
type physical activity can reduce the accelerated
rate of bone loss in postmenopausal women in
the absence of estrogen replacement therapy.

Falling

1. There is promising evidence that strength train-
ing and other forms of exercise in older adults
preserve the ability to maintain independent liv-
ing status and reduce the risk of falling.

Obesity
1. Low levels of activity, resulting in fewer kilocalo-
ries used than consumed, contribute to the high
prevalence of obesity in the United States.
2. Physical activity may favorably affect body fat
distribution.

Mental Health

1. Physical activity appears to relieve.symptoms of
depression and anxiety and improve mood.
2. Regular physical activity may reduce the risk of
developing depression, although further research
is required on this topic.

Health-Related Quality of 1 ife
1. Physical activity appears to improve health-
related quality of life by enhancing psychological
well-being and by improving physical function-
ing in persons compromised by poor health.

Adverse Effects
1. Most musculoskeletal injuries related to physi-
cal activity are believed to be preventable by
gradually working up to a desired level of
activity and by avoiding excessive amounts of
activity.

2. Serious cardiovascular events can occur with
physical exertion, but the net effect of regular
physical activity is a lower risk of mortality from
cardiovascular disease.

Research Needs

1.






2.




3.





4.





5.





6.

Delineate the most important features or combi-
nations of features of physical activity (total
amount, intensity, duration, frequency, pattern,
or type) that confer specific health benefits.
Determine specific health benefits of physical
activity for women, racial and ethnic minority
groups, and people with disabilities.
Examine the protective effects of physical activ-
ity in conjunction with other lifestyle character-
istics and disease prevention behaviors.
Examine the types of physical activity that pre-
serve muscle strength and functional capacity in
the elderly.

Further study the relationship between physical
activity in adolescence and early adulthood and
the later development of breast cancer.

Clarify the role of physical activity in preventing or
reducing bone loss after menopause.

150


The Effects of Physical Activity on Health and Disease

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172


     CHAPTER 5
PATTERNS AND TRENDS
IN PHYSICAL ACTWIN

Contents

Introduction  ..........................................................
Physical Activity among Adults in the United States  ...........................
Recent Patterns of Leisure-Time Physical Activity  ..........................
  Physical Inactivity during Leisure Time  ...............................
  Regular, Sustained Physical Activity during Leisure Time  .................
  Regular, Vigorous Physical Activity during Leisure Time  ..................
  Participation in Specific Physical Activities  .............................
Leisure-Time Physical Activity among Adults with Disabilities  ................
Trends in Leisure-Time Physical Activity  .................................

Physical Activity among Adolescents and Young Adults in the United States
Physical Inactivity  ............................................
Vigorous Physical Activity  .....................................
Other Physical Activity  ........................................
Physical Education in High School  ...............................
Sports Team Participation  ......................................

. 175

177

177

. 177

177

181

.  184

.  186

186

186

188

189

192

198

200

Conclusions  ............................................................... 200

ResearchNeeds  .......................................................... 201

Appendix A: Sources of National Survey Data . . . . . . . . 201

Appendix B: Measures of Physical Activity in Population Surveys . . . . . _ . . . . _ . 203

References ._...._....,.....__......._.........................,,........... 206


     CHAPTER 5
PATTERNS AND TRENDS

Introduction

T his chapter documents patterns and trends of
reported leisure-time physical activity of adults
and adolescents in the United States and compares
the findings to the goals set by Healthy People 2000
(U.S. Department of Health and Human Services
(USDHHS] 1990; see Chapter 2, Appendix A, for
the 1995 revised Healthy People 2000 objectives for
physical activity and fitness). The information pre-
sented here is based on cross-sectional data from
national- and state-based surveillance systems, spon-
sored by the Centers for Disease Control and Preven-
tion (CDC), that track health behaviors including
leisure-time physical activity. Although self-reported
survey information about physical activity is likely
to contain errors of overreporting, there is no other
feasible way to estimate physical activity patterns of
a population. Moreover, there is no widely accepted
"gold standard" methodology for measuring physi-
cal activity (see Chapter 2).

Occupational and most domestic physical activi-
ties are not presented because such information is
not available. Most national goals address leisure-
time rather than occupational physical activity be-
cause people have more personal control over how
they spend their leisure time and because most
people do not have jobs that require regular physical
exertion. Nonetheless, measuring only leisure-
time physical activity leads to an underestimate of
total physical activity, especially for those people
with physically demanding jobs.
Five surveys provided data oh physical activity
for this review: 1) the National Health Interview
Survey (NHIS), which included questions on physi-
cal activity among adults in 1985, 1990, and 1991;
2) the Behavioral Risk Factor Surveillance System
(BRFSS), a state-based survey of adults that was
conducted monthly by state health departments, in

IN PHYSICAL ACTIVITY

collaboration with the CDC, and included questions
on physical activity from 1986 through 1992 and in
1994; 3) the Third National Health and Nutrition
Examination Survey (NHANES 111) of U.S. adults
from 1988 through 1994 (data from Phase 1, 1988-
199 1, were available for presentation in this report);
4) the 1992 household-based NHIS Youth Risk Be-
havior Survey (NHIS-YRBS) of 12- through 21-year-
olds; and 5) the national school-based Youth Risk
Behavior Survey (YRBS), which was conducted in
1991, 1993, and 1995 among students in grades 9-
12. The methodologies of these surveys are summa-
rized in Table 5-1 and are described in detail in
Appendices A and B of this chapter.
When adult data from the NHIS, BRFSS, and
NHANES III are presented for comparison, they are
shown from the most nearly contemporaneous sur-
vey years. Otherwise, the most recent data are pre-
sented. For determining trends, BRFSS data are
restricted to those states that collected physical ac-
tivity information each year.

Responses to questions included in the surveys
were compiled (see Appendix B) into categories
approximately corresponding to the Healthy People
2000 physical activity objectives. These objectives
are based on the health-related physical activity
dimensions of caloric expenditure, aerobic intensity,
flexibility, and muscle strength (Caspersen 1994).
Thus the "regular, sustained physical activity" cat-
egory used here pertains to total caloric expenditure
and includes a summation of activities of any inten-
sity, whereas the "regular, vigorous" category per-
tains to aerobic intensity and therefore includes only
activities of vigorous intensity. Because some ac-
tivities (e.g., vigorous activity of 30 minutes dura-
tion) fall into bothof these categories, the categories
are not mutually exclusive. Adding together the
proportion of people in each category thus yields an


Physical Activity and Health

Table 5-l. Sources of national and state-based data on physical activity*
                     Mode of                         Physical
Survey   Abbreviated         survey         Population, Response  Sample   activity
title     title     Sponsor   administration Years    aliF       rate      size     measure+

Adults

National   NHIS
Health
Interview
Survey

Behavioral BRFSS
Risk Factor
Surveillance
System

National   Household
Center for interview
Health
Statistics
(NOW,
Centers for
Disease
Control and
Prevention
(CDC)

National   Telephone
Center for interview
Chronic
Disease
Prevention
and Health
Promotion
(NCCDPHP),
CDC

Third    NHANES III NCHS,    Household
National           CDC      interview
Health and
Nutrition
Examination
Survey

Youths

Youth Risk YRBS
Behavior
Survey

NCCDPHP, Self-
CDC     administered
       in school

National   NHIS-     NCHS,    Household
Health    YRBS     CDC     administration
Interview             via au.diotape
Survey-                  and self-
Youth Risk             completed
Behavior                answer sheets
Survey

1985,
1990,
1991

I 986
1991

1992

1994

i 988-91
(Phase I)

1991,
1993,
1995






1992

us, ia+
years

83-88s

36,399
in 1985,
41,104
in 1990,
43,732
in 1991

25 states*
and D.C.,
1 a+ years

62-71%

48 states
and D.C.
1 a+ years

7 1%

Approx.
35,000-
50,000

96,343

49 states
and D.C.
1 a+ years
us, ia+
years

70%

82%

106,030



9,901

us gth-
12; grades   70-78% of  12,272
       selected   in 1991,
(approxi-   schools;   16,296
mately    86-90% of in 1993,
15-18     students   10,904
years)             in 1995

us, 12-21
years

74%     10,645

F/I/W
over past
2 weeks

F/I/T/D
over
past
month

F/T

over
past
month

F/I/T/D
over
past
week

F/I/T
over
past
week

*Available at the time this report was compiled.
`F = frequency; I = intensity; T = type; D = duration.
*Alabama, Arizona, California, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Kentucky, Massachusetts, Minnesota, Missouri, Montana,
New Mexico, New York. North Carolina, North Dakota, Ohio, Rhode Island, South Carolina, Tennessee, Utah, West Virginia, and Wisconsin.

176


avercstimate of the proportion of people who are
regularly physically active. More clear-cut is the
(;,tcgory of inactivity, which is considered to be the
InoSt detrimental to health and is thus important to
,,,onitor as an indicator of need for intervention.
\lcusurcs ofstretching and strength training are also
d,.ri\ed, when possible, from the survey responses.
The various surveys differ in the means by
\i.hich they are conducted, in the wording of ques-
tlons, in the time of year, in population sampling
frames, in response rates, and in definitions of
physical activity-all of which may cause differ-
t`rlccs in the resulting physical activity estimates.
1 ~o~vever, even with these differences, the data from
,tlc several data collection systems reveal a number
(,I consistencies in patterns and trends in self-
reported leisure-time physical activity.

Physical Activity among Adults
in the United States

Recent Patterns of Leisure-lime
Physical Activity

Physical Inactivity during Leisure Time
i'hysical inactivity during leisure time is one of the
c.;\sicst measures to define in population surveys.
Ill:lctivity was conceptualized in the NHIS, BRFSS,
.~ntL NHANES III as no reported leisure-time physi-
.11 ;lctivity in the previous 2 to 4 weeks. Healthy
I'c.c~plc 2000 objective 1.5 states that the proportion
01 Icisure-time physical inactivity among people
.~gcd 6 years and older should be no more than 15
percent by the year 2000 (USDHHS 1990).
The proportion of U.S. adults aged 18 years and
~~Iclt`r who were classified as physically inactive dur-
111% leisure time varied somewhat among the three
: cccnt surveys (Table 5-2). In the 1991 NHIS, 24.3
,Icrccnt reported no activity in the previous 2 weeks.
111 the 1992 BRFSS, 28.7 percent of adults reported
[l(l activity during the previous month: In the 1988-
1991 NHANES III, in which for operational reasons
l)Jrtlcipants tended to be surveyed in the North in
lhc summer and the South in the winter, the preva-
lc'nce of inactivity during the previous month was
-0mcwhat lower-21.7 percent,
Thus, despite minor differences, the surveys are
s onsistent in finding that about one-fourth of U.S.

Patterns and Trends in Physical Activity

adults do not engage in any leisure-time physical
activity, a proportion far from the 15 percent target
of Healthy People 2000 objective 1.5. Also evident
across the surveys is that more women than men are
physically inactive (Figure 5-l). The ratio of physi-
cal inactivity prevalence for women relative to that
for men ranged from 1.2 to 1.7 across the three
surveys. Findings for racial and ethnic groups, unad-
justed for socioeconomic differences, were general11
in accord across the surveys (Table 5-2): whites had
a lower prevalence of leisure-time inactivity than
blacks, Hispanics, and persons categorizedas "other."
Among the sex-specific racial and ethnic groups,
white men were the least likely to be inactive (< 26
percent). White women had a prevalence of inactiv-
ity (23.1-29.0 percent) similar to that among black
men and lower than that among Hispanic men. At
least one-third of black women and Hispanic women
reported no physical activity in their leisure time.
In all three surveys, the prevalence of physical
inactivity was higher in older groups (Figure 5-l).
Fewer than one in four adults aged 18-29 years
engaged in no physical activity, whereas about one in
three men and one in two women over 74 years of age
were inactive (Table 5-2). For the most part, the
prevalence of physical inactivity was greater among
persons with lower levels of education and income.
For example, there was twofold to threefold more
inactivity from lowest to highest income categories:
only 10.9 to 17.8 percent of participants with an
annual family income of $50,000 or more reported
no leisure-time physical activities, whereas 30.3 to
41.5 percent of those with an income less than
$10,000 reported this.

The prevalence of inactivity among adults tended
to be lower in the north central and westernstates than
in the northeastern and southern states (Table 5-2).
Participants surveyed in the winter months reported
being physically inactive substantially more often than
did those surveyed during the summer months (Fig-
ure S-2). In the 1994 BRFSS, state-specific prevalences
of physical inactivity from 49 states and the District of
Columbia ranged from 17.2 to 48.6 (Table 5-3).

Regular, Sustained Physical Activity
during Leisure Time
Healthy People 2000 objective 1.3 proposes that at
least 30 percent of people aged 6 years and older
should engage regularly, preferably daily, in light to

177


Physical Activity and Health

Table 5-2. Percentage of adults aged 18+ years reporting no participation in leisure-time physical activity, by
   various demographic characteristics, National Health Interview Survey (NHIS), Third National
   Health and Nutrition Examination Survey (NHANES Ill), and Behavioral Risk Factor Surveillance
    System (BRFSS), United States

Demographic group

1991 NHIS'         1988-l 991 NHANES Ill*   1992 BRFSS*+

Overall
Sex
  Males
  Females

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanics
   Males
   Females
  Other
   Males
   Females

Age (years)
  Males
    18-29
    30-44
    45-64
    65-74
    75+
  Females
    18-29
    30-44
    45-64
    65-74
    75+
Education
  < 12 yrs
   12 yrs
   Some college (13-l 5 yrs)
   College (16+ yrs)
lncomeq
  < $10,000
   $10,000-19,999
   $20,000-34,999
   $35,000-49,999
   $50,000+
Geographic region
  Northeast
  North Central
  South
   West

24.3 (23.2, 25.3)*        21.7 (19.0, 24.5)

21.4 (20.2, 22.6)
26.9 (25.8, 28.0)

15.8 (12.4, 19.2)
27.1 (23.0, 31.3)

22.5  (21.4, 23.7)
20.3  (19.0, 21.6)
24.6  (23.4, 25.8)
28.4  (26.4, 30.4)
22.5  (20.0, 25.0)
33.2  (30.8, 35.6)
33.6  (31.0, 36.3)
29.6  (26.0, 33.2)
37.4  (34.1, 40.8)
26.7  (23.4, 30.0)
22.8  (18.2, 27.3)
30.8  (27.0, 34.7)

17.6 (15.8, 19.4)
21.1 (19.8, 22.5)
23.9 (22.1, 25.7)
23.0 (20.4, 25.6)
27.1 (23.8, 30.4)

25.0  (23.4, 26.6)
25.2  (23.8, 26.61
27.4  (25.9, 28.91
27.8  (25.7, 29.9)
37.9  (35.3, 40.6)

37.1  (35.3, 38.9)
25.9  (24.7, 27.1)
19.0  (17.8, 20.2)
14.2  (13.1, 15.3)

30.3 (28.4, 32.2)
30.2 (28.5, 32.0)
24.3 (22.9, 25.7)
19.5 (18.1, 20.9)
14.4 (13.2, 15.6)

25.9 (24.5, 27.3)
20.8 (18.7. 22.91
27.0 (25.2, 28.8)
22.5 (19.5, 25.5)

18.2 (15.6, 20.8)
12.9  (9.6, 16.1)
23.1 (19.0, 27.11
30.4 (25.6, 35.3)
20.6 (14.5, 26.8)
38.1 (30.9, 45.2)
36.0 (32.5, 39.51
29.1 (24.3, 33.9)
43.8 (38.5, 49.1)


II

12.5  (9.0, 16.0)
14.5 (10.9, 18.1)
16.9 (13.0, 20.8)
17.5 (12.2, 22.8)
34.5 (28.0, 41 .l)

17.4 (13.4, 21.4)
24.9 (20.6, 29.3)
29.4 (24.6, 34.2)
32.5 (25.9, 39.2)
54.3 (47.9, 60.6)

34.5 (31.2, 37.8)
20.8 (17.4, 24.3)
15.7 (11.4, 19.9)
11.1  (6.9, 15.4)

34.5 (30.3, 38.7)
28.5 (24.5, 32.6)
18.7 (14.8, 22.6)
15.9 (10.9, 20.9)
10.9 (6.7, 15.1)

21.6 (8.5, 34.6)
16.7 (7.6, 25.8)
24.8 (18.4, 31.1)
22.6 114.8, 30.5)

28.7 (28.3, 29.11

26.5 (25.9, 27.1)
30.7 (30.1, 31.3)

26.8 (26.4, 27.2)
25.3 (24.7, 25.91
28.2 (27.6, 28.8)
38.5 f36.9, 40.1)
33.1 (30.9, 35.3)
42.7 (40.7, 44.7)
34.8 (32.8, 36.8)
30.2 (27.3, 33.1)
39.0 (36.5, 41.5)
31.4 (28.9, 33.9)
27.6 (24.1, 31.11
35.8 (32.3, 39.3)

18.9 (17.7, 20.1)
25.0 (24.0, 26.0)
32.0 (30.8, 33.2)
33.2 (31.2, 35.2)
38.2 (35.3, 41.1)

25.4 (24.2, 26.6)
26.9 (25.9, 27.9)
32.1 (30.9, 33.3)
36.6 (34.8, 38.4)
50.5 (48.5, 52.5)

46.5 (45.3, 47.7)
32.8 (32.1, 33.6)
22.6 (21.9, 23.4)
17.8 (17.0, 18.5)

41.5 (40.1, 42.9)
34.6 (33.6, 35.6)
26.9 (26.1, 27.7)
23.0 (22.0, 24.0)
17.7 (16.9, 18.5)

29.5 (28.5, 30.5)
28.6 (27.8, 29.4)
32.4 131.6, 33.2)
22.0 (21.0, 23.0)

Sources: Centers for Dtsease Control and Preventton, National Center ior Health Statistics, NHIS, public use data tapes, 1991; Centers for
Disease Control and Prevention, Nattonal Center for Health Stattstics, NHANES, public use data tapes, 1988-1991 ; Centers for Disease
Control and Preventton, National Center for Chronic Disease Prevention and Health Promotion, BRFSS, 1992.
o NHlS asked about the prior 2 weeks; BRFSS asked about the prror month. `Based on data from 48 states and the Distrtct of Columbia
`95% confidence intervals. q Hispanic reflects Mexican-Americans in NHANES III. "Estimates unreliable.
IAnnual income per family (NHIS) or household (BRFSS).

178


Patterns and Trends in Physical Activity

Figure 5-1. Percentage of adults aged 18+ years reporting no participation in leisure-time physical activity by

sex and age

60 r

cl 75+
0 65-74
O 45-64
I 3044
g 18-29

2
E 30
a


  20




  10




   0

NHANES Women
  1988-l 991

BRFSS Men    BRFSS Women
  1992         1992

NHIS Men    NHIS Women   NHANES Men
1991         1991       1988-l 99 1

Survey-sex group

Figure 5-2. Percentage of adults aged 18+ years reporting no participation in leisure-time physical activity
     by month

  40







  30





E
8 20
z
a




  10







   0

r

1992 BRFSS

December

January

December      January

Monthly trend within survey

179

1991 NHIS


Physical Activity and Health

Table 5-3.  Percentage of adults aged 18+ years reporting participation in no activity; regular, sustained
     activity; and regular, vigorous activity, by state,* Behavioral Risk Factor Surveillance System
      (BRFSS), 1994, United States

Overall
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
D.C.
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi

No activity

29.4 (29.0, 29.8)+
45.9 (43.2,48.6)
22.8 (19.9, 25.7)
23.7 (21.2,26.2)
35.1  (32.6,37.6)
21.8 (20.2, 23.4)
17.2 (15.0, 19.4)
22.1  (19.9, 24.3)
36.4 (34.0,38.8)
48.6  (45.3,51.9)
28.0 (26.2,29.8)
33.0 (30.6,35.4)
20.8 (18.6, 23.0)
21.9 (19.7, 24.1)
33.5  (31.1,35.9)
29.7 (27.7, 31.7)
33.2  (31.2,35.2)
34.5  (31.8, 37.2)
45.9 (43.5,48.3)
33.5  (30.8, 36.2)
40.7  (37.8,43.6)
30.5  (28.9, 32.1)
24.0  (21.6,26.4)
23.1  (21.1, 25.1)
21.8 (20.4,23.2)
38.5  (35.6,41.4)

Regular,
sustained activity

19.7 (19.3,20.1)
17.1 (14.9,19.3)
28.3 (24.8,31.8)
17.8 (15.4,20.2)
17.2 (15.0,19.4)
21.9 (20.3,23.5)
26.5 (24.1,28.9)
26.9 (24.5,29.3)
17.7 (15.7,19.7)
11.6  (9.4, 13.8)
23.8 (22.2,25.4)
18.0 (16.0,20.0)
25.5 (23.3,27.7)
26.3 (23.8,28.8)
15.7 (13.9,17.5)
18.8 (17.0,20.6)
15.9 (14.3,17.5)
16.8 (14.6,19.0)
13.2 (11.6,14.8)
16.8 (14.8,18.8)
13.0 (11 .o, 15.0)
17.6 (16.2,19.0)
23.2 (21.0,25.4)
21.8 (19.8,23.8)
20.1 (18.7,21.5)
14.0 (12.0, 16.0)

moderate physical activity requiring sustained,
rhythmic muscular movements for at least 30 min-
utes per day WSDHHS 1990). Regular, sustained
activity derived from the NHIS and the BRFSS was
defined as any type or intensity of activity that
occurs 5 times or more per week and 30 minutes or
more per occasion (see Appendix B >. This defini-
tion approximates the activity goal of the healtlty
People 2000 objective but includes vigor'ous activity
of at least 30 minutes duration as well. Comparable
information was unavailable in the NHANES III.
The percentage of U.S. adults meeting this defini-
tion of regular, sustained activity during leisure
time was about 22 percent in the two surveys
(23.5 in the NHlS and 20.1 in the BRFSS; see

14.0 (13.6, 14.4)
11.2 (9.4,13.0)
15.1 (12.4,17.8)
17.9 (15.4,20.4)
10.7 (9.lIl2.3)
15.7(14.5,16.9)
15.9(14.1,17.7)
16.9(14.9,18.9)
14.1 (12.5,15.7)
8.7 (6.9,10.5)
20.0 (18.6,21.4)
13.5 (11.9,lS.l)
18.3(16.3,20.3)
15.7 (13.7,17.7)
14.6 (12.8,16.4)
13.0 (11.4,14.6)
13.3 (11.9,14.7)
13.9 (11.9,15.9)
11.3  (9.9,12.7)
11.3 (9.5,13.1)
11.3 (9.5,13.1)
14.5 (13.3,15.7)
17.4(15.4,19.4)
14.5(12.9,16.1)
15.4(14.2,16.6)
9.8 (8.2, 11.4)

Regular,
vigorous activity

Table 5-4)-S percentage points lower than the
Healthy People 2000 target.

The prevalence of regular, sustained activity
was somewhat higher among men than women;
male:female ratios were 1.1:1.3. The two surveys
found no consistent association between racial/
ethnic groups and participation in regular, sustained
activity. The prevalence of regular, sustained activity
tended to be higher among 1% through 29-year-olds
than among other age groups, and it was lowest (5 15
percent) among women aged 75 years and older.
Education and income levels were associated posi-
tively with regular, sustained activity. For example,
adults with a college education had an approxi-
mately 50 percent higher prevalence of regular, sus-
tained activity than those with fewer than 12 years of

180


Patterns and Trends in Physical Activity

Table 5-3. Continued

/GGZGi
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming

No activity
32.0 (29.3, 34.7)
21 .O (18.6, 23.4)
24.3  (22.1,26.5)
21.7  (19.5,23.9)
25.8 (23.3, 28.3)
30.9 (28.2, 33.6)
19.8  (17.3, 22.3)
37.1  (34.7,39.5)
42.8 (40.3,45.3)
32.0 (29.6,34.4)
38.0 (35.1,40.9)
30.4  (28.0,32.8)
20.8 (19.2, 22.4)
26.5  (24.9, 28.1)
31.4 (29.2,33.6)
30.8 (28.4,33.2)
39.7 (37.7,41.7)
27.8 (25.1,30.5)
21.0  (18.8,23.2)
23.3  (21.5, 25.1)
23.0 (20.6,25.4)
18.2 (16.8, 19.6)
45.3  (43.1,47.5)
25.9 (23.2, 28.6)
20.9  (18.4, 23.4)

Regular,
sustained activity
18.0 (15.8,20.2)
21.8 (19.3,24.3)
16.7 (14.7,18.7)
25.3 (22.9,27.7)
21.2 (19.0,23.4)
20.7 (18.3,23.1)
25.5 (22.6,28.4)
14.8 (13.2,16.4)
12.7 (11.1,14.3)
20.2 (18.0,22.4)
15.9 (13.7,18.1)
23.0 (20.8,25.2)
27.3 (25.3,29.3)
21.2 (19.6,22.8)
15.1 (13.3, 16.9)
19.4 (17.4,21.4)
15.0 (13.6,16.4)
20.7 (18.2,23.2)
21.6 (19.4,23.8)
25.7 (23.7,27.7)
24.6 (22.2,27.0)
25.7 (24.1,27.3)
14.3 (12.7,15.9)
22.7 (20.2,25.2)
27.9 (24.8,31.0)

Regular,
vigorous activity
10.8 (9.0,12.6)
15.0(12.6,17.4)
14.7(12.9,16.5)
14.1 (12.3,15.9)
17.0(14.8,19.2)
11.6  (9.8,13.4)
18.4 (16.0,20.8)
10.6  (9.2,12.0)
9.3  (7.9,10.7)
13.9 (12.1,15.7)
12.4 (10.4,14.4)
11.1  (9.5,12.7)
18.7(17.1,20.3)
14.5(13.3,15.7)
11.9(10.3,13.5)
11.9(10.3,13.5)
12.7(11.3,14.1)
13.0 (11 .o, 15.0)
14.3(12.5,16.1)
18.4(16.6,20.2)
14.6(12.8, 16.4)
16.8(15.4,18.2)
9.8  (8.4, 11.2)
12.7 (10.7, 14.7)
16.3(13.9,18.7)

Source: Centers for Disease Control and Preventjon, National Center for Chronic Disease Prevention and Health Promotion, BRFSS, 1994

*Includes 49 states and the Dlstrlct of Columbia. Data for Rhode Island were unavailable
`9% confidence Intervals.

education. Among the regions of the United States,
the West tended to have the highest prevalence of
adults participating in regular, sustained activity
(Table 5-4). Regular, sustained activity, which com-
prises manyoutdooractivities, was most prevalent in
the summer. In the 1994 BRFSS, state-specific
prevalences of regular, sustained activity ranged
from 11.6 to 28.3 (Table 5-3).

Regular, Vigorous Physical Activity during
1 eisore Time
People who exercise both regularly and vigorously
would be expected to improve cardiovascular fitness
the most. The NHIS and the BRFSS defined regular,
vigorous physical activity as rhythmic contraction of

large muscle groups, performed at 50 percent or more
of estimated age- and sex-specific maximum cardio-
respiratory capacity, 3 times per week or more for at
least 20 minutes per occasion (see Appendix B). The
prevalence of regular, vigorous leisure-time activ-
ity reported by U.S. adults was about 15 percent
(16.4 percent in the 1991 NHIS and 14.2 percent in
the 1992 BRFSS; see Table 5-5). This prevalence is
lower than the goal stated in Healthy People 2000
objective 1.4, which is to have at least 20 percent of
people aged 18 years and older engage in vigorous
physical activity at 50 percent or more of individual
cardiorespiratory capacity 3 days or more per week
for 20 minutes or more per occasion (USDHHS
1990).

181


Physical Activity and Health

Table 5-4. percentage of adults aged 1 B+ Years reporting participation in regular, sustained physical activity
  (5+ times per week for 30+ minutes per occasion), bY various demographic characteristics,
National Health Interview Survey (NHIS) and Behavioral Risk Factor Surveillance System (BRFSS),
      United States
                   1991 NHIS*          1992 BRFSS*+

                 23.5 (22.9, 24.1)'          20.1 (19.7, 20.5)

Demographic group
Overall

21.5 (20.9, 22.1)
18.9 (18.4, 19.3)

Sex
  Males
  Females
Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
  Hispanic
    Males
    Females
   Other
    Males
    Females

Age (years)
  Males
   18-29
   30-44
   45-64
   65-74
    75+
  Females
   18-29
   30-44
    45-64
    65-74
    75+

Education
  < 12 yrs

12 yrs

SOme college (13-l 5 yrs)

  College (16+ yrs)
Income*
< $10,000
  $1 o,ooo-19,999
  .$20,000-34,999
  $35,00049,999
   950,000+
Geographic region
  Northeast
  North Central
  south

18.1 (17.0, 19.2)
21.9 (21.0, 22.7)
26.8 (25.7, 28.0)
28.5 (27.3, 29.6)

23.6 (21.8, 25.5)
20.4 (19.3, 21.4)
23.2 (22.2, 24.2)
23.9 (22.7, 25.1)
28.0 (26.8, 29.2)

17.6 (16.6, 18.6)
18.7 (17.9, 19.5)
20.3 (19.5, 21.1)
20.9 (19.9, 21.9)
23.5 (22.5, 24.5)

West

26.1 (24.b, ~1.3~

23.9 (22.8, 25.0)
24.2 (22.7, 25.6)
21.1 (19.9, 22.2)
     -. , -7 I-,

20.2 (19.; !, 21.2)
18.2 (17.' 4, 19.0)
lg.0 (18.4, 19.6)
24.0 (23.0, 25.c
       -- 3)
            -

sources: Centers for Disease Control and Prevention, National Center for Health Statistics, NH% public use data tapes,
Disease Control and Prevention, National center for Chronic Disease Prevention and Health PromotIon, BRFSS, lgg2.

26.6 (25.7, 27.5)
20.7 (19.9, 21.5)

24.0 (23.2, 24.7)
26.7 (25.7, 27.6)
21.5 (20.6, 22.4)
22.9 (21.4, 24.4)
28.9 (26.6, 31.3)
18.0 (16.2, 19.8)
20.0 (18.1, 21.9)
23.7 (20.6, 26.7)
16.5 (14.3, 18.7)
23.4 (20.5, 26.2)
25.5 (21.0, 30.0)
21.1  (17.7, 24.6)

32.0 (30.2, 33.7)
24.1  (22.8, 25.3)
24.2 (22.8, 25.6)
29.2 (27.0, 31.4)
24.6 (21.8, 27.4)

23.2 (21.6, 24.8)
20.4 (19.4, 21.4)
20.6 (19.4, 21.8)
21.3 (19.5, 23.0)
13.8 (12.2, 15.4)

20.8 (20.4, 21.2)
21.9 (21.3, 22.5)
19.8 (19.2, 20.4)
15.2 (14.0, 16.4)
18.5 (16.5, 20.5)
12.6 (11.4, 13.8)
20.1 (18.5, 21.7)
21.4 (18.9, 23.9)
18.9 (16.7, 21.1)
17.3 (15.1, 19.5)
lg.7 (16.6, 22.8)
14.5 (12.0, 17.0)

26.8 (25.4, 28.2)
17.4 (16.6, 18.2)
18.9 (17.7, 20.1)
26.8 (24.8, 28.8)
23.2 (20.5, 25.9)

lg.9 (18.7, 21.1)
18.5 (17.7, 19.3)
19.4 (18.4, 20.4)
19.0 (17.6, 20.4)
15.0 (13.4, 16.6)

15.6 (14.6, 16.6)
17.8 (17.2, 18.4)
22.7 (21.9, 23.5)
23.5 (22.7, 24.3)

*Based on data from 48 states and the District of Columbia.
`~~1s asked about the prior 2 weeks; BRFSS asked about the Prior month.
*gS% confidence intervals.
~~~~~~~ Income per family (NHIS) or household (BRFSS).


                              182

1 ggl ; Centers for


Patterns and Trends in Physical Activity

Table 5-5. Percentage of adults aged 18+ years participating in regular, vigorous physical activity (3+ times
    per week for 20+ minutes per occasion at 5O+ percent of estimated age- and sex-specific maximum
    cardiorespiratory capacity), by various demographic characteristics, National Health Interview
    Survey (NHIS) and Behavioral Risk Factor Surveillance System (BRFSS), United States

Demographic group
Overall

Sex
  Males
  Females
Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females
  Other
   Males
   Females

Age (years)
  Males
    18-29
    30-44
    45-64
    65-74
    75+
  Females
    18-29
    30-44
    45-64
    65-74
    75-t

Education
  < 12 yrs
   12 yrs
  Some college (13-l 5 yrs)
  College (1 6+ yrs)
Income5
  < $10,000
   $10.000-19,999
   $20,000-34,999
   $35,000-49,999
   $50,000+
Geographic region
  Northeast
  North Central
  South
  West

1991 NHlS*

16.4 (15.9, 16.9)*

18.1 (17.4, 18.8)            12.9 (12.5, 13.3)
14.9 (14.3, 15.5)             15.8 (15.4, 16.2)

17.2  (16.6, 17.7)                15.3  (14.9, 15.7)
18.6  (17.9, 19.3)               13.3  (12.7, 13.9)
15.9  (15.2, 16.6)                17.1  (16.5, 17.7)
12.9  (11.7, 14.0)                9.4  (&6, 10.2)
16.0  (13.9, 18.0)                9.5  (8.1, 10.9)
10.4  (9.0, 1 1.7)                9.4  (8.4, 10.4)
13.6  (11.9, 15.2)                11.9  (10.5, 13.3)
15.6  (12.9, 18.3)               12.4  (10.2, 14.6)
11.7  (9.9, 13.4)                11.4  (9.8, 13.0)
16.8  (14.5, 19.1)                11.8  (10.0, 13.6)
18.8  (15.2, 22.3)               11.5  (9.0, 14.0)
14.8  (11.9, 17.8)               12.2  (10.0, 14.4)

19.7 (18.3, 21.1)                8.0  (7.2,  8.83
13.7 (12.8, 14.6)                 11.1  (10.3,  11.9)
14.9 (13.7, 16.1)                16.3  (15.3, 17.3)
27.3 (25.2, 29.5)               20.6  (18.8, 22.4)
38.3 (35.2, 41.5)                20.6  (18.1, 23.1)

16.0 (14.7, 17.3)             11.4 (10.6, 12.2)
13.3 (12.4, 14.1)             18.0 (17.2, 18.8)
12.1 (11.1, 13.0)             17.7 (16.7, 18.7)
18.5 (16.9, 20.1)             16.5 (15.1, 17.9)
22.6 (20.5, 24.7)             12.8 (11.4, 14.2)

11.9 (11.1, 12.8)                 8.2  (7.4, 9.0)
13.6 (13.0, 14.3)             11.5 (10.9, 12.1)
18.9 (17.9, 19.9)             14.9 (14.3, 15.5)
23.5 (22.4, 24.6)             21.9 (21.1, 22.7)

15.5 (14.1, 17.0)                9.0  (8.2,  9.8)
14.4 (13.5, 15.4)               10.8  (10.2, 1 1.4)
15.5 (14.6, 16.4)                14.2  (13.6, 14.8)
16.0 (14.9, 17.0)               16.3  (15.5, 17.1)
21.5 (20.4, 22.6)                20.5  (19.5, 21.5)

16.1 (15.2, 16.9)             13.8 (13.0, 14.6)
76.5 (15.5, 17.5)            13.7 (13.1, 14.3)
14.7 (13.9, 15.5)             13.8 (13.2, 14.4)
19.2 (17.9, 20.5)              16.8 (16.0. 17.6)

1992 BRFSS*+

14.4 (14.0, 14.8)

Sources: Centers for Disease Control and Prevention, National Center for Health Statistics, NHIS, 1991; Centers for Disease Control and
Prevention, National Center for Chronic Disease Prevention and Health Promotion, BRFSS, 1992.
`NHIS asked about the prior 2 weeks; BRFSS asked about the prior month
`Based on data from 48 states and the District of Columbia.
`95% confidence intervals.
`Annual income per family (NHIS) or household (BRFSS).

183


Physical Activity and Health

The proportion performing regular, vigorous ac-
tivity was 3 percentage points higher among men than
women in the NHIS, but it was 3 percentage points
higher among women than men in the BRFSS. This
difference between sexes in the surveys may be related
to the BRFSS's use of a correction procedure (based on
speeds of activities like walking, jogging, and swim-
ming) to create intensity coding (Appendix B;
Caspersen and Powell [unpublished technical mono-
graph] 1986; Caspersen and Merritt 1995). Regular,
vigorous activity tended to be more prevalent among
whites than among blacks and Hispanics (Table 5-5).
These racial and ethnic patterns were somewhat more
striking among women than among men.
The relationship between regular, vigorous physi-
cal activity and age varied somewhat between the
two surveys. In the NHIS, the prevalence of regular,
vigorous activity was higher for men and women
aged 18-29 years than for those aged 30-64 years,
but it was highest among men and women aged 65
years and older. Among men participating in the
BRFSS, regular, vigorous activity increased with age
from those 18-29 years old to those 2 65 years old.
Amongwomen participating in the BRFSS, the preva-
lence of regular, vigorous activity was higher for
those aged 30-74 years than for those aged 18-29
years and L 75 years.

The finding of generally lower prevalences of
regular, vigorous activity among younger than older
adults (Table 5-5) may seem .unexpected. It is ex-
plained partly by both the greater leisure time of
older adults and the use of an age-related relative
intensity classification (Caspersen, Pollard, Pratt
1987; Stephens and Caspersen 1994; Caspersen and
Merritt 1995). Because cardiorespiratory capacity
declines with age, activities that would be moder-
ately intense for young adults, such as walking,
become more vigorous for older people. If the two
surveys had instead used an absolute intensity clas-
sification, the estimated prevalence of people.engag-
ing in regular, vigorous physical activity would have
fallen dramatically with age. (This age-related drop
in activities of high absolute intensity is shown in
Table 5-6 and described in the next section.) Like-
wise, the male:female ratio ofvigorousactivitypreva-
lence in Table 5-5 would rise if an absolute intensity
classification were used, because women have a
lower average cardiorespiratory capacity than men.

In both surveys, the proportion of adults report-
ing regular, vigorous activity was higher in each
successive educational category (Table 5-S). Adults
who had college degrees reported regular, vigorous
activity approximately two to three times more often
than those who had not completed high school. In
the NHIS, a similar positive association was seen
between income and regular, vigorous physical ac-
tivity. In the BRFSS, the prevalence of regular, vigor-
ous physical activity was highest at the highest
income level. The prevalence of regular, vigorous
physical activity was not consistently related to em-
ployment status or marital status in the two surveys.
It was higher in the West than in other regions of the
United States and in warmer than in colder months.
In the 1994 BRFSS, state-specific prevalences of
regular, vigorous activity ranged from 6.7 to 16.9
(Table 5-3).

Participation in Specific Physical Activities
NHIS participants reported specific activities in the
previous 2 weeks (Table 5-6). By far, walking was the
most commonly reported leisure-time physical ac-
tivity, followed by gardening or yard work, stretch-
ingexercises, bicycling, strengthening exercises, stair
climbing, jogging or running, aerobics or aerobic
dancing, and swimming. Because these percentages
are based on all participants in the year-round NHIS,
they underestimate the overall prevalence of partici-
pation in seasonal activities, such as skiing.

Substantial differences exist between the sexes
for many activities. Gardening or yard work, strength-
ening exercises, jogging or running, and vigorous or
contact sports were more commonly reported by
men than women. Women reported walking and
aerobics or aerobic dancing more often than men and
reported participation in stretching exercises, bicy-
cling, stair climbing, and swimming about as often as
men. Participation in most activities, especially weight
lifting and vigorous or contact sports, declined sub-
stantially with age (Table 5-6). The prevalence of
walking, gardening or yard work, and golf tended to
remain stable or increase with age. Among adults
aged 65 years and older, walking (> 40 percent
prevalence) and gardening or yard work (> 20 per-
cent prevalence) were by far the most popular
activities.

184


Patterns and Trends in Physical Activity

Table 5-6. Percentage of adults aged 18+ years reporting participation in selected common physical activities in
    the prior 2 weeks, by sex and age, National Health Interview Survey (NHIS), United States, 1991

Activity category
\vcllking for exercise

Gardening or
vard work
Stretching exercises
l\/erp,ht lifting or
other exercise
to increase
mscle strength
~,,eji~ng or running
.\probics or aerobic
  dance
titling a bicycle or
exercise bike

\t<jlr climbing
\i~~mrning for
  cwrcise

I(~IlIliS

Ilowllng

(k)lf

t~wball or softball

I I.~ndhall, racquet-
11,111, or squash

.klirlg

( II)\\ country skiing
II',>tcar skiing

lLi4dbJII

~iJll~\hiII


h x ccLr

~1~~l1,`~ll

Jthcr sports

All

Males                      Females

ages
and

18-29  30-44  45-64  65-74   75+   All    18-29  30-44  45-64  65-74   75+   All   sexes

32.8   37.6   43.3   50.1

22.2   36.0   39.8   42.6

32.1   27.2   20.0   15.5

33.6   21.2   12.2    6.4

22.6   14.1    7.7    1.4

3.4    3.3    2.1    1.6

18.7   18.5   14.0   10.8

10.5    11.4    9.6    6.0

10.1    7.6    5.3    3.1

5.7    3.3    2.9    1.1

7.0    5.2    3.0    2.8

7.9    8.6    7.9    9.7

11.0    6.9    1.8    0.4

5.2    2.8    1.5

115    1.0    0.4

0.1    0.5    0.5

1.5    0.7    0.3

24.2   10.5    2.4

6.8    3.0    1 .l

3.3    1.4    0.3

7.6    1.8    0.4

8.6    7.9    6.0

0.3

0.1

0.2

-


0.1

0.2

0.1

0.2

6.2

47.1   39.4



38.4   34.2

15.7   25.0

4.7   20.0

0.5   12.8



1.0    2.8



8.4   16.2

4.0   9.9



1.4   6.9

0.4    3.5

1.6    4.7

4.9    8.2

-    5.8



-    2.7

-    0.9

0.4    0.4

-    0.7

0.1   10.5

0.2   3.1

-    1.4

-    2.7

5.2   7.3

47.4   49.1   49.4   50.1   40.5   48.3   44.1

15.4   28.6   29.6   28.2   21.5   25.1   29.4

32.5   27.7   21.4   21.9   17.9   26.0   25.5

14.5   10.6   5.1   2.8    1.1    8.8   14.1

11.6    6.5    2.5    0.8    0.4    5.7    9.1

19.3   12.3   6.6    4.2    1 .6   11.1    7.1

17.4   16.9   12.6   11.4    6.0   14.6   15.4

14.6   12.8   10.3    7.3    5.6   11.6   10.8

8.0    7.5   4.6    4.2

3.1    2.4   1.3    0.6

4.8    4.2    2.8    2.5

1.4    1.7    2.2    3.3

3.2    1.7   0.3    0.2

6.2    6.5

2.0    2.7

3.6    4.1

1.8    4.9

1.4    3.5

1.0    0.4    0.4    0.1

0.9    0.6    0.3    0.0

0.3    0.4   0.6    0.2

0.7    0.5    0.1    0.0

3.1    1.7   0.4     -


4.4    1.9   0.5    0.0

0.9    0.4   0.1     -

0.7    0.4    0.0     -

4.5    4.5   3.6    4.3

0.5    1.6

0.5    0.7

0.4    0.4

0.4    0.5

1.5    5.8

1.8    2.5

0.4    0.9

0.3    1.5

4.1    5.7

\olc>: 0.0 = quantity less than 0.05 but greater than zero; - = quantity is equal to zero.
")UR c': Centers for Disease Control and Prevention, National Center for Health Statistics, NHIS, 1991

185


Physical Activity and Health

Healthy People 2000 objective 1.6 recommends
that at least 40 percent of people aged 6 years and
older should regularly perform physical activities
that enhance and maintain muscular strength, mus-
cular endurance, and flexibility (USDHHS 1990).
National surveys have not quantified all these activi-
ties but have inquired about specific sentinel activi-
ties, such as weight lifting and stretching. In the 1991
NHIS, 14.1 percent of adults reported "weight lifting
and other exercises to increase muscle strength" in
the previous 2 weeks (Table 5-7). Participation in
strengthening activities was more than twice as preva-
lent among men than women. Black men tended to
have the highest participation (26.2 percent) and
black women the lowest (6.9 percent). Participation
was much higher among younger than older adults,
among the more affluent than the less affluent, and
in the West than in other regions of the United States.
Of special concern, given the promising evi-
dence that strengthening exercises provide substan-
tial benefit to the elderly (see Chapter 4), is the low
prevalence of strengthening activities among those
aged 65 or older (I 6.4 percent in men and I 2.8
percent in women; see Table 5-7).
  Adult participation in stretching activity over
the previous 2 weeks was 25.5 percent in the NHIS
(Table 5-7). Stretching participation declined with
age and tended to be associated positively with levels
of education and income and to be lower in the South
than in other regions of the United States.

Leisure-lime Physical Activity among
Adults with Disabilities

Although little information is available on physical
activity patterns among people with disabilities, one
recent analysis was based on the special NHIS Health
Promotion and Disease Prevention Supplement from
1991. Heath and colleagues (1995) compared physi-
cal activity patterns among people with disabilities
(i.e., activity limitations due to a chronic health
problem or impairment) to those among people
without disabilities. People with disabilities were
less likely to report engaging in regular moderate
physical activity (27.2 percent) than were people
without disabilities (37.4 percent). People with dis-
abilities were also less likely to report engaging in
regularvigorousphysicalactivity (9.6percentvs. 14.2
percent). Correspondingly, people with disabilities

were more likely to report being inactive (32 percent
vs. 27 percent).

Trends in Leisure-Time Physical Activity
Until the 20th century, people performed most
physical activity as part of their occupations or
in subsistence activities. In Western populations,
occupation-related physical demands have declined,
and the availability of leisure time has grown. It is
generally believed that over the past 30 years, as
both the popularity of sports and public awareness
of the role of physical activity in maintaining health
have increased, physical activity performed during
leisure time has increased (Stephens 1987; Jacobs
et al. 1991). Stephens concluded that the increase
was greater among women than men and among
older than younger adults and that the rate of
increase probably was more pronounced in the
1970s than between 1980 and 1985 (Stephens 1987).
However, no systematic data were collected on
physical activity among U.S. adults until the 1980s.
Even now, few national data are available on
consistently measured trends in physical activity.
The NHIS has data from 1985,1990, and 1991, and
the BRFSS has consistent data from the same 25
states and the District of Columbia for each year
between 1986 and 1992 and for 1994. According to
the NHIS, participation in leisure-time physical ac-
tivity among adults changed very little between the
mid-1980s and the early 1990s (Table 5-8 and Figure
5-3). Similarly, in the BRFSS (Table 5-8 and Figure
5-4), little improvement was evident from 1986
through 1994.

Physical Activity among Adolescents
and Young Adults in the United States
The most recent U.S. data on the prevalence of
physical activity among young people are from the
1992 household-based NHIS-YRBS, which sampled
all young people aged 12-21 years, and the 1995
school-based YRBS, which included students in
grades 9-12. Variations in estimates between the
NHIS-YRBS and the YRBS may be due not only to the
distinct populations represented in each survey but
also to the time of year each survey was conducted,
the mode of administration, the specific wording of

186


Demographic group

Overall

Sex
  Males
  Females

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females
  Other
   Males
   Females

Age (years)
  Males
    18-29
    30-44
    45-64
    65-74
    75+
  Females
    18-29
    30-44
    45-64
    65-74
    75+

Education
  < 12 yrs

                               7.4  (6.6, 8.1)             14.7 (13.5, 15.8)
   12 yrs                    12.3 (11.7, 13.0)             22.6 (21.7, 23.6)
  Some college (I 3-l 5 yrs)          18.3 (17.3, 19.2)             31.3 (29.9, 32.7)
  College (16+ yrs)              19.6 (18.6, 20.6)             35.4 (34.0, 36.9)

income*
  < s 10,000                   12.9 (11.4, 14.4)             23.4 (21.7, 25.1)
   B 10,000-$19,999              10.7 (9.8, 11.6)             21.0 (19.7, 22.3)
   $20,000-834,999              14.3 (13.4, 15.1)             25.6 (24.4, 26.9)
   $35,000-849,999             15.3 (14.3, 16.3)             28.9 (27.4, 30.4)
   $50,000+                  19.1 (18.1, 20.2)             33.5 (32.1, 34.9)
Geographic region
  Northeast                  13.8 (12.9, 14.8)             24.9 (23.6, 26.2)
  North Central               14.5 (13.6, 15.3)             28.5 (26.5, 30.6)
  South                     12.4 (11 .6, 13.3)            20.8 (19.2, 22.4)
  West                     16.5 (15.4, 17.7)             29.9 (28.1, 31.7)

Source: Centers tar Disease Control and PreventIon, National Center for Health Statistics, NHIS, 1991.

Strengthening activities      Stretching exercises
14.1 (13.6, 14.6)+            25.5 (24.7, 26.4)


20.0 (19.2, 20.7)             25.0 (24.0, 26.1)
8.8 (8.3, 9.2)             26.0 (25.1, 27.0)


13.7 (13.2, 14.2)             25.9 (24.9, 26.8)
18.8 (18.0, 19.6)             24.9 (23.8, 26.0)
9.0 (8.5, 9.6)             26.7 (25.7, 27.8)
15.5 (14.2, 16.9)            24.2 (22.5, 26.0)
26.2 (23.7, 28.7)             24.7 (22.1, 27.3)
6.9 (5.8, 8.0)             23.9 (21.7: 26.0)
15.8 (13.9, 17.6)             22.4 (19.9, 24.9)
23.4 (20.3, 26.5)             23.6 (20.4, 26.7)
8.6 (7.0, 10.3)             21.3 (18.3, 24.3)
14.9 (12.3, f7.5)             30.0 (26.2, 33.8)
20.3 (16.0, 24.7)             31.4 (26.0, 36.8)
9.2 (6.6, 11.7)             28.5 (24.3, 32.7)




33.6 (31.7, 35.5)             32.1 (30.1, 34.2)
21.2 (20.1, 22.3)             27.2 (25.8, 28.6)
12.2  (11.1, 13.4)             20.0 (18.6, 21.5)
6.4  (5.1, 7.7)             15.5 (13.4, 17.6)
4.7  (3.1, 6.3)              15.7 (13.2, 18.3)


14.5  (13.3, 15.6)             32.5 (30.7, 34.2)
10.6  (9.9, 11.4)             27.7 (26.3, 29.0)
5.1  (4.5, 5.8)             21.4 (20.1, 22.8)
2.8  (2.0, 3.7)             21.9 (20.0, 23.8)
1.1   (0.7, 1.6)             17.9 (16.0, 19.9)

                          Patterns and Trends in Physical Activity


Table 5-7. Percentage of adults aged 18+ years reporting participation in any strengthening activities* or
    stretching exercises in the prior 2 weeks, by various demographic characteristics, National Health
     Interview Survey (NHIS), United States, 1991

*Strengthening actwities include weight lifting and other exercises to increase muscle strength.
`95% confidence intervals.
*Annual income per family.

187


Physical Activity and Health


Table 5-8. Trends in the percentage of adults aged 18+ years reporting participation in no activity; regular,
    sustained activity; and regular, vigorous activity, by sex, National Health Interview Survey (NHlS)
    and Behavioral Risk Factor Surveillance System (BRFSS), United States, from 1985-I 994
         1985,1990,1991 NHIS                 1986-l 994 BRFSS'

     Males        Females       Total        Males       Females      Total

No activity
1985  19.9 (18.8, 20.9)+ 26.3 (25.3, 27.3)  23.2 (22.3, 24.1)
1986                                   31.2 (30.0, 32.4)  34.3 (33.3, 35.3)   32.8 (32.0, 33.6)
1987                                  29.6 (28.4, 30.8)  33.9 (32.9, 34.9)  31.8 (31.0, 32.6)
1988                                   27.5 (26.5, 28.5)  31.5 (30.5, 32.5)   29.6 (28.8, 30.4)
1989                                  28.8 (27.8, 29.8)  33.6 (32.6, 34.6)  31.3 (30.5, 32.1)
1990 24.9 (23.9, 25.9)  32.4 (31.4, 33.4)  28.3 (28.0, 29.7) 28.6 (27.6, 29.6)  32.3 (31.3, 33.3)  30.5 (29.7, 31.3)
1991  21.4 (20.2, 22.6)  26.9 (25.8, 28.0)  24.3 (23.2, 25.3) 29.0 (28.0, 30.0)  32.8 (32.0, 33.6)   31.0 (30.4, 31.6)
1992                                  26.7 (25.9, 27.5)  31.4 (30.6, 32.2). 29.2 (28.6, 29.8)
1993
1994                                  28.7 (27.9, 29.5)  33.0 (32.2, 33.8)   30.9 (30.3, 31.5)
Regular, sustained activity
1985 27.5 (26.6, 28.4)  22.5 (21.7, 23.3)  24.9 (24.2, 25.5)
1986                                   19.5 (18.5, 20.5)  18.1 (17.3, 18.9)   18.8 (18.2, 19.4)
1987                                  20.0 (18.8, 21.2)  17.6 (16.8, 18.4)   18.8 (18.2, 19.4)
1988                                  20.5 (19.5, 21.5)   19.6 (18.8, 20.4)   20.0 (19.4, 20.6)
1989                                  20.0 (19.0, 21.0)  18.0 (17.2, 18.8)  19.0 (18.4, 19.6)
1990 29.0 (28.1, 29.9)  22.7 (22.0, 23.4)  25.7 (25.1, 26.3) 20.5 (19.5, 21.5)  18.5 (17.7, 19.3)   19.4 (18.8, 20.0)
1991   26.6 (25.7, 27.5)  20.7 (19.9, 21.5)  23.5 (22.9, 24.1) 19.5 (18.7, 20.3)  18.3 (17.5, 19.1)  18.9 (18.3, 19.5)
1992                                   21.0 (20.2, 21.8)  18.4 (17.8, 19.0)  19.7 (19.1, 20.3)
1993
1994                                  19.3 (18.5, 20.1)   18.1 (17.5, 18.7)  18.7 (18.1, 19.3)
Regular, vigorous activity
1985  17.2 (16.1, 18.3)   15.1 (14.3, 15.8)   16.1 (15.3, 16.8)
1986                                   11.2 (10.4, 12.0)   10.3 (9.7, 10.9)   10.7 (10.1, 11.3)
1987                                    10.7 (9.9, 11.5)   10.6 (10.0, 11.2)   10.7 (10.1, 11.31
1988                                    11.1 (10.3, 11.9)   12.3 (11.5, 13.1)   11.7 (11.1, 12.3)
1989                                   11.3 (10.5, 12.1)   11.9 (11.3, 12.5)   11.6 (11.2, 12.0)
1990  18.9 (18.1, 19.7)  15.9 (15.3, 16.4)  17.3 (16.8, 17.8) 11.0 (10.2, 11.8)   12.9 (12.3, 13.5)   12.0 (11.6, 12.4)
1991  18.1 (17.4, 18.8)  14.9 (14.3, 15.5)  16.4 (15.9, 16.9) 11.2 (10.6, 11.8)  12.6 (12.0, 13.2)   11.9 (11.5, 12.3)
1992                                  11.8 (11.2, 12.4)   12.2 (11.6, 12.8)   12.0 (11.6, 12.4)
1993
1994                                  11.4 (10.8, 12.0)   11.4 (10.8, 12.0)   11.4 (11.0, 11.8)
Sources: Centers for Disease Control and PreventIon, National Center for Health Statistics, NHIS, 1985, 1990, 1991; Centers for Disease Control
and Prevention, National Center for Chronic Disease Prevention and Health Promotion, BRFSS, 1986-1992 and 1994.
`25 states and the District of Columbia
`95% confidence intervals.



questions, and the age of respondents. Trends over   Physical Inactivity
time can be monitored only with the YRBS, which   Healthy People 2000 objective 1.5 calls for reducing
was conducted in 1991 and 1993 as well as in 1995.   to no more than 15 percent the proportion of people
An assessment of the test-retest reliability of the   aged 6 years and older who are inactive (USDHHS
YRBS indicated that the four physical activity items   1990). For this report, inactivity was defined as
included in the study had a kappa value (an indicator   performing no vigorous activity (exercise or sports
of reliability) in the "substantial" (i.e., 61-80) or "al-   participation that made the respondent "sweat or
most perfect" (i.e., 81-100) range (Brener et al. 1995).   breathe hard" for at least 20 minutes) and performing




                                188


Figure 5-3. Trends in leisure-time physical activity of
    adults aged 18+ years, NHIS

40 r

01
1985                    1990 1991
               Year

Figure 5-4. Trends in the percentage of adults aged
    18+ years participating in no leisure-time
    activity, BRFSS*
40 r

Ior

Men

10 1

L   `D&I wtrlcted to the 25 states and D.C. for
    which data were available for each oi the5e years
O--I    I     I     I     I     I          J

1986 1987 1988 1989 1990  1991  1992     1994

                Year

no light to moderate activity (walking or bicycling
for at least 30 minutes) during any' of the 7 days
preceding the survey. Among 12- through 21-year-
olds surveyed in the 1992 NHIS-YRBS, the preva-
lence of inactivity in the previous week was 13.7
percent and was higher among females than males
(15.3 percentvs. 12.1 percent) (Table S-9). Overall,
there was no difference among racial and ethnic
groups, but black females had a higher prevalence

Patterns and Trends in Physical Activity

than white females (20.2 percent vs. 13.7 percent).
For both males and females, inactivity increased
with age.

Similarly, in the 1995 school-based YRBS, the
prevalence of inactivity in the previous week was
10.4 percent (Table 5-9) and was higher among
females than males (13.8 percent vs. 7.3 percent).
The prevalence was higher among black students
than white students (15.3 percent vs. 9.3 percent)
and among black females than white females (21.4
percent vs. 11.6 percent). Among female high school
students, a substantial increase in inactivity was
reported in the upper grades.
Thus the Healthy People 2000 goal for inactivity
has been met for adolescents overall but not for black
females or for young adults.

Vigorous Physical Activity
Healthy People 2000 objective 1.4 (USDHHS 1990)
proposes to increase to at least 75 percent the pro-
portion of children and adolescents aged 6-17 years
who engage in vigorous physical activity that pro-
motes cardiorespiratory fitness 3 days or more per
week for 20 minutes or more per occasion. In the
1992 NHIS-YRBS, 53.7 percent of 12- through 21-
year-olds reported having exercised or taken part in
sports that made them "sweat and breathe hard"
during 3 or more of the 7 days preceding the survey
(Table 5-10). However, one-fourth reported no vig-
orous activity during the same time period.
Prevalences of vigorous activity were higher among
males than females (60.2 percent vs. 47.2 percent)
and among white youths than Hispanic youths (54.6
percent vs. 49.5 percent) (Table 5-10). Vigorous
physical activity declined with age. Among males,
the prevalence of vigorous activity was at least 60
percent for those aged 12-17 years but was lower at
older ages (e.g., 42.2 percent among 21-year-olds).
Among females aged 12-14 years, the prevalence
was at least 60 percent but was lower at older ages
(e.g., 30.2 percent among 21-year-olds). The preva-
lence of vigorous activity was associated positively
with income and was higher during the spring than
during other seasons.

In the 1995 YRBS, 63.7 percent of students in
grades 9-12 reported having exercised or taken part
in sports that made them "sweat and breathe hard"
for at least 20 minutes during 3 or more of the 7 days

189


Physical Activity and Health

Table 5-9. Percentage of young people reporting no participation in vigorous or moderate physical activity
  during any of the 7 days preceding the survey, by demographic group, 1992 yational Health
  Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS) and 1995 Youth Risk Behavior Survey
     (YRBS), United States

Demographic group

1992 NHIS-YRBS*                1995 YRBS+

Overall

13.7 (12.9, 14.5?

Sex
  Males
  Females

12.1 (11.0, 13.2)
15.3 (14.1, 16.5)

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females

13.4  (12.4, 14.5)
13.1  (11.7, 14.6)
13.7  (12.4, 15.1)
14.7 (12.7, 16.6)
9.2  (6.9, 11.5)
20.2  (17.0, 23.5)
14.3  (12.4, 16.3)
11.1  (8.4, 13.8)
17.8  (14.9, 20.7)

Age (years)
  Males
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
  Females
    12
     13
     14
    15
     16
     17
    18
    19
    20
    21

7.7  (5.1, 10.2)
6.0  (3.6,  8.3)
3.6  (2.1,  5.1)
6.3  (3.7,  8.9)
9.6  (6.8, 12.4)
10.5  (7.2, 13.9)
18.8  (14.4, 23.3)
18.6  (14.7; 22.5)
22.3  (17.9, 26.8)
18.1  (14.3, 21.9)

8.4  (5.2, 11.5)
6.8  (4.4,  9.2)
8.3  (5.1, 11.5)
9.8  (7.0, 12.6)
14.4  (10.9, 17.9)
16.8  (13.2, 20.3)
18.7  (14.5, 22.8)
22.3  (18.1, 26.5)
25.0  (21.0, 28.9)
19.6  (16.4, 22.9)

Annual family income
< $10,000
  $10,000-19,999
  $20,000-34,999
  $35,000-49,999         13.8 (11.6, 15.9)

14.9 (12.6, 17.3)
16.0 (14.1, 17.9)
12.2 (10.6, 13.8)

10.4 (9.0, 11.9)

7.3 (6.5, 8.1)
13.8 (11.2, 16.3)

Grade in school
Males

9.3  (7.9, 10.7)
7.3  (6.4,  8.1)
11.6  (8.7, 14.4)
15.3  (12.4, 18.2)
8.1  (5.4, 10.7)
21.4  (16.9, 25.8)
11.3  (8.6, 14.1)
7.5  (5.1,  9.9)
15.0  (10.6, 19.5)

9             6.0 (3.4, 8.7)
10             5.2 (3.0, 7.4)
11            7.9 (4.3, 11.4)
12            10.0 (7.4, 12.5)

Females

9             8.7 (6.1, 11.3)
10             9.2 (7.3, 11.0)
11            17.8 (13.6, 22.0)
12            18.5 (13.3, 23.7)

$50,000+            11.2 (9.8, 12.7)

Sources: Centers for Disease Control and Prevention, National Center for Health Statistics, NHIS-YRBS, 1992 machine readable data file and
documentation, 1993; Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion,
YRBS 1995 data tape (in press).
*A national household-based survey oi youths aged 12-21 years.
`A national school-based survey oi students in grades 9-12.
`95% confidence intervals.

190


Patterns and Trends in Physical Activity

Table 5-l 0.  Percentage of young people reporting participation in vigorous physical activity during 3 or more
     of the 7 days preceding the survey, by demographic group, 1992 National Health Interview
     Survey-Youth Risk Behavior Survey (NHIS-YRBS) and 1995 Youth Risk Behavior Survey (YRBS),
        United States

Demographic group          1992 NHIS-YRBS*                  1995 YRBS+

Overall                  53.7 (52.5, 54.9)'                      63.7 (60.4, 66.9)

Sex
  Males
  Females

60.2 (58.6, 61.8)                     74.4 (72.1, 76.6)
47.2 (45.6, 48.8)                     52.1 (47.5, 56.8)

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females

54.6  (53.2, 56.0)                          67.0  (62.6, 71.4)
60.2  (58.4, 62.0)                         16.0  (73.0, 78.9)
49.0  (46.8, 51.2)                         56.7 ( 50.0, 63.4)
52.6  (49.9, 55.3)                         53.2  (49.6, 56.8)
62.7  (58.8, 66.6)                          68.1  (62.8, 73.4)
42.3  (38.6, 46.0)                        41.3  (35.5, 42.1)
49.5  (46.6, 52.4)                         57.3  (53.7, 60.9)
56.7  (52.6, 60.8)                          69.7  (64.9, 74.5)
41.7  (38.2, 45.2)                          45.2  (39.9, 50.6)

Age (years)
  Males
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
  Females
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21

70.8  (66.7, 74.9)
73.7  (69.4, 78.0)
76.1  (72.2, 80.0)
72.6  (68.1, 71.1)
65.6  (60.3, 70.9)
60.2  (54.7, 65.7)
48.4  (43.1, 53.7)
44.1  (38.4, 49.8)
43.4' (38.5, 48.3)
42.2  (37.1, 47.3)

Grade in school
Males

9             80.8 (75.9, 85.6)
10             75.9 (72.5, 79.3)
11              70.2 (67.5, 72.9)
12             66.9 (63.0, 70.7)

Females

66.2  (62.1, 70.3)
63.1  (58.0, 68.2)
63.1  (58.4, 67.8)
56.6  (51.9, 61.3)
50.9  (45.6, 56.2)
43.6  (38.1, 49.1)
37.5  (32.2, 42.8)
32.6  (27.3, 37.9)
28.2  (23.9, 32.5)
30.2  (25.5, 34.9)

9              60.9 (54.8, 67.0)
10              54.4 (47.6, 61.3)
11              44.7 (40.6, 48.9)
12              41.0 (34.6, 47.5)

Annual family income
< $10,000
$10,000-19,999
$20,000-34,999
$35,000-49,999
$50,000+

46.7 (43.2, 50.2)
4i.5 (46.0, 51.1)
55.0 (52.5, 57.6)
58.4 (55.5, 61.3)
60.2 (57.9, 62.6)

Sources: Centers for Disease Control and Prevention, National Center for Health Statistics, NHIS-YRBS, 1992 machine readable data file and
documentatron, 1993; Centers for Disease Control and Prevention, Natronal Center for Chronic Disease Prevention and Health Promotion,
YRBS 1995 data tape fin press).
*A national household-based survey of youths aged 12-2 1 Years.
`A natronal school-based survey of students in grades 9-l 2.
`9S% confidence intervals.

191


physical Activity and Health

preceding the survey (Table 5-10). However, 16.0
percent reported no vigorous physical activity dur-
ing the same time period. Subgroup patterns were
similar to those reported for the NHIS-YRBS. Vigor-
ous physical activity was more common among male
than female students (74.4 percent vs. 52.1 percent)
and among white than black or Hispanic students
(67 percent vs. 53.2 percent and 57.3 percent, re-
spectively). Among both male and female students,
vigorous activity was less common in the upper
grades. From 1991 through 1995, the overall preva-
lence did not change significantly among students in
grades 9-12 (data not shown).
NHIS-YRBS and YRBS data clearly show that the
prevalence ofvigorous physical activity among young
people falls short of the Healclty People 2000 goal of
75 percent.

Other Physical Activity

Healthy People 2000 objective 1.6 (USDHHS 1990)
aims for at least 40 percent of people aged 6 and older
to regularly perform physical activities that enhance
and maintain muscular strength, muscular endur-
ance, and flexibility. The 1992 NHIS-YRBS indicated
that 45.6 percent of 12- through 21-year-olds had
participated instrengtheningor toningactivities (e.g.,
push-ups, sit-ups, or weight lifting) during at least 3
of the 7 days preceding the survey (Table 5- 11). These
activities were more common among males than
females (54.6 percent vs. 36.4 percent) and among
white and Hispanic youths than black youths (46.4
percent and 45.4 percent, respectively, vs. 39.8 per-
cent). Among both males and females, the prevalence
of strengthening or toning activities decreased as age
increased and was greater among young people living
in households with higher incomes.
  Similar to the NHIS-YRBS, the 1995 YRBS indi-
cated that 50.3 percent ofstudentsin grades9-12 had
participated in strengthening or toning activities dur-
ing at least 3 of the 7 days preceding the survey (Table
5-11). Subgroup patterns were similar to those re-
ported for the 1992 NHIS-YRBS. Male students were
more likely than female students to participate in
strengthening or toning activities (59.1 percent vs.
41.0 percent), and white students were more likely
than black students to do so (52.8 percent vs. 41.4
percent). Among female students, participation was
greater among those in lower grades, but this practice

did not vary by grade among male students. Between
1991 and 1995, the overall prevalence of strengthening
or toning activities among students in grades 9-12 did
not change (data not shown).

In the 1992 NHIS-YRBS, 48.0 percent of 12-
through 21-year-olds reported having participated
instretchingactivities (e.g., toe touching, knee bend-
ing, ot leg stretching) during at least 3 of the 7 days
preceding the survey. White and Hispanic youths
were more likely than black youths to report this
(49.2 percent and485 percent, respectively, vs. 40.7
percent). Overall, the prevalence of stretching activi-
ties did not differ by sex, although these activities
were more common among black males than among
black females (44.9 percent vs. 36.5 percent). Among
both males and females, the prevalence was higher in
the younger age categories. Participation was also
higher with higher family income.

In the 1995 YRBS, 53.0 percent of students in
grades 9-12 reported having participated in stretch-
ing activities during at least 3 of the 7 days preceding
the survey (Table 5-12). Subgroup patterns were
generally similar to those reported for the NHIS-
YRBS. Similar proportions of male and female stu-
dents participated in stretching activities (55.5
percent and 50.4 percent, respectively), and white
students were more likely than black students to do
so (55.1 percent vs. 45.4 percent). Participation in
stretching activities declined across grades for both
male and female students. Between 1991 and 1995,
the overall prevalence among students in grades 9-12
did not change significantly (data not shown).
Thus the Healthy People 2000 objective for
strengthening and stretching activities has been met
overall among adolescents and young adults but not
among all subgroups.

Healthy People 2000 objective 1.3 (USDHHS
1990) proposes to increase to at least 30 percent the
proportion of people aged 6 and older who engage
regularly, preferably daily, in light to moderate physi-
cal activity for at least 30 minutes per day. Walking
and bicycling can be used to measure light to mod-
erate physical activity among young people. In the
1992 NHIS-YRBS, 26.4 percent of 12- through 21-
year-olds reported having walked or bicycled for 30
minutes or more on at least 5 of the 7 days preceding
the survey (Table 5-13). These activities were more
common among males than females (29.1 percent
vs. 23.7 percent) and among Hispanic youths than

192


Patterns and Trends in Physical Activity

Table 5-11. Percentage of young people reporting participation in strengthening or toning activities during 3 or
    more of the 7 days preceding the survey, by demographic group, 1992 National Health Interview
    Survey-Youth Risk Behavior Survey (NHIS-YRBS) and 1995 Youth Risk Behavior Survey (YRBS),
       United States

Demographic group         1992 NHIS-YRBS'                 1995 YRBS+

Overall                45.6 (44.4, 46.8)*                     50.3 (46.6, 54.0)

Sex
  Males
  Females

54.6 (53.0, 56.2)                     59.1 (56.1, 62.1)
36.4 (34.8, 38.0)                    41.0 (36.0, 46.0)

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females

46.4  (45.0, 47.8)                        52.8  (47.2, 58.4)
54.4  (52.6, 56.2)                         60.3  (56.4, 64.2)
38.4  (36.4, 40.4)                   24.4  (36.4,  2.4)
39.8  (37.5, 42.2)                         41.4  (37.9, 45.0)
53.2  (49.3, 57.1)                        54.2  (49.7, 58.6)
26.2  (23.1, 29.3)                         31.3  (26.7, 35.9)
45.4  (42.5, 48.3)                          47.4  (41.8, 53.1)
53.3  (49.4, 57.2)                         57.8  (51.9, 63.8)
36.9  (33.2, 40.6)                         37.4  (29.6, 45.2)

Age (yeaN
  Males
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
  Females
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21

Grade in school
Males

59.4  (54.7, 64.1)
66.3  (62.2, 70.4)
61.1  (56.0, 66.2)
66.6  (61.9, 71.3)
61.3  (56.0, 66.6)
53.9  (48.6, 59.2)
46.0  (41.3, 50.7)
45.2  (39.7, 50.7)
42.0  (37.5, 46.5)
40.5  (35.8, 45.2)

9             65.3 (58.0, 72.5)
10             60.0 (55.8, 64.2)
11             55.9 (52.5, 59.2)
12             54.7 (49.7, 59.7)

Females

43.9  (39.6, 48.2)
46.9  (41.6, 52.2)
47.6  (42.7, 52.5)
44.0  (39.1, 48.9)
38.1  (33.6, 42.6)
37.1  (32.0, 42.2)
31.1  (25.6, 36.6)
26.4  (22.1, 30.7)
26.3  (22.0, 30.6)
23.2  (19.3, 27.1)

9             51.3 (42.9, 59.8)
10             45.6 (38.3, 53.0)
11             31.0 (27.6, 34.3)
12             30.0 (25.1, 34.9)

36.4 (33.7, 39.1)
44.6 (41.9, 47.3)
46.5 (44.0, 49.1)
49.6 (46.7, 52.5)

Annual family income
  <$10,000
   $10,000-$19,999
   $20,000-$34,999
   $35,000-$49,999
   $50,000+             51.4 (49.1, 53.8)
Sources: Centers for Disease Control and Prevention, National Center ior Health Statrstics, NHIS-YRBS.1992 machine readable data iile and
documentatron, 1993; Centers for Disease Control and Prevention, National Center ior Chronic Disease Prevention and Health Promotion,
YRBS 1995 data tape trn press).
`A national household-based survey oi youths aged 12-21 years.
`A national school-based survey oi students in grades 9-l 2.
`95% coniidence intervals.

193


Physical Activity and Health

Table 5-12. Percentage of young people reporting participation in stretching activities during 3 or more
   of the 7 days preceding the survey, by demographic group, 1992 National Health Interview
   Survey-Youth Risk Behavior Survey (NHIS-YRBS) and 1995 Youth Risk Behavior Survey
      (YRBS), United States

Demographic group         1992 NHIS-YRBS'                 1995 YRBS+

Overall                 48.0 (46.8, 49.2)'

Sex
  Males
  Females

48.2 (46.6, 49.8)
47.9 (46.3, 49.5)

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females

49.2  (47.8, 50.6)                          55.1  (50.8, 59.3)
48.0  (46.0, 50.0)                         56.1  (52.1, 60.1)
50.4  (48.4, 52.4)                          53.9 (48.2,' 59.5)
40.7  (38.0, 43.4)                          45.4  (41.7, 49.0)
44.9  (41 .o, 48.81                          50.5  (45.0, 55.9)
36.5  (32.8, 40.2)                          41.5  (36.6, 46.3
48.5  (45.8, 51.2)                           49.1  (45.0, 53.2)
49.9  (46.0, 53.8)                         54.8  (50.1, 59.6)
47.0  (43.3, 50.7)                          43.5  (37.6, 49.5)

Age (years)
  Males
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
  Females
    12
    13
     14
    15
    16
    17
    18
    19
    20
    21

Grade in school
Males

55.4  (50.5, 60.3)
62.0 (57.3, 66.7)
57.9  (53.2, 62.6)
56.1  (51.0, 61.2)
54.0  (48.7, 59.3)
48.2  (42.9, 53.5)
36.2  (31.1, 41.3)
36.7  (32.0, 41.4)
32.9  (28.4, 37.4)
38.5  (33.4, 43.6)

9             65.7 (58.9, 72.6)
10             51.1 (47.8, 54.4)
11             52.9 (48.1, 57.6)
12             49.8 (42.0, 57.7)

Females

62.5  (58.0, 67.0)
62.5  (57.2, 67.8)
61.6  (56.7, 66.51
57.9  (53.0, 62.8)
52.0  (47.1, 56.9)
42.0  (37.1, 46.9)
38.5  (33.0, 44.0)
33.1  (28.0, 38.2)
33.9  (29.6, 38.2)
35.0  (30.9, 39.1)

9            59.9 (52.8, 67.0)
10             55.8 (49.6, 61.9)
11             39.5 (33.7, 45.3)
12             38.4 (32.7, 44.1)

40.8 (37.7,. 43.9)
44.5 (41.8, 47.2)
48.2 (45.9, 50.6)
51.9 (49.2, 54.6)

Annual family income
  < $10,000
  $10,000-$19,999
  $20,000-$34,999
  $35,000-$49,999
   4 50,000+             54.2 (51.7, 56.8)
Sources: Centers for Disease Control and Prevention, National Center ior Health Statistics, NHIS-`fRt%, 199.7 machine readable data
file and documentation, 1993; Centers for Disease Control and Preventton, National Center for Chronic Disease Preventjon and
Health Promotion, YRBS 1995 data tape (in press).
*A national household-based survey of youths aged 12-21 years.
`A national school-based survey oi students in grades 9-l 2.
`95% confidence intervals.

53.0 (49.9, 56.2)

55.5 (52.3, 58.7)
50.4 (46.6, 54.3)

194


Patterns and Trends in Physical Activity

Table 5-l 3.  Percentage of young people reporting participation in walking or bicycling for 30 minutes or more
     during 5 or more of the 7 days preceding the survey, by demographic group, 1992 National Health
     Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS) and 1995 Youth Risk Behavior Survey
      (YRBS), United States

Demographic group          1992 NHIS-YRBS*                   1995 YRBS+

Overall                  26.4 (25.4, 27.4)'                      21.1 (18.7, 23.5)

Sex
  Males
  Females

29.1 (27.5, 30.7)                      21.6 (18.4, 24.8)
23.7 (22.3, 25.1)                      20.5 (17.8, 23.2)

Race/Ethnicity
White, non-Hispanic
   Males
   Females
Black, non-Hispanic
   Males
   Females
Hispanic
   Males
   Females

25.1  (23.9, 26.3)                          18.3  (15.0, 21.6)
27.5  (25.7, 29.3)                           19.7  (15.5, 23.8)
22.7  (21.1, 24.3)                      16.8  (13.9, 19.8)
26.9  (24.6, 29.2)                          27.0  (23.2, 30.9)
29.8  (26.7, 32.9)                          27.2  (23.2, 31.2)
23.9  (20.2, 27.6)                          26.4  (20.8, 32.0)
32.3  (29.8, 34.9)                         26.8  (22.6, 31.0)
35.5  (31.6, 39.4)                         26.0  (19.9, 32.1)
28.8  (25.5, 32.1)                           27.6  (23.8, 31.5)

Age (years)
  Males
    12
    13
    14
    15
    16
    17
    18
    19
   20
    21
  Females
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21

38.9  (34.6, 43.2)
37.3  (32.4, 42.2)
35.3  (31.2, 39.4)
33.9  (29.0, 38.8)
29.9  (25.6, 34.2)
22.2  (17.7, 26.7)
23.3  (18.6, 28.0)
21.3  (17.2, 25.4)
22.0  (17.9, 26.1)
23.3. (19.0, 27.6)

Grade in school
Males

9              27.9 (22.1, 33.7)
10              21.7 (17.8, 25.6)
11               19.2 (16.2, 22.1)
12              17.7 (13.1, 22.3)

Females

32.2 (28.1, 36.3)
28.5 (24.0, 33.0)
28.7 (23.8, 33.6)
22.9 (18.8, 27.0)
22.9  (1 8.8, 27.0)
19.4  (1 5.5, 23.3)
20.1  (1 6.0, 24.2)
18.8  (1 4.5, 23.1)
20.8  (1 6.7, 24.9)
22.1  (1 8.4, 25.8)

9              22.5 (18.5, 26.5)
10              22.8 (18.5, 27.2)
11              16.8 (13.3, 20.3)
12              76.1 (11.6, 20.6)

Annual family income
< $10,000
  $10,000-$19,999
   $20,000-$34,999
   $35,000-$49,999
   $50,000+

27.8 (25.1, 30.5)
29.5 (26.8, 32.2)
27:6 (25.2, 30.0)
25.5 (23.2, 27.9)
23.5 (21.5, 25.5)

Sources: Centers for Disease Control and Prevention, National Center for Health Statistics, NHIS-YRBS, 1992 machine readable data fife and
documentation, 1993; Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion,
YRBS 1995 data tape (in press).
*A national household-based survey of youths aged 12-21 years.
`A national school-based survey of students in grades 9-l 2.
`95% confidence intervals.

195


Physical Activity and Health

Table 5-l 4. Percentage of young people reporting participation in selected physical activities during 1 or more
    of the 7 days preceding the survey, by demographic group, 1992 National Health Interview Survey-
    Youth Risk Behavior Survey (NHIS-YRBS),' United States
-

                   Aerobics         Baseball, softball,     Basketball, football,
Demographic group       or dancing         or Frisbee@               or soccer
-

Overall

38.2 (37.1,39.2)+      22.4 (21.4,23.4)       45.8 (44.6,47.1)

Sex
Males
Females

Race/Ethnicity
White, non-Hispanic
Black, non-Hispanic
Hispanic

Age (years)
Males
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21

Females
12
13
14
15
16
17
18
19
20
21

22.6 (21.3,24.0)       27.2 (25.7,28.8)       61.7 (60.fI63.3)
53.9 (52.4,55.5)       17.5 (16.4,18.7)       29.7 (28.2,31.3)

35.0 (33.7,36.2)       23.6 (22.3,24.9)    44.7 i43.1,46.2)
49.4 (46.6,52.1)       16.6 (14.3,18.9)       49.5 (46.7,52.3)
42.0 (39.0,45.0)       23.4 (21.1,25.7)       47.1 (44.4,49.8)

26.9 (22.5,31.2)        46.4 (41.6,51.3)        81.2 (77.4,85.0)
23.4 (19.6,27.3)        40.6 (35.8,45.3)        84.3 (80.8,87.9)
22.0 (18.4,25.7)        40.9 (36.6,45.2)         78.5 (74.3,82.6)
21.9 (17.7,26.1)        25.6 (21.0,30.3)         76.7 (72.5,81.0)
24.5 (20.2,28.9)        27.4 (22.9,31.9)        69.6 (64.5,74.6)
20.8 (16.8,24.6)        22.5 (18.1,26.9)        59.3 (54.2,64.3)
19.0 (14.9,23.1)        20.8 (16.3,25.2)        54.6 (49.1,60.0)
24.0 (19.6,28.4)        17.5 (13.8,21.2)         43.8 (38.5,49.0)
21.2 (17.2,25.2)        17.0 (13.3,20.8)         38.5 (33.9,43.2)
21.4 (17.2,25.7)        15.6 (12.1,lq.l)         32.4 (27.6,37.1)

63.1 (58.7,67.5)         37.9 (33.4,42.5)
63.7 (59.5,67.9)        30.3 (26.2,34.3)
63.7 (59.0,68.3)        29.1 (24.7,33.5)
62.0 (57.5,66.4)         22.6 (18.3,26.9)
55.7 (50.5,60.9)        16.0 (12.3,19.6)
54.0 (48.8,59.2)        10.2  (7.4,13.1)
50.3 (45.2,55.5)        11.4  (7.3,15.4)
44.8 (39.1,50.4)         6.9  (4.4, 9.3)
40.7 (36.2,45.2)          7.6  (4.8,10.4)
45.6 (41.0,50.2)         8.4  (5.9,10.9)

white or black youths (32.3 percent vs. 25.1 p&cent
and 26.9 percent, respectively). Walking or bicy-
cling decreased as age increased and was more preva-
lent in the fall than in other seasons.

In the 1995 YRBS, 21.1 percent of students in
grades 9-12 reported having walked or bicycled for
30 minutes or more on at least 5 of the 7 days
preceding the survey (Table 5-13). Male and female
students reported similar prevalences of these activi-
ties. Black and Hispanic students were more likely

62.6 (57.6,67.6)
61.6 (56.9,66.3)
51.9 (46.8,57.1)
41.6 (37.2,46.1)
28.0 (23.3,32.6)
23.4 (19.0,27.7)
13.8 (10.2,17.4)
8.5  (6.0, 11.0)
6.9  (4.7, 9.1)
7.5 (5.2, 9.8)

than white students to have walked or bicycled (27.0
percent and 26.8 percent, respectively, vs. 18.3 per-
cent). Between 1993 and 1995, the overall preva-
lence among students in grades 9-12 did not change
significantly (data not shown).

It thus appears that the Healthy People 2000
objective for light to moderate physical activity has
not been attained by adolescents and young adults.
The 1992 NHIS-YRBS provided information on
participation in seven additional types of physical

196


Patterns and Trends in Physical Activity

Table 5-14. Continued

House cleaning or yard
work for 2 30 minutes

82.8 (81.7, 83.8)

Running, jogging,
or swimming
55.3 (54.1,56.6)

Skating, skiing,
or skateboarding

13.3 (12.5,14.0)

Tennis, raquetball,
or squash

10.5 (9.8, 11.2)

78.1 (76.6, 79.5)         57.6 (55.9,59.3)         15.9
87.5 (86.3, 88.7)         53.0 (51.4,54.7)         10.6

83.1 (81.9, 84.3)         55.8 (54.3,57.3)         15.2
84.2 (81.9, 86.5)          52.4 (49.5,55.3)          9.0
80.1 (77.9, 82.4)          53.6 (50.9,56.4)          9.8

14.8,17.0)        11.7 (10.7,12.8)
(9.6, 11.5)        9.3 (8.4,10.2)


14.2,16.2)        11.4 (10.6,12.3)
(7.3,10.8)        5.4 (4.2, 6.6)
(8.2, 11.5)         8.0 (6.7, 9.4)

76.9 (72.9, 81.0)          72.8 (68.3,77.3)         32.5 (27.8,37.3)         14.4 (10.8,18.0)
83.3 (80.1, 86.5)          74.3 (70.1,78.4)          26.2 (22.1,30.3)         13.3 (10.3,16.4)
79.4 (75.5, 83.4)          71.2 (66.8,75.6)         20.7 (16.9,24.5)         14.5 (11.3,17.8)
82.9(79.3, 86.5)         70.8 (66.5,75.1)         19.9 (15.9,23.9)         15.3 (11.7,lB.g)
79.6 (75.7, 83.6)         63.4 (58.8,68.1)         13.4 (10.0,16.8)         10.4  (7.4, 13.3)
78.7 (74.5, 82.9)          55.3 (49.9,60.7)         12.2  (8.6,15.7)         11.3  (8.0,14.6)
70.9 (65.9, 75.9)          47.4 (42.2,52.5)          9.4  (6.3,12.4)          11.6  (8.3,14.9)

75.0(69.6, 80.4)
74.4 (70.3, 78.5)
77.6 (73.7, 81.5)

88.0 (84.8, 91.2)
88.1 (85.1, 91 .l)
87.2 (83.9, 90.4)
88.5 (85.3, 91.7)
89.1 (85.7, 92.5)
86.0 (82.6, 89.4)
87.0 (83.4, 90.5)
82.6 (78.1, 87.1)
87.1 (83.0, 91.2)
89.8 (86.2, 93.4)

46.3 (41.3,51.2)
34.4 (29.9,38.9)
39.8 (34.1,45.5)

80.5 (76.4,84.53
76.2 (72.1,80.3)
72.9 (68.6,77.2)
65.4 (60.7,70.1)
59.7 (54.8,64.6)
49.0 (43.5,54.4)
41.5 (35.8,47.3)
32.9 (27.8,38.0)
30.8 (25.8,35.7)
30.3 (26.0,34.6)

10.8 (7.7, 14.0)
8.6 (6.1, 11.2)
5.9 (3.8, 7.9)

24.9 (20.5,29.3)
19.7 (16.1,23.4)
14.8 (11.6,18.0)
10.0  (7.0, 12.9)
8.9  (6.2, 11.7)
4.8  (2.7, 6.8)
8.1  (5.5,10.7)
6.6  (4.1, 9.1)
5.8  (3.5, 8.0)
4.8  (3.1, 6.6)

9.9  (6.9,12.8)
8.2  (5.5,lO.a)
9.5  (6.5,12.5)

13.9
12.4
13.0
16.1
11.1
8.0
6.9
3.8
5.8
4.1

10.5,17.3)
(9.2,15.6)
10.0,15.9)
12.6,19.6)
(8.0,14.2)
(5.4,10.5)
(4.4, 9.5)
(2.1, 5.4)
(3.6, 8.0)
(2.2, 5.9)

Source: Centers for Disease Control and Prevention. National Center for Health Statistics, NHIS-YRBS, 1992 machine readable data file and
documentation, 1993.

*A national household-based survey of youths aged 12-21 years.
`95% confidence intervals.

activity during 1 or more of the 7 days preceding the
survey: aerobics or dancing; baseball, softball, or
Frisbee@`; basketball, football, or soccer; houseclean-
ing or yard work for at least 30 minutes; running,
jogging, or swimming for exercise; skating, skiing,

or skateboarding; and tennis, racquetball, or
squash (Table 5-14). Among 12- through 21-year-
olds, males were more likely than females to
participate in baseball, softball, or Frisbee@; in
basketball, football, or soccer; in running, jogging,
or swimming for exercise; in skating, skiing, or

`Use of trade names is for identification only and does not imply
endorsement by the U.S. Department of Health and Human Services.

skateboarding; and in tennis, racquetball, or squash.

197


Physical Activity and Health

Table 5-l 5. Percentage of students in grades 9-T 2 reporting enrollment in physical education class, daily
    attendance in physical education class, and participation in exercise or sports for at least
    20 minutes during an average physical education class, by demographic group, 1995 Youth
     Risk Behavior Survey (YRBS),' United States

Demographic group

Enrolled in       Attended physical    Exercised or played sports
physical education    education daily     2 20 minutes per class+

Overall           59.6(48.6, 70.5?      25.4 (15.8, 34.9)      69.7 (66.4,72.9)

Sex
  Males
  Females

62.2 (52.5,71.8)      27.0 (16.8, 37.2)      74.8 (71.8, 77.8)
56.8 (44.1, 69.6)      23.5 (14.5, 32.4)      63.7 (59.3,68.1)

Race/Ethnicity
White, non-Hispanic
   Males
   Females

62.9 (49.8, 76.1)
64.2 (52.6,75.8)
61.7(46.4, 77.0)

Black, non-Hispanic    50.2(45.1,55.3)
Males           56.8(50.6,62.9)
Females         44.4(37.3,51.5)

Hispanic          51.0(40.9,61.2)
Males           57.6(48.6, 66.6)
Females         44.6 (3 1.2, 58.0)

21.7  (9.9,33.5)
23.3 (11.2,35.3)
19.9  (8.0, 3 1.8)

33.8 (29.9,37.8)
37.7 (32.3,43.0)
30.1 (25.8,34.5)

33.1 (24.5,41.8)
36.2 (28.8,43.6)
30.1 (18.7, 41.5)

71.3 (67.d, 75.6)
74.8 (71.1,78.5)
67.1 (60.5, 73.8)

59.0 (54.6,63.3)
71.8 (65.9,77.8)
46.6 (39.3, 53.8)

68.5 (62.8, 74.1)
76.0 (67.0,85.0)
59.0 (52.5,65.6)

Grade in school
  Males
    9
   10
   11
   12

80.5(75.1,85.9)       42.1 (23.3,60.8)       76.5 (72.2,80.9)
72.6 (62.3,82.8)       34.8 (18.9, 50.8)       73.1 (67.9, 78.3)
51.5 (32.8, 70.1)        17.4  (9.3, 25.6)       75.8 (70.3,81.2)
45.4(29.0,61.91        14.8  (9.2,20.4)       73.7 (68.1,79.3)

Females
  9
10
11
12

80.8 (73.8,87.8)        39.7 (21.5, 58.0)       65.6 (57.2, 74.1)
71.4(59.3,83.5)        33.8 (17.4, 50.3)       63.9 (58.8,68.9)
41.2 (22.8, 59.6)        12.3  (7.6,17.1)       57.2 (48.4,66.0)
39.1 (20.9, 57.2)        11.1  (6.5, 15.7)       66.0 (59.7,72.4)

Source: Centers ior Disease Control and PreventIon, NatIonal Center t'or Chronic Disease Prevention and Health Promotion, YRBS 1995 data
tape (in press).
`A national school-based survey of students in grades 9-12.
`Among students enrolled in physical education.
`95% confidence Intervals.

Females were more likely than males to participate
in aerobics or dancing and in house cleaning or   skating, skiing, or skateboarding. For females, par-
                    ticipation in aerobics or dancing and in tennis,
                     racquetball, or squash also decreased by age.

                   Physical Education in High School
                    The YRBS provides data on enrollment and daily
                     attendance in school physical education for students
                    in grades 9-12. (See Chapter 6 for a discussion of the
                     availability of physical education programs.) In 1995,

yard work for at least 30 minutes. White youths
were more likely than black or Hispanic youths to
participate in skating, skiing, or skateboardingand
in tennis, racquetball, or squash. For both males
and females, increasing age was associated with
decreasing participation in baseball, softball, or
Frisbee@; in basketball, football, or soccer; in run-
ning, jogging, or swimming for exercise; and in

198


Patterns and Trends in Physical Activity

Fable 5-l 6. Percentage of students in grades 9-l 2 reporting participation on at least one sports team run by a
    school or by other organizations during the year preceding the survey, by demographic group,
     1995 Youth Risk Behavior Survey (YRBS),* United States

Demographic group
Overall

Sex
  Males
  Females
Race/Ethnicity
White, non-Hispanic
    Males
    Females
Black, non-Hispanic
    Males
    Females
Hispanic
    Males
     Females

Grade in school
  Males
      9
     10
     11
     12

  Females
      9
     10
     11

Participation on sports
team run by a school
50.3 (46.6, 54.0)+


57.8 (53.7, 62.0)
42.4 (38.6, 46.2)


53.9(49.6, 58.2)
59.9 (54.8, 65.0)
47.1 (43.0, 51.2)

45.0 (39.9, 50.2)
57.9 (52.6, 63.2)
34.9 (28.2,41.7)

37.8(33.6,42.0)
48.6 (44.0, 53.2)
27.3 (21.9, 32.7)




61.7 (54.0, 6" -j
55.6 (50.1. :.l)
56.0 (49 _ 52.4)
58.3 (= w.0, 64.6)


.3.7 (39.2,48.2)
47.9(42.8, 53.0)
39.4 (32.1, 46.7)

Participation on sports team
run by other organization
36.9(34.4, 39.4)


46.4(43.4,49.3)
26.8 (24.2, 29.4)


39.1'(35.7, 42.5)
47.2 (43.0, 51.4)
29.9 (26.8. 32.9)

32 4 (29.0 35.9)
  .
46.8 (42.4: 51.1)
21.1 (16.5, 25.8)

32.0 (28.5, 35.6)
43.2 (37.9, 48.4)
21.2 (16.5, 25.9)



52.8(47.0, 58.7)
46.9 (42.4, 51.4)
43.1 (40.6, 45.7)
42.8 (39.2,46.3)


32.0 (28.2, 35.9)
32.4(26.8, 38.0)
23.8 (19.9, 27.6)

12

38.8 (32.4; 45.1)            19.8 (15.2, 24.3)

Source: Centers ior Disease Control a+  evention, National Center for Chronic Disease Prevention and Health Promotion, YRBS 1995 data
tape (in press).
`A national school-based surw .Y  (! 1 ,n grades 9-l 2.
+95'% confidence intervals.

59.6 tiercent ofsrudents in grades 9-12 were enrolled in
-Iqsical education (Table 5-15). Enrollment did not
vary by sex or rat .LF rcity, but it decreased by grade.
Between 1991 3njA lW.3, overall enrollment in physical
education am.)ng ` udents in grades 9-12 did not
change sigmficantl- (data not shown).

HeaIt/i> Pea: .e 2000 objective 1.8 (USDHHS
1990) recommr ;Ids increasing to at least 50 percent
the propo; tion If children and adolescents in grades l-
12 11 ;ro parti;,pate in daily school physical education.

I ne 1995 `iRBS indicated that daily attendance in

physical education among high school students was
25.4 percent and did not vary by sex or race/ethnicity
(Table 5-15). Daily attendance decreased with in-
creasing grade for both male and female students.
Between 1991 and 1995, overall daily attendance in
physical education classes in grades 9-12 decreased
significantly, from 41.6 percent to 25.4 percent (data
not shown). Current trend data thus indicate that the
Healthy People 2000 goal of 50 percent has not been
attained and is also becoming more distant.

Healthy People 2000 objective 1.9 (USDHHS
1990) recommends that students be active for at

199


Physical Activity and Health

least 50 percent of the class time they spend in
physical education. In 1995, 69.7 percent of stu-
dents in grades 9-12 who were taking physical
education reported being physically active for at
least 20 minutes, which is about half of a typical
class period (Table S-15). This active participa-
tion was more common among male students than
female students (74.8 percent vs. 63.7 percent)
and among white students than black students
(71.3 percent vs. 59.0 percent). Between 1991 and
1995, the overall percentage of students in grades
9-12 taking physical education who reported be-
ing physically active for at least 20 minutes de-
creased from 80.7 percent to 69.7 percent (data
not shown). Decreases between 1991 or 1993 and
1995 occurred for students in all grades. Thus a
decreasing proportion of the high school students
who are enrolled in physical education classes are
meeting the Healthy People 2000 goal for time
spent being physically active in class.

Only 18.6 percent of all high school students
were physically active for at least 20 minutes on a
daily basis in physical education classes (data not
shown).

Sports Team Participation

The YRBS provides data on participation on sports
teams during the 12 months preceding the survey
for students in grades 9-12. In 1995, 50.3 percent
of students participated on sports teams run by a
school, and 36.9 percent participated on sports
teams run by other organizations (Table 5-16).
Participation on sports teams run by a school was
more common among male students than female
students (57.8 percent vs. 42.4 percent) and among
white students than Hispanic students (53.9 per-
cent vs. 37.8 percent). Between 1991 and 1995,
participation on sports teams run by a school in-
creased significantly among high school students
overall, from 43.5 percent to 50.3 percent (data not
shown). Specific increases were identified among
female students, white and black students, and
students in grades 11 and 12.

Participation on sports teams run by other orga-
nizations besides a school was more common among
male students than female students (46.4 percent
vs. 26.8 percent) and among white students than
Hispanic students (39.1 percent vs. 32.0 percent).

Between 1991 and 1995, overall participationamong
students in grades 9-12 on sports teams run by
other organizations did not change significantly
(data not shown).

Conclusions

Adults

1.





2.






3.



4.







5.

Approximately 15 percent of U.S. adults engage
regularly (3 timesa week for at least 20 minutes)
in vigorous physical activity during leisure time.
Approximately 22 percent of adults engage regu-
larly (5 times a week for at least 30 minutes) in
sustained physical activity of any intensity dur-
ing leisure time.

About 25 percent of adults report no physical
activity in their leisure time.

Physical inactivity is more prevalent among
women than men, among blacks and Hispanics
than whites, among older than younger adults,
and among the less affluent than the more affluent.

The most popular leisure-time physical activities
among adults are walking and gardening or yard
work.

Adolescents and Young Adults

1.







2.





3.









4.

Only about one-half of U.S. young people (ages
12-21 years) regularly participate in vigorous
physical activity. One-fourth report no vigorous
physical activity.

Approximately one-fourth of young people walk
or bicycle (i.e., engage in light to moderate activ-
ity) nearly every day.

About 14 percent of young people report no
recent vigorous or light to moderate physical
activity. This indicator of inactivity is higher
among females than males and among black
females than white females.

Males are more likely than females to participate
in vigorous physical activity, strengthening ac-
tivities, and walking or bicycling.

5. Participation in all types of physical activity
declines strikingly as age or grade in school
  increases.

100


6.

Among high school students, enrollment in
physical education remained unchanged during
the first half of the 1990s. However, daily atten-
dance in physical education declined from ap-
proximately 42 percent to 25 percent.

The percentage of high school students who were
enrolled in physical education and who reported
being physically active for at least 20 minutes in
physical education classes declined from approxi-
mately 81 percent to 70 percent during the first
half of this decade.

Only 19 percent of all high school students report
being physically active for 20 minutes or more in
daily physical education classes.

Research Needs

1, Develop methods to monitor patterns of regular,
moderate physical activity.
2. Improve the validity and comparability of self-
reported physical activity in national surveys.
3. Improve methods for identifying and tracking
physical activity patterns among people with
disabilities.

4. Routinely monitor the prevalence of physical
activity among children under age 12.

5. Routinely monitor school policy requirements
and of students' participation in physical educa-
tion classes in elementary, middle, and high
schools.

Patterns and Trends in Physical Activity

Appendix A:
Sources of National Survey Data
National Health Interview Survey (NHIS)
This analysis used data from the 1991 NHIS to
determine current prevalences of physical activity,
and from 1985, 1990, and 1991 to determine physi-
cal activity trends, among U.S. adults aged 18 years
and older (National Center for Health Statistics
[NCHS] 19881993; NCHS unpublished data). Since
1957, NCHS has been collecting year-round health
data from a probability sample of the civilian,
noninstitutionalized adult population of the United
States. The design included oversampling of blacks
to provide more precise estimates. For the 1985,
1990, and 1991 special supplement on health promo-
tion and disease prevention, one adult aged 18 years or
older was randomly selected from each family for
participation from the total NHIS sample. Interviews
were conducted in the homes; self-response was re-
quired for this special supplement, and callbacks
were made as necessary. The sample was poststratified
by the age, sex, and racial distribution of the U.S.
population for the survey year and weighted to
provide national estimates. The overall response rate
for the NHIS has been 83 to 88 percent.

Behavioral Risk Factor Surveillance
System (BRFSS)
The Centers for Disease Control and Prevention
(CDC) initiated the BRFSS in 1981 to help states
obtain prevalence estimates of health behaviors, in-
cluding physical activity, that were associated with
chronic disease. The BRFSS conducts monthly, year-
round, telephone interviews of adults aged 18 years
of age and older sampled by random-digit dialing
(Remington et al. 1988; Siegel et al. 1991; Frazier,
Franks, Sanderson 1992). Physical activity ques-
tions have been consistent since 1986, except for a
minor change from 1986 to 1987. In 1994, the most
recent survey available, 49 states and the District of
Columbia participated. Only 25 states and the District
of Columbia have participated continuously since
1986. For 1986-1991, sample sizes ranged from
approximately 35,000 to 50,000, and response rates
from 62 to 7 1 percent; for 1992, the sample size was
96,343, and the response rate 71 percent; for 1994,
the sample size was 106,030, and the response rate

201


Physical Activity and Health

70 percent. For examination of trends, analysis was
restricted to the 25 states and the District of Colum-
bia, that had consistently participated from 1986
through 1994. For 1992 cross-sectional analyses,
data were included from all 48 states that had
participated that year and from the District of
Columbia. For 1994 cross-sectional analyses, data
were included from the 49 participating states and
from the District of Columbia.

Third National Health and Nutrition
Examination Survey (NHANES III)

NHANES 111 is the seventh in a series of national
health examination surveys that began in the 1960s.
The sample for NHANES 111 (NCHS 1994a) was
selected from 81 counties across the United States.
The survey period covered 1988-1994 and consisted
of two phases of equal length and sample size. Both
Phase 1(1988-1991) and Phase 11(1992-1994) used
probability samples of the U.S. civilian noninstitu-
tionalized population. Black and Mexican American
populations were oversampled to obtain statistically
reliable estimates for these minority groups. Phase II
data were not available at the time this report was
prepared. In Phase I, the selected population was
12,138 adults 18 years of age or older, of which 82
percent (9,901) underwent a home interview that
included questions on physical activity. Participants
in NHANES III also underwent a detailed medical
examination in a mobile examination center.
NHANES III data were weighted to the 1990 U.S.
civilian noninstitutionalized population to provide
national estimates.

Youth Risk Behavior Survey (YRBS)
The CDC developed the YRBS (Kolbe 1990; Kolbe,
Kant-t, Collins 1993) to measure six categories of
priority health-risk behaviors among adolescents: 1)
behaviors that contribute to intentional and unin-
tentional injuries; 2) tobacco use; 3) alcohol and
other drug use; 4) sexual behaviors that result in
unintended pregnancy and sexually transmitted dis-
eases, including HIV infection 5) unhealthy dietary
behaviors; and 6) physical inactivity. Data were
collected through national, state, and local school-
based surveys of high school students in grades 9-12
during the spring of odd-numbered years and through

a 1992 national household-based survey of young
people aged 12-21 years. The 1991,1993, and 1995
national school-based YRBS (Kann et al. 1993; CDC
unpublished data) used three-stage cluster sample
designs. The targeted population consisted of all
public and private school students in grades 9-12 in
the 50 states and the District of Columbia. Schools
with substantial numbers of black and Hispanic
students were sampled at relatively higher rates than
all other schools.

Survey procedures were designed to protect stu-
dent privacy and allow anonymous participation. The
questionnaire was administered in the classroom by
trained data collectors, and students recorded their
responses on answer sheets designed for scanning by
computer. The school response rates ranged from 70
to 78 percent, and the student response rate ranged
from 86 to 90 percent. The total number of students
who completed questionnaires was 12,272 in 1991,
16,296 in 1993, and 10,904 in 1995. The data were
weighted to account for nonresponse and for
oversampling of black and Hispanic students.

National Health Interview Survey-Youth
Risk Behavior Survey (NHIS-YRBS)

To provide more information about risk behaviors
among young people, including those who do not
attend school, the CDC added a youth risk behavior
survey to the 1992 National Health Interview Survey
(CDC 1993; NCHS 1994b). The survey was con-
ducted as a follow-back from April 1992 through
March 1993 among 12- through 2 I-year-olds from a
national probability sample of households. School-
aged youths not attending school were oversampled.
NHIS-YRBS interviews were completed for 10,645
young people, representing an overall response rate
of 74 percent.

The questionnaire for this survey was adminis-
tered through individual portable cassette players
with earphones. After listening to questions, respon-
dents marked their answers on standardized answer
sheets. This methodology was designed to help young
people with reading problems complete the survey
and to enhance confidentiality during household
administration. Data from this report were weighted
to represent the U.S. population of 12- through
2 1 -year-olds.

202


Patterns and Trends in Physical Activity

Appendix B:
Measures of Physical Activity
in Population Surveys

There is no uniformly accepted method of assessing
physical activity. Various methods have been used
(Stephens 1989); unfortunately, estimates of physi-
cal activity are highly dependent on the survey
instrument. The specific problems associated with
using national surveillance systems-such as those
employed here- to monitor leisure-time physical
activity have been reviewed previously (Caspersen,
Merritt, Stephens 1994).

All of the population surveys cited have em-
ployed a short-term recall of the frequency, and in
some cases the duration and intensity, of activities
that either were listed for the participant to respond
to or were probed for in an open-ended manner. The
validity of these questions is not rigorously estab-
lished. Estimates of prevalence of participation are
influenced by sampling errors, seasons covered, and
the number and wording of such questions; gener-
ally, the more activities offered, the more likely a
participant will report some activity. Besides defin-
ing participation in any activity or in individual
activities, many researchers have found it useful to
define summary indices of regular participation in
vigorous activity or moderate activity (Caspersen
1994; Caspersen, Merritt, Stephens 1994). These
summary measures often require assumptions about
the intensity of reported activities and the frequency
and duration of physical activity required for health
benefits.

National Health Interview Survey (NHIS)
Participants in the NHIS were asked in a standard-
ized interview whether they did any of 22 exercises,
sports, or physically active hobbies in the previous 2
weeks: walking for exercise, jogging or running,
hiking, gardening or yard work, aerobics or aerobic
dancing, other dancing, calisthenics or general exer-
cise, golf, tennis, bowling, bicycling, swimming or
water exercises, yoga, weight lifting or training,
basketball, baseball or softball, football, soccer, volley-
ball, handball or racquetball or squash, skating, and
skiing (National Center for Health Statistics [NCHS]
1992). They were also asked, in an open-ended

fashion, for other unmentioned activities performed
in the previous 2 weeks. For each activity, the inter-
viewer asked the number of times, the average min-
utes duration, and the perceived degree to which
heart rate or breathing increased (i.e., none or
small, moderate, or large).

The physical activity patterns were scored by
using data for frequency and duration derived di-
rectly from the NHIS. To estimate the regular,
vigorous physical activity pattern, a previously pro-
posed convention was followed (Caspersen, Pol-
lard, Pratt 1987). One of two sex-specific regression
equations was used to estimate the respondent's
maximum cardiorespiratory capacity (expressed in
metabolic equivalents [METS]) (Jonesand Campbell
1982): [60-0.55 o age (years)]/3.5 for men, and
[48-0.37 o age (years)]/3.5 for women. One MET is
the value of resting oxygen uptake relative to total
body mass and is generally ascribed the value of 3.5
milliliters of oxygen per kilogram of body mass per
minute (for example, 3 METS equals 3 times the
resting level; walking at 3 miles per hour on a level
surface would be at about that intensity). Indi-
vidual activity intensity was based on reported
values (Taylor et al. 1978; Folsom et al. 1985;
Stephens and Craig 1989).

The final activity intensity code for a specific
activity was found by selecting one of three condi-
tions corresponding to the perceived level of effort
associated with usual participation. The perceived
effort was associated with none or small, moderate,
or large perceived increases in heart rate or breath-
ing. For example, the activity intensity code for
three levels of volleyball participation would be 5,
6, and 8 METS as the perceived effort progressed
from none or small to large increases in heart rate or
breathing. In some cases, a single intensity code
was averaged for several types of activity participa-
tion that were not distinguished in the NHIS. This
averaging was done for such activities as golf, calis-
thenics or general exercise, swimming or water
exercises, skating, and skiing. To determine if an
activity would qualify a person to meet the intensity
criterion of vigorous physical activity, each inten-
sity code had to meet or exceed 50 percent of the
estimated age- and sex-specific maximum cardio-
respiratory capacity.

203


Physical Activity and Health

For this report, three patterns of leisure-time
activity were defined (Caspersen 1994):

o No pltysical activity: No reported activity during
the previous 2 weeks.

o Rcgnlar, sirstnincd activity: 2 5 times per week
and 2 30 minutes per occasion of physical activ-
ity of any type and at any intensity.

o Regular, vigorous activity: 2 3 times per week and
2 20 minutes per occasion of physical activity
involving rhythmic contractions of large muscle
groups (e.g., jogging or running, racquet sports,
competitive group sports) performed at > 50
percent of estimated age- and sex-specific maxi-
mum cardiorespiratory capacity.

Behavioral Risk Factor Surveillance
System (BRFSS)
The BRFSS questionnaire first asks, "During the past
month, did you participate in any physical activities
or exercises such as running, calisthenics, golf, gar-
dening, or walking for exercise?" If yes, participants
were asked to identify their two most common
physical activities and to indicate the frequency in
the previous month and duration per occasion
(Caspersen and Powell 1986; Caspersen and Merritt
1995). If running, jogging, walking, or swimming
were mentioned, participants were also asked the
usual distance covered.

The reported frequency and duration of activity
were used for scoring. Intensity of physical activity
was assigned by using the same intensity codes as the
NHIS, and a correction procedure (explained later in
this section) based on speeds of activities was used to
create intensity codes for walking, running/jogging,
and swimming (Caspersen and Powell 1986;
Caspersen and Merritt 1995).

The estimate of speed was made by dividing the
self-reported distance in miles by the duration in
hours. The speed estimate was entered into specific
regression equations to refine the intensity code for
these four activities, because the application of a
single intensity code is likely to underestimate or
overestimate the intensity. Based on previously pub-
lished formulae (American College of Sports Medi-
cine 1988), five equations were constructed for
predicting metabolic intensity of walking, jogging,
and running at various calculated speeds:

Equation 1 METS = 1.80
     (Speeds < 0.93 mph)

Equation 2  METS = 0.72 x mph + 1.13
     (Speeds 2 0.93 but < 3.75 mph)

Equation 3 METS = 3.76 x mph - 10.20
    (Speeds L 3.75 but < 5.00 mph)

Equation 4  METS = 1.53 x mph + 1.03
     (Speeds 2 5.00 but < 12.00 mph)

Equation 5  METS = 7.0 or 8.0
     (Speeds 2 1200,mph)

Below 0.93 mph, an intensity code of 1.8 METS
(Equation 1) wasused, to beconsistentwithMontoye's
intensity code for residual activities like those associ-
ated withslow movements (Montoye 1975). Equation
2 is extrapolated to include speeds as slow as 0.93
mph-the point at which metabolic cost was set at 1.8
METS. Persons whose calculated speeds fell between
0.93 and 12.0 mph were assigned an intensity from
equations 2, 3, or 4, regardless of whether they said
they walked, jogged, or ran. Equation 3 was created by
simply connecting with a straight line the last point of
equation 2 and the first point of equation 4. This
interpolation was seen as a reasonable way to deter-
mine intensity within the range of speed where walk-
ing or jogging might equally occur. This assignment
method was considered to be more objective, specific,
and generally conservative than assigning an intensity
code based solely on the self-reported type of activity
performed. Thus, as a correction procedure for self-
reported speeds judged likely to be erroneously high,
an intensity of 2.5 METS was assigned for walking
speeds above 5.0 mph, 7.0 METS for jogging speeds
above 12.0 mph, and 8.0 METS for running speeds
above 12.0 mph.

Another set of regression equations predicted
metabolic intensity from swimming velocity:

Equation 6 METS = 1.80
     (Speeds < 0.26 mph)

Equation 7  METS = 4.19 x mph - 0.69
     (Speeds 2 0.26 but < 2.11 mph)

Equation 8  METS = 8.81 x mph - 9.08
     (Speeds 2 2.11 but < 3.12 mph)

Equation 9 METS = 5.50
     (Speeds 2 3.12 mph)


These equations were set forth in a Canadian mono-
graph of energy expenditure for recreational activi-
ties (Groupe d'etude de Kino-Quebec sur le systcme
de quantification de la depense energetique 1984).
However, swimming speeds up to 3.12 mph for the
crawl and backstroke, in the derivation of equations
7 and 8, were obtained from published research
(Holmer 1974a; Holmer 1974b; Passmore and Durnin
1955). Default intensity codes were assigned as fol-
lows: 1.8 METS for swimming speeds less than 0.26
mph, and 5.5 METS for velocities greater than 3.12
mph, because such speeds are improbable and likely
reflected errors in self-report.

Definitions used for leisure-time physical activ-
ity were the same as those described for the NHIS
earlier in this appendix,

Third National Health and Nutrition
Examination Survey (NHANES III)

The NHANES III questions that addressed leisure-
time physical activity (NCHS 1994a) were adapted
from the NHIS. Participants firstwere asked how often
they had walked a mile or more at one time in the
previous month. They were then asked to specify their
frequency of leisure-time physical activity during the
previous month for the following eight activities:
jogging or running, riding a bicycle or an exercise
bicycle, swimming, aerobics or aerobicdancing, other
dancing, calisthenics or exercises, gardening or yard
work, and weight lifting. An open-ended question
asked for information on up to four physical activities
not previously listed. Information on duration of
physical activity was not collected. Northern sites
selected for NHANES III tended to be surveyed in
warm rather than cold months, which might have led
to a greater prevalence of reported physical activity
than would otherwise be obtained from a year-round
survey. No physical activity was defined as no re-
ported leisure-time physical activity in the previous
month. Regular, sustained activity and regular, vigor-
ous activity were not defined for NHANES III because
of the lack of information on activity duration.

Youth Risk Behavior Survey (YRBS)
In the YRBS questionnaire (Kann et al. 1993), stu-
dents in grades 9-12 were asked eight questions
about physical activity. The question on vigorous
physical activity asked, "On how many of the past

Patterns and Trends in Physical Activity

7 days did you exercise or participate in sports
activities for at least 20 minutes that made you sweat
and breathe hard, such as basketball, jogging, fast
dancing, swimming laps, tennis, fast bicycling, or
similar aerobic activities?" The questionnaire asked
separately about the frequency of three specific ac-
tivities in the previous 7 days: 1) stretching exer-
cises, such as toe touching, knee bending, or leg
stretching; 2) exercises to strengthen or tone the
muscles, such as push-ups, sit-ups, or weight lifting;
and 3) walking or bicycling for at least 30 minutes at
a time. Participants were asked about physical edu-
cation, "In an average week when you are in school,
on how many days do you go to physical education
(PE) classes?" and "During an average physical edu-
cation (PE) class, how many minutes do you spend
actually exercising or playing sports?" Students were
also asked, "During the past 12 months, on how
many sports teams run by your school did you play?
(Do not include PE classes.)" and "During the past
12 months, on how many sports teams run by orga-
nizations outside of your school did you play?"

National Health Interview Survey-Youth
Risk Behavior Survey (NHIS-YRBS)

The NHIS-YRBS questionnaire (NCHS 1994b) ascer-
tained the frequency of vigorous physical activity
among U.S. young people aged 12-21 years by asking,
"On how many of the past 7 days did you exercise or
take part in sports that made you sweat and breathe
hard, such as basketball, jogging, fast dancing, swim-
ming laps, tennis, fast bicycling, or other aerobic
activities?" Ten other questions asked about the prc-
vious 7 days' frequency of participating in the fol'.: . -
ing specific activities: 1) stretching exercises. P h as
toe touching, knee bending, or leg strc' _ nir . . 2)
exercises to strengthen or tone muscles ,uch as push-
ups, sit-ups, or weight lifting; 3) house cleaning or
yard work for 2 30 minutes at a ttmt  : ) walking or
bicycling for 2 30 minutes at a I` Le; 5) baseball,
softball, or Frisbee@`; 6) bask< ! &, football, or soc-
cer; 7) roller skating, ice st aLmg, skiing, or skate-
boarding; 8) running, jogging, or swimming for
exercise; 9) tennis. ry.,quetball, or squash; and 10)
aerobics or danc-,-. Questions about duration and
intensity werL not asked.

`Use cl! mde names is for identification only and does not imply
end! (rsement by the U.S. Department of Health and Human Services.

LO5


Physical Activity and Health

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Remington PL, Smith MY, Williamson DF, Anda RF,
Gentry EM, Hogelin GC. Design, characteristics, and
usefulness of state-based behavioral risk factor sur-
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366-375.

Siegel PZ, Brackbill RM, Frazier EL, Mariolis P, Sanderson
LM, Waller MN. Behavior Risk Factor Surveillance,
1986-1990. Morbidity and Mortality Weekly Report
1991; 40(No. SS-4):1-23.

Stephens T. Design issues and alternatives in assessing
physical activity in general population surveys. In:
Drury TF, editor. Assessingphysicaffitness andphysical
activity in population-based surveys. Hyattsville, MD:
U.S. Department of Health and Human Services, Pub-
lic Health Service, Centers for Disease Control, Na-
tional Center for Health Statistics, 1989:197-210.
DHHS Publication No. (PHS)89-1253.

Stephens T. Secular trends in adult physical activity:
exercise boom or bust? Research Quarterlyfor Exercise
and Sport 1987;58:94-105.

Stephens T, Caspersen CJ. The demography of physical
activity. In: Bouchard C, Shephard RJ, Stephens T,
editors. Physical activity, fitness, and health: intema-
tional proceedings andconsensus statement. Champaign.
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Stephens T, Craig CL. Fitness and activity measurement
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editor. Assessingphysicalfitness and physical activity in
population-based surveys. Hyattsvilie, MD: U.S. De-
partment of Health and Human Services, Public Health
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for Health Statistics, 1989:401-32. DHHS Publication
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Taylor HL, Jacobs DR Jr, Schucker B, Knudsen J, Leon AS,
DeBacker G. A questionnaire for the assessment of
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207


           CHAPTER 6
UNDERSTANDING AND PROMOTING
       PHYSICAL ACTIVITY

Contents

tntroduction . . . . . . . . . . . . . . . . . . . . . . . .._....._......_._._................_... 211

Fhcories and Models Used in Behavioral and Social Science Research on Physical Activity  ...  211
LcarningTheories  ........................................................  211

HcalthBehefModel  .......................................................  213

Transtheoretical Model  ....................................................  213
Relapse Prevention Model  ..................................................  213
Theory of Reasoned Action and Theory of Planned Behavior  ......................  213
Social Learning/Social Cognitive Theory  ......................................  214

SocialSupport  ...........................................................  214
EcologicalApproaches  .....................................................  214

Summary  ...............................................................  215

I1ehavioral Research on Physical Activity among Adults  .............................  215
Factors Influencing Physical Activity among Adults  .............................  215

   Modifiable Determinants  ................................................  215
  Determinants for Population Subgroups  ....................................  216

  Summary  ............................................................  217

lnterventions to Promote Physical Activity among Adults  .........................  217
Individual Approaches  ..................................................  217
Interventions in Health Care Settings  ......................................  226
Community Approaches  ................................................  227
Worksite Programs   ....................................................  229
Communications Strategies  ..............................................  23 1
Special Population Programs  .............................................  232

   Racial and Ethnic Minorities  ..........................................  232
  People Who Are Overweight  ..........................................  232


Contents, continued

   Older Adults  ....................................................  . . . . . 233
  People with Disabilities  ...........................................  . 233
   Summary  ......................................................  . . . . 234
Behavioral Research on Physical Activity among Children and Adolescents  .......  . . . . 234
Factors Influencing Physical Activity among Children and Adolescents  ........  . . . . 234

   Modifiable Determinants  ..........................................  . . . 234
  Determinants for Population Subgroups  ..............................  . . . . . 235

   Summary  ......................................................  . . 236
Interventions to Promote Physical Activity among Children and Adolescents  ...  . . . . . 236
  SchoolPrograms   ................................................  . . . 236
   School-Community Programs  ......................................  . . . . . 242
   Interventions in Health Care Settings  ................................  . . 242
  Special Population Programs  .......................................  . . 243
   Summary  ......................................................  . . . , . 243

Promising Approaches, Barriers, and ,Resources  .........................
Environmental and Policy Approaches  ..............................
Community-Based Approaches  ....................................
Societal Barriers  ................................................
Societal Resources  ..............................................
Summary  .....................................................

.

.  243

. 244

245

. 246

. . 247

. 248

Chapter Summary __.............,,..,,_............._....................... 248

Conclusions  ............................................................... 249

ResearchNeeds  ............................................................ 249
Determinants of Physical Activity  ............................................ 249
Physical Activity Interventions  .............................................. 249

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._.. 249


          CHAPTER 6
UNDERSTANDING AND PROMOTING
       PHYSICAL ACTIVITY

introduction

A s the benefits of moderate, regular physical
activity have become more widely recognized,
the need has increased for interventions that can
promote this healthful behavior. Because theories
and models of human behavior can guide the
development and refinement of intervention efforts,
this chapter first briefly examines elements of be-
havioral and social science theories and models that
have been used to guide much of the research on
physical activity. First for adults, then for children
and adolescents, the chapter reviews factors influ-
cncing physical activity and describes interven-
[tons that have sought to improve participation in
regular physical activity among these two age
groups. To put in perspective the problem of
increasing individual participation in physical
activity, the chapter next examines societal barri-
ers to engaging in physical activity and describes
csisting resources that can increase opportunities
for activity. The chapter concludes with a sum-
mary of what is knouln about determinant and
intervention research on physical activity and makes
recommendations for research and practice.

Theories and Models Used in
Behavioral and Social Science
Research on Physical Activity
Numerous theories and models have been used in
behavioral and social science research on physical
activity. These approaches vary in their applicability
to physical activity research. Some models and theo-
ries were designed primarily as guides to under-
5tanding behavior, not as guides for designing
Interventions. Others were specifically constructed
\vith a view toward developing interventions, and

some of these have been applied extensively in inter-
vention research as well. Because most were devel-
oped to explain the behavior of individuals and to
guide individual and small-group intervention pro-
grams, these models and theories may have only
limited application to understanding the behavior of
populations or designing communitywide interven-
tions. Key elements most frequently used in the
behavioral and social science research on physical
activity are described below and summarized in
Table 6-1.

Learning Theories

Learning theories emphasize that learning a new,
complex pattern of behavior, like changing from a
sedentary to an active lifestyle, normally requires
modifying many of the small behaviors that compose
anoverall complex behavior (Skinner 1953). Principles
of behavior modification suggest that a complex-
pattern behavior, such as walking continuously for
30 minutes daily, can be learned by first breaking it
down into smaller segments (e.g., walking for 10
minutes daily). Behaviors that are steps toward a
final goal need to be reinforced and established first,
with rewards given for partial accomplishment if
necessary. Incremental increases, such as adding 5
minutes to the daily walking each week, are then
made as the complex pattern ofbehaviors is "shaped"
toward the targeted goal. A further complication to
the change process is that new patterns of physical
activity behavior must replace or compete with former
patterns of inactive behaviors that are often satisfy-
ing (e.g., watching television), habitual behaviors
(e.g., parking close to the door), or behaviors cued by
the environment (e.g., the presence of an elevator).

Reinforcement describes the consequences that
motivate individuals either to continue or discon-
tinue a behavior (Skinner 1953; Bandura 1986).


Physical Activity and Health

Table 6-l. Summary of theories and models used in physical activity research
Theory/model              Level           Key concepts

Classic learning theories        Individual           Reinforcement
                                      Cues
                              Shaping

Health belief model

Individual

Perceived susceptibility
Perceived severity
Perceived benefits
Perceived barriers
Cues to action
Self-efficacy

Transtheoretical model

Relapse prevention           Individual

Social cognitive theory

Interpersonal

Theory of planned behavior

Social support

Individual

Interpersonal

Interpersonal

Environmental

Precontemplation
Contemplation
Preparation
Action
Maintenance

Skills training
Cognitive reframing
Lifestyle rebalancing

Reciprocal determinism
Behavioral capability
Self-efficacy
Outcome expectations
Observational learning
Reinforcement

Attitude toward the behavior
Outcome expectations
Value of outcome expectations
Subjective norm
Beliefs of others
Motive to comply with others
Perceived behavioral control

Instrumental support
Informational support
Emotional support
Appraisal support

Ecological perspective

Multiple levels of influence
Intrapersonal
interpersonal
Institutional
Community
Public policy

Source: Adapted from Glanz K and Rlmer BK. Theory at-a-glance: a guide ior health promotion practice, U.S. Department of Health and
Human Services, 1995.

212


ltost behaviors, including physical activity, are
learned and maintained under fairly complex sched-
ules of reinforcement and anticipated future re-
il,ards. Future rewards or incentives may include
physica1 consequences (e.g., looking better), extrin-
sic rewards (e.g., receiving praise and encourage-
,ncnt from others, receiving a T-shirt), and intrinsic
rc\vards (e.g., experiencing a feeling of accomplish-
I11ent or gratification from attaining a personal mile-
stone). lt is important to note that although providing
praise, encouragement, and other extrinsic rewards
may help people adopt positive lifestyle behaviors,
>uch external reinforcement may not be reliable in
,ustaininglong-termchange(GlanzandRimer 1995).

Health Belief Model

The health belief model stipulates that a person's
hcaith-related behavior depends on the person's per-
ccption of four critical areas: the severity of a poten-
teal illness, the person's susceptibility to that illness,
the benefits of taking a preventive action, and the
h;\rritrs to taking that action (Hochbaum 1958;
iioscnstock 1960, 1966). The model also incorpo-
rates cues to action (e.g., leaving a written reminder
to oneself to walk) aS important elements in eliciting
or maintaining patterns of behavior (Becker 1974).
fhc construct of self-efficacy, or a person's confi-
tlcncc in his or her ability to successfully perform an
.Ic`tlon (discussed in more detail later in this chap-
rcr), has been added to the model (Rosenstock 19901,
I)crhaps allowing it to better account for habitual
Ochaviors, such as a physically active lifestyle.

Transtheoretical Model

In this model, behavior change has been conceptual-
l=cd as a five-stage process or continuum related to
`1 person's readiness to change: precontemplation,
contemplation, preparation, action, and maintenance
prochaska and DiClemente 1982.1984). People are
thought to progress through these stages at varying
rates, often moving back and forth' along the con-
`muurn a number of times before attaining the goal
of maintenance. Therefore, the stages of change are
better described as spiraling or cyclical rather than
linear (Prochaska, DiClemente, Norcross 1992). In
rtlls model, people use different processes of change
1s they move from one stage of change to another.
Efficient self-change thus depends on doing the right

Understanding and Promoting Physical Activity

thing (processes) at the right time (stages) (Prochaska,
DiClemente, Norcross 1992). According to this
theory, tailoring interventions to match a person's
readiness or stage of change is essential (Marcus and
Owen 1992). For example, for people who are not
yet contemplating becoming more active, encourag-
ing a step-by-step movement along the continuum of
change may be more effective than encouraging
them to move directly into action (Marcus, Banspach,
et al. 1992).

Relapse Prevention Model

Some researchers have used concepts of relapse
prevention (Marlatt and Gordon 1985) to help new
exercisers anticipate problems with adherence. Fac-
tors that contribute to relapse include negative emo-
tional or physiologic states, limited coping skills,
social pressure, interpersonal conflict, limited social
support, low motivation, high-risk situations, and
stress (Brownell et al. 1986; Marlatt and George
1990). Principles of relapse prevention include iden-
tifying high-risk situations for relapse (e.g., change
in season) and developing appropriate solutions
(e.g., finding a place to walk inside during the
winter). Helping people distinguish between a lapse
(e.g., a few days of not participating in their planned
activity) and a relapse (e.g., an extended period of
not participating) is thought to improve adherence
(Dishman 1991; Marcus and Stanton 1993).

Theory of Reasoned Action and
Theory of Planned Behavior
The theory of reasoned action (Fishbein and Ajzen
1975; Ajzen and Fishbein 1980) states that indi-
vidual performance of a given behavior is primarily
determined by a person's intention to perform that
behavior. This intention is determined by two major
factors: the person's attitude toward the behavior
(i.e., beliefs about the outcomes of the behavior and
the value of these outcomes) and the influence of the
person's social environment or subjective norm (i.e.,
beliefs about what other people think the person
should do, as well as the person's motivation to
comply with the opinions of others). The theory of
planned behavior (Ajzen 1985, 1988) adds to the
theory of reasoned action the concept of perceived
control over the opportunities, resources, and skills
necessary to perform a behavior. Ajzen's concept of

213


Physical Activity and Health

perceived behavioral control is similar to Bandura's
(1977a) concept of self-efficacy-a person's percep-
tion of his or her ability to perform the behavior
(Ajzen 1985, 1988). Perceived behavioral control
over opportunities, resources, and skills necessary to
perform a behavior is believed to be a critical aspect
of behavior change processes.

Social Learning/Social Cognitive Theory
Social learning theory (Bandura 1977b), later re-
named social cognitive theory (Bandura 1986),
proposes that behavior change is affected byenviron-
mental influences, personal factors, and attributes of
the behavior itself (Bandura 1977b). Each may affect
or be affected by either of the other two. A central
tenet of social cognitive theory is the concept of self-
efficacy. A person must believe in his or her capability
to perform the behavior (i.e., the person must possess
self-efficacy) and must perceive an incentive to do so
(i.e., the person's positive expectations from perform-
ing the behavior must outweigh the negative expecta-
tions). Additionally, a person must value the outcomes
or consequences that he or she believes will occur as
a result of performing a specific behavior or action,
Outcomes may be classified as having immediate
benefits (e.g., feeling energized following physical
activity) or long-term benefits (e.g., experiencing
improvements in cardiovascular health as a result of
physical activity). But because these expected out-
comes are filtered through a person`s expectations or
perceptions of being able to perform the behavior in
the first place, self-efficacy is believed to be the single
most important characteristic that determines a
person's behavior change (Bandura 1986).
Self-efficacy can be increased in several ways,
among them by providing clear instructions, ptovid-
ing the opportunity for skill development or training,
and modeling the desired behavior. To be effective,
models must evoke trust, admiration, and respect
from the observer; models must not, however, appear
to represent a level of behavior that the observer is
unable to visualize attaining (Bandura 1986).

Social Support

Often associated with health behaviors such as
physical activity, social support is frequently used
in behavioral and social research. There is, how-
ever, considerable variation in how social support

is conceptualized and measured (Israel and Schurman
1990). Social support for physical activity can be
instrumental, as in giving a nondriver a ride to an
exercise class; informational, as in telling someone
about a walking program in the neighborhood; emo-
tional, as in calling to see how someone is faring with
a new walking program; or appraising, as in provid-
ing feedback and reinforcement in learning a new
skill (Israel and Schurman 1990). Sources of support
for physical activity include family members, friends,
neighbors, co-workers, and exercise program lead-
ers and participants.

Ecological ApproacheS

A criticism of most theories and models of behavior
change is that they emphasize individual behavior
change processes and pay little attention to sociocul-
tural and physical environmental influences on be-
havior (McLeroy et al. 1988). Recently, interest has
developed in ecological approaches to increasing
participation in physical activity (McLeroy et al.
1988; CDC 1988; Stokols 1992). These approaches
place the creation of supportive environments on a
par with the development of personal skills and the
reorientation of health services. Stokols (1992) and
Simons-Mortonandcolleagues (CDC 1988; Simons-
Morton, Simons-Morton, et al. 1988) have illus-
trated thisconceptofa health-promotingenvironment
by describing how physical activity could be pro-
moted by establishing environmental supports, such
as bike paths, parks, and incentives to encourage
walking or bicycling to work.

An underlying theme of ecological perspectives
is that the most effective interventions occur on
multiple levels. McLeroy and colleagues (1988), for
example, have proposed a model that encompasses
several levels of influences on health behaviors:
intrapersonal factors, interpersonal and group fac-
tors, institutional factors, community factors, and
public policy. Similarly, a model advanced by Simons-
Morton and colleagues (CDC 1988) has three levels
(individual, organizational, and governmental) in
four settings [schools, worksites, health care institu-
tions, and communities). Interventions that simulta-
neously influence these multiple levels and multiple
settings may be expected to lead to greater and
longer-lasting changes and maintenance of existing
health-promoting habits. This is a promising area for

214


the design of future intervention research to pro-
mote physical activity.

summary

some similarities can be noted among the behavioral
.,& social science theories and models used to un-
<lcrstand and enhance health behaviors such as physi-
(,I\ activity. Many of the theoretical approaches
highlight the role of the perceived outcomes of
t,chavior, although different terms are used for this
reinstruct, including perceived benefits and barriers
( health belief model) and outcome expectations (so-
(.i:11 cognitive theory and theory of planned behav-
i,,r) (Table 6-l). Several approaches also emphasize
I IIC influence of perceptions of control over behav-
lc~r; this influence is given labels such as self-efficacy
chcalth belief model, social cognitive theory) and
pcrccived behavioral control (theory of planned be-
havior). Other theories and models feature the role
of social influences, as in the concepts of observa-
11ona1 learning (social cognitive theory), perceived
~l~~rm(theoryofreasonedactionandtheoryofplanned
`behavior), social support, and interpersonal influ-
~`IIC`CS (ecological perspective). Most of the theories
,111cl modtls, however,do not address the influence of
111~ environment on health behavior.

Behavioral Research on
Activity among Adults
`;~~havloral research in this area

Physical

includes studies on

l)oth the factors influencing physical activity among
.\dults (determinants research) and the effectiveness
oI strategies and programs to increase this behavior
j Intcrvcntions research). Although many of the key
~nccpts presented in the preceding section are
!c.lrurcd in both types of research presented here,
.l~~lthcr area is limited to those concepts only.

Factors Influencing Physical Activity
among Adults
Ilcsearch on the determinants of physical activity
lhtifies those factors associated with, or predictive
of. this behavior. This section reviews determinants
\ludics in which the measured outcome was overall
\h\xical activity, adherence to or continued partici-
,111on in structured physical activity programs, or
ilovernent from one stage of change to another (e.g.,

Understanding and Promoting Physical Activity

from contemplation to preparation). The section
does not review studies in which the outcome mea-
sured was an intermediate measure of physical activ-
ity (e.g., intentions concerning future participation
in physical activity). Although researchers have stud-
ied a wide array of potential influences on physical
activity among adults, the section focuses on factors
that can be modified, such as self-efficacy and social
support, rather than on factors that cannot be
changed, such as age, sex, and racdethnicity.

Modifiable Determinants

The modifiable determinants of adult physical activ-
ity include personal, interpersonal, and environ-
mental factors (Table 6-l). Self-efficacy, a construct
from social cognitive theory, has been consistently
and positively associated with adult physical activit)
(Courneya and McAuley 1994; Desmond et al. 1993;
Hofstetter et al. 1991; Yordy and Lent 1993), physi-
cal activity stage of change (Marcus, Eaton, et al.
1994; Marcus and Owen 1992; Marcus, Pinto, et al.
1994; Marcus, Selby, et al. 1992), and adherence to
structured physical activity programs (DuCharme
and Brawley 1995; Duncan and McAuley 1993;
McAuley, Lox, Duncan 1993; Poag-DuCharme and
Brawley 1993; Robertson and Keller 1992). The
evidence is less conclusive, however, for the theory
of planned behavior's construct of perceived behav-
ioral control (Courneya 1995; Courneya and McAule)
1995; Godin et al. 1991,1995; Godin,Valois, Lepage
1993; Kimiecik 1992; Yordy and Lent 1993).

Several studies have found no association be-
tween adult physical activity (whether physical ac-
tivity, stage of change, or adherence) and either the
health belief model's constructs of perceived benefits
(Hofstetter et al. 1991; Mirotznik, Feldman, Stein
1995; Oldridge and Streiner 1990; Taggart and
Connor 1995) and perceived barriers (Desmond et
al. 1993; Godin et al. 1995; Neuberger et al. 1994:
Oldridge and Streiner 1990; Taggart and Connor
1995) or the theory of reasoned action and theory of
planned behavior's construct of attitude toward the
behavior (Courneya and McAuley 1995; Godin,
Valois, Lepage 1993; Hawkes and Holm 1993). None-
theless, the cumulative body of evidence supports
the conclusion that expectations of both positive
(e.g., benefits) and negative (e.g., barriers) behav-
ioral outcomes are associated with physical activity
among adults. Expectation of positive outcomes or

215


Physical Activity and Health

perceived benefits of physical activity has been con-
sistently and positively associated with adult physical
activity (Ali and Twibell1995; Neuberger et al. 1994),
physical activity stage of change (Booth et al. 1993;
Calfas et al. 1994; Eaton et al. 1993; Marcus, Eaton, et
al. 1994; Marcus and Owen 1992; Marcus, Pinto, et al.
1994; Marcus, Rakowski, Rossi 1992), and adherence
to structured physical activity programs (Lynch et al.
1992; Robertson and Keller 1992). Conversely, the
construct of perceived barriers to physical activity has
been negativelyassociated'withadult physical activity
(Ali and Twibell1995; Dishman and Steinhardt 1990;
Godin et al. 1991; Hofstetter et al. 1991; Horne 19941,
physical activity stage of change (Calfas et al. 1994;
Lee 1993; Marcus, Eaton, et al. 1994; Marcus and
Owen 1992; Marcus, Pinto, et al. 1994; Marcus,
Rakowski, Rossi 1992>, and adherence to structured
physical activity programs (Howze, Smith, DiGilio
1989; Mirotznik et al. 1995; Robertson and Keller
1992). Additionally, attitude toward the behavior
(outcome expectations and their values) has been
consistently and positively related to physical activity
(Courneya and McAuley 1994; Dishman and
Steinhardt 1990; Godin et al. 1987, 1991; Kimiecik
1992; Yordy and Lent 1993) and stage of change
(Courneya 1995).

Social support from family and friends has been
consistently and positively related to .adult physical
activity (Felton and Parsons 1994; Horne 1994; Minor
andBrown 1993;Sallis,Hovell,Hofstetter 1992;Treiber
et al. 19911, stage of change (Lee 1993), and adher-
ence to structured exercise programs (Duncan and
McAuley 1993; Elward, Larson, Wagner 1992). Be-
havioral intention, a construct from the theory of
reasoned action and the theory of planned behavior,
also has consistently been associated with adult physi-
cal activity (Courneya and McAuley 1994; Godin et al.
1987, 1991; Godin, Valois, Lepage 1993; Kimiecik
1992;YordyandLent 1993),stageofchange(Courneya
1995), and adherence to structured exercise programs
(CourneyaandMcAuley 1995;DuCharmeandBrawley
1995). Conversely, the construct of subjective norm
from these theories has been both positively associ-
ated(Courneya 1995;Godinetal. 1987,199l;Hawkes
and Holm 1993; Kimiecik 1992; Yordy and Lent
1993) and not associated (Courneya and McAuley
1995; Godin et al. 1995; Hofstetter et al. 1991) with
adult physical activity, stage ofchange, and adherence
to structured exercise programs.

There is also mixed evidence regarding the posi-
tive relationship between the health belief model's
construct of perceived severity of diseases and either
physical activity (Godin et al. 1991) or adherence to
structured exercise programs (Lynch et al. 1992;
Mirotznik, Feldman, Stein 1995; Oldridge and
Streiner 1990; Robertson and Keller 1992). Addi-
tionally, that model's construct of perceived suscep-
tibility to illness has been unrelated to adult adherence
to structured exercise programs (Lynch et al. 1992;
Mirotznik et al. 1995; Oldridge and Streiner 1990).

The cumulative body of determinants research
consistently reveals that .exercise enjoyment is a
determinant that has been positively associated with
adult physical activity (Courneya and McAuley 1994;
Horne 1994; McAuley 1991), stage of change (Calfas
et al. 1994), and adherence to structured exercise
programs (Wilson et al. 1994). Conversely, there has
been no relationship between locus of control beliefs
(i.e., perceptions of personal control over health,
fitness, or physical activity) and either adult physical
activity (Ali and Twibell 1995; Burk and Kimiecik
1994; Dishman and Steinhardt 1990; Duffy and
MacDonald 1990) or adherence to structured exer-
cise programs (Lynch et al. 1992; Oldridge and
Streiner 1990). Although previous physical activity
during adulthood has been consistently related to
physical activity among adults (Godin et al. 1987,
1993; Minor and Brown 1993; Sharpe and Connell
1992) and stage of change (Eaton et al. 1993), history
of physical activity during youth has been unrelated
to adult physical activity (Powell and Dysinger 1987;
Sallis, Hovell, Hofstetter 1992).

Determinants for Population Subgroups
Few determinants studies of heterogeneous samples
have examined similar sets of characteristics in sub-
groups. Self-efficacy is the variable with the stron-
gest and most consistent association with physical
activity in different subgroups from the same large
study sample. Self-efficacy has been positively re-
lated to physical activityamongmen, women, younger
adults, older adults (Salliset al. 19891, Latinos (Hovel]
et al. 19911, overweight persons (Hovel1 et al. 19901,
and persons with injuries or disabilities (Hofstetter
et al. 1991). The generalizability of the self-efficacy
associations is extended by studies of universit)
students and alumni (Calfas et al. 1994; Courneya
and McAuley 1994; Yordy and Lent 19931, employed

216


\vomcn (Marcus, Pinto, et al. 1994), participants in
structured exercise programs (Duncan and McAuley
1993; McAuley, Lox, Duncan 1993; Poag-DuCharme
,,nd Brawley 1993), and people with coronary heart
dlscase (CHD) (Robertson and Keller 1992).

Summary

ldcally. theories and models of behavioral and social
s;cIcncc could be used to guide research concerning
the factors that influence adult physical activity. In
.ictuality, the application of these approaches to deter-
nlinants research in physical activity has generally
\Jccn limited to individual and interpersonal theories
.Ind models. Social support and some factors from
s~jcial cognitive theory, such as confidence in one's
.lbiIity to engage in physical activity (i.e., self-efficacy)
.tnd beliefs about the outcome of physical activity,
tl;l\,c been consistently related to physical activity
.Irnong adults. Factors from other theories and mod-
~15. however, have received mixed support. Although
pcrccptionsof the benefits of, and barriers to, physical
.lctlvity have been consistently related to physical
,~c.[~vity amongadults, other constructs from the health
hcllcf model, such as perceptions of susceptibility to,
,111d the severity of, disease, have not been related to
x1~1lt physical activity. Further, constructs from the
1 hco7 of reasoned action and the theory of planned
I~chavior, including intentions and beliefs about the
rlutcomes of behavior, have been consistently related
10 ,ldult physical activity, whereas there has been
r.qulvocal evidence of this relationship for normative
hcllcfs and perceptions of the difficulty of engaging in,
the behavior. Exercise enjoyment, a determinant that
ciocs not derive directly from any of the behavioral
rhcorics and models, has been consistently associated
\vlth adult physical activity.

Few studies have specifically contrasted physi-
( .lI activity determinants among different sex, age.
.~ciaVcthnic, geographic location, or health status
\llbgroups. Many studies contain relatively homoge-
n~)us samples of groups, such as young adults,
cldcrly persons, white adults, participants in weight
10~s groups, members of health clubs, persons with
heart disease, and persons with arthritis. Because the
nllmbers of participants in the studies that include
lhcse subgroups are small, and because the studies
\.aluated different factors, making comparisons be-
i\veen studies is problematic.

Understanding and Promoting Physical Activity

Interventions to Promote

Physical Activity among Adults
This section reviews intervention studies in which
the measured outcome was physical activity, adher-
ence to physical activity, or movement in stage of
change (Table 6-2). It does not include intervention
studies designed to assess the effect of physical
activity on health outcomes or risk factors (see
Chapter 4). Further, this review places special em-
phasis on experimental and quasi-experimental stud-
ies, which are better able to control the influence of
other factors and thus to-determine if the outcomes
were due to the intervention itself (Weiss 1972).

Individual Approaches

Individual behavioral management approaches, in-
cluding those derived from learning theories, relapse
prevention, stages of change, and social learning
theory, have been used with mixed success in nu-
merous intervention studies designed to increase
physical activity (Table 6-2). Behavioral manage-
ment approaches that have been applied include self-
monitoring, feedback, reinforcement, contracting,
incentives and contests, goal setting, skills training
to prevent relapse, behavioral counseling, and
prompts or reminders. Applications have been car-
ried out in person, by mail, one-on-one, and in group
settings. Typically, researchers have employed these
in combination with other behavioral management
approaches or with those derived from other theo-
ries, such as social support, making it more difficult
to ascertain their specific effects. In numerous in-
stances, physical activity was only one of several
behaviors addressed in an intervention, which also
makes it difficult to determine the extent that physi-
cal activity was emphasized as an intervention com-
ponent relative to other components.
Self-monitoring of physical activity behavior has
been one of the most frequently employed behavioral
management techniques. Typically, it has involved
individuals keeping written records of their physical
activity, such as number of episodes per week, time
spent per episode, and feelings during exercising. In
one study, women who joined a health club were
randomly assigned to a control condition or one of
two intervention conditions-self-monitoring of at-
tendance or self-monitoring plus extra staff attention
(Weber and Wertheim 1989). Overall, women in the

217


Physical Activity and Health

Table 6-2. Studies of interventions to increase physical activity among adults
Study           Design          Theoretical approach

Population

Individual approaches
Weber and Wertheim
(1989)

King, Haskell, et al.
(1995)

Lombard, Lombard,
Winett (1995)

Cardinal and Sachs
(1995)

Belisle (1987)

Gossard et al. (1986)

3 month
experimental

2 year
experimental

24 week
experimental

12 week
experimental

10 week
quasi-experimental
with 3-month follow-up

12 week
experimental

King, Carl, et al. (1988)

16 week
pretest-posttest

King and Frederiksen      3 month
(1984)           experimental

King, Taylor, et al.
(1988)

Self-monitoring

Behavioral management

Stages of change

Stages of change

Relapse prevention

Behavioral management

Behavioral management

Relapse prevention,
social support,
behavioral management

55 women who joined a
gym; mean age = 27

269 white adults
aged SO-65 years

155 university faculty and
staff; mostly women

113 clerical staff at a
university; mean age = 37;
63% black

3.50 people enrolled in
beginning exercise groups

64 overweight healthy
men aged 40-60 years

38 blue-collar university
employees; mean age = 45

58 college women
aged 18-20 years

Study 1: 6 month
experimental

Relapse prevention,
behavioral management

152 Lockheed employees
aged 42-55 years

             Study 2: 6 month
             experimental

I = intervention; C = control or comparison group.

Behavioral management

Lockheed employees from
Study 1

218


Understanding and Promoting Physical Activity

Intervention

Findings and comments

l-1 : Self-monitoring of attendance, fitness exam
l-7: Self-monitoring, staff attention, fitness exam
c: Fitness exam

l-l had better attendance than l-2 overall; interest in self-
monitoring waned after 4 weeks

I.1 : Self-monitoring, telephone contact, vigorous
  exercise at home

I-2: Self-monitoring, telephone contact, moderate
  exercise at home

Better exercise adherence at 1 year in home-based groups; at
year 2 better adherence in vigorous home-based group; 5
times per week schedule may have been difficult to follow

l-3: Self-monitoring, vigorous exercise in group

I- I : Weekly calls, general inquiry          Frequent call conditions had 63% walking compared with
I-?: Weekly calls, structured inquiry         26% and 22% in the infrequent condition; frequent call and
1.3: Call every 3 weeks, general inquiry       structured inquiry had higher rate of walking than other
I--J: Call every 3 weeks, structured inquiry        groups

1-1 : Mail-delivered lifestyle packet based on
stages of change

No difference in stage of change status among or
within groups

I-.!: Mail-delivered structured exercise packet
with exercise prescription
(-: Mail-delivered fitness feedback packet

I:  Exercise class and relapse prevention training
(1: Exercise class

Higher attendance in relapse prevention group over 10
weeks and at 3 months; high attrition and inconsistent

results across experimental groups

I- 1 : Vigorous self-directed exercise, staff telephone
calls, self-monitoring

I 2: Moderate self-directed exercise, staff
telephone calls, self-monitoring
(.. Staff telephone calls

Better adherence in the moderate-intensity group at 12 weeks
compared with vigorous (96% vs. 90%) (no statistical tests
reported); travel, work schedule conflicts, and weather
were noted as barriers to physical activity

I:  90-minute classes 2 times/week after work,
parcourse, self-monitoring, contests
(1: None

Twofold increase in bouts of exercise compared with
nonparticipants. Participants different from nonparticipants
at baseline

t-1 : Team building, relapse prevention training;
  sroup exercise

i-2: Team building, group exercise
I- i: Relapse prevention training and jogging alone
I`: logging alone

l-2 and 1-3 had twice the jogging episodes as l-l and C at
5 weeks; at 3 months, 83% of l-3 were jogging compared
with 38% of l-l and l-2 and 36% of C

1-l : Home-based moderate exercise, self-
monitoring with portable monitor, relapse
prevention training, telephone calls from staff
i-2: Same as l-l without telephone calls from staff

NO difference in number of sessions and duration reported
at 6-month follow-up

i-1 : Daily self-monitoring
-2: a'eekly self-monitoring

I-1 had more exercise bouts per month (11 vs. 7.5)

219


Physical Activity and Health

Table 6-2. Continued
Study

Marcus and Stanton
(1993)

Design

18 week
experimental

Theoretical approach

Relapse prevention,
social learning
theory

Population

120 female university
employees, mean
age = 35

McAuley et al. (1994)

5 month
experimental

Social learning theory

114 sedentary middle-
aged adults

Owen et al. (1987)

12 week
quasi-experimental

Robison et al. (1992)

6 month
quasi-experimental

Interventions in health care settings
Logsdon, Lazaro,
Meier (1989)
(INSURE)

1 year
quasi-experimental

Calfas et al.
(in press)

Community approaches
Luepker et al. (1994)
(Minnesota Heart
Health Project)

Young et al.
(in press)
(Stanford Five-City Project)

2 week
quasi-experimental

5 to 6 year
quasi-experimental;
3 matchedpairs

7 year
quasi-experimental

Behavioral management

Behavioral management,
social support

None mentioned

Stage of change

Diffusion of innovations,   Community longitudinal
social learning theory,    cohort (n = 7,097),
community organization,   independent survey
communication theory    (n = 300-500)

Social learning theory,
communication theory,
community organization

2 sets of paired, medium-
sized cities (5th city used
for surveillance only)

.

343 white-collar and pro-
fessional workers, mean
age = 36, mostly women

137 university staff at
6 campus worksites,
mean age = 40

2,218 patients from multi-
specialty group practice
sites

212 patients

Macera et al. (1995)

4 year
quasi-experimental
(2 matched communities)

None specified

Community residents
2 18 years;
24% African American (I),
35% African American (Cl

Brownson et al. (1996)

4 year
quasi-experimental

Social learning theory,    Rural communities; largely
stage theory of innovation  African American

I = intervention; C = control or comparison group.

220


Understanding and Promoting Physical Activity

Intervention                  Findings and comments

t-1 : Relapse prevention training and exercise
1-2: Scheduled reinforcement for attendance
  and exercise
i: Exerc.ise only

1:  Modeling of exercise, provision of efficacy-
based information (mastery accomplishments,
social modeling, social persuasion,
physiological response), walking program
(1: Biweekly meetings on health information,
walking program

1.  Self-management instruction, exercise class
(.: Exercise class

I:  Weekly group meetings, contracts, cash
incentives, social support, exercise
(`: Exercise, diary

~  Screening and counseling from physicians
who received continuing education; preventive
visits at no charge

I:  Physician counseling; booster call from
  a health educator
r`: Nothing

Screening and education; mass media; com-
munity participation; environmental change;
professional education; youth and adults
(:: Nothing

I:  Print materials; workshops and seminars;
organized walking; organized walking events;
"Heart & Sole" groups; worksite programs;
TV spots

1.  Community cardiovascular risk reduction
  activities
(1: None specified

`1  Community organization; development of 6 coa-
litions; exercise classes and walking classes and
walking clubs; demonstrations; sermons; news-
paper articles; community improvements; $5,000
to each coalition from the state health department

Better attendance in f-1 at 9 weeks; no difference at
18 weeks or 2-month follow-up

Better class attendance (67% vs. 55%) and more minutes
and miles walked among intervention group than controls

I

No difference in activity levels at 6 months

Higher attendance among experimental groups than
comparison groups (93-99% vs. 19%)

Increase in starting to exercise among intervention patients
(34% to 24%)

Intervention patients increased walking (37 minutes vs.
10 minutes per week)

Percent physically active higher in independent survey at
3 years; higher in the cohort at 7 years

Men increased participation in vigorous activities;
men and women in the intervention communities
increased their overall number of physical activities;
significant differences between intervention and
comparison communities at baseline

No difference in physical activity prevalence, physican
counseling for exercise, or exercise knowledge

Increased physical activity levels in coalition communities,
declining levels in communities without; net effect was 7%.
Planned Approach to Community Health education planning
model

221


Physical Activity and Health

Table 6-2. ConGnued

Study           Design

Theoretical approach

Population

6 week
pretest-posttest
uncontrolled

Stages of change

610 sample of community
residents, mean age = 42

Marcus, Banspach, et al.
(1992) (Pawtucket Heart
Health Program: imagine
Action)

Worksites

Blair et al. (1986)
(Live for Life)

Fries et a). (1993)

Heirich et al. (1993)

Communication
Osler and Jespersen
(1993)

Owen et al. (1995)

Brownell, Stunkard,
Albaum (1980)

2 year
quasi-experimental

24 month
experimental

3 year
experimental

2 year
quasi-experimental

2 year
pretest-posttest

Study 1: 8 week
quasi-experimental

Study 2: 4 month
quasi-experimental

None

None

4,300 Johnson & Johnson
employees

4,712 Bank of America
retirees

None specified

1,300 automobile plant
workers

Social learning theory,    Rural communities in
communications      Denmark (n = 8,000 [II)
(diffusion of innovations);
community organization

Social learning theory,
social marketing theory

2 national physical activity
campaigns in Australia

None specified

None specified

21,091 general public
observations at a mall,
train station, bus terminal

24,603 general public
observations at a train
station

Blarney, Mutrie,
Aitchison (1995)

16 week
quasi-experimental

None

22,275 subway users
observations

I = intervention; C = control or comparison group

222


Understanding and Promoting Physical Activity

Intervention

Written materials, resource manual, weekly fun
,yalks, and activity nights

Findings and comments

Participants more active after intervention with movement
toward action and low relapse to earlier stage; suggests
stage-based community intervention can result in movement
toward action; study uncontrolled

1:  Screening; lifestyle seminar; exercise programs;  20% of women and 30% of men began vigorous exercise
newsletters; contests; health communications;   of 2 years

no smoking policies
C: Screening only

I-I : Health risk appraisal; feedback letter;
behavioral management materials; personalized
health promotion program
t-2: Health risk appraisal; no feedback; full
program in year 2
C: No intervention

I- 1 : Fitness facility

I-L: Outreach and counseling to high risk employees
I- 1: Outreach and counseling to all employees
C: Health education events

I:  Heart Week with assessments, health
education, weekly community exercise, TV,
radio, newspaper community messages
(`: Not specified

I:  Messages to promote walking and readiness to
become active; modeling activity; radio and TV
PSAs; T-shirts; special scripting of soap operas

I:  Sign reading "Your heart needs exercise-
  here's your chance"

1. Sign reading "Your heart needs exercise-     Number of people using the stairs increased from 12% to
here's your chance"            18%; effect remained for 1 month after sign was removed

1:  Sign reading "Stay Healthy, Save Time,
  Use the Stairs"

.

No difference in physical activity year 1; l-l greater
physical activity in year 2 over l-2

Percent exercising 3 times per week: I-1 = 30%, ,
l-2 = 44%, l-3 = 45%, c = 37%

No difference in self-reported physical activity, but
intervention community expressed more interest in becoming
active; low response rate to surveys (59%); became mainly
a media campaign with little community involvement

1 st campaign-increase in percent who walked for exercise
(70% to 74%), greatest impact on 50+ age group (twofold
increase in reported walking-not significant)
2nd campaign-small declines in reported walking and
in intentions to be more active

Number of people using the stairs increased from 5%
to 14% when sign was up. Use declined to 7% when
sign was removed

Baseline stair use increased to 15-l 7% when sign
was up; persisted at 12 weeks after sign removal;
larger increase among men

223


Physical Activity and Health

Table 6-2. Conhued
Stdy           Design
Special populations: ethnic minorities
Heath et al. (1991)      2 year
             quasi-experimental

Theoretical approach


None specified

Population



86 Native Americans
with diabetes

Lewis et al. (1993)

Nader et al. (1989)
(San Diego Family
Health Project)

Baranowski et al.
(1990)

3 year
quasi-experimental

3 month
experimental
9 month
maintenance

14 weeks

Special populations: persons at risk for chronic disease
Perri et al. (1988)        18 month
             experimental

Jeffery (1995)

King et al. (1989)

7 year
uncontrolled

2 year
experimental

Special Populations: older adults
Mayer et al. (1994)       2 year
             experimental

Constituency-based
model

African American
residents of 6 public
housing units
    .

Social learning theory

623 Mexican and Anglo-
American families with
5th grade children

None specified

94 black families (63
adults, 64 children)

Behavioral management   123 overweight adults

None mentioned

280 community
members trying
to lose weight

None mentioned

96 men trying to
maintain weight
loss

Social learning theory

1,800 Medicare
beneficiaries in HMO,
mostly white, high SES

I = intervention; C = control or comparison group.

224


Understanding and Promoting Physical Activity

intervention

Findings and comments

I:  Exercise class
c-: Nonparticipants

I.1 : Basic exercise program
I-.!: Basic exercise program; social; goal setting;
attention; information; barrier reduction

I:  Family newsletter; telephone; mail; personal
contact; feedback; family behavior manage-
ment; physical activity; nutrition education
(-: Periodic evaluation

I.  Individual counseling, small group education,
aerobic activity, incentives (babysitting,
transportation), telephone prompts, assessment
(.: Assessment only

I- I : Behavior therapy

I-.!: Behavior therapy, maintenance
I- 1: Behavior therapy, maintenance, social influence
I--$: Behavior therapy, maintenance, exercise
I-5: Behavior therapy, maintenance, exercise, social

influence

! 1: Diet management
). Weight management, including exercise
_
in i: Physical activity

I.  Monthly mailings, advice and tips for coping,
staff telephone calls
(`: No intervention

  Health risk appraisal, feedback, health    No change in physical activity (3+ times a week) at 1 year,
education sessions, medical tests, immuniza-  but 21% vs.1 4% moved from sedentary to active
tions, goal setting, self-monitoring     (no statistical test reported); attrition 16% in experimental
(1: Not specified                 group at 1 year

-

Participants in the exercise program lost 4 kg of weight
on average, compared with 0.9 kg among nonparticipants;
improvements occurred in fasting blood glucose
levels and medication requirements

Communities that were better organized and had more
committed leaders had better program attendance and
higher physical activity levels

No difference in physical activity at 1 year

No difference in energy expenditure; low
participation (20%)

Difference adherence in high exercise groups at 6 months;
no differences at 12 and 18 months; high attrition (24"/0)

t-2 resulted in greater weight loss at end, but no
differences were observed at 1 year

Men who exercised and received the intervention regained
less weight in year 2 than exercisers who did not get
the intervention or dieters who were exposed to the
    intervention

225


Physical Activity and Health

self-monitoring group had significantly better
adherence over 12 weeks than those in the self-
monitoring plus attention or control groups; how-
ever, adherence over the last 6 weeks of the study was
significantly better in the self-monitoring plus atten-
tion group. Actual differences were not large, amount-
ing to 4 to 5 days of gym attendance over 3 weeks,
compared with about 3 days among controls. In all
three groups, adherence dropped off most sharply
during the first 6 weeks of the study.
  Classes, health clubs, and fitness centers are
resources to promote physical activity, and numer-
ous studies have been undertaken to improve atten-
dance (Table 6-2). However, many people prefer to
exercise on their own. Several studies have used
behavioral management techniques to encourage
people to do so on their own (Table 6-2). In some
studies, training in behavioral management tech-
niques has occurred in a group setting before the
participants began exercising on their own; in oth-
ers, information has been provided by mail. Results
have been equivocal. King, Haskell, and colleagues
(1995) assigned 50- through 6%year-old partici-
pants to one of three conditions: a vigorous, group-
based program (three 60-minute sessions); a
vigorous, home-based program (three 60-minute
sessions); and a moderate, home-based program
(five 30-minute sessions). At 1 year, a'dherence was
significantly greater in both home-based programs
than in the group-based program. At 2 years, how-
ever, the vigorous, home-based program had higher
adherence than the other two programs. Research-
ers hypothesize that it was more difficult for the
moderate group to schedule 5 days of weekly physi-
cal activity than for the vigorous group to schedule
3 days. Another study encouraged self-monitoring
and social support (walking with a partner) and
also tested a schedule of calling participants to
prompt them to walk. Frequent calls (once a week)
resulted in three times the number of reported
episodes of activity than resulted from calling every
3 weeks (Lombard, Lombard, Winett 1995). Cardi-
nal and Sachs (1995) randomly assigned 133 women
to receive one of the three packets of information
promoting physical activity: self-instructional pack-
ages that were based on stage of change and that
provided tailored feedback; a packet containing a
standard exercise prescription; and a packet pro-
vidingminimal information about health status and

exercise status. No significant differences were
observed among the three groups at baseline, 1
month, or 7 months.

The advent of interactive expert-system com-
puter technologies has allowed for increased indi-
vidualization of mailed feedback and other types of
printed materials for health promotion (Skinner,
Strecher, Hospers 1994). Whether these technolo-
gies can be shown to be effective in promoting
physical activity at low cost is yet to be determined.

Insummary, behavioral management approaches
have been employed with mixed results. Where an
effect has been demonstrated, it has often been small.
Evidence of the effectiveness of techniques like self-
monitoring, frequent follow-up telephone calls, and
incentives appear to be generally positive over the
short run, but not over longer intervals. Evidence on
the relative effectiveness of interventions on adher-
ence to moderate or vigorous activity is limited and
unclear. Because of the small number of studies, the
variety of outcome measures employed, and the di-
versity of settings examined, it is not clear under what
circumstances behavioral management approaches
work best.

In a number of studies, methodological issues,
such as high attrition rates, short follow-up, small
sample sizes, lack of control or comparison groups,
incomplete reporting of data, or lack of clarity about
how theoretical constructs were operationalized.
also make it difficult to determine the effectiveness
of behavioral management approaches or to general-
ize results to other settings or population groups.
Stages of change theory suggests that people move
back and forth across stages before they become able
to sustain a behavior such as physical activity. The
relatively short time frame of many studies and the
use of outcome measures that are not sensitive to
stages of change may have limited the ability to
determine if and to what extent possessing behav-
ioral management skills is useful in the maintenance
of regular physical activity.

Interventions in Health Care Settings
Health care settings offer an opportunity to indi-
vidually counsel adults and young people about
physical activity as well as other healthful behaviors,
such as dietary practices (U.S. Preventive Services
Task Force 1996). Approximately 80 percent of the

226


U.S. population see a physician during a l-year
period (National Center for Health Statistics 1991),
but the extent to which physicians counsel their
patients to be physically active is unclear. One survey
of physicians found 92 percent reporting that they or
someone in their practice counseled patients about
exercise (Mullen and Tabak 1989), but in a more
rcccnt study, only 49 percent of primary care physi-
cians stated they believed that regular daily physical
nctivity was very important for the average patient
c\Vechsler et al. 1996). Counseling is likely to be
brief, often less than 2 minutes (Wells et al. 1986),
.tnd ineffective counseling approaches are often
cmpfoyed (Orleans et al. 1985). Physicians may be
\css likely to counsel patients about health habits if
their own health habits are poor (Wells et al. 1984).
Only three studies attempting to improve the
physical activity counseling skills of primary care
physicians have been reported in the literature; the
rcsufts suggest small but generally positive effects on
patients, with from 7 to 10 percent of sedentary
l,crsons starting to be physically active (Table 6-2).
( )nc feasibility trial ofmultiple risk factorreduction-
IIK Industrywide Network for Social, Urban, and
Rural Efforts (INSURE) Project-indicates that con-
ttnuing medical education seminars, combined with
rclmbursement for prevention counseling and re-
rntndcrs to providers, can increase the.percentage of
I lrcsc physicians' patients who subsequently start exer-
t 151ng (Logsdon, Lazaro, Meir 1989). The Physician-
`j.t~d Assessment and Counseling for Exercise (PACE)
l)rogram incorporated social cognitive theory and the
trnnstheoretical model to individualize brief (2-5
Inlnutcs) counseling messages for patients. Com-
p;u-cd with patients who did not receive the program
c,ounseling, those who did had significantly greater
Improvements at 4-6 weeks in their reported stage of
i~h!sical activity readiness, their reported amount of
: ,rlking for exercise, and their scores from an activity
,n0nitor (Calfas et al. in press).

The Canadian Task Force on the Periodic Health
Examination (1994) cited insufficient evidence as
the reason for not making a recommendation regard-
ing physical activity counseling. However, several
other professional organizations have recently rec-
ommended routine physical activity counseling. The
`~mcrican Heart Association (Fletcher et al. 1992),
`Jc American Academy of Pediatrics (1994), the
.`mcrican Medical Association (1994)) the President's

227

Understanding and Promoting Physical Activity

Council on Physical Fitness and Sports (1992), and
the U.S. Preventive Services Task Force (1989,1996)
all recommend including physical activity counsel-
ing as part of routine clinical preventive services for
both adults and young people.
In summary, many providers do not believe that
physical activity is an important topic to discuss with
their patients, and many lack effective counseling
skills. The studies that have attempted to increase
provider counseling for physical activity demonstrate
that providers can be effective in increasing physical
activity among their patients. It is not known what
alternative approaches to provider counseling can be
used effectively in health care settings, although the
work of Mayer and colleagues (1994) suggests that
well-trained counselors conducting health education
classes with patients may help older adults make
changes in their stage of physical activity.

Community Approaches

Communitywide prevention programs have evolved
from the concept that a population, rather than an
individual, approach is required to achieve primary
prevention of disease through risk factor reduction
(Luepker et al. 1994). Behaviors and lifestyle choices
that contribute to an individual's risk profile are
influenced by personal, cultural, and environmental
factors (Bandura 1977b). Much of the current knowl-
edge regarding community-based prevention strate-
gies has been gained over the past 20 years from three
U.S. research field trials for community-based health
promotion-including physical activity promotion-
to reduce cardiovascular disease (Table 6-2).
These three trials, which were funded by the
National Heart, Lung, and Blood Institute during the
198Os, were the Minnesota Heart Health Program
(MHHP) (Luepker et al. 1994), the Pawtucket Heart
Health Program (PHHP) (Carleton et al. 1995), and
the Stanford Five-City Project (SFCP) (Farquhar et al.
1990). The MHHP advocated regular physical activity
as part of its broad effort to reduce risk for CHD in
whole communities in the upper Midwest (Crow et al.
1986; Mittelmark et al. 1986). Three intervention
communities received a 5- to 6-year program designed
to reduce smoking, serum cholesterol, and blood
pressure and to increase physical activity; three other
communities served as comparison sites. Mass media
were used to educate the public about the relationship


Physical Activity and Health

between regular physical activity and reduced risk for
CHD and to increase opportunities for physical activ-
ity. Health professionals promoted physical activity
through their local organizations, through their advi-
sot-y committees on preventive practice. and through
serving as role models and opinion leaders. Systematic
risk factor screening and education provided on-site
measurement, education, and counseling aimed in
part at increasing to 60 percent the prevalence of
physical activity among the residents in the three
intervention communities. The adult education com-
ponent made available personal, intensive, and mul-
tiple-contact programs to increase physical activity;

this strategy focused on self-management and in-
eluded changes in existing behaviors, in the meaning
of those behaviors, andin the environmental cues that
supported them. Direct education programs forschool-
aged children promoted physical activity in young
people and their parents. The MHHP investigators
reported small but significant effects for physical
activity in the first 3 years among people in the cross-
sectional study group; that effect disappeared with an
increasing secular trend in physical activity in the
comparison groups. The cohort group (followed over
time) showed no intervention effect until the last
follow-up survey (Figure 6-l).
                       .

Figure 6-l. Results of the Minnesota Heart Health Program on physical activity. Graph compares the
   percentage of respondents reporting regular physical activity in intervention cities and the
     secular trend estimated from control cities

I         I         I        I        I

-4      -2       0        2       4       6       8
            Education year
75                     I
                      I               1

Panel 1: Cross-sectional
Fitted secular trend
and MHHP education
program effect estimates

m-v- Education effect
I  95% Confidence
   bounds
- Secular trend

                      I
45 -                   I
                      I
     Baseline       I
                      I         Follow-up
                      I
35         I          I         I         I        I
-4       -2       0       2        4       6       8
             Education year

Panel 2: Cohort

Fitted cohort levels
and MHHP education
program effect estimates

---- Education effect
I  95% Confidence
   bounds
- Cohort levels

Sours e: Luepker RV et Ji. American ]ourna/ oi PuOlic Health 1994 (reprinted with permission).
Note: Adjusted for age, sex. and education.

228


  The PHHP fostered communiry involvement in
heart healthy behavior changes in Pawtucket, Rhode
\s\and(Carletonetal. 1995).Thefocuswasongrassroots
organizing, volunteer delivery, and partnerships with
existing organizations rather than on using electronic
media (Lasater et al. 1986). In the area of physical
.Ictlvity promotion, the emphasis was on environmen-
t,ll and policy change through partnerships with city
oo\,ernment and others. Working with the Department
I-
of Parks and Recreation, the PHHP was instrumental in
establishing cardiovascular fitness trails in both of the
c~t).`sparks. Earlyin itsexistence, the PHHPalso helped
that department place on the ballot and pass a large
bond issue in return for renovations (e.g., lights, fenc-
ing to keep stray dogs out, resurfacing) to an existing
c,ciarter-mile track for walking. The Pawtucket 6-
Lvcck Imagine Action Program, designed around the
stages of change model, enrolled more than 600
participants, who subsequently reported being more
.IC`~IVC as a result of the program (Marcus, Banspach, et
,11. 1992). Results of this uncontrolled study suggest
I 11`11 ;I stage-based approach may be effective in moving
people toward regular physical activity.
  The SFCP included two intervention and two
comparison communities in northern California (only
morbidity and mortality data were monitored in the
hfth city, and those results were not reported in this
ytucly). This project was designed to increase physical
~cr~viry and weight control and to reduce plasma cho-
Icstcrol levels, cigarette use, and blood pressure
l'nrquhar et al. 1990). Greater emphasis was placed on
rlutrition, weight control, and blood pressure than on
physical activity. The program used concepts from
\ocial learning theory, diffusion theory, community
organization, and social marketing in combination
\vlth a communication and behavior change model
(Flora, Maccoby, Farquhar 1989). The program relied
heavily on the use of electronic and print media for the
Jchvery of health education information. General edu-
.ition was supplemented by four to five annual educa-
IIon campaigns targeting specific risk factors. Direct
face-to-face activities included classes, contests, and
school-based programs (Farquhar et al. 1990). Overall,
Ihe educational intervention had no significant im-
pact on physical activity levels, knowledge, self-
efficacy, or attitudes toward physical activity (Young
ct al. T in press). In the cross-sectional sample, men in
`he experimental communities were significantly more

Understanding and Promoting Physical Activity

likely than those in the control communities to engage
in at least one vigorous activity. For women in both the
cross-sectional and cohort studies, a small but signifi-
cant increase was observed in the number of moderate
activities engaged in (Young et al., in press).
Among smaller-scale community studies, the re-
sults of efforts to promote physical activity have been
mixed (Table 6-2). One exception was the community-
based cardiovascular disease prevention program
aimed at black residents in rural communities in the
Missouri "Bootheel" (Brownson et al. 1996). In this 5-
year, low-cost intervention project, educational ef-
forts were combined w,ith environmental changes.
Local coalitions formed walking clubs, built walking
trails, started exercise classes in churches, and orga-
nized special events to promote both physical activity
and good nutrition. Although no difference in levels of
physical inactivity was observed between the Bootheel
and the rest of the state at follow-up, physical inactiv-
ity declined an average of 3 percent in Bootheel
communities that had coalitions and increased an
average of 3.8 percent in those without, for a net
improvement of 6.8 percent.

In summary, results of community-based inter-
ventions to increase physical activity have been
generally disappointing. Measurement of physical
activity has varied across studies, making compari-
sons difficult. The presence of active communiry
coalitions, widespread community involvement, and
well-organized community efforts appear to be im-
portant, however, in increasing physical activity
levels.

Worksite Programs

Physical activity programs conducted on the worksite
have the potential to reach a large percentage of the
U.S. population (Bezold, Carlson, Peck 1986; Na-
tional Center for Health Statistics 1987). As settings
for physical activity promotion, manyworksites have
easy access to employees and supportive social net-
works and can make changes in the environment to
help convey physical activity as an organizational
norm (Shephard, in press).

The proportion of worksites offering physical
activity and fitness programs has grown in recent
years, from 22 percent in 1985 to 42 percent in 1992
(Table 6-3). For two groups of employers, those
with 50-99 employees and those with loo-249

229


Physical Activity and Health

Table 6-3. Summary of progress toward Healthy People 2000 objective 1 .lO
        "Increase the proportion of worksites offering employer-sponsored
           physical activity and fitness programs as follows:"

Year 2000 objective                 1985            1992        Year 2000 target
Physical activity and fitness
worksites with:
SO-99 employees                 14%             33%              20%
loo-249 employees               23%            47%              35%
250-749 employees               32%             66%              50%
750+ employees                 54%             83%              80%
Source: U.S. Department of Health and Human Services, 1992 National Survey of Worksite Health Promotion Activities, 1993.

r

employees, the percentage with exercise programs
more than doubled over that time period. In each
worksitesize category, the percentage with exercise
programs had already (i.e., in 1992) exceeded the
year 2000 national objective for worksite health
promotion listed in Healtlly People 2000 (USDHHS
1993). Generally, the extent of participation, effec-
tiveness, and quality of those programs is unknown,
for only a few worksite physical activity programs
have been evaluated (Table 6-2).
In the Johnson 6;r Johnson Live for Life program
(Wilbur 1983), employees at four experimental sites
participated in lifestyle seminars, contests, and exer-
cise programs and received newsletters on health
issues and other health communications. Experi-
mental and control sites both received an annual
health assessment. Overall, at the end of 2 years, 20
percent of women and 30 percent of men in the
experimental sites reported beginning a vigorous
exercise program; the prevalence at three compari-
son sites was 7 percent for women and 19 percent for
men (Blair et al. 1986).

Fries and associates (1993) evaluated the effec-
tiveness of a health promotion program that included
physical activity for Bank of America retirees. In one
intervention group, each participant paid $30 for a
personalized. mail-delivered program that included a
health risk appraisal and behavioral management
books and other materials. A second group received a
risk appraisal and nothing else for the first 12 months,
after which it received the full intervention. A control
group was monitored for claims data only. The first

intervention group did not differ from the second in
self-reported physical activity at the end of year 1 but
was significantly different in year 2.

Worksite programs less often attract sedentary,
blue-collar, or less-educated employees, but interven-
tions that are tailored to these persons' needs and
interests (King, Carl, etal. 1988) and provide counsel-
ing and peer support (Heirich et al. 1993) show
promise. In a controlled study, Heirich and colleagues
(1993) compared different programs at four automo-
tive manufacturing plants of like size and employee
populations. The three approaches tested were 1) a
staffed physical fitness facility, 2) one-to-one counsel-
ingandoutreachwith high-riskemployees (i.e., those
who had hypertension, were overweight, or smoked
cigarettes), and 3) one-to-one counseling and out-
reach to all employees, peer support, and organiza-
tional change (e.g., the institution of nonsmoking
areas). The fourth site, which served as a control,
offered health education classes and special events.
After 3 years, exercise prevalence at the four sites was
lowest at the plant with the exercise facility _ In the two
counseling and outreach sites, nearly half of the
employees reported exercising 3 times a week.

In summary, considerable progress has been
made in meeting the Healthy People 2000 goals for
worksite physical activity programs. Too few studies
exist to clearly determine what elements are required
for physical activity programs at work to be effective
in increasing physical activity levels among all em-
ployees, attracting diverse employee groups (such as
blue-collar workers), or maintaining exercise levels


over time. However, the limited research available
suggests that widespread employee involvement and
support coupled with organizational commitment
evidenced by the presence of policies and programs
may be important factors in increasing levels of
physical activity. Existing controlled studies have
been done in larger worksites; studies have not yet
shown what might work in smaller worksites and in
diverse worksites (e.g., where many employees travel
or facilities may not exist).

Communications Strategies

Communications strategies, both electronic and print,
\lave the potential for reaching individuals and com-
munities with a rapidity unmatched by other inter-
ifcntion strategies. For the general population, media
can play several roles: to increase the perceived
importance of physical activity as a health issue, to
communicate the health and other benefits of physi-
cal activity, to generate interest in physical activity
;md awareness about available programs, to provide
role models for physically active lifestyles, and to
provide cues to action, such as getting people to
request further information on physical activity,
\,isit an exercise site, or begin exercising (Donovan
and Owen 1994).

The effectiveness of different forms of media
alone, including broadcast and print media, for
promoting either initial adoption or subsequent
maintenance of physical activity remains unclear
hccause the few systematically evaluated interven-
I [(Ins employing communications strategies have
\hown mixed results (Osler and Jespersen 1993;
liooth et al. 1992; Owen et al. 1995; Luepker et al.
1994; Farquhar et al. 1990). The SFCP, discussed
cnrlier, resulted in small increases in the number of
moderate activities engaged in by women and vig-
orous activity engaged in by men. Two national
mass media campaigns to increase physical activity,
i~nrticularly walking, to prevent cardiovascular dis-
I"KC were conducted in Australia in 1990 and 1991
(Booth et al. 1992). Drawing on social marketing
`lnd social learning theories, both campaigns in-
cluded paid advertisements on national television,
Pllblic service announcements on radio, scripted
episodes on two nationally broadcast television
clrarnas, posters and leaflets, stickers, T-shirts and
-\\,catshirts, magazine articles, distribution of a

Understanding and Promoting Physical Activity

professional article, soap operas specially scripted
to feature physical activity, and publicity tours by
two experts in heart health. The budgets and paid
television coverage for the 1990 and 1991 cam-
paigns were similar. Both campaigns were evalu-
ated by one-on-one, home-based interviews with
structured cross-sectional random samples of ap-
proximately 2,500 people 2 weeks before and 3 to 4
weeks after each campaign. Both campaigns re-
sulted in significant differences in message aware-
ness (46 percent vs. 71 percent in 1990; 63 percent
vs. 74 percent in 1991). The 1990 postcampaign
survey revealed significant increases in walking for
exercise (p < 0.01) compared with the precampaign
period, although the actual percentage increase was
small (73.9 percent vs. 70.1 percent). In particular,
adults over 50 years of age were nearly two times
more likely to report walking at follow-up than
before the campaign. The 1991 campaign produced
different results. Evaluation showed that the per-
centage of persons reporting walking in the previ-
ous 2 weeks declined from precampaign levels
among all adult age groups except people over 60
years of age. Intention to become more active also
declined overall, from 26.3 percent to 24.8 percent
(Owen et al. 1995).

  Communications intended to serve as cues to
action have been tested at places where people can
choose whether to walk or ride. This approach in-
volves placing signs to use the stairs near escalators
in public places like train and bus stations or shop-
ping malls (Brownell, Stunkard, Albaum 1980;
Blarney, Mutrie, Aicchison 1995). For example, signs
that said "Stay Healthy, Save Time, Use the Stairs"
increased the percentage of people using stairs in-
stead of an adjacent escalator from 8 percent to 1%
17 percent (Blarney, Mutrie, Aitchison 1995). Twelve
weeks after the sign was removed, the increase in
stair use remained significant but showed a trend
toward baseline.

In summary, communications strategies have
had limited impact. It is not clear if communications
approaches would be more effective in getting people
to be regularly active if they were linked with oppor-
tunities to act on messages or if messages were
tailored to stages of change or to the needs of sub-
groups in the population (Carleton et al. 1995;
Donovan and Owen 1994; Young et al. in press).

231


physical Activity and Health

Appropriately placed communications that serve as
cues to action appear to increase the decision to use
the stairs instead of ride the escalator.

Special Population Programs

Racial and Ethnic Minorities

The few interventions studies that have been con-
ducted with racial and ethnic minorities have pro-
duced mixed results. The Bootheel Project referred
to earlier in this chapter found increased levels of
physical activity in black communities with coali-
tions. The Physical Activity for Risk Reduction project
(Lewis et al. 1993) was undertaken in black commu-
nities in Birmingham, Alabama, using a combination
of behavioral management and community organi-
zation approaches. In the intervention groups, com-
munity members played roles in defining needs,
identifying strategies, and conducting interventions.
In those communities where strong organization,
leadership, and commitment to the project were
observed, statistically significant increases in physi-
cal activity were also noted.

Results of two family-based health promotion
programs that used behavioral management ap-
proaches to promote physical activity showed no
greater increase in physical activity among those
participating in the programs than among those in a
control group. Nader and colleagues (1989) con-
ducted a nutrition and physical activity program for
Anglo-American and Mexican American families with
children in fifth and sixth grades; the program im-
proved dietary habits but did not succeed in increas-
ing physical activity levels, although participation in
the program was high. Another family-based pro-
gram, a 14week intervention for African American
families that included educational sessions and twice-
weekly fitness center activities, had low attendance
and did not increase physical activity (Baranowski et
al. 1990).

The Indian Health Service undertook the
community-based Zuni Diabetes Project to increase
physical activity and decrease body weight among
Zuni Indians in New Mexico who had non-insulin-
dependent diabetes mellitus (NIDDM) (Leonard,
Leonard, Wilson 1986). The exercise program con-
sisted of several l-hour aerobic sessions offered during
the week. Zuni Indians who were trained in exercise
and group leadership methods helped coordinate the

program and build community ownership. After par-
ticipating in aerobic sessions through the program, 43
percent of the participants began and maintained an
at-home exercise program, whereas only 18 percent
of a comparison group of previously sedentary non-
participants with NIDDM did so (Heath et al. 1987).

People Who Are Overweight

Being overweight increases the risk of developing
chronic diseases (see Chapter 4). Results of inter-
ventions to promote physical activity for weight loss
have been mixed (Perri et al. 1988; Jeffery 1995;
King et al. 1989).

The MHHP , one of the large community inter-
vention trials discussed earlier in this chapter
(Luepker et al. 1994), developed a series of compo-
nent programs containing strategies to increase physi-
cal activity for losing weight or preventing weight
gain Ueffery 1995). The Building Your Fitness Fu-
tures program was a 4-week adult education class
that focused on how to develop a regular exercise
program. The Wise Weighs programs was an g-week
adult education class that emphasized weight man-
agement strategies related to diet and exercise. The
third MHHP intervention, a correspondence course,
addressed diet and exercise through monthly news-
letters and tested two levels of financial contract
incentives ($5 and $60 dollars). Each of these pro-
grams was evaluated in the MHHP randomized trial.
The Building Your Fitness Futures and the Wise
Weighs programs resulted in only small weight loss
that was not significant after 1 year. The correspon-
dence course resulted in significantly greater weight
loss among participants with $60 incentives than
among those with $5 incentives.
Preventing weight gain may be easier than promot-
ing weight loss. Wing (1995) suggests that there are
three time periods during which interventions to pre-
vent weight gain might be most effective: in the years
between ages 25 and 35 years, in the peri-menopausal
period for women, and in the year following successful
weight loss. A fourth MHHP program that addressed
physical activity, the Weight Gain Prevention Pro-
gram, was a randomized trial of 211 communityvolun-
teers. The participants (approximately two-thirds
women) were randomly assigned to either the inter-
vention group (n = 103) or the no-contact control
group (n = 108). This program was for normal-weight
adults and included monthly newsletters and four


classes emphasizing diet and regular exercise as well
as a financial incentive component linked to weight
maintenance. The intervention group lost 2 pounds
on average over the course of the year and were
significantly less likely to gain weight than the control
group (82 percent vs. 56 percent) (Jeffery 1995).

Older Adults

\lany of the diseases and disabling conditions asso-
elated with aging can be prevented, postponed, or
ameliorated with regular physicalactivity (see Chap-
tcr 4). The few interventions that have been tested to
Increase physical activity levels among older adults
,how generally positive results. The 1990 Australian
ticart Week campaign reviewed earlier resulted in a
t\vofold increase in walking among adults over 50
\`ears of age (Owen et al. 1995). Retirees in the study
by Fries (1993), also discussed earlier, showed sig-
nlficantly greater improvements in physical activity
In year 2 than did persons in the control group.
Pnrricipants in a longitudinal study of Medicare
rcclpients (n = 1,800) who belonged to a health
maintenance organization were randomly assigned
10 a preventive care or a control group (Mayer et al.
1094). The intervention employed information and
hchavior modification approaches. Participants re-
ccived recommended immunizations, completed a
health risk appraisal, received face-tq-face counsel-
~ng that included goal setting, received follow-up
rclcphone counseling, and participated in educa-
~lonal sessions on health promotion topics. A focus
~III physical activity was a priority in goal-setting
dIscussions; 42 percent of participants selected in-
creasing physical activity as their goal. Members of
both groups were largely white, well educated, and
~~enerally had above-average incomes. The preva-
r cnce of physical activity was high in both groups at
llaseline; approximately 60 percent reported get-
llng regular exercise. At 1 year, the intervention
croup showed a significant 7 percent increase in
yell-reported physical activity.

Much of the published research on physical activ-
I$ describes researcher-initiated interventions. How-
ever, individuals and small groups of people often
Imtiate physical activity on their own, independent of
nny formal program. A qualitative research study by
Duncan, Travis, and McAuley (1995) used observa-
`ions and in-depth interviews to examine motivation

Understanding and Promoting Physical Activity

for initiating and maintaining mall walking by older
persons in rural West Virginia. Most participants in
this study reported becoming physically active at the
urging of their physicians; several others were moti-
vated by personal interest in health maintenance, and
some were encouraged by family members. Mall walk-
ers maintained a regular routine, showing up at the
same time each day, walking in pairs or small groups,
and then adjourning to a mall eatery for coffee or
breakfast. Interviews revealed that participants per-
ceived mall walking as meaningful "work" to be doing
during retirement. A need for socializing with others,
a sense of belonging to a community of mall walkers,
and the safe environment of the mall were other
factors contributing to adherence. Study researchers
recommended that community-based physical activ-
ity programs try to replicate various aspects of work,
such as keeping attendance records and providing
occasional recognition or acknowledgment of a job
well done (such as pins, certificates, or celebrations).

People with Disabilities

People with disabilities have similar health promo-
tion and disease prevention needs as persons with-
out disabilities. Interventions to promote physical
activity for risk reduction among persons with mo-
bility, visual, hearing, mental, or emotional impair-
ments are largely absent from the literature. Physical
activity interventions for managing chronic condi-
tions, on the other hand, have led to enhanced
cardiorespiratory fitness and improved skeletal
muscle function in persons with multiple sclerosis
(Ponichtera-Mulcare 1993), increased walking ca-
pacity and reduction in pain for patients with low
back pain (Frost et al. 1995), and improvements in
endurance among patients with chronic obstructive
pulmonary disease (Atkins and Robert 1984).

In summary, interventions that have been suc-
cessful in increasing physical activity among minori-
ties have employed community organization
strategies, such as coalition building and community
engagement at all levels. Family-oriented interven-
tions in community centers that have employed
behavioral management approaches have not re-
sulted in increases in physical activity. Physical
activity interventions incorporating incentives show
promise for promoting weight loss or preventing
weight gain. Although there are a limited number of

233


Physical Activity and Health

studies, positive effects have been shown for inter-
ventions and communications strategies promoting
physical activity in older adult populations, at least
among older white adults with moderate incomes
and education levels. What is not well known is what
interventions may be effective with racial or ethnic
minority older adults who may face barriers such as
language, transportation, income, education, or dis-
ability. It is not clear what interventions might be
effective to promote physical activity. other than for
disease management, among people with disabili-
ties, or what strategies might assist with the manage-
ment of pain, periods of illness, environmental
barriers, or other circumstances to improve adher-
ence with physical activity recommendations.

Summary

The review of adult intervention research literature
provides limited evidence that interventions to pro-
mote physical activity can be effective in a variety of
settings using a variety of strategies. Controlled
interventions that have been effective at the work-
place, in health care settings, and in communities
have resulted in increased physical activity, although
effects have tended to be small, in the range of 5-10
percent, and short-lived. Multiple interventions con-
ducted over time may need to be employed to sustain
physical activity behavior. Most experimental and
quasi-experimental intervention research has been
theory-based, much if not most relying largely on
behavioral management strategies, often in combi-
nation with other approaches, such as communica-
tions and social support. Mixed results have made it
impossible to determine what theory or theories
alone or in combination have most relevance to
physical activity. Research strategies that appear
promising include the tailoring of interventions to
people's needs, experiences, and stages of change;
the timing of intervention strategies to reinforce new
behaviors and prevent relapse (such as through
frequent follow-up telephone calls); peer involve-
ment and support; and an engaged community at all
levels. It is not known if interventions could be
strengthened by combining them with policy ap-
proaches (Luepker 1994; Winkleby 1994).
  Intervention studies with adults were often con-
ducted over a brief period of time, had little or no
follow-up, and focused on the endpoint of specified
vigorous physical activity rather than on moderate-

234

intensity physical activity or total amount of activity.
Studies used different endpoints, such as class par-
ticipation versus specified changes in behavior, mak-
ing them difficult to compare. Because physical
activity interventions were often only one compo-
nent of an intervention to reduce multiple risk fac-
tors, they may not have been robust enough to result
in much or any increase in physical activity. Few if
any studies compared their results to a standard of
effectiveness, such as recommended frequency or
duration of moderate or vigorous physical activity,
or clearly stated the extent of stage-based change.

Behavioral Research on Physical
Activity among Children and
Adolescents

Behavioral research in this area includes studies on
the factors influencing physical activity among
young people as well as studies examining the effec-
tiveness of interventions to increase this behavior.
This research, however, is more limited than the
determinants and interventions literature for adults.

Factors Influencing Physical Activity among
Children and Adolescents

The emphasis in this section is on factors that influ-
ence unstructured physical activity during free time
among youths rather than on supervised physical
activity, such as physical education classes. Studies
of organized youth sports have also been excluded.
Only studies with some measure of physical activity
as the outcome, however, are included in this re-
view. For example, studies that investigated atti-
tudes toward physical activity and did not relate
those to a measure of physical activity were ex-
cluded. As was the case in the adult section, this
section focuses on studies that address modifiable
determinants of physical activity, such as self-
efficacy, rather than on studies that examine factors
that cannot be altered to influence participation in
physical activity, such as age, sex, and racejethnicity.

Modifiable Determinants

The modifiable determinants of youth physical ac-
tivity include personal, interpersonal, and environ-
mental factors (Table 6-l). Self-efficacy, a construct


from social cognitive theory, has been positively
associated with physical activity among older chil-
dren and adolescents (Reynolds et al. 1990; Trost et
al. 1996; Zakarian et al. 1994). Similarly, perceptions
of physical or sports competence (Biddle and
Armstrong 1992;BiddleandGoudas 1996; Dempsey,
Kimiecik, Horn 1993; Ferguson et al. 1989; Tappe,
Duda, Menges-Ehrnwald 1990) also have been posi-
tively associated with physical activity among older
children and adolescents.

Expectations about the outcomes of physical
activity are associated with physical activity among
preadolescents and adolescents. Perceived benefits
have been positively associated (Ferguson et al.
1989; Tappe, Duda, Menges-Ehrnwald 1990;
Zakarian et al. 1994), whereas perceived barriers
have been negatively associated (Stucky-Ropp and
DiLorenzo 1993; Tappe, Duda, Menges-Ehrnwald
1990; Zakarian et al. 1994). Intention to be active, a
construct from the theory of reasoned action and the
theory of planned behavior, has been consistently
und positively related to physical activity among
older children and adolescents (Biddle and Goudas
1996; Ferguson et al. 1989; Godin and Shephard
1986; Reynolds et al. 1990) .

Enjoyment, the major reason young people en-
gage in physical activity (Borra et al. 1995), has been
positively associated with physical activity among
both children and adolescents (Stucky-Ropp and
DiLorenzo 1993; Tinsley et al. 1995). Favorable
,Ittitudes toward physical education also have been
llositively related to adolescent participation in
physical activity (Ferguson et al. 1989; Zakarian et
111. 1994).

Social influences-such as physically active role
models and support for physical activity-are im-
portant determinants of physical activity among
\`onng people (Tinsley et al. 1995). Parental activity
i Moore et al. 1991; Poest et al. 1989; Sallis, Patterson,
`ilcKenzie et al. 1988) is positively related to physical
.\ctivity among preschoolers. Studies reveal no rela-
[ionship between parental physical activity and physi-
cal activity among elementary school children
(McMurray et al. 1993; Sallis, Alcaraz, et al. 1992),
and either no relationship (Biddle and Goudas 1996;
Garcia et al. 1995; Stucky-Ropp and DiLorenzo 1993;
jallis, Patterson, Buono, et al. 1988) or positive
:efationships (Anderssen and Wold 1992; Butcher

Understanding and Promoting Physical Activity

1985; Gottlieb and Chen 1985; Stucky-Ropp and
DiLorenzo 1993; Sallis, Patterson, Buono, et al.
1988) to the physical activity of middle school stu-
dents (grades 5-8). Parental physical activity is posi-
tively related to physical activity among older
adolescents (Reynolds et al. 1990; Zakarian et al.
1994). The physical activity of friends (Anderssen
and Wold 1992; Stucky-Ropp and DiLorenzo 1993;
Zakarian et al. 1994) and siblings (Perusse et al.
1989; Salhs, Patterson, Buono, et al. 1988) also is
positively associated with physical activity among
older children and adolescents.

Parental encouragement is positively related to
physical activity among*preschoolers (McKenzie,
Sallis, et al. 1991; Klesges et al. 1984, 1986; Sallis et
al. 1993), and parental or adult support for physical
activity is positively associated with physical activity
among adolescents (Anderssen and Wold 1992;
Biddle and Goudas 1996; Butcher 1985; Zakarian et
al. 1994). Friends' support for physical activity
(Anderssen and Wold 1992; Zakarian et al. 1994)
also is positively related to physical activity among
adolescents.

Direct help from parents, such as organizing
exercise activities (Anderssen and Wold 1992) or
providing transportation (Sallis, Alacraz, et al. 1992>,
is positively related to physical activity among older
children and younger adolescents. Access to play
spaces and facilities (Garcia et al. 1995; Sallis et al.
1993; Zakarian et al. 1994) is positively related to
physical activity among youths of all ages. The avail-
ability of equipment has been positively related to
physical activity among preadolescent and adoles-
cent girls (Butcher 1985; Stucky-Ropp and DiLorenzo
1993). Further, two studies of young children have
demonstrated that time spent outdoors is a positive
correlate of physical activity level (Klesges et al.
1990; Sallis et al. 1993).

Determinants for Population Subgroups
Among the limited number of subgroup-specific
determinants studies, sex-specific differences are
investigated most frequently. In two studies of ado-
lescents (Kelder et al. 1995; Tappe, Duda, Menges-
Ehrnwald 199O), competition motivated boys more
than girls, and weight management motivated girls
more than boys. Additionally, boys have higher
levels of self-efficacy than girls (Trost et al. 1996)

235


physical Activity and Health

and higher levels of perceived competence (Tappe,
Duda, Menges-Ehrnwald 1990) for physical activity.

Summary

Few studies of the factors that influence physical
activity among children and adolescents have applied
the theories and models of behavioral and social
science. The research reviewed in this section, how-
ever, has revealed that many of the factors that influ-
ence physical activity among adults are also
determinants of physical activity among children and
adolescents. Older children's and adolescents' inten-
tions to engage in physical activity, as well as their
perceptions of their ability to engage in such activity
(i.e., self-efficacy and perceived competence), are
positively related to their participation in physical
activity. Social influences, such as parental and peer
engagement in, and support for, physical activity, also
are positively related to physical activity among young
people. Further, exercise enjoyment and positive atti-
tudes toward physical education have been positively
associated with physical activity among older chil-
dren and adolescents. Research is limited, however,
on patterns of determinants for population subgroups,
such as girls, ethnic minorities, and children with
disabilitiesorchronic healthconditions (e.g.,asthma).

Interventions to Promote Physical Activity
among Children and Adolescents
The most extensive and promising research on in-
terventions for promoting physical activity among
young people has been conducted with students in
schools, primarily at the elementary school level.
Although many school-based studies have focused
on short-term results, a few studies have also exam-
ined long-term behavioral outcomes. There is lim-
ited evidence concerning the effectiveness of
school-community programs, interventions in health
care settings, family programs, and programs for
special populations. In this section, the emphasis is
on interventions designed to promote both unstruc-
tured physical activity during free time and super-
vised physical activity, such as physical education
classes. Interventions designed to increase participa-
tion in, or adherence to, organized youth sports have
been excluded from this review. The review places
special emphasis on experimental studies, which
feature random assignment of individuals or groups

to intervention (experimental) or comparison (con-
trol) conditions, or quasi-experimental studies, which
feature intervention and comparison groups.

School Programs

Because most young people between the ages of 6 and
16 years attend school, schools offer an almost
populationwide setting for promoting physical activ-
ity to young people, primarily through classroom
curricula for physical education and health educa-
tion. The CDC (in press) recommends that compre-
hensive school and community health programs
promoting physical activity among children and ado-
lescents be developed to increase knowledge about
physical activity and exercise, develop behavioral and
motor skills promoting lifelong physical activity, fos-
ter positive attitudes toward physical activity, and
encourage physical activity outside ofphysical educa-
tion classes. CDC's 1994 School Health Policies and
Programs Study (Kann et al. 1995) examined the
current nationwide status of policies and programs
for multiple components of a school health program.
The study examined kindergarten through 12th-grade
health education and physical education at state,
district, school, and classroom levels (Errecart et al.
1995). Results from the health education component
of this study revealed that physical activity and fitness
instruction were required in 65 percent of states and
82 percent of districts and were included in a required
health education course in 78 percent of schools.
Only 41 percent of health education teachers pro-
vided more than one class period of instruction on

these physical activity topics during the school year
(Collins et al. 1995).

Results from the physical education component
of the School Health Policies and Program Study
revealed that physical education instruction is re-
quired by most states (94 percent) and school dis-
tricts (95 percent) (Pate, Small, et al. 1995). These
policies, however, do not require students to take
physicaleducationeveryyear. Forinstance,although
most middle and junior high schools (92 percent)
and most senior high schools (93 percent) require at
least one physical education course, only half of
these middle and junior high schools and only 26
percent of these senior high schools require the
equivalent of at least 3 years of physical education.
Additionally, only 26 percent of all states require

236


Understanding and Promoting Physical Activity

schools to offer a course at rhe senior high school
level in lifetime physical activity (i.e., physical activ-
it!, that can be practiced throughout one's lifetime)
(Pate. Small, et al. 1995). The School Health Policies
.Ind Programs Study also revealed that instructional
practices in physical education often do not reflect
the emphasis on lifetime physical activity that is
recommended in the national objectives in Healrl~y
Pcoplc 2000 (USDHHS 1990), in the National Physi-
cal Education Standards (National Association for
Sport and Physical Education 1995), and in the
CDC's Guiddincs for Schwa and Community Health
Proyrams to Promote Physical Activity Among Youth
(In press). More than half of physical education
teachers devoted multiple class periods to traditional
bports activities, such as basketball (87 percent),
volleyball (82 percent), and baseball/softball (82
percent), whereas much smaller proportionsof teach-
ers devoted multiple class periods to lifetime physi-
cal activities, such as jogging (47 percent), aerobic

dance (30 percent), and swimming (14 percent)
(Pate, Small, et al. 1995) (Table 6-4). Additionally,
only 15 percent of all physical education teachers
required students to develop individualized fitness
programs (Pate, Smail, et al. 1995). Despite current
guidelines' emphasis on lifetime physical activity,
during the 2 years preceding the study only 22
percent of physical education teachers received in-
service training on developing individualized fitness
programs, and only 13 percent received training on
increasing students' physical activity outside of
physical education class (Pate, Small, et al. 1995).
Detailed findings from the School Health Poli-
cies and Programs Study are important because
school-based physical education may be the most
widely available resource for promoting physical
activity among young people in the United States.
For physical education to meet public health goals,
it should provide all students with recommended
amounts of weekly physical activity (USDHHS 1990).

Table 6-4. Percentage of all physical education courses in which more than one class period was devoted to
    each activity, by activity, School Health Policies and Programs Study, 1994
Activity                Percentage of all courses           -
Uasketball                               86.8

Volleyball                              82.3

lL~seball/soitball                          ai .5

Flag/touch football                        68.5

Soccer                                65.2

logging                              46.5*
Weight lifting or training                     37.3*

Tennis                               30.3*

Aerobic dance                            29.6*
LYalking quickly                           14.7*
Swimming                             13.6*

Handball                              13.2*
Racquetball                            4.9+
HikinGackpacking                        3.0'
Bicycling                               1.3*
hxe: Adapted from Pate RP et al. School physical education. /ournal oikhool Healfh 1 Y95 (reprinted with permission).
`LIfetIme physical activities

237


Physical Activity and Health

Ironically, observations of physical education classes
indicate that insufficient class time is spent actually
engaging in physical activity (McKenzie et al. 1995;
McKenzie et al., in press; Simons-Morton et al. 1991,
1993, 1994).

The School Health Policies and Programs Study
provided a national overview of the status of school
health programs (Kann et al. 1995). Intervention
research has been reported from several studies
(Table 6-5). Most of the early research in schools
focused on knowledge-based health education class-
room lessons; these studies generally reported posi-
tive changes in knowledge and attitudes but not in
behaviors. Summarized in review articles (Sallis,
Simons-Morton, et al. 1992; Simons-Morton, Parcel,
O'Hara et al. 1988), these studies suffered from
methodological problems, such as small samples and
measurement limitations. Contemporary programs
emphasize the importance of multicomponent inter-
ventions that address both the individual and the
environmental level to support engagement in physi-
cal activity among youths (Kelder, Perry, Klepp
1993; Luepker et al. 1996; McKenzie et al., in press;
Perry et al. 1990, 1992; Simons-Morton, Parcel,
O'Hara 1988; Stone et al. 1995).
The Know Your Body (KYB) program (Williams,
Carter, Eng 1980) has been the focus of three school-
based cardiovascular risk reduction studies (Bush,
Zuckerman, Taggart, et al. 1989; Bush, Zuckerman,
Theiss, etal. 1989; Resnicowetal. 1992; Walter 1989).
This program includes health screening, behavior-
oriented health education curricula, and special
interventions for students with one or more cardio-
vascular disease risk factors (e.g., hypercholester-
olemia, hypertension, obesity, lack of exercise,
cigarette smoking) (Williams, Carter, Eng 1980).
Although this program was designed to improve
students' knowledge, attitudes, and behaviors re-
lated to physical activity, nutrition, and cigarette
use, the measurement and reporting of physical
activity behavior has been inconsistent among the
three studies. In the first study, the measure for self-
reported physical activity was found to be unreliable,
and the results related to this measure were not
reported (Walter 1989). In the second KYB study,
students' physical activity behavior was not assessed
(Resnicow et al. 1992). The third study was a 5-year,
randomized cardiovascular risk reduction trial among
1,234 African American students in grades four

through six from nine schools stratified for socio-
economic status (Bush, Zuckerman, Taggart, et al.
1989; Bush, Zuckerman, Theiss, et al. 1989). This
project included the KYB health education curricu-
lum, health screening, parent education, and KYB
advisory boards for parents, community members,
students, and physicians. After 4 years, students
from both the intervention and control schools had
significant increases in health knowledge at posttest,
and intervention students had significantly better
gains in health knowledge (Bush, Zuckerman, Theiss,
et al. 1989). Physical activity, however, decreased
significantly amongstudents f&m both the interven-
tion and control schools, and there was no difference
in physical activity between the intervention and
control schools.

The Stanford Adolescent Heart Health Program
(Killen et al. 1988) was a classroom-based random-
ized cardiovascular disease risk reduction trial for
1,447 tenth graders from four matched high schools
within two school districts. One school within each
district was designated at random to receive a 20-
week risk reduction intervention, and the other
school served as the control. The classroom-based
intervention focused on three cardiovascular risk
factors, including physical activity. At the 2-month
follow-up, students from the intervention schools
had significantly higher gains in knowledge about
physical activity than did students in the control
schools. Among students not regularly exercising at
baseline, those in the intervention schools had sig-
nificantly greater increases in physical activity than
did those in control schools. Additionally, students
who received the intervention had significantly lower
resting heart rates and subscapular and triceps
skinfold measures. The long-term effectiveness of
this program was not reported.

An Australian study (Dwyer et al. 1979, 1983)
was one of the first randomized trials that investi-
gated the effects of daily physical activity on the
health of elementary school students. The study
included 513 fifth-grade students from seven
Adelaide metropolitan schools. Three classes from
each school participated in the study and were ran-
domly assigned to one of three conditions: fitness,
skills, or control. Students in the control condition
received the usual three 30-minute physical educa-
tion classes per week. The students in both interven-
tion conditions received 75 minutes of daily physical

238


Understanding and Promoting Physical Activity

education: one condition emphasized fitness activi-
ties featuring high levels of physical activity, and the
other emphasized skill development activities with-
out special emphasis on the intensity or duration of
physical activity. With the class as the unit of analy-
sis, the fitness condition led to significantly greater
Increases in endurance fitness and decreases in
skinfold measurements. Although this study did not
evaluate the impact of increased physical education
on students' engagement in physical activity outside
of class, it showed that academic test scores did not
differ between the intervention and control groups,
despite the additional 275 minutes of class time the
intervention groups spent on physical education
rather than on traditional academic subjects.
Go For Health (GFH) was a 3-year school health
project designed to promote healthful diet and exer-
cise behaviors among elementary school students
(Parcel et al. 1987; Simons-Morton, Parcel, O'Hara
1988; Simons-Morton et al. 1991). This project in-
volved four elementary schools (kindergarten
through fourth grade) from the Texas City Indepen-
clcnt School District. Two schools were assigned to
serve as controls, and the other two were designated
JS GFH intervention schools. The intervention was
hased on social cognitive theory and included a GFH
health education curriculum, physical education
classes that focused on vigorous physical activity,
and lower-fat school lunches. The physical activity
results revealed a significant increase from pretest to
posttest (2 years) in the percentage of physical edu-
cation class time that students in the intervention
schools were engaged in moderate-to-vigorous physi-
cal activity. Additionally, posttest values were sig-
nificantly greater than those for the control schools
(Simons-Morton et al. 1991). Although this study
did not examine changes in physical activity outside
of physical education classes, it highlighted the im-
portance of organizational changes to promote physi-
cal activity among students.

The Sports, Play, and Active Recreation for Kids
(SPARK) study, conducted in San Diego, California,
tested the effects ofcombininga health-related physi-
cal education curriculum and in-service programs
on the quantity and quality of physical education
classes in elementary schools (McKenzie et al. 1993).
In a single school district, 28 fourth-grade classes in
jeven schools were randomly assigned to one of

three conditions: 10 classes were taught in their
usual manner by classroom teachers (control group);
10 classes were taught the SPARK program by cfass-
room teachers who had received in-service training
and follow-up consultations; and 8 classes were
taught the SPARK program by physical education
specialists hired by the research project. Direct ob-
servation found that students assigned to either of
the two intervention groups engaged in significantly
more weekly physical activity during physical edu-
cation classes than did controls. Teachers who re-
ceived the new physical education curriculum and
in-service training provided significantly higher-
quality instruction than did teachers in the control
group, although the trained classroom teachers' in-
struction did not match the quality of the instruction
provided by the physical education specialists. This
study demonstrated that an improved physical edu-
cation curriculum, combined with well-designed
training for physical education specialists and class-
room teachers, can substantially increase the amount
of physical activity children receive in school
(McKenzie et al. 1993) and can help ensure that the
resulting physical education classes are enjoyable
(McKenzie et al. 1994).

  The Child and Adolescent Trial for Cardiovas-
cular Health (CATCH) study was a multicenter,
randomized trial to test the effectiveness of a cardio-
vascular health promotion program in 96 schools in
four states (Luepker et al. 1996; Perry et al. 1990,
1992; Stone 1994). A major component of CATCH
was an innovative health-related physical education
program, beginning at the third grade, for elemen-
tary school students. For 2.5 years, randomly assigned
schools received a standardized physical education
intervention, including new curriculum, staff de-
velopment, and follow-up consultations. In these
intervention schools, observed participation in
moderate-to-vigorous activity during physical
education classes increased from 37.4 percent of
class time at baseline to 51.9 percent (Luepker et al.
1996). This increase represented an average of 12
more minutes of daily vigorous physical activity in
physical education classes than was observed among
children in control schools (Luepker et al. 1996;
McKenzie et al. 1995). Figure 6-2 shows the effect of
CATCH on physical activity during physical educa-
tion class. The CATCH study showed that children's

239


Physical Activity and Health

Table 6-5. Studies of interventions to increase physical activity among children and adolescents
---
study             Design         Theoretical approach    Population

School programs

Bush, Zuckerman,
Taggart, et al. (1989),
Bush, Zuckerman,
Theiss, et al. (1989)
(Know Your Body)

4 year
experimental

Social learning theory

1,234 students initially
in grades 4-6, follow-up
in grades 7-9

Killen et al. (1988)         7 week
(Stanford Adolescent      experimental
Heart Health Program)     2-month follow-up

Dwyer et al. (1983)

14 week
experimental

Social cognitive theory

1,447 students in grade 10

None

513 students in grade 5

Simons-Morton et al.
(1991) (Go For Health)

3 year
quasi-experimental

Social cognitive theory

409 grades 3 and 4
PE classes

McKenzie et al.
(1993) (SPARK)

Luepker et al. (1996);
McKenzie (in press);
Edmundson et al.
(1996) (CATCH)

8 month
experimental

3 year
experimental

112 PE lessons

Social cognitive theory

96 schools; 3,239 students
initially in grade 3,
follow-up at grade 5

School-community programs

Kelder, Perry, Klepp
(1993) (Minnesota
Heart Health Program:
Class of 1989 Study)

7 year
quasi-experimental

Social learning theory

Students in grade 6 from
2 Minnesota Heart Health
Program communities

I = tnterventlon; C = control or comparison; HE = health education; PE = physical education.

240


Understanding and Promoting Physical Activity

Intervention
.----

Findings and comments

t-1 : -I5 minutes, 2 times/week, Know Your Body
HE curriculum; health screening and results
t-2: -t5 minutes, 2 times/week, Know Your Body
HE curriculum; health screening
C: Health screening

I:  20 classroom PE sessions, 50 minutes each,
3 times/week, HE risk reduction curriculum
(1: No intervention

I-I : 75 minutes daily PE, fitness curriculum    Physical activity not assessed; no differences in academic
I-?: 75 minutes daily PE, skill curriculum      achievement between intervention and control
C: 30 minutes PE 3 times/week, standard     groups despite additional 275 minutes of time
  curriculum                 spent in PE by intervention groups

I:  6 behaviorally based HE modules; five 6- to
8-week modules of PE, children's active PE
curriculum; reduced fat and sodium school
  lunch

C: No intervention

I-1 : PE provided by PE specialists
I-J: PE provided by "specially trained" classroom
  teachers

(1: PE provided by classroom teachers

I-1 : HE curricula; PE featuring enjoyable
moderate-to-vigorous physical activity;
  EAT SMART school food service intervention
I-2: Same as I-1 with family involvement
(1: No intervention

I:  Peer-led physical activity challenge at grade 8;
10 lesson Slice of Life HE curriculum at grade 10
(1: No intervention

Decrease in physical activity for both groups between pretest
and follow-up. No difference in physical activity between
groups at posttest. Increase in posttest knowledge by each
group. Great increases in knowledge by intervention groups
at posttest, 18% response rate at 4-year follow-up

Intervention groups compared with control had a higher
proportion of nonexercisers at baseline exercising at
follow-up

Increase from pretest to posttest in the percent of PE class
time intervention school students spent in moderate-to-
vigorous physical activity; higher percentage of PE class
time spent in moderate-to-vigorous physical activity by
intervention schools compared with controls in posttest

At posttest PE specialists spent more minutes per lesson on
very active physical activity and fitness activities than
specially trained classroom teachers and classroom
teachers; specially trained classroom teachers spent more
minutes per lesson on very active physical activity and fitness
activities than classroom teachers

Intervention schools compared to control schools provided a
greater percentage of PE time spent in moderate to vigorous
physical activity at posttest; family involvement had no
effect on physical activity and psychosocial outcomes; data
from the intervention groups combined for comparison with
the control groups; intervention students were not different
from control students in total daily physical activity at posttest;
intervention students spent 12 more minutes per day engaged
in vigorous physical activity than controls; pretest-to-posttest
increases in students' perceptions of self-efficacy for
exercise and positive social reinforcement for exercise
among both intervention and control students; intervention
students' posttest scores on these and other psychosocial
measures were not different from those of control students

At 7-year follow-up students from schools in intervention
community had higher levels of physical activity than
students from schools in control community, particularly
among girls; 45% response rate at 7-year follow-up

241


Physical Activity and Health

Figure 6-2. Moderate-to-vigorous and vigorous
    physical activity observed during Child
     and Adolescent Trial for Cardiovascular
    Health (CATCH) physical education classes
   60

                      Intervention

Intervention

  --- -__L -L------/H
            Vigorous
lo-

Ol       I        I        I        I        I
      2      3      4      5     6
           Semester

Source: Luepker RV et al. journal of the American Medical
Association 1996 (reprinted with permission).

Note: Observed at six time points, 1991 through 1994. The CATCH
intervention, introduced during semester 2. increased the percentage
of time spent in moderate-to-vigorous and vigorotis activity JS
measured by the System for Observtng Fitness Instruction Time
classroom observation system. Intervention and control curves
diverged significantly according to repeated-measures analysis of
variance with the class session as the unit of analysis: ior moderate-
to-vigorous activity, P = 2.17, df = 5, 1979, P = .02; for vigorous
activity, F = 2.95, df = 5, 1979, P = 04. Analysts controlled for CATCH
site, the location of the lesson, the specialty of the teacher, and random
variation among schools and weeks of observation.

physical activity can be increased by a standardized
intervention applied to existing physical education
programs in four geographically and ethnically di-
verse regions. Although the intervention students
showed significant pretest to follow-up increases in
their perceptions of positive social reinforcement
and self-efficacy for exercise (Edmundson et al.
1996), these psychosocial determinants were not
significantly more prevalent than those observed
among the control groups at follow-up (Luepker et
al. 1996). Although the family intervention compo-
nent produced no additional increase in physical
activity among students (Luepker et al, 1996), the

CATCH physical education and classroom programs
successfully increased moderate-to-vigorous physi-
cal activity in physical education class and increased
students' daily participation in vigorous physical
activity.

School-Community Programs

The Class of 1989 Study (Kelder, Perry, Klepp 1993;
Kelder et al. 1995), an ancillary study of the MHHP
(Luepker et al. 1994), tested the efficacy of a school-
based health promotion program. One of three
MHHP intervention communities and its matched
pair were involved in the Class of 1989 Study. The
intervention cities were engaged in an extensive
communitywide intervention program designed to
improve eating, exercise, and smoking patterns for the
entire population. The physical activity intervention
included a peer-led physical activity challenge, in which
students were encouraged to engage in out-of-school
exercise activities. The program's assessment included
annual measurements collected from a large number of
students (baseline n = 2,376) for 7 years, beginning in
the sixth grade. Throughout most of the follow-up
period, physical activity levels were significantly higher
among female students in the intervention community
than among those in the control community. For male
students, the levels did not differ significantly between
the communities. Results suggest that at least among
female students, a multicomponent intervention that
includes peer-led behavioral education in schools and
complementary communitywide strategies can increase
levels of regular physical activity (Kelder, Perry, Klepp
1993; Kelder et al. 1995).

Interventions in Health Care Settings
Health professionals also have a potential role in
promoting physical activity, healthy eating, and other
health behaviors among children and adolescents
(American Medical Association 1994; U.S. Preventive
Services Task Force 1996). Results of a national sur-
vey of pediatricians showed that one-half of respon-
dents believed that regular exercise during childhood
is important in preventing cardiovascular disease in
adulthood (Nader et al. 1987). However, only one-
fourth believed they would be effective in counseling
their young patients to get regular vigorous exercise.
The American Medical Association's Guidelines for
Adolescent Preventive Health Services (1994) is one

242


example of practical counseling recommendations
that have been developed for those who provide
health services to adolescents.

Special Population Programs

Physical activity can assist in the treatment or reha-
bilitation of several diseases that occur during youth
(Rowland 1990; Greenan-Fowler 1987); however,
relatively few interventions have been conducted to
examine how to promote physical activity among
young people with special needs. The most extensive
study is a series of randomized investigations of
children who are overweight (Epstein, Wing, Valoski
1985; Epstein, McCurley, et al. 1990; Epstein, Valoski,
et al. 1990; Epstein et al. 1994). In this series, family-
based treatments of 5- to 12-year-old obese children
incorporated both physical activity and nutrition in-
terventions, and the programs were based specifically
on principles of behavior modification. Parents were
trained to improve their children's physical activity by
setting behavioral change goals with their children, by
identifying effective reinforcers (e.g., spending time
with parents), and by reinforcing children when goals
were met. Ten-year follow-ups of children in these
four randomized studies revealed that 30 percent of
children receiving family-based interventions were
no longer obese, and 20 percent had decreased their
percentage overweight by 20 percent or more (Epstein
ct al. 1994). The lo-year follow-up investigation also
revealed that the percentage of overweight children in
each study decreased most when the intervention
involved both the parent and the child or when a
change in lifestyle exercise was emphasized. Epstein
and colleagues (1994) also compared the effective-
ness of three forms of physical activity interventions:
lifestyle physical activity, in which activity was incor-
porated into daily routines; structured aerobic exer-
cise; and calisthenics. At the lo-year follow-up, the
lifestyle group had lost the most weight, and both the
lifestyle group and the aerobic exercise group had
greater weight-loss results than the calisthenics group
(Epstein et al. 1994).

Summary

The preceding review of the research literature on
interventions among young people reveals that
school-based approaches have had consistently
strong effects on increasing physical activity in

Understanding and Promoting Physical Activity

elementary school students when the intervention
orients the physical education program toward de-
livering moderate-to-vigorous physical activity.
Further, social learning theory appears to have had
the widest application to this interventions re-
search. Much research has taken place at the el-
ementary school level; very little is known about
increasing children's physical activity in middle
and high school physical education classes or in
settings other than school physical education classes.
It seems likely that these interventions would be
strengthened by designing programs that combine
school and community policy with health educa-
tion and physical education. Data are lacking on
ways to tailor interventions to the needs and inter-
ests of young people and to prevent the rapid
decline in physical activity that occurs during late
childhood and adolescence, especially among girls.
Additionally, few physical activity interventions
and research studies encompass populations par-
ticularly characterized by race/ethnicity, socioeco-
nomic status, risk factor status, disabilities, or
geographic location.

Promising Approaches, Barriers,
and Resources

Many questions remain about how best to pro-
mote physical activity in the general population of
young people and adults, as well as in clinical
populations and other subgroups. Policy initia-
tives, the provision of more physical activity facili-
ties and programs, and media campaigns are
promising, but studies testing their effects are
limited. The following two sections describe exist-
ing policy and program approaches' that have the
potential to increase population levels of physical
activity but have received little or no evaluation.
They are reviewed separately from the previously
discussed, better-documented research studies.

`Descriptions of specific physical activity programs across the
United States can be found in the Combined Health Information
Database, a computerized bibliographic database of health infor-
mation and health promotion resources developed and managed
by several federal agencies, including the CDC, the National
Institutes of Health, the Department of Veterans Affairs, and the
Health Resources and Services Administration. Intended for all
health professionals who need to locate health information for
themselves or their clients, this resource is available in many
libraries, state agencies, and federal agencies.

243


Physical Activity and Health

Environmental and Policy Approaches
Most interventions that have been evaluated in re-
search studies are discrete programs targeting popu-
lation subgroups (e.g., employees, schoolchildren)
or communities. Interventions have shown some
success in promoting physical activity, but their
results have been inconsistent. A possible reason for
limited results is a lack of concomitant support from
the larger environment within which such interven-
tions take place. Many physical activity researchers
believe that environmental and policy interventions
must occur to complement interventions that focus
on behavior change among individuals or small
groups. This larger perspective recognizes the pow-
erful moderating effect that environment has on
individual volition. As King, Jeffery, and colleagues
(1995) observe, "Environmental and policy inter-
ventions are based on the recognition that people's
health is integrally connected to their physical and
social environments" (p. 501).
Two premises underlie environmental and policy
approaches. First, interventions addressing chronic
disease risk factors, such as physical inactivity, re-
quire comprehensive, population-based approaches
that incorporate both individual and societal-level
strategies (Green and Simons-Morton 1996; Schmid,
Pratt, Howze 1995). Second, strategies should not
rely solely on active approaches requiring individual
initiative, such as enrolling in exercise classes, but
should also incorporate passive approaches, such as
providing walking trails or policies that permit em-
ployees to exercise during work hours (Schmid,
Pratt, Howze 1995). An example of intervention
elements combining passive and active approaches is
a school board policy that permits school facilities
to remain open before and after school for commu-
nity use, together with health communications that
make citizens aware of these facilities and encour-
age their use.

As presented previously, ecological models of
health behavior (McLeroy et al. 1988; CDC 1988;
Stokols 1992) provide frameworks for conceptualiz-
ing what the role of policy approaches is to health
promotion and how individuals interact with their
social, institutional, cultural, and physical environ-
ments. The concept of the health-promoting envi-
ronment suggests that communities and other settings
can facilitate healthy behaviors by providing envi-
ronmental inducements to be active, such as by

244

offering safe, accessible, and attractive trails for
walking and biking.

National objectives and recommendations have
encouraged the development of policies, programs,
and surveillance strategies that would help create
an environment that promotes physical activity
(USDHHS 1990; Pate, Pratt, et al. 1995; National
Association for Sport and Physical Education 1995;
U.S. Department OfTransportation [USDOT] 1994).
Increasing national levels of physical activity and of
cardiorespiratory fitness has also been targeted as a
priority health objective in Healthy People 2000
(USDHHS 1990) and the Dietary Guidelines far
Americans (U.S. Department of Agriculture and
USDHHS 1995).

Many efforts to raise public awareness and pro-
mote physical activity are under way. In 1994, the
American Heart Association, the American College
of Sports Medicine, and the American Alliance for
Health, Physical Education, Recreation and Dance
formed a National Coalition for Promoting Physical
Activity. The coalition's goals are to increase public
awareness of the benefits of physical activity, pro-
vide an opportunity for forming effective partner-
ships, and enhance delivery of consistent messages
about physical activity (National Coalition for Pro-
moting Physical Activity 1995). The CDC has estab-
lished guidelines for promoting physical activity and
healthy eating among young people (CDC 1996;
CDC in press) and has initiated a public education
effort to encourage active lifestyles and healthy eat-
ing among Americans. The National Institutes of
Health (NIH) has used national campaigns to pro-
mote messages to both the general public and pa-
tients on the importance of physical activity and a
heart healthy diet. The NIH also sponsors research
on physical activity in special populations, includ-
ing women from diverse economic backgrounds,
and in various settings, such as worksites, schools,
and health care institutions. In 1995, the NIH spon-
sored the Consensus Development Conference on
Physical Activity and Cardiovascular Health, which
recommended regular physical activity for most
persons aged 2 years and older (see Appendix B in
Chapter 2). The President's Council on Physical
Fitness and Sports works with a broad range of
partners in private industry, voluntary organiza-
tions, and the media to promote physical activity,
fitness, and sports participation by Americans of all


ages. As part of the midcourse review of the physical
activity and fitness objectives of Healtlry People 2000,
the council presented a synopsis of ongoing grassroots
activities by Healthy People 2000 Consortium mem-
bers in support of increasing participation in physi-
cal activity and improvement in fitness (USDHHS
1995). The President's Council on Physical Fitness
and Sports is also an advisory body to the President
and to the Secretary of the DHHS on matters involv-
ing physical activity, fitness, and sports that enhance
and improve health. Thirty-nine Governor's Coun-
cils on Physical Fitness and Sports stimulate state
;rnd local activities and program development; these
efforts target fitness promotion for school-aged
),ouths, older adults, working adults, and families
(National Association of Governor's Councils on
Physical Fitness and Sports 1996).

Community-Based Approaches
Community-based programs can be tailored to meet
the needs of their specific populations. More col-
laborative work is under way between state and local
governments, community groups, and businesses to
reduce risk factors among employees and residents.
Two-year follow-up data from one such effort in
Smyth County, Virginia, suggested that 40 percent of
school system employees had increased their physi-
cal activity participation during the program period
(CDC 1992).

Two large subpopulations may be especially im-
portant to address in community-based programs:
)`oung people and older adults. Communities will face.
a growing need to provide a supportive environment
for their children and adolescents. Between 1995 and
2020. the number of young people under 18 years old
will increase by an estimated 13 percent, from 69
million to 78 million (Bureau of the Census 1996).
The framework for community-level physical activity
programs for young people is already in place: mil-
lions of American youths participate in sports spon-
sored by community leagues, religious organizations,
social service organizations, and schools. In addition
to organized sports, communities need to provide
recreational programs and opportunities for all young
people in a community, because such programs may
encourage a lifetime habit of physical activity as well
~1s other immediate community benefits. According to
The Trust for Public Land, arrests among young
people in one community decreased by 28 percent

Understanding and Promoting Physical Activity

after the community instituted an academic and rec-
reational support program for teenagers (National
Park Service 1994). In another community, juvenile
crime dropped 55 percent when community recre-
ational facilities stayed open until 2 a.m. (National
Park Service 1994).

  Communities will also need to meet the chal-
lenges of a growing population of older adults. Be-
tween 1995 and 2020, the number of people over the
age of 60 will increase by 43 percent, from 44 to 63
million (Bureau of the Census 1996). Programs and
facilities designed to meet the needs of aging baby
boomers and older adultscan help ensure that these
rapidly growing segments of the population obtain
the health benefits of regular, moderate physical
activity. In one community, 35 age-peer exercise
instructors for older adults were recruitedand trained
by a local university as volunteers to conduct age-
appropriate physical activity programs on a regular
basis at sites such as libraries, senior centers, and
nursing homes in their neighborhoods. Because they
were age peers, the instructors were sensitive to
many of the concerns that older adults had about
physical activity, such as fear of falling and fracturing
a hip. Over the following year, instructors conducted
more than 1,500 half-hour exercise programs for
more than 500 older adults at 20 sites (DiGilio,
Howze, Shack 1992 >.

Places of worship represent a potentially effec-
tive site for physical activity promotion programs in
communities, since these settings can provide the
impetus for starting-and the social support for
maintaining-behavioral regimens (Eng, Hatch,
Callan 1985; Eng and Hatch 1991) such as regular
physical activity. Among the advantages of such
settings are a history of participating in a range of
community health and social projects; large mem-
berships, including families; a presence in virtually
every U.S. community; and connections to minority,
and low-income communities typically underserved
by health promotion programs (King 1991). The
Fitness Through Churches Project promoted aero-
bic exercise in conjunction with other health behav-
iors to African American residents of Durham, North
Carolina (Hatch et al. 1986). The results from this
pilot program suggest that physical activity pro-
grams offered at places of worship are feasible and
attractive to clergy and their congregations. Another
project, the Health and Religion Project (HARP) of

245


Physical Activity and Health

Rhode Island (Lasater et al. 1986), found that volun-
teets can be trained to provide heart health pro-
grams, including physical activity, in church settings
(DePue et al. 1990).

Societal Barriers

The major barrier to physical activity is the age in
which we live. In the past, most activities of daily
living involved significant expenditures of energy. In
contrast, the overarching goal of modern technology
has been to reduce this expenditure through the
production of devices and services explicitly de-
signed to obviate physical labor. From the days of
hunting and gathering to turn-of-the-century farm-
ing practices and early industrial labor, the process
of earning a living was once a strenuous activity.
Today, many Americans engage in little ot no physical
activity in the course of a working day typically spent
sitting at a desk or standing at a counter or cash
register. A large part of many people's time is spent
inside buildings where elevators or escalators are
prominent features and stairs ate difficult to find and
may seem unsafe. Motorized transportation carries
millions of Americans to and from work and on
almost every errand. These inactive daily expedi-
tions occur virtually door-to-door, with the help of
parking lots built as neat to destinations as possible
to minimize walking and increase convenience and
safety. Whereas older cities and towns, were built on
the assumption that stores and services would be
within walking distance of local residents, the design
of most new residential areas reflects the supposition
that people will drive from home to most destina-
tions. Thus work, home, and shopping ate often
separated by distances that not only discourage walk-
ing but may even necessitate commuting by motor-
ized transportation.

Television viewing, video games, and computer
use have contributed substantially to the amount of
time people spend in sedentary pursuits (President's
Council on Physical Fitness and Sports and Spotting
Goods Manufacturers Association 1993). Next to
sleeping, watching TV occupies the greatest amount
of leisure time during childhood (Dietz 1990).
Preschoolers exhibit the highest rate of TV watching
(27-28 hours per week). By the time a person gradu-
ates from high school, he ot she will likely have spent

15,000-18,000 hours in front of a television-and
12,000 hours in school (Strasburger 1992).

In the face of these powerful societal induce-
ments to be inactive, efforts must be made to encour-
age physical activity within the course of the day and
to create environments in communities, schools,
and workplaces that afford maximum opportunity to
be active. Policy interventions can address public
concerns about safety, financial costs, and access to
indoor and outdoor facilities. Such interventions
also can address the concerns of employers and
governments about liability in the event of injury. At
the state and local level, governments determine
building codes and public safety, traffic, and zoning
statutes that have potential bearing on physical ac-
tivity opportunities in communities.

Concerns about crime can be a major barrier to
physical activity for both adults and young people. In
a national survey of patents, 46 percent believed
their neighborhood was not very safe from crime for
their children (Princeton Survey Research Associates
1994). Minority parents were about half as likely as
white parents to report that their neighborhoods
were safe. Successful implementation ofpolicy inter-
ventions may help address such concerns. For ex-
ample, decisions to put more police on a beat in a
high-crime area may help residents feel safer going
outside to walk. Similarly, neighborhood watch
groups formed to increase safety and reduce crime
may be a vehicle for promoting physical activity.
Opening schools for community recreation and malls
for walking can provide safe and all-weather venues
that enable all members of the community to be
active.

Transportation, health, and community plan-
ners as well as private citizens can help ensure that
children living in areas near schools can safely walk
or bike to school and that adults can walk or bike to
work. Fear of traffic is one of the most frequently
cited reasons for not bicycling (USDOT 1993). Adult
pedestrians and bicyclists account for 14 percent of
yearly traffic fatalities (USDOT 1994). In a survey of
adults, those who rode a bicycle in the preceding year
were asked whether they would commute to work by
bicycle under specific conditions. Fifty-three per-
cent said they would do so if safe, separate, desig-
nated paths existed; 47 percent would if their

246


employer offered financial or other incentives; 46
percent would if safe bike lanes were available; and
45 percent would if their workplace had showers,
lockers, and a secure area for bike storage (USDOT
1994). More than half the respondents indicated
they would walk, or walk mote, if there were safe
pathways (protected from automobile hazards) and
if crime were not a consideration. A majority also
wanted their local government to provide better
opportunities to walk and bicycle.

These percentages stand in sharp relief against
current practice: only 4.5 percent of Americans com-
mute to work by bicycle or on foot (USDOT 1994).
Even in such comparatively small numbers, these
people are estimated to save as much as 1.3 billion
gallons of gasoline yearly and to prevent 16.3 million
metric tons of exhaust emissions (USDOT 1994).
Every mile walked or cycled for transportation saves
5 to 22 cents that would have been spent for a mile
by automobile, including reduced cost from pollu-
tion and oil imports (USDOT 1994). The Intermodal
Surface Transportation Efficiency Act, passed in
1991, promotes alternatives to automobile use by
making funds available for states to construct or
improve bicycling facilities and pedestrian walkways
(USDOT 1993). Decisions on how these funds are
used ate made locally, and organizations such as
local transportation, health, and parks departments
can promote the use of these funds in ways that
increase the prevalence of physical activity in their
communities.

In a growing number of communities, concerns
nbout environmental quality have led to zoning
restrictions that protect open spaces and other areas
that can subsequently be used for recreational pur-
suits. Such greenways, or linear open space, can
connect neighborhoods and foster the use of bicy-
cling and walking for transportation (Indianapolis
I)cpartment of Parks and Recreation 1994).

Societal Resources

.Jlthough there is no comprehensive listing of physi-
cal activity resources in the United States, such
a document would be extensive. Millions of
,Jmericans have sports supplies, bicycles, and exercise
lnachines in their homes or have access to public and
private resources such as tennis courts, parks, play-
<rounds, and health clubs. Numerous organizations

247

Understanding and Promoting Physical Activity

promote physical activity as part of their mission ot
in fund-raising efforts such as walks or runs. In
addition, TV programs, magazines, books, videos,
and CD-ROMs on physical activity are marketed.
Although using a computer is a sedentary activity,
physical activity interest and advocacy groups are on
the Internet, and the World Wide Web contains
information about many organizations and resources
related to physical activity. The multitude of physi-
cal education teachers, aerobics instructors, dance
instructors, recreation leaders, coaches, and per-
sonal trainers constitute an energetic pool of physi-
cal activity advocates and role models.
Ensuring the availability and accessibility of
environments and facilities conducive to exercise
is central to seeing that the public has the oppot-
tunity to obtain regular physical activity. Facili-
ties should be convenient, affordable, comfortable,
and safe (King et al. 1992). Many communities
offer sufficient facilities, but unless they are also
accessible and affordable, people may not use
them (Sallis et al. 1990). Walking for exercise
needs no more equipment than a comfortable pair
of shoes, but it does require a safe environment.
Other activities vary widely in the resources they
require-specialized clothing and equipment, play-
grounds, bicycle lanes, swimming pools, fields for
outdoor games, courts for indoor games, fitness
facilities for weight lifting and aerobic exercise,
studios for dancing, to mention a few.
Proximity of resources to home or worksites is
particularly important (Sallis et al. 1990). In a tele-
phone survey, 72 percent of respondents indicated
that there was a park ot playground within walking
distance of their home, and 75 percent of these
persons had used them (Godbey et al. 1992). Rural
residents are less likely to have such access (Godbey
et a1.1992), but they may have open spaces of other
kinds. In addition, large indoor areas, such as shop-
ping malls and schools, have become popular venues
for individuals and for walking groups and clubs. In
some communities, schools stay open before or after
the school day so community residents can use them
for hall walking (King, Jeffery, et al. 1995). Results
from a survey of exercise facilities in San Diego,
California, suggest that schools may be the most
available yet least-used resource for physical activity
among community residents (Sallis et al. 1990).


physical Activity and Health

Summary

The scope, quality, and effectiveness of the wide
range of policies and programs described in this
section have the potential to foster more physically
active lifestyles in the U.S. population. These efforts
could be targeted to meet the needs of population
subgroups and could be designed to use effective
strategies. Public health goals for physical activity
and fitness are more likely to be achieved if policies
and programs are guided by approaches known to be
effective and tailored to meet the needs of all mem-
bers of the community. Policies and programs should
be periodically evaluated to learn how they can be
improved to promote physical activity.
The discussion of existing barriers and resources
makes it clear that attention should be given to
addressing not only the challenges of individual
behavior change but also the environmental barriers
that inhibit a populationwide transition from a sed-
entary to an active lifestyle. Expenditure of resources
for bike paths, parks, programs, and law enforce-
ment to make playgrounds and streets safer will
encourage physical activity in daily living and should
thus be viewed as contributing to the health of all
Americans. At the same time, evaluations of such
changes can occur and more research accordingly
conducted to clarify how much the availability of
community spaces, facilities, and programs might
encourage physical activity. Such information would
better inform specific public policy decisions about
providing environmental supports and resources to
promote physical activity.

Behavioral and social scientists, exercise special-
ists, recreation specialists, health professionals, ar-
chitects, city planners, and engineers-all these
disciplines need to work together to engage commu-
nities, schools, and worksites in creating opportuni-
ties and removing barriers to physical activity. To
create lasting behavior change in communities, poli-
cies as well as individuals must change. Interven-
tions that simultaneously influence individuals,
community organizations, and government policies
should lead to greater and longer-lasting changes.

Chapter Summary

This chapter has reviewed approaches taken by re-
searchers to understand and encourage physical ac-
tivity among adults, children, and adolescents living

in a technologically advanced society. Behavioral and
social science research on physical activity is a rela-
tively recent endeavor, and many questions remain to
be answered about not only increasing but also sus-
tainingphysical activity. Several factorsseem to be key
influences on physical activity levels for both adults
and young people. Having confidence in one's ability
to be active (self-efficacy); enjoying physical activity;
receiving support from family, friends, or peers; and
perceiving that the benefits of physical activity out-
weigh its barriers or costs appear to be central deter-
mining factors influencing activity levels across the
life span.

For adults, some interventions in communities,
in health care settings, in worksites, and at home
have resulted in small increases in physical activity,
which if widely applied could create significant pub-
lic health benefits. Among young people, school-
based programs are the most widely available resource
for promoting physical activity and have the poten-
tial for reaching large numbers of children and ado-
lescents. Research indicates that children's levels of
physical activity in physical education class are greater
when physical education teachersare specially trained
in methods to increase the time their students spend
engaging in moderate-to-vigorous physical activity.
Few studies, however, have been conducted at middle
and high school levels-a time when most adoles-
cents decrease their physical activity.
Only limited information exists about the needs
of population subgroups of all ages and how determi-
nants of physical activity may change over the life span
because of puberty, the normal aging process, health
conditions, type of occupation, and other biological,
social, and environmental influences. Effective ap-
proaches for weight gain prevention are few, espe-
cially in light of the recently observed trend of
increasing weight among U.S. adults and children
(Kuczmarski et al. 1994; Troiano et al. 1995). Al-
though recommendations given by health care pro-
viders can increase physical activity among adults, a
similar effect of counseling for children and adoles-
cents has not been examined. It is unclear what
approaches can help people recover from relapses into
inactivity-whether from illness, the weather, de-
mands at work or at home, or other reasons-and
sustain the habit of regular physical activity over time.
Questions also remain about how to address barriers
to physical activity and how to more effectively use

248


resources in communities, schools, and worksites to
increase physical activity. Recent research and prom-
ising approaches have begun to address some of these
questions and provide direction for future research
and interventions to promote physical activity among
all Americans.

Conclusions

Consistent influences on physical activity pat-
terns among adults and young people include
confidence in one's ability to engage in regular
physical activity (e.g., self-efficacy), enjoyment
of physical activity, support from others, posi-
tivc beliefs concerning the benefits of physical
activity, and lack of perceived barriers to being
physically active.

For adults, some interventions have been suc-
cessful in increasing physical activity in commu-
nities, worksites, health care settings, and at
home.

Interventions targeting physical education in el-
ementary school can substantially increase the
amount of time students spend being physically
active in physical education class.

Research Needs

Determinants of Physical Activity
1. Assess the determinants of various patterns of
physical activity among those who are sedentary,
intermittently active, routinely active at work,
and regularly active.

1. Assess determinants of physical activity for
various population subgroups (e.g.? by age,
  sex, race/ethnicity, socioeconomic status,
health/disability status, geographic location).

3. Examine patterns and determinants of physical
activity at various developmental and life transi-
tions, such as from school to work, from one job
or city to another, from work to retirement, and
from health to chronic illness.

-t. Evaluate the interactive effects of psychosocial,
cultural, environmental, and public policy influ-
ences on physical activity.

Understanding and Promoting Physical Activity

Physical Activity Interventions

1.





2.

Develop and evaluate the effectiveness of inter-
ventions that include policy and environmental
supports.

3.

Develop and evaluate interventions designed to
promote adoption and maintenance of moderate
physical activity that addresses the specific needs
and circumstances of population subgroups, such
as raciauethnic groups, men and women, girls
and boys, the elderly, the disabled, the over-
weight, low-income groups, and persons at life
transitions, such as adqlescence, early adulthood,
family formation, and retirement.

Develop and evaluate the effectiveness of inter-
ventions to promote physical activity in combi-
nation with healthy dietary practices that can be
broadly disseminated to reach large segments of
the population and can be sustained over time.

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Physical Activity and Health

LIST OF TABLES AND FIGURES

Chapter 2: Historical Background, Terminology, Evolution of Recommendations,
      and Measurement

Table 2-l.  Glossary of terms
Table 2-2.  Selected physical activity recommendations in the United States (1965-1996)
Table 2-3.  Assessment procedures and their potential use in epidemiologic research
Table 2-4.  Classification of physical activity intensity, based on physical activity lasting up to
        60 minutes

Table 2.5.  Correlation of twosurvey instruments with physiologic measures of caloric exchange

Chapter 3: Physiologic Responses and Long-Term Adaptations to Exercise

Table 3-1.

Table 3-2.

Figure 3-l.

Figure 3-2.

Figure 3-3.

Figure 3-4.
Figure 3-5.

A summary of hormonal changes during an episode of exercise
A hypothetical example of alterations in selected physiological variables consequent
to a B-month endurance training program in a previously sedentary man compared
with those of a typical elite endurance runner
Changes in cardiac output (A), heart rate (B), and stroke volume (0 with increasing
rates of work on the cycle ergometer

Changes in arterial and mixed venous oxygen content with increasing rates of work
on the cycle ergometer

Changes in oxygen uptake and blood lactate concentrations with increasing rates of
work on the cycle ergometer

Changes in irOL max with increasing age from 6 to 18 years of age in boys and girls
Changes in 90, max with aging, comparing an active population and sedentary
population (the figure also illustrates the expected increase in o02 max when a
previously sedentary person begins an exercise program)

Chapter 4: The Effects of Physical Activity on Health and Disease

Table 4-1.  Population-based studies of association of physical activity or cardiorespiratory
       fitness with total cardiovascular diseases

Table 4-2.  Population-based studies of association of physical activity or cardiorespiratory
     fitness with coronary heart disease
Table 4-3.  Population-based studies of association of physical activity with stroke (CVA)
Table 4-4.  Population-based cohort studies of association of physical activity with hypertension

261


A Report of the Surgeon General

Table 4-5.  Epidemiologic studies of leisure-time or leisure-time plus occupational
     physical activity and colon cancer
Table 4-6.  Epidemiologic studies of leisure-time or leisure-time plus occupational
     physical activity and hormone-dependent cancers in women
Table 4-7.  Epidemiologic studies of leisure-time or total physical activity or
     cardiorespiratory fitness and prostate cancer
Table 4-8.  Cohort studies of association of physical activity with non-insulin-dependent
      diabetes mellitus (NIDDM)

Table 4-9.  Longitudinal population-based studies of physical activity as related to
      depressive symptoms                                                I
Table 4-10.  Duration of various activities to expend 150 kilocalories for an average
      70 kg adult

Chapter 5: Patterns and Trends in Physical Activity

Table 5-l.

Table 5-2.

Table 5-3.

Table 5-4.

`Table 5-5.

Table 5-6.

Table 5-7.

Sources of national and state-based data on physical activity
Percentage of adults aged 18+ years reporting no participation in leisure-time
physical activity, by various demographic characteristics, National Health
Interview Survey (NHIS), Third National Health and Nutrition Examination
Survey (NHANES III), and Behavioral Risk Factor Surveillance
System (BRFSS), United States

Percentage of adults aged 18+ years reporting participation in no activity;
regular, sustained activity; and regular, vigorous activity, by state,* Behavioral
Risk Factor Surveillance System (BRFSS), 1994, United States
Percentage of adults aged 18+ years reporting participation in regular,
sustained physical activity (5+ times per week for 30+ minutes per occasion),
by various demographic characteristics, National Health Interview Survey
(NHIS) and Behavioral Risk Factor Surveillance System (BRFSS),
United States

Percentage of adults aged 18+ years participating in regular, vigorous
physical activity (3+ times per week for 20+ minutes per occasion at 50+
percent of estimated age- and sex-specific maximum cardiorespiratory
capacity) by various demographic characteristics, National Health Interview
Survey (NHIS) and Behavioral Risk Factor Surveillance System (BRFSS),
United States

Percentage of adults aged 18+ years reporting participation in selected
common physical activities in the prior 2 weeks, by sex and age, National
Health Interview Survey (NHIS), United States, 1991
Percentage of adults aged 18+ years reporting participation in any
strengthening activities or stretching exercises in the prior 2 weeks, by
various demographic characteristics, National Health Interview Survey
(NHIS), United States, 199 1

262


Physical Activity and Health

Table 5-8.

Table 5-9.

Table 5-10.

Table 5-l 1.

Table 5-12.

Table 5-13.

Table 5-14.

Table 5-15.

Table 5-16.

Figure 5-l.

Figure 5-2.

Figure 5-3.
Figure 5-4.

Trends in the percentage of adults aged 18+ years reporting participation in
no activity; regular, sustained activity; and regular, vigorous activity, by sex,
National Health Interview Survey (NHIS) and Behavioral Risk Factor
Surveillance System (BRFSS), from 1985-1994
Percentage of young people reporting no participation in vigorous or moderate
physical activity during any of the 7 days preceding the survey, by demographic group,
1992 National Health Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS)
and 1995 Youth Risk Behavior Survey (YRBS), United States
Percentage of young people reporting participation in vigorous physical activity
during 3 or more of the 7 days preceding the survey, by demographic group, 1992
National Health Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS) and
1995 Youth Risk Behavior Survey (YRBS), United States               r
Percentage of young people reporting participation in strengthening or toning
activities during 3 or more of the 7 days preceding the survey, by demographic group,
1992 National Health Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS)
and 1995 Youth Risk Behavior Survey (YRBS), United States
Percentage of young people reporting participation in stretching activities during
3 or more of the 7 days preceding the survey, by demographic group, 1992
National Health Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS) and
1995 Youth Risk Behavior Survey (YRBS), United States
Percentage of young people reporting participation in walking or bicycling for 30
minutes or more during 5 or more of the 7 days preceding the survey, by demographic
group, 1992 National Health Interview Survey-Youth Risk Behavior Survey
(NHIS-YRBS) and 1995 Youth Risk Behavior Survey (YRBS), United States
Percentage of young people reporting participation in selected physical activities
during 1 or more of the 7 days preceding the survey, by demographic group,
1992 National Health Interview Survey-Youth Risk Behavior Survey (NHIS-YRBS),
United States

Percentage of students in grades 9-12 reporting enrollment in physical education
class, daily attendance in physical education class, and participation in exercise
or sports for at least 20 minutes during an average physical education class, by
demographic group, 1995 Youth Risk Behavior Survey (YRBS), United States
Percentage of students in grades 9-12 reporting participation on at least one sport
team run by a school or by other organizations during the year preceding the survey,
by demographic group, 1995 Youth Risk Behavior Survey (YRBS), United States
Percentage of adults aged 18+ years reporting no participation in leisure-time physical
activity by sex and age

Percentage of adults aged 18+ years reporting no participation in leisure-time physical
activity by month
Trends in leisure-time physical activity of adults aged 18+ years, NHIS
Trends in the percentage of adults aged 18+ years participating in no leisure-time
activity, BRFSS

263


A Report of the Surgeon General

Chapter 6: Understanding and Promoting Physical Activity

Table 6- 1.

Table 6-2.

Table 6-3.

Table 6-4.

Table 6-5.
Figure 6-l.

Figure 6-2.

Summary of theories and models used in physical activity research
Studies of interventions to increase physical activity among adults
Summary of progress toward Healthy People 2000 objective 1.10
Percentage of all physical education courses in which more than one class period
was devoted to each activity, by activity, School Health Policies and Programs
Study, 1994

Studies of interventions to increase physical activity among children and adolescents
Results of the Minnesota Heart Health Program on physical activity. Graph
compares the percentage of respondents reporting regular physical activity in
intervention cities and the secular trend estimated from control cities

Moderate-to-vigorous and vigorous physical activity observed during Child and
Adolescent Trial for Cardiovascular Health (CATCH) physical education classes

264


INDEX

A

Abdominal fat, 135
Absolute intensity scale, 66
Acid-base equilibrium, 62
Adenosine diphosphate (ADP), 65
Adenosine triphosphate (ATP), 65, 66
Adipocytes, 128
Adipose tissue, 128, 133, 134
Adolescents and physical activity
bicycling activities, 200, 205
bone mass development, 131, 132
breast cancer incidence, 117
cardiovascular disease risk factors, 9 1, 102
high school physical education, 204, 205
injuries, 142
no regular activity, 189
obesity, 43, 47, 133
recommendations, 28-29
regular, vigorous activity, 191, 196-197, 205
school-based interventions, 6, 236-243
sports team participation 200
stretching activities. 194, 200-201
surveys, 175, 205
trends, 8
walking activities, 200, 205
Adults and physical activity
assessment procedures, 30
cardiovascular response, 75
communications strategies, 229-230, 231
community approaches, 227-229,234
determinants, modifiable, 215, 234
exercise enjoyment, 215, 216
health care settings, 226-227, 242
individual approaches, 217, 226, 234
promotion, 217, 234
pulmonary ventilation rates in untrained, 64
recommendations, 24-27, 43

self-efficacy, 214-215, 217, 248
self-monitoring, 217, 226, 234
social support, 216, 226
surveys, 175
trends, 8

worksites, 229-231, 234, 229
                    -
Aerobic exercise, 66
Aerobics Center Longitudinal Study, 86
Affective disorders, 135
African Americans
adult activity interventions, 232, 236, 232
bicycling activities by, 203
Fitness Through Churches Project, 245
high school physical education enrollment, 205
no regular physical activity, 177, 192, 195
physical activity trends in, 8
regular, sustained physical activity, 183
regular, vigorous physical activity, 185, 187,
    196-197

sports team participation, 200
strengthening activities by, 189, 191, 198, 193
stretching activities by, 191, 194, 201
walking activities by, 203
Age factors, 74-76

cardiorespiratory capacity and, 187
exercise intensity and, 3 l-33
hypertension and, 103
no regular activity and, 177, 179, 192, 195
physical activity and mortality rates, 86
regular, sustained activity and, 183
regular, vigorous activity and, 185, 187
weight gain prevention and, 133, 232-233
Agility. See Psychomotor performance
Alabama

Physical Activity for Risk Reduction project,
  232


A Report of the Surgeon General

Amenorrhea, 131,143
American Academy of Pediatrics, 28
American Alliance for Health, Physical Education,
Recreation and Dance, 3, 244
American Association of Cardiovascular and
Pulmonary Rehabilitation, 23
American Association of Health, Physical
Education, and Recreation (AAHPER), 18
Health Related Physical Fitness Test, 18
Youth Fitness Test, 18
American Cancer Society (ACS), 112
American College of Sports Medicine (ACSM), 5
cardiorespiratory fitness (endurance) and, 4, 20
consultation for report by, 3
Guidelinesfor Exercise Testing and Prescription, 23
National Coalition for Promoting Physical
   Activity, 244

physical activity recommendations, 33, 148
American Diabetes Association, 127
American Heart Association (AHA), 244
cardiorespiratory endurance (fitness) and, 4
consultation for report by, 3
National Coalition for Promoting Physical
   Activity, 244

physical activity counseling
   recommendation, 244
American Hospital Association, 23
American Medical Association (AMA)
exercise and physical fitness, 17
Guidelines for Adolescent Preventive Services
   (GAPS), 28,242
Health and Fitness Program, 17
physical activity counseling
   recommendation, 244
Anemia, 143

Angina pectoris, 45, 110-112, 143
Anovulation, 143
`Anxiety, 8, 137, 150
Anxiety disorders, 135, 136
Aortic aneurysms, 103
Aortic valve stenosis, 45

Appetite, 135
Arrhythmias, 110, 112, 143
Arterial baroreflex, resetting of, 63
Arterial-mixed venous oxygen (A-GO,), 62,64, 70,

75-77

Arterial vasodilatation, 111
Arthritis, 7, 129-130, 142
Arthritis, rheumatoid, 129
Asthma, 143

Atherosclerosis, 5, 102, 103, 110-111, 128
Australian Heart Week (1990) campaign, 233

B

B-lymphocytes. See Lymphocytes
Balance. See Equilibrium
Bank of America physical activities program, 230
Basal metabolic rate, 66
Bed rest, prolonged, 71, 72
Behavioral sciences, adult
ecological perspective, 214-215, 244
health-belief model, 213, 217
intervention studies. See under Intervention
  studies (adolescent; adult; children)
learning theories, 211, 214,226, 228, 230
planned behavior theory, 213-214,226
reasoned action theory, 213-214,217
relapse prevention model, 213, 226, 228
social learning (cognitive) theory, 214, 217,
   226, 228,230,235,236
social support, 220, 214, 227, 228
  transtheoretical model, 213, 235
Behavioral sciences, children and adolescents,
  234-243
planned behavior theory, 213
  reasoned action theory, 213
social learning (cognitive) theory, 214
Biogenic monoamines, 141
Blood flow, 63,64, 65, 71, 111, 112, 128

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Physical Activity and Health

Blood pressure, 16, 71, 90, 110, 111, 145
adaptation to exercise, 73
diastolic, 63, 70, 72, 102, 110
end-diastolic volume, 71, 72
mean arterial, 63

response to resistance exercise, 65
systolic, 63, 64, 70, 102, 110
See related Hypertension; Hypotension
Blood volume, 70, 71, 72
Body composition, 21, 22, 35, 54, 134
Body fat, 7,35, 102, 128-129, 134, 135, 145
Body mass index, 35,90,102,126-127,133, 134
Body surface area to mass ratio, 73-74
Body temperature, 62, 64, 141
Body weight, loss practices, 50, 44
Bone density, 69, 72, 73, 75, 130, 131, 132
Bone marrow, 67

Breast cancer, 7, 117-119, 123
British Association for the Advancement of
Science, 19

Building Your Fitness Futures program, 232

C

Calcium, balance, 72
Caloric expenditure, 147
Calorimetry, 21, 29, 32
indirect, 21, 32
Cancer, 43, 67, 149
breast, 7, 117-119
colon, 4, 5, 7, 114, 144, 145, 149
endometrial, 7, 120-121, 149
hormone-dependent in women, 117-121
mortality incidence, 113
ovarian, 7, 120, 149
physical activity and, 7
prostate, 7, 121-122, 124-125
testicular, 7, 124, 149
rectal, 7, 113, 116
uterine, 117, 120-121

Capillaries, 71

density of, 63, 65, 73
endurance training and, 69
Carbohydrate, adenosine triphosphate
production, 66

Carbon dioxide (CO,), 18, 32, 61-62, 66
Cardiac output (Q), 62,71
contribution to mean arterial blood pressure,
    63
and heart rate, 62
maximal (Cj max),.62, 70, 71
rest vs. exercise, 63
stroke volume, 62, 63, 65
Cardiomyopathy, hypertrophic, 45
Cardiorespiratory endurance (fitness), 4, 6, 17
age and, 187
cholesterol, total, and, 102
epidemiologic studies of, 131, 137, 143, 147,

   182,187,201-205
interventions, 244
measurement of, 19-20,32-37
multiple sclerosis and, 233
population-based studies, 85-90
prostate cancer and, 121-125
regular, intermittent exercise, 5
sex factors and, 187
See also Physical fitness
Cardiovascular diseases, 87
of adolescents, interventions for, 236-243
community-based intervention programs for,
    227-229

of children, interventions for, 236-243
diabetes risk factors for. 127
health care interventions for, 242
myocardial infarction, 5, 43, 45, 112, 143
physical activity and, 43-48, 43-45, 47
Cardiovascular system adaptations, 5, 7, 19
to exercise, 7, 21, 61-62, 65, 70, 71, 87
myocardial wall stress in, 63-64, 71
Cartilage, 130, 143

Catecholamine, 64, 66, 74

267


A Report of the Surgeon General

Causality, 144-145
Centers for Disease Control and Prevention
(CDC), 5

Behavioral Risk Factor Surveillance System
(BRFSS), 175, 205

exercise recommendations, 23, 28, 33, 148
Guidelines for School and Community Health
Programs to Promote Physical Activity
Among Youths, 237, 244
School Health Policies and Programs Study,
  236-237

Youth Risk Behavior Survey, 175, 176, 189,
193-199, 205

Cerebrovascular disorders, 7, 47,45, 102-103,
104-107, 110

Child and Adolescent Trial for Cardiovascular
Health (CATCH) study, 239, 244
Children and physical activity, 75
assessment procedures, 29
behavioral research, 234-243
bone mass development, 131, 132
cardiovascular factors, 75,91, 102
environmental factors, 73-74
goals, 28, 43
hypertension, 87
injuries, 142
minimum health standard, 17-18, 19
no regular activity, 4
obesity, 43, 47, 133, 134
obesity interventions, 248
regular, vigorous activity, 191
school-based interventions, 6
school program interventions, 236-243
Cholesterol, 19, 23, 47, 91, 102, 110-111
Church programs, 245
Cognition, 135, 141, 142
College Alumni Study, 36
Colon cancer, 4, 5, 7, 113-117, 146, 149
Colorectal cancer, 113
Communications interventions, 230-231
Community-based programs, 6, 227-229, 245-246

Community behavioral approaches, 227-229
Coronary artery

perfusion pressure increase, 64
vasodilation of, 64
Coronary artery bypass, 45
Coronary circulation, 63-64
Coronary disease, 16, 23, 28, 35, 37, 49, 47, 133,
140,144-147,149
inverse association with physical activity, 91
physical activity and, 4, 5, 7, 87, 90-91
population-based studies, 92-101
Coronary plaque, 110, 111, 112
Crime. 246-247

D

Dehydration, 75, 143
Dementia, 136

Depression, 8, 135, 136, 140, 150
Detraining, 21, 61, 72
Diabetes mellitus, 4-6, 28, 35, 37, 43, 90, 125,

133, 144-149, 232

Diabetic retinopathy, 128
Diastolic blood pressure. See under Blood pressure
Diet, 5, 12-13, 116, 127, 128, 134, 232-233
Dietary Guidelines for Americans, 5, 28, 244
Disability. See Physically handicapped
Disuse atrophy, 72-73
Dyslipoproteinemia, 133

E

Eating disorders, 136
Edema, 133
Educational factors
no physical activity and, 177, 178, 196
regular sustained physical activity, 183
regular, vigorous physical activity, 183, 187
strengthening activity, 191
stretching activity, 191

268


Physical Activity and Health

Eisenhower, President Dwight D., 17, 18
Elderly persons

behavioral intervention programs for, 233
cardiovascular response to exercise, 75-76
cold stress in, 74

community-based programs for, 245-246
falling, 7, 132
health-related quality of life, 142
maximal oxygen uptake in, 32, 70
osteoporosis, 130-133
physical activity interventions for, 233
physical assessment procedures for, 30
psychomotor performance of, 35
resistance training and, 44
Electrocardiographic changes, 111
Emotional functioning, 141
Emphysema, 140
End-diastolic volume. See under Blood pressure
Endocrine factors, 66, 67, 70
Endocrine glands, 5, 7
hormonal responses to exercise, 66
See related Hormones
Endometrial cancer, 7, 114, 120, 149
Endorphins, 141
Endurance training, 4, 18, 19, 21, 61, 63, 65
capillary increase by, 69
health benefits of, 7, 43
health-related quality of life, 142
insulin sensitivity and, 127
ischemia and, 112
lactate threshold and, 67
metabolic adaptations, 69-70
muscle fibers in, 67
obesity and, 135
osteoporosis and, 150
Enkephalins, 141
Environmental exposure, 19, 73-74
air pollution, 74
cold climate disorders, 74
hot and humid conditions, 63, 73, 143

Epicondylitis, 143
Equilibrium, 35, 44
Ergometer tests. See under Exercise tests
Erythropoietin, 68, 74
Estradiol-progesterone, 68
Estrogen, 130, 131
Estrogen replacement therapy, 132
Exercise, 20, 21, 140. See also Physical activity;
Physical activity, specific; Physical fitness:
Physical fitness programs
Exercise physiology
research, 18-20
responses to, 61
textbooks on, 61
Exercise tests
accelerometers, 32
bicycle ergometry, 62-63, 64, 66, 74-75
maximal, 86, 87, 90
motion sensors, 31-32
for muscle fitness, 34-35
pedometers, 31
stabilometers, 32
submaximal, 86, 87,89
treadmill, 32, 34, 122
Exercise training
American College of Sports Medicine
   recommendations, 22
benefits, 7
bone adaptations, 67, 69
cardiovascular diseases and, 45
definition of, 20
diabetes mellitus and, 128
frequency of, 61
interval vs. continuous, 19
  and lipoprotein, HDL, 43
muscle, skeletal, adaptations, 67, 69
triglycerides and, 111
ventricular fibrillation, 112

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F

H

Falls, 143, 150
Fatty acids, 111
Fibrinogen, 43
Fibrinolysis, 43, 112
Fitness Through Churches Project, 245
Foot injuries, 128, 143
Fractures, 130-132, 143

G

Gastrointestinal system
problems, 130

transit time, 122
Genetic factors
diabetes mellitus, 126-127
maximal oxygen uptake and, 66, 70
training and. 65
Glossary, 21
Glucagon, 69

Glucose intolerance, 72, 123
Glucose tolerance, 127
Glucose-6-phosphate, 132
Glycogen, muscle storage of, 69
Glycolysis

energy system for, 65-67
muscle fiber capacity, 66
Go For Health (GFH), 239
Governor's Councils on Physical Fitness and
Sports, 245

Guidelines for Adolescent Preventive Services
(GAPS), 28

Guidelinesfor Excrcisc Testing and Prescription
(ACSM), 23. 28

Guidelinesfor School and Community Health
Programs to Promote Physical Activity
Among Youths, 237, 244

Handicapped. See Physically handicapped
Harvard University, 16
alumni study, 86

Fatigue Laboratory, 19
Health, 16-18, 22, 141
American College of Sports Medicine 1990
   recommendations, 22-23
exercise physiology research and, 18-20
physical activity recommendations, 28-30
World Health Organization definition of, 141
Health and Human Services (HHS),
Department of, 245
Office of Public Health and Science, 3
Health and Religion Project (HARP), 245
Health-related fitness, 20, 22
Health-related quality of life, 141-142, 150
Healthy People 2000, 23
cardiorespiratory fitness, 244
daily, moderate physical activity, 181, 200
exercise intensity in, 33
leisure-time activity target, 177
muscle strength, endurance, 187, 189, 192,
   199,200

objectives, 5, 175, 237, 245
physical education, 205
regular, vigorous activity, 182
worksite programs, 229-231
Heart, adaptation to exercise, 71
Heart defects, congenital, 45
Heart disease, 142
Heart failure, congestive, 45, 103
Heart rate (HR), 31-32, 62, 72, 73
coronary circulation and, 66
maximal, 21
mean daily, 31
oxygen consumption and, 63
resting, 19,31
training response and, 71
Heat stress disorders, 74
Heat exhaustion, 74

270


Physical Activity and Health

Heat stroke, 74
Hematocrit, 43
Hematuria, 143

Hemoconcentration, 74
Hemoglobinuria, 143
High blood pressure See Hypertension
Hill's causality criteria, 144-145
Hip fracture, 130, 132
Hispanics

bicycling activities by, 203
child behavioral intervention program, 232
diabetes mellitus and occupational physical
activity, 126

high school physical education enrollment and,
  205

no regular activity by, 177, 195
physical activity trends in, 8
regular, sustained activity by, 183
regular, vigorous activity by, 183, 187, 183,
  196-197

sports team participation by, 200
strengthening activities by, 191, 193, 198,
stretching activities by, 191, 194, 201
walking activities by, 203
Home care programs, 46
Hyaline cartilage, 130
Hydrogen ions (H+) concentration, 64
Hygiene, 11-18
Hyperglycemia, 127
Hyperinsulinism, 72
Hyperplasia, 69
Hypertension, 4-5, 7, 23, 47,43, 63, 66, 71,
126-127, 133
obesity and, 133
physical activity and, 103, 110, 144-145, 149
population studies of, 108-109
Hyperthermia, 143
Hypertrophy, 69, 71, 76, 103
Hypoglycemia, 127-128, 143
Hypotension, 63, 74

I

Immobilization, 71-72, 130
Immune system, responses to exercise, 7, 67
Immunoglobins, 67
Immunosuppression, 143
Inactivity. See Physical inactivity
Indian Health Service, 232
Industrywide Network for Social, Urban, and
Rural Efforts (INSURE) project, 227
Infection control and exercise, 67
Injuries, 5

exercise-related, 8, 44, 69, 150, 248
joint, 129

musculoskeletal, 142-143
sports-related, 7

Insulin, 44, 67,68, 72, 125-129
Intermodal Surface Transportation Efficiency Act,
  247

International Consensus Conference
of Physical Activity Guidelines for Adolescents
   (1993), 28
on Physical Activity, Physical Fitness, and
   Health (1988>, 22
Interpersonal relationships, 46
behavioral sciences theories, 213,
social support role in activity, 214, 243
Intervention studies, adolescent, 8, 236
accessibility, 236
church programs for, 245
determinants, modifiable, 243
factors influencing, 243
health care settings, 242
outdoor activities, 243
parental involvement, 243
school-community programs, 242, 245
school programs, 236-243, 236-243
self-efficacy, 242, 248
societal barriers, 246-247
societal resources, 247

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Intervention studies, adult, 8, 217
communications, 229-230
community approaches to, 227-229, 234,
   227-229,234, 245
church programs for, 245
environmental approach to, 244-245
factors influencing, 215-2 17
health care settings, 226-227
individual approaches, 217, 226, 234
mental disorders, 136
policy approaches, 244-245
promotion of, 226, 234
societal barriers, 246-247
societal resources, 247
worksites, 229-23 1, 229-23 1, 236
Intervention studies, children, 8, 236
accessibility, 243
church programs for, 246
determinants, modifiable, 243
factors influencing, 243
health care settings, 242
outdoor activities, 243
parental involvement, 243
school-community programs, 242, 245
school programs, 236-243
self-efficacy, 242, 248
societal barriers, 246-247
societal resources, 247
Intervertebral disc displacement, 142
Intra-abdominal fat distribution, 128-129
Ischemia, 110, 11 l-l 12

J

Johnson, President Lyndon B., 18
Johnson &Johnson Live for Life program, 230

K

Kennedy, President John F., 18
Kilocalorie (kcal), 21, 29, 140, 143, 146-147, 148
Kilojoule (kjoule), 21, 29
Know Your Body (KYB) program, 238

1

Lacerations, 143
Lactate threshold (LT), 66, 67, 69, 70
Lactates, 66, 67, 70, 74      .
Leukocytes, 128
Ligaments, 69
Lipoproteins, 110
HDL, 43,91, 102
LDL, 91, 102
lipase activity, 111
profile, 111, 145
Low back pain, 233-234
Lung diseases, obstructive, 233-234
Lymphocytes, 67

M

Magnetic resonance imaging, 35
Marfan syndrome, 45
Mass spectrometer, 32
Maximal oxygen uptake (\iO, max), 21,23,32-34,
62-63,66, 67,69-70,72,75-77, 110
Media. See Communications interventions
Men and physical activity
no regular activity, 4, 8, 177, 178, 188, 189
regular, sustained activity, 183, 188, 205
regular vigorous activity, 185, 187, 188, 205
selected physical activities, 188
strengthening activities, 191
trends, 8

Menopause, 130, 131
Mental disorders, 135
Mental health, 4, 8, 135-141, 150

272


Physical Activity and Health

Mental retardation, 73
Metabolic equivalent (MET), 21, 29, 32, 33, 66,
  148,204
Metabolic rate, 66
Metabolism
aerobic, 20, 21
bed rest and disturbances of, 72
benefits, 7
carbohydrate, 128
energy expenditure, 134
glucose, 65, 128
fat, 68
muscle, skeletal, 65-67, 71-72
protein, 66
response to exercise, 18-19, 121, 64, 69-70
Metropolitan Life Insurance Company weight
tables, 133
Minnesota Heart Health Program (MHHP),
  227-228,232
Minnesota Leisure-Time Physical Activity
Questionnaire, 3 1, 36
Missouri "Bootheel" behavioral sciences study,
229,232
Mitochondria, 66
Monocyte-macrophage system, 67
Mortality, 85-87, 149
all-cause, 133
diabetes mellitus, 125
heart disease, 87
lowering, 7
premature, 4, 16
traffic fatalities, 246
Multiple sclerosis, 73, 233-234
Muscle contractions, 34
Muscle fatigue, 65
Muscle fibers, 21
fast- and slow-twitch, 65, 67, 69, 73

Muscles, skeletal, 5
adaptations to exercise, 7, 44, 65, 67, 69
atrophy of, 69, 72-73
capillaries in trained, 71
energy metabolism of, 65-67
fibers in, 65, 67, 69, 73
immobilization and, 72-73
insulin and, 125, 130
metabolic adaptations of, 69-70
multiple sclerosis and, 233-234
soreness in, 69

structural damage to, 69
Muscular endurance (fitness), 21, 34-35
Muscular strength, 34, 44
Myocardial contraction, 65, 72
Myocardial infarction, 5, 44, 45, 112, 143
Myocardium, 111
Myosin ATP, 65

-70

N

National Association for Sport and Physical
Education, National Physical Education
Standards, 244

National Coalition for Promoting Physical
Activity, 244

National Institutes of Health (NIH), 5
Consensus Development Conference
  Statement, Physical Activity and
   Cardiovascular Health, 5, 23, 28, 48, 148,
      245

intervention campaigns, 245
National Physical Education Standards, 244
Native Americans, I2
adult physical activity interventions, 232
behavioral intervention program,232
Neoplasms. See Cancer
Neural factors, 67
Neuromas, 143

Nitric oxide, 132
Nitrogen, balance, 72

273


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0

Obesity, 7,43, 133-135, 150, 248
abdominal, 35, 128-129
adult physical activity interventions, 232-234
behavioral intervention programs, 232-233
in adolescents, 102
in children, 102

childhood intervention, 244
trends in, 47, 46

Occupational medicine, 15
Occupational physical activity, 113, 116, 175, 189
See also Worksite physical fitness programs

Olympic Games, 12, 15
Osteoarthritis, 7, 129-130, 133, 149-150
Osteoporosis, 7, 23, 43, 69, 130-133, 150.
See related Bone density
Otitis externa, 143
Ovarian cancer, 7, 114, 116-118, 149
Overtraining, 21, 140
Overweight, 133. Set also Obesity
Oxidative capacity, of muscle fibers, 65, 67
Oxidative energy system, 65, 66
Oxygen

arterial-mixed venous, 62, 63, 70
ATP production within mitochondria, 66
body's use of, 61
delivery, 74

extraction, blood flow, 63
myocardial demand/use, 63, 64
Oxygen consumption (VOL), 18, 31,32,34, 66,
70, 74, 110

Oxygen uptake. See Maximal oxygen uptake

P

Pain threshold, 130

--

Paleolithic rhythm, 11
Pawtucket Heart Health Program (PHHP), 229
Pediatricians, physical activity counseling by, 244

Peripheral vascular disease, 45
Personality disorders, 136
Phosphocreatine (PCr), 65
Physical activity, 21
of adolescents. See Adolescents and physical

activity

of adults. See Adults and physical activity
adverse effects of, 142-144
approaches to, 46-47
of children. See Children and physical activity
definition of, 20
dosage, 146-148
duration of, 44, 147, 148
evolution of recommendations, 22-28
frequency of, 44
intensity of, 29-33,35-36,44
measures of, 211-215
no regular, 15-16, 23, 50, 46-48, 177-189,

188, 195, 248

regular, intermittent, 11, 148
regular, sustained, 4, 6, 23, 37,49, 43, 110,

146-147, 182-183, 244
regular, vigorous, 4, 6, 11, 23, 37, 50, 110,

   127-128, 146-147,182-187,188,244
research considerations, 47, 150
social environmental approaches to, 244-245
surveys of, 175,177
Physical activity, specific
aerobics, 200, 205
baseball, 129, 143, 200, 205
basketball, 143, 200, 205
bicycling, 4, 143, 144, 187, 200,203
boxing, 143
carpentry, 140
dancing, 14, 143, 144, 148, 187, 200, 205,
football, 129, 143, 200, 205
Frisbee, 197-198, 205
gardening, 8, 140, 144, 147, 187
golfing, 140

hockey, 140, 148
horseback riding, 14


housecleaning, 147, 148, 200, 205
jogging, 140, 142, 144, 148, 187, 198, 205,
kickball, 12
lacrosse, 12

racquetball, 143, 197-198, 205
running, 4, 12, 65, 66, 70, 129, 140, 142, 143,

144, 148, 187, 198, 205
skating, 197-198, 205
skateboarding, 197-198, 205
skiing, 197-198, 205
soccer, 129, 143, 197-198, 205
softball, 144, 197-198, 205,
stair climbing, 127, 147, 187
squash, 197-198,205
swimming, 140,143,144,197-198,205,
tennis, 14, 140, 197-198, 205
volleyball, 4, 148,
walking, 4, 8, 14, 33, 127, 140, 144, 148, 187,

   197-198,203,204,205,233
weight lifting, 129, 143
yard work, 4, 8, 147, 187, 202, 200,205, 205
Physical Activity for Risk Reduction (PARR)
project, 232

Physical education, 8, 16-18
enrollment in, 4

in high school, 205, 205
school program interventions, 243, 246-249
Physical examination, 6, 45, 47
Physical fitness, 16-18, 21
assessment procedures, direct monitoring,
   31-36

assessment procedures, self-reporting, 29-31
definition of, 20
level of, 61

maintenance of, 71-72
maximal oxygen uptake and. See Maximal

oxygen uptake

measurement of, 33-35
physical activity relationship, 43
worksite programs, 48,46,48
See also Cardiorespiratory endurance (fitness)

Physical Activity and Health

Physical fitness programs
detraining and, 61, 72
endurance training, 61, 63. 65, 67, 69-70
exercise training, 6 1, 67, 69
resistance training, 61, 65, 69, 70
Physical functioning, 141
Physical inactivity, 5, 6, 72, 73, 145-146, 148
bone loss and muscle atrophy in, 69
diseases of, 15-16

exercise programs and, 37
health burden of lifestyle, 42-43
mortality and, 86    I
percentage of, 4
physical activity recommendations for, 29
physiological alterations after endurance
training, 70

societal inducements for, 254-247
working toward recommendations, 44
Physically handicapped, 73
behavioral intervention programs, 233-234
childhood interventions, 233, 244
no regular activity and, 189
regular, moderate activity and, 189
regular, vigorous activity and, 189
Physician-based Assessment and Counseling for
Exercise (PACE), 227
Plasma insulin concentration, 128
Plasma lipid/lipoprotein, 110, 111
Plasma volume, 71, 72, 74
Platelet function, 43
Population attributable risk (PAR), 145-146
Postmenopause, 131
Postpoliomyelitis syndrome, 73
Power, 21, 85

President's Citizens Advisory Committee on the
Fitness of American Youth, 18
President's Conference on Fitness of American
Youth, 18

President's Council on Physical Fitness, 18, 23
President's Council on Physical Fitness and Sports
(PCPFS), 3, 5, 18, 227, 245


A Report of the Surgeon General

President's Conference on Youth Fitness, 18
Presidential Physical Fitness Award, 18
Preventive medicine, 11-18
Prostaglandin, 68, 113-l 17, 124
Prostate cancer, 7, 121-122, 124-125
Proteoglycan synthesis, 130
Psychological assessments, 136-137
Psychomotor performance, 17, 19-20, 35,44
Pulmonary ventilation, 64, 71
Pulse rate, 16

Q

Quadriplegia, 75
Quality of life, 8, 141-142, 150
Quetelet's index, 133

R

Rating of perceived exertion (RPE) scale, 33
Reaction time, 21
Receptors, sensory, 141
Rectal cancer, 7, 113, 116, 122, 149
Relative perceived exertion (RPE), 21
Renin-angiotensin system, 68
Resistance training, 4, 19, 21, 29, 37, 44, 61,
65,69
adolescent, 196, 198-200
elderly persons and, 7, 132-133
glucose-insulin dynamics, 128
muscle, skeletal effects of, 69
obesity and, 135
osteoporosis and, 150
risk factors, 67

strengthening activities for, 187, 189, 191-192,
193, 199-200
sex factors, 70

Respiration rate (RR), 70, 71

Respiratory system, 5
adaptation to exercise, 71
physiological alterations after endurance
  training, 70

resistance exercise and, 65
response to exercise, 61-62, 64
Retraining, 21

Rhabdomyolysis, 143
Rhode Island

Department of Parks and Recreation, 229
Health and Religion Project, 245
Pawtucket Heart Health Program, 229
Roosevelt, President Franklin D., 17

S

Schizophrenia, 136
School program interventions, 6, 236-243,
  246-248

Sedentary persons. See Physical inactivity
Self concept, 130, 141, 142
Self-help, 13-15, 29-31
Senior citizens. See Elderly persons
Sex factors

in exercise training, 70, 76-77
hormonal responses to exercise, 67
hormone-dependent cancers in men, 121-125
hormone-dependent cancers in women,
  114-121

physical inactivity and, 177-178
specific physical activities and, 187-189
strengthening, stretching activities by, 191
weight gain prevention and, 232
Shoulder dislocation, 142
Skeletal muscles. See Muscles, skeletal
Skin, receiving cardiac output at rest vs. exercise,
  63

Skinfold measures, 133, 134
Sleep disorders, 136

276


Physical Activity and Health

Social environment
barriers, 246-247
behavioral influences, 215,
resources, 247
Social functioning, 141
Social sciences. Set Behavioral sciences, adult;
children and adolescents
Socioeconomic factors
bicycling activities and, 203
physical inactivity and, 177, 178, 196
resistance training and, 193
stretching activities and, 194
walking activities and, 200
Speed, 21,203-204
Splanchnic circulation, 63
Sports, Play, and Active Recreation for Kids
(SPARK) study, 239
Stanford Adolescent Heart Health Program, 238
Stanford Five-City Project (SFCP), 229
Strength, 21, 22

Training heart rate (THR), 21
Transient constriction, 111
Triglycerides, 111
Trust for Public Land, The, 245

Ulnar nerve palsies, 143
United Kingdom Testicular Cancer Study Group,
  122

U

United States regions
East, 12
Midwest, 229
North central, 177, 187
Northeast, 177, 187
South, 177, 189, 187
Southwest, 12
West, 177, 182, 187, 189, 187
U.S. Preventive Services Task Force, 28
Urogenital system, 143
Uterine cancer, 114, 120-121

Strength testing, 16, 34

Strength training. See Resistance training
Stretching activities, 187, 191-192
Stroke volume (SV), 62, 71-73    '
Substance use disorders, 136
Suicide, 135, 140
Systolic blood pressure (SBP), 63, 64, 70

T
T-lymphocytes. See Lymphocytes
Tai chi chuan, 12,113
Taoism, 12
Tecumseh questionnaire, 31
Temperature. See Body temperature
Tendinitis, 143
Tendons, 69

V

Vasoconstriction, 76
Ventilatory volume (V,), 70, 74
Ventricular dysfunction, left, 103
Ventricular end-diastolic volume, 71, 72
Ventricular fibrillation, 112
Vertebral fractures, 130
Virginia
Smyth County program, 245

W

Water-electrolyte imbalance, 143
Weather factors

Testicular cancer, 7, 124, 147              seasonality, 184, 196, 196, 200, 204
Thrombosis, 102, 110, 112                 summer months, 184, 187
Thymus gland, 67                   walking, bicycling activities and, 204
Tidal volume (TV), 70, 71              Weight Gain Prevention Program, 232

277


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West Virginia

elderly mall walking campaign in, 233
Whites

behavior intervention program for, 232
bicycling activities by, 203
high school physical education enrollment, 205
no regular activity, 177, 188, 195
physical activity trends in, 8
regular, sustained activity, 183
regular, vigorous activity, 183, 187, 188,

196-197

sports team participation, 200
strengthening activities by, 189, 191, 193, 199
stretching activities by, 191, 194, 201
walking activities by, 203
Wise Weighs program, 232
Women and physical activity
no regular activity, 177, 178, 188, 205
regular, sustained activity, 183, 188, 205
regular, vigorous activity, 185, 187, 188, 189
selected physical activities, 188
strengthening activities, 191
trends. 8

Work rate, 64, 71
energy metabolism and, 65
energy systems and, 65-66
increasing, 62-63, 64
Worksite physical fitness programs, 48,46, 48,
  184

World Health Organization, definition of health,
  141

World War I, 16
World War II, 17, 18, 19

Y

YMCA, 23
Yoga, 12

Z

Zuni Diabetes Project, 232

278