Physical Activity Guidelines Advisory Committee Report
Part A. Report Summary
Disease prevention and health promotion are high priority features of
President George W. Bush's Healthier US initiative and Secretary of Health and
Human Services (HHS) Michael O. Leavitt's Prevention Priority. Getting routine
medical screenings, making healthy choices and avoiding risks, eating a
nutritious diet, and being physically active are major components of chronic
disease prevention. On October 27, 2006, Secretary Leavitt announced plans for
the development of Federal Physical Activity Guidelines for Americans
to be issued in 2008. These Federal guidelines will serve as the benchmark and
single, authoritative voice for providing science-based guidance on physical
activity, fitness, and health for Americans. In preparation for the development
by HHS of these guidelines, an important first step was to conduct a
comprehensive review and analysis of the scientific literature on physical
activity and health published since 1995. This task was assigned to the
Physical Activity Guidelines Advisory Committee (PAGAC).
The Physical Activity Guidelines Advisory
Committee
Following the announcement by the HHS Secretary of plans to develop
physical activity guidelines, nominations for membership on the PAGAC were
solicited through the Federal Register. PAGAC members were expected to
be respected and published experts in the science of physical activity and its
role in health promotion and disease prevention; be familiar with the purpose,
communication, and application of Federal guidelines; not be employees of the
Federal Government; and be free of any commercial conflicts of interest. In
February 2007, the Secretary of HHS appointed 13 members to the PAGAC,
including a chair and vice-chair. Secretary Leavitt's charge to the PAGAC was
to review existing scientific literature to identify where there is sufficient
evidence to develop a comprehensive set of specific physical activity
recommendations and identify areas where further scientific research is needed.
The intent of HHS is to develop physical activity recommendations for all
Americans that will be tailored as necessary for specific subgroups of the
population. PAGAC was not to prepare guidelines or policy statements. This
report is the result of work by the Committee, consultants to the Committee,
and HHS support staff. Names and affiliations of PAGAC members, consultants,
and HHS support staff are listed at the beginning of this report.
Initially, the PAGAC formed 9 subcommittees, focused on the 9 health
outcomes identified by the CDC team assigned to assist the PAGAC: all-cause
mortality, cardiorespiratory health, metabolic health, energy balance,
musculoskeletal health, functional health, cancer, mental health, and adverse
events. PAGAC members then added 2 other subcommittees: youth and understudied
populations (i.e., populations not covered in other chapters — persons
with disabilities, women during pregnancy and the postpartum period, and races
and ethnicities other than non-Hispanic white). The conclusions in this report
represent the consensus of the entire PAGAC.
Report Contents
This report includes 3 major components. The first provides an
introduction to the PAGAC process; definition of key terms used in the report;
background information on dose response, recent trends in physical activity
among Americans, and an overview of physical activity guidelines development in
the United States; a summary and integration of the science reviewed by PAGAC;
and an explanation of the development and use of the Physical Activity
Guidelines for Americans Scientific Database. The second component
includes 11 sections that review and summarize the scientific literature
relating physical activity to individual health outcomes. The third component
provides a summary of the PAGAC's collective recommendations for future
research. References cited are at the end of each section.
Review of the Science on Physical Activity
and Health
One of the PAGAC's major goals was to integrate the scientific
information on the relation between physical activity and health and to
summarize it in a manner that could be used effectively by HHS personnel to
develop the Physical Activity Guidelines for Americans and related
policy statements. The resulting consensus statements based on the evidence
relating physical activity to health are provided in
Part E: Integration and Summary of the
Science and the conclusions in each of the chapters in
Part G: The Science
Base. A number of the key conclusions by the PAGAC, based on
their review of the scientific literature, are summarized below.
Overall Benefits of Physical Activity on
Health
Very strong scientific evidence based on a wide range of well-conducted
studies shows that physically active people have higher levels of
health-related fitness, a lower risk profile for developing a number of
disabling medical conditions, and lower rates of various chronic diseases than
do people who are inactive.
Children and Youth
Strong evidence demonstrates that the physical fitness and health status
of children and youth are substantially enhanced by frequent physical activity.
Compared to inactive young people, physically active children and youth have
higher levels of cardiorespiratory endurance and muscular strength, and
well-documented health benefits include reduced body fatness, more favorable
cardiovascular and metabolic disease risk profiles, enhanced bone health, and
reduced symptoms of anxiety and depression.
Adults and Older Adults
Strong evidence demonstrates that, compared to less active persons, more
active men and women have lower rates of all-cause mortality, coronary heart
disease, high blood pressure, stroke, type 2 diabetes, metabolic syndrome,
colon cancer, breast cancer, and depression. Strong evidence also supports the
conclusion that, compared to less active people, physically active adults and
older adults exhibit a higher level of cardiorespiratory and muscular fitness,
have a healthier body mass and composition, and a biomarker profile that is
more favorable for preventing cardiovascular disease and type 2 diabetes and
for enhancing bone health. Modest evidence indicates that physically active
adults and older adults have better quality sleep and health-related quality of
life.
Older Adults
In addition to those benefits listed above, strong evidence indicates
that being physically active is associated with higher levels of functional
health, a lower risk of falling, and better cognitive function.
Women During Pregnancy and the Postpartum
Period
Strong evidence indicates that moderate-intensity physical activity
during pregnancy by generally healthy women increases cardiorespiratory and
metabolic fitness without increasing the risk of low birth weight, preterm
delivery, or early pregnancy loss. Moderate-intensity physical activity during
the postpartum period does not appear to adversely affect milk volume or
composition or infant growth. Physical activity alone does not produce weight
loss in postpartum women except when combined with dietary changes.
Persons With Disabilities
For many physical and cognitive disabilities, scientific evidence for
various health and fitness outcomes is still limited due to the lack of
research. Moderate to strong evidence indicates that increases in aerobic
exercise improve cardiorespiratory fitness in individuals with lower limb loss,
multiple sclerosis, stroke, spinal cord injury, and mental illness. Limited
data show similar results for people with cerebral palsy, muscular dystrophy,
and Alzheimer's disease. Moderate to strong evidence also exists for
improvements in walking speed and walking distance in patients with stroke,
multiple sclerosis, and intellectual disabilities. Moderately strong evidence
indicates that resistance exercise training improves muscular strength in
persons with such conditions as stroke, multiple sclerosis, cerebral palsy,
spinal cord injury, and intellectual disability. Although evidence of benefit
is suggestive for such outcomes as flexibility, atherogenic lipids, bone
mineral density, and quality of life, the data are still very limited.
Racial and Ethnic Diversity
Only a limited number of prospective observational or experimental
studies investigating the relation between physical activity and health
outcomes have had adequate samples of non-Hispanic white men or women and one
or more other race/ethnicities to allow a direct comparison of benefits.
However, in the few studies where direct comparisons have been made, no
meaningful difference appears to exist, and studies conducted in other
countries with race-ethnic populations other than non-Hispanic white report
similar results. Thus, based on the currently available scientific evidence,
the dose of physical activity that provides various favorable health and
fitness outcomes appears to be similar for adults of various races and
ethnicities.
Persons Who Are Overweight or Obese
Strong evidence shows that physically active adults who are overweight
or obese experience a variety of health benefits that are generally similar to
those observed in people of optimal body weight (body mass index [BMI] =
18.5-24.9). These benefits include lower rates of all-cause mortality, coronary
heart disease, hypertension, stroke, type 2 diabetes, colon cancer, and breast
cancer. Some of these benefits appear to be independent of a loss in body
weight, while in some cases weight loss in conjunction with an increase in
physical activity results in even greater benefits. Because of the health
benefits of physical activity that are independent of body weight
classification, adults of all sizes and shapes gain health and fitness benefits
by being habitually physically active.
Patterns of Physical Activity Associated
With Better Health and Fitness
PAGAC members recognized that, when considering the intensity of an
activity, it is most appropriate scientifically to express the intensity
relative to a person's capacity (relative intensity). However, the PAGAC also
recognized that communicating to the public the process of determining relative
intensity is difficult and that intensity expressed in absolute terms is a
reasonable alternative. Table D.1
and Figure D.1 located in
Part D: Background
provide information on the relation between absolute and relative intensity.
Also, the committee concluded that, when classifying activities by intensity
using metabolic equivalents (METs), the appropriate classification of
moderate-intensity activity is 3.0 to 5.9 rather than 3.0 to 6.0 METs and
vigorous intensity is 6.0 or greater METs (Table D.2).
Based on the existing science, it is not possible to be highly precise
in selecting a single expression of activity amount that provides improved
health because of the diversity in the types of physical activity reported and
the conditions under which they are performed, the different questionnaires
used to assess these activities, and the various units of measurement used to
express the characteristics of the activity. Also, the baseline activity and
fitness levels of the population and the targeted health outcomes influence the
effective dose. The committee constructed a table to assist in translating the
different units of measurements for the amount of activity performed for a
range of activity intensities performed for 150 and 300 minutes per week (2.5
and 5 hours per week) (Table D.3).
Children and Youth
Few studies have provided data on the dose response for various health
and fitness outcomes in children and youth. However, substantial data indicate
that important health and fitness benefits can be expected to accrue to most
children and youth who participate daily in 60 or more minutes of moderate to
vigorous physical activity. Certain specific types of physical activity should
be included in an overall physical activity pattern in order for children and
youth to gain comprehensive health benefits. These include regular
participation in each of the following types of physical activity on 3 or more
days per week: resistance exercise to enhance muscular strength in the large
muscle groups of the trunk and limbs, vigorous aerobic exercise to improve
cardiorespiratory fitness and cardiovascular and metabolic disease risk
factors, and weight-loading activities to promote bone health. Experiences
consistent with these goals involve participation in physical activities that
are developmentally appropriate, that minimize the potential risks of
overtraining and injuries, and that provide children and youth with
opportunities for enjoyable participation in a wide range of specific forms of
physical activity.
Adults and Older Adults
Data from a large number of studies evaluating a wide variety of
benefits in diverse populations generally support 30 to 60 minutes per day of
moderate to vigorous intensity physical activity on 5 or more days of the week.
For a number of benefits, such as lower risk for all-cause mortality, coronary
heart disease, stroke, hypertension, and type 2 diabetes in adults and older
adults, lower risk is consistently observed at 2.5 hours per week (equivalent
to 30 minutes per day, 5 days per week) of moderate to vigorous intensity
activity. The amount of moderate to vigorous intensity activity most
consistently associated with significantly lower rates of colon and breast
cancer and the prevention of unhealthy weight gain or significant weight loss
by physical activity alone is in the range of 3 to 5 hours per week.
It is possible to combine aerobic activities of different types and
intensities into a single measure of amount of activity. For many studies, the
amount of moderate and vigorous intensity activity associated with
significantly lower rates of disease or improvements in biomarkers and fitness
is in the range of 500 to 1,000 MET-minutes per week. An adult can achieve a
target of 500 MET-minutes per week by walking at about 3.0 miles per hour for
approximately 150 minutes per week (7.5 miles), walking faster at 4.0 miles per
hour for 100 minutes (6.6 miles), or jogging or running at 6 miles per hour for
about 50 minutes per week (5.0 miles). To achieve 1,000 MET-minutes per week,
these amounts of activity would need to be doubled. For an explanation of the
use of METs and MET-minutes for calculating the amount of activity see
Part D: Background,
especially Table D.2 and its
associated text.
Resistance or muscle-strengthening exercises are important for
maintaining muscle and bone health, and these exercises enhance functional
status and contribute to a reduction of falls in older adults. Most of the
evidence supports a resistance activity program with the following
characteristics: progressive muscle strengthening exercises that target all
major muscle groups performed on 2 or more days per week. To enhance muscle
strength, 8 to 12 repetitions of each exercise should be performed to
volitional fatigue. One set is effective; however, limited evidence suggests
that 2 or 3 sets may be more effective.
Older Adults
If a person has a low exercise capacity (physical fitness), the
intensity and amount of activity needed to achieve many health-related and
fitness benefits are less than for someone who has a higher level of activity
and fitness. Because the exercise capacity of adults tends to decrease as they
age, older adults generally have lower exercise capacities than younger
persons. Thus, they need a physical activity plan that is of lower absolute
intensity and amount (but similar in relative intensity and amount) than is
appropriate for more fit people, especially when they have been sedentary and
are starting an activity program.
Older Adults at Risk of Falls
For older adults at risk of falling, strong evidence exists that regular
physical activity is safe and reduces falls by about 30%. Most evidence
supports a program of exercise with the following characteristics: 3 times per
week of balance training and moderate-intensity muscle-strengthening activities
for 30 minutes per session, with additional encouragement to participate in
moderate-intensity walking activities 2 or more times per week for 30 minutes
per session. Some evidence, albeit less consistent, suggests that tai chi
exercises also reduce falls. There is no evidence that planned physical
activity reduces falls in adults and older adults who are not at risk of
falls.
Persons With Disabilities
For a majority of the studies reviewed involving persons with
disabilities, the exercise regimen followed was that currently recommended for
the general public — aerobic exercise of 30 to 60 minutes, 3 to 5 days
per week at moderate intensity, and resistance training with 1 or 2 sets of 8
to 12 repetitions using appropriate muscle groups 2 to 3 times per week.
Although other activity regimens might be effective, they have not been
adequately evaluated.
Persons Achieving Weight Stability
The optimal amount of physical activity needed for weight maintenance
(defined as less than 3% change in body weight) over the long-term is unclear.
However, the evidence is clear that physical activity provides benefit for
weight stability. A great deal of inter-individual variability exists with
physical activity and weight stability, and many persons may need more than 150
minutes of moderate-intensity activity per week to maintain their weight at a
stable level. Data from recent well-designed randomized controlled trials
lasting up to 12 months indicate that aerobic physical activity performed to
achieve 13 to 26 MET-hours per week is associated with approximately a 1% to 3%
weight loss (i.e., an amount generally considered to represent weight
stability). Thirteen MET-hours per week is approximately equivalent to walking
at 4 miles per hour for 150 minutes per week or jogging at 6 miles per hour for
75 minutes per week.
Persons Achieving Weight Loss
A wide range of studies provides evidence of a dose-response relation
between physical activity and weight loss. Clear, consistent data show that a
large volume of physical activity is needed for weight loss in the absence of
concurrent dietary changes. The physical activity equivalent of 26 kilocalories
per kilogram of body weight (1,560 MET-minutes) or more per week is needed for
weight loss of 5% or greater. Smaller amounts of weight loss are seen with
smaller amounts of physical activity. This relatively high volume of physical
activity is equivalent to walking about 45 minutes per day at 4 miles per hour
or about 70 minutes per day at 3 miles per hour, or jogging 22 minutes per day
at 6 miles per hour.
The role of energy intake (diet) must be considered in any discussion
of weight control. When calorie intake is carefully controlled at a baseline
level, the magnitude of any weight loss is what would be expected given the
energy expenditure of the person's physical activity. However, in situations in
which people's dietary intake is not controlled, the amount of weight loss due
to the increase in physical activity is not commensurate to what would be
expected. Therefore, for most people to achieve substantial weight loss (i.e.,
more than 5% decrease in body weight), a dietary intervention also is needed.
The dietary intervention could include either maintenance of baseline caloric
intake, or a reduction in caloric intake to accompany the physical activity
intervention. The magnitude of change in weight due to physical activity is
additive to that associated with caloric restriction.
Persons Achieving Weight Maintenance After
Weight Loss
The scientific evidence for the effectiveness of physical activity alone
in preventing weight regain following significant weight loss is limited.
Available data indicate that to prevent substantial weight regain over 6 months
or longer, many adults need to exercise in the range of 60 minutes of walking
or 30 minutes of jogging daily (approximately 4.4 kilocalories per kilogram per
day of activity energy expenditure). The literature generally supports the
concept that "more is better" for long-term weight maintenance following weight
loss. Further, the evidence indicates that individuals who are successful at
long-term weight maintenance appear to limit caloric intake in addition to
maintaining physical activity.
Special Considerations Related to the
Pattern of Physical Activity and Health
The following section presents additional findings from the Committee's
review of the literature. These findings represent important considerations for
developing comprehensive physical activity guidelines for Americans.
Some Physical Activity Is Better Than
None
The least active people in the population generally have the highest
risk of a variety of negative health outcomes. Although the minimum amount of
physical activity needed to decrease this risk is not clear, increasing
evidence suggests that participating in no more than 1 hour per week of
moderate-intensity physical activity is associated with lower risk of all-cause
mortality and the incidence of coronary heart disease. At this lower amount and
intensity of activity, the benefits usually are less than that observed with
greater amounts of activity, and studies are much less consistent about the
nature and magnitude of these benefits. Nevertheless, the dose-response curves
for the major health benefits clearly indicate an inverse relation between the
dose of activity and rate of disease. Although the minimum amount of activity
needed to produce a benefit cannot be stated with certainty, nothing would
suggest a threshold below which there are no benefits.
Additional Health Benefits With More
Physical Activity
Reasonably strong evidence demonstrates that participating in moderate
to vigorous physical activity for more than 150 minutes per week is associated
with greater health benefits for a variety of health outcomes, including
chronic disease prevention, improvement of various disease biomarkers, and the
maintenance of a healthy weight. However, in a number of studies where such a
dose response is observed in preventing chronic disease or reducing all-cause
mortality, the relation appears to be curvilinear. This means that the absolute
increase in benefits becomes less and less for any given increase in the amount
of physical activity.
Additional Benefits With Vigorous Physical
Activity
Strong evidence indicates that an increase in intensity is associated
with greater improvements for some health outcomes compared to those observed
with moderate-intensity activity. This is especially true for outcomes related
to fitness. However, it should be noted that an increase in intensity was often
associated with an increase in volume of activity for many observational and
experimental studies, and it is difficult to separate the benefits of each.
Frequency of Physical Activity
Very limited published research has systematically evaluated health or
fitness benefits in response to different frequencies of activity sessions per
week when the amount of activity is held reasonably constant. Although the data
are limited, the results suggest that for health and fitness benefits, the
frequency of activity is much less important than the amount or intensity. Many
experimental studies since 1995 have demonstrated beneficial effects of 120 to
150 minutes per week of moderate- or vigorous-intensity activity, usually
performed during 3 to 5 sessions per week, so we know that this frequency of
activity is effective. Only limited data are available comparing the benefits
from just 1 or 2 sessions per week with multiple sessions spread throughout the
week with activity amount and intensity held constant.
Accumulation of Physical Activity
The concept of accumulation refers to performing multiple short bouts of
physical activity throughout the day. Some scientific evidence of moderate
strength suggests that accumulating 30 or more minutes of moderate- to
vigorous-intensity aerobic activity throughout the day in bouts of 10 minutes
or longer produces improvements in cardiorespiratory fitness. Limited data
indicate that accumulated short bouts of 8 to 10 minutes improve selected
biomarkers for cardiovascular disease in a manner generally similar to that
observed when activity of a similar amount and intensity is performed in a
single bout of 30 or more minutes. Data on the effects of accumulating activity
involving multiple short bouts for the prevention of major clinical outcomes,
such as all-cause mortality, cardiovascular disease, diabetes, and selected
cancers, are very limited due to the type of data collected from the
questionnaires in most prospective observational studies. In these studies,
people are generally asked about the total amount of physical activity
performed, and it has not been possible to precisely differentiate between
activities conducted in a single, long bout versus those conducted in multiple,
short bouts over the day.
Health Benefits of Brisk Walking
Strong evidence shows that a regimen of brisk walking provides a number
of health and fitness benefits for adults and older adults, including lower
risk of all-cause mortality, cardiovascular disease, and type 2 diabetes. Some
evidence is available indicating that walking at faster pace is associated with
greater health benefits than walking at a slower pace. Strong evidence also
shows that frequent bouts of walking increase cardiorespiratory and metabolic
fitness, especially in people who have been performing little activity on a
regular basis. Limited to moderate evidence suggests that walking helps to
maintain bone density and reduce fractures over time, especially in women, and
helps to maintain joint health and functional ability in adults and older
adults.
Safety and Adverse Events
Activity-related adverse events such as musculoskeletal injuries are
common but are usually mild, especially for moderate intensity activities such
as walking. Overall, the health benefits of regular physical activity outweigh
the risks. Much of the research that has addressed adverse events during
physical activity has evaluated the risk of musculoskeletal injuries or sudden
cardiac death during vigorous physical activity (e.g., jogging, running,
competitive sports, military training). Few well-conducted studies are
available evaluating risk during moderate-intensity activity intended primarily
to improve health. Injury rates are higher for collision and contact sports
than for activities with fewer and less forceful contact with other people or
objects. Walking for exercise, gardening or yard work, dancing, swimming, and
golf are activities with the lowest injury rates. Injuries are more likely to
happen when people are more physically active than usual, and the risk is
related to the size of the increase. A series of small increments in physical
activity, each followed by a period of adaptation, is associated with lower
rates of musculoskeletal injuries than is an abrupt increase to the same final
level. For sudden cardiac adverse events, intensity appears to be more
important than frequency or duration. The protective value of a medical
consultation for persons with or without chronic diseases who are interested in
increasing their physical activity level is not established.
Research Recommendations
Individual chapters in Part G: The
Science Base provide a list of recommendations regarding
issues that should receive priorities for future research. The PAGAC felt that
it would be valuable to collate the major research recommendations into one
section, Part H: Research
Recommendations, and to include some overarching
recommendations that pertain to more than one health outcome. For example, it
became apparent during the PAGAC's review that various populations are
underrepresented in studies on physical activity and health. These populations
represent a substantial portion of the population at risk because of their high
prevalence of sedentary behavior. They include persons of low socioeconomic
status, racial-ethnic minorities, persons with disabilities, and women during
pregnancy and the postpartum period. Also, inadequate data are available to
answer a number of questions about dose response for a variety of health
outcomes, such as the effects of activity intensity, bout duration, or
frequency when total amount or volume of activity is held constant. More data
are needed to better define both the low and high ends of the dose-response
relation for various health outcomes. Additional research on the basic
biological mechanisms modified by changes in physical activity will help
establish causality for specific clinical outcomes. National surveillance
systems also are needed to track trends in total daily activity energy
expenditure in various populations throughout the lifespan.
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Last revised: June 11, 2008
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