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Construct Overview of Physical Activity

Please note that this section is an archive and is no longer being updated.

Background

Physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure.¹ Physical activity includes exercise but also recreational, household, and occupational activities as well as other types of movement. Physical activity is related to but distinct from physical fitness, which refers to an individual's capacity to perform physical activity,¹ and functional limitation, which refers to restriction in the ability to perform certain physical activities.² In other words, the broader concept of "physical activity" should be distinguished from terms that are defined by ability rather than performance, as well as from terms that imply a specific goal or functionality for movement.

Regular physical activity is associated with a broad range of health benefits, including improved cardiovascular function,³ improved lipid metabolism,⁴ lower blood pressure,^5,6 reductions in perceived stress, anxiety, and depression,^7-9 and, in older adults, improved cognitive function.¹⁰ In contrast, chronic, very low levels of physical activity (i.e., sedentary lifestyles) increase the risk for hypertension,¹¹ coronary artery disease,¹² Type II diabetes,¹³ and obesity.¹⁴ Sedentary persons are at greater risk for all-cause mortality than non-sedentary groups.¹⁵ However, a substantial proportion of American adults do not engage in a level of physical activity sufficient to confer health benefits; epidemiological data indicate that 27% of Americans are inactive, and an additional 28% are infrequently active.¹⁶

VA Relevance

Disorders linked to modifiable health behaviors, such as obesity, hypertension, and Type II diabetes, are prevalent within the VA user population and occur at rates at least as high as those within the general U.S. adult population.^17-20 Obesity is closely associated with physical activity levels¹⁴ and is itself a risk factor for additional health problems. Data from the 2000 Behavioral Risk Factor Surveillance System (BRFSS) indicated that 25% of VA users were obese, slightly higher than the rate in the general U.S. adult population.²⁰

Most obese VA users in the BRFSS study reported that they did not adhere to the recommendation of 30 minutes of physical activity five or more times per week, even if they endorsed attempts to lose weight.²⁰ Similarly, the majority of veterans enrolled in a study of Type II diabetes outcomes reported limited physical activity.²¹ Despite increasingly widespread information about the health benefits of physical activity, more active interventions appear necessary to increase levels of physical activity at the population level.

Outcomes of interventions designed to promote physical activity have been mixed, and little is known about the efficacy of specific intervention strategies.²² Studies of physical activity interventions in veteran populations suggest that well-designed programs can improve physical functioning and mental health outcomes,^23-25 although less is known about their clinical significance or long-term effects on behavior. Moreover, it is unclear how findings from carefully controlled intervention studies can be applied to routine practice. Interventions designed to increase VA health providers' competence in physical activity counseling have shown modest effects on patient behavior in only one of two studies.^26,27 Further work will be required to develop effective physical activity promotion strategies for VA users.

Measurement

Physical activity may be measured by self-report (questionnaires or interviews), observation, or technical methods. Accurate measurement of physical activity is especially important to ensure compliance with a prescribed regimen (e.g., in prospective controlled studies of exercise training). However, to the extent that the process of measurement alters typical behavior, the validity of naturalistic physical activity studies may be threatened by the more invasive monitoring methods. The use of multiple measurement strategies in many recent studies of physical activity reflects the relative advantages and disadvantages of different methods.²⁸

Self-report measures of physical activity are in widespread use and include retrospective recall questionnaires, activity logs or diaries, and proxy reports from individuals close to the subject. Though cost effective and generally easy to administer, self-report measures may have significant limitations. For example, socially desirable responding can inflate estimates of physical activity; memory errors may lead to over- or underreporting of physical activity. Although diary or activity log measures may reduce problems associated with recall, they do not entirely eliminate the potential for overreporting,²⁹ and they are generally more burdensome to subjects, necessitating compliance monitoring to ensure data integrity.

However, diary measures may yield information on patterns of activity over hours, days, weeks, or longer periods that may not be captured by retrospective measures. The variability in physical activity over time, though often an outcome of interest, complicates the observed test-retest reliability of an instrument; a guideline is that the test-retest interval should be the same as the recall period assessed by the initial test.³⁰

Content validity is critical to the development of sensitive physical activity measures that are appropriate for their intended applications. Relevant aspects of physical activity type, frequency, duration, and intensity may differ across populations. For example, an arbitrary choice of instrument for use among less active populations may result in floor effects, preventing discrimination of the truly sedentary from individuals who perform very light physical activity,³¹ and physical activity measures that focus on leisure activity may neglect physical activity performed through occupational, household, and other roles.³² In addition to providing an adequate range of content, measures should provide clear and appropriate definitions of physical activity to the groups of respondents who are being assessed. In the absence of a universal, "gold standard" self-report tool, it is especially important for physical activity self-report measures to have been validated, if not developed originally, in the population for which they will be used.³³

An alternative to self-report measures of physical activity is direct observation by an investigator, although observer coding schemes have been predominantly validated for use in children.³⁴ A growing array of objective, technology-based measures of physical activity are also available. These techniques are often used in conjunction with self-report measures (sometimes as validity criteria) and include accelerometer-based activity monitors, pedometers, heart rate monitors, calorimetry, and the doubly labeled water technique.^36,37 Objective assessment methods vary considerably in accuracy, invasiveness, cost, subject burden, and correlation with self-report measures; for review of the most commonly used objective measures see references 36-39.

Through literature review, METRIC identified four commonly used self-report instruments for measuring physical activity. These are ranked according to number of citations, as determined by the ISI Web of Knowledge.⁴⁰ What follows is a brief summary of each instrument and three applicable references.

Most Frequently Cited Instruments

1. Paffenbarger Physical Activity Questionnaire
   [916 Citations]
2. Minnesota Leisure-Time Physical Activity Questionnaire (MLTPA)
   [613 Citations]
3. Seven-Day Physical Activity Recall (PAR)
   [543 Citations]
4. Baecke Habitual Physical Activity Questionnaire (BQHPA)
   [517 Citations]

1. Caspersen CJ, Powell KE, Christenson GM. Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research. Public Health Rep 1985;100:126-131. [Abstract]
2. Tager IB, Haight T, Sternfeld B, Yu Z, van Der Laan M. Effects of physical activity and body composition on functional limitation in the elderly. Epidemiology 2004;15:479-493. [Abstract]
3. Pate RR, Durstine JL. Cardiorespiratory adaptations to chronic endurance exercise. In Seefeldt V (Ed), Physical Activity & Well-being (pp. 276-299). Reston, VA: American Alliance for Health, Physical Education, Recreation, and Dance; 1986.
4. King AC, Haskell WL, Young DR, Oka RK, Stefanik ML. Long-term effects of varying intensities and formats of physical activity on participation rates, fitness, and lipoproteins in men and women aged 50 to 65 years. Circulation 1995;91:2596-2604. [Abstract]
5. Braith RW, Pollock ML, Lowenthal DT, Graves JE, Limacher MC. Moderate- and high-intensity exercise lowers blood pressure in normotensive subjects 60 to 79 years of age. Am J Cardiol 1994;74:1124-1128. [Abstract]
6. Hagberg JM, Montain SJ, Martin WH III, Ehsani AA. Effect of exercise training in 60- to 69-year-old persons with essential hypertension. Am J Cardiol 1989;64:348-353. [Abstract]
7. Brosse AL, Sheets ES, Lett HS, Blumenthal JA. Exercise and the treatment of clinical depression in adults: recent findings and future directions. Sports Med 2002;32:741-760. [Abstract]
8. King AC, Taylor CB, Haskell WL. Effects of differing intensities and formats of 12 months of exercise training on psychological outcomes in older adults. Health Psychol 1993;12:292-300. [Abstract]
9. Petruzzello SJ, Landers DM, Hatfield BD, Kubitz KA, Salazar W. A meta-analysis on the anxiety-reducing effects of acute and chronic exercise: outcomes and mechanisms. Sports Med 1991;11:143-182. [Abstract]
10. Colcombe S, Kramer AF. Fitness effects on the cognitive function of older adults: A meta-analytic study. Psychol Sci 2003;14:125-130. [Abstract]
11. Slama M, Susic D, Frohlich ED. Prevention of hypertension. Curr Opin Cardiol 2002;17:531-536. [Abstract]
12. Powell KE, Thompson PD, Caspersen CJ, Kendrick JS. Physical activity and the incidence of coronary heart disease. Annu Rev Public Health 1987;8:235-287. [Abstract]
13. Helmrich SP, Radland DR, Leung RW, Paffenbarger RS. Physical activity and reduced occurrence of non-insulin-dependent diabetes mellitus. N Eng J Med 1991;325:147-152. [Abstract]
14. Hill JO, Wyatt HR. Role of physical activity in preventing and treating obesity. J Appl Physiol 2005;99:765-770. [Abstract]
15. Fletcher GF, Balady G, Blair SN, et al. Statement on exercise: benefits and recommendations for physical activity programs for all Americans. Circulation 1996;94:857-862. [Abstract]
16. Mokdad AH, Bowman BA, Ford ES, Vinicor F, Marks JS, Koplan JP. The continuing epidemics of obesity and diabetes in the United States. JAMA 2001;286:1195-1200. [Abstract]
17. Miller DR, Safford MM, Pogach LM. Who has diabetes? Best estimates of diabetes prevalence in the Department of Veterans Affairs based on computerized patient data. Diabetes Care 2004;27(Sup 2):B10-B21. [Abstract]
18. Reiber GE, Koepsell TD, Maynard C, Haas LB, Boyko EJ. Diabetes in nonveterans, veterans, and veterans receiving Department of Veterans Affairs health care. Diabetes Care 2004;27(Sppl 2):B3-B9. [Abstract]
19. Siegel D, Lopez J, Meier J. Pharmacologic treatment of hypertension in the Department of Veterans Affairs during 1995 and 1996. Am J Hypertens 1998;11:1271-1278. [Abstract]
20. Wang A, Kinsinger LS, Kahwati LC, et al. Obesity and weight control practices in 2000 among veterans using VA facilities. Obes Res 2005;13:1405-1411. [Abstract]
21. Murata GH, Shah JH, Wendel CS, et al. Risk factor management in stable, insulin-treated patients with type 2 diabetes: the Diabetes Outcomes in Veterans Study. J Diabetes Complications 2003;17:186-191. [Abstract]
22. Hillsdon M, Foster C, Thorogood M. Interventions for promoting physical activity. Cochrane Database Syst Rev 2005;25:CD003180. [Abstract]
23. Gardner AW, Katzel LI, Sorkin JD, et al. Exercise rehabilitation improves functional outcomes and peripheral circulation in patients with intermittent claudication: a randomized controlled trial. J Am Geriatr Soc 2001;49:755-762. [Abstract]
24. Meuleman JR, Brechue WF, Kubilis PS, Lowenthal DT. Exercise training in the debilitated aged: strength and functional outcomes. Arch Phys Med Rehabil 2000;81:312-318. [Abstract]
25. Otter L, Currie J. A long time getting home: Vietnam veterans' experiences in a community exercise rehabilitation programme. Disabil Rehabil 2004;26:27-34. [Abstract]
26. Ackermann RT, Deyo RA, LoGerfo JP. Prompting primary providers to increase community exercise referrals for older adults: a randomized trial. J Am Geriatr Soc 2005;53:283-289. [Abstract]
27. Eckstrom E, Hickam DH, Lessler DS, Buchner DM. Changing physician practice of physical activity counseling. J Gen Int Med 1999;14:376-378. [Abstract]
28. Treuth MS. Applying multiple methods to improve the accuracy of activity assessments. In Welk GJ (Ed), Physical Activity Assessments for Health-Related Research (pp. 213-225). Champaign, IL: Human Kinetics Publishers; 2002.
29. Jakicic JM, Polley BA, Wing RR. Accuracy of self-reported exercise and the relationship with weight loss in overweight women. Med Sci Sports Exerc 1998;30:634-638. [Abstract]
30. Sallis JF, Saelens BE. Assessment of physical activity by self-report: status, limitations, and future directions. Res Q Exerc Sport 2000;71:1-14. [Abstract]
31. Tudor-Locke CE, Myers AM. Challenges and opportunities for measuring physical activity in sedentary adults. Sports Med 2001;31:91-100. [Abstract]
32. Young DR, Miller KW, Wilder LB, Yanek LR, Becker DM. Physical activity patterns of urban African Americans. J Community Health 1998;23:99-112. [Abstract]
33. Warnecke RB, Johnson TP, Chávez N, et al. Improving question wording in surveys of culturally diverse populations. Ann Epidemiol 1997;7:334-342. [Abstract]
34. McKenzie TL. Use of direct observation to assess physical activity. In Welk GJ (Ed), Physical Activity Assessments for Health-Related Research (pp. 179-195). Champaign, IL: Human Kinetics Publishers; 2002.
35. Bouchard C, Shephard RJ, Stephens T (Eds). Physical Activity, Fitness and Health: Consensus Statement. Champaign, IL: Human Kinetics Publishers; 1993.
36. Dale D, Welk GJ, Matthews CE. Methods for assessing physical activity and challenges for research. In Welk GJ (Ed), Physical Activity Assessments for Health-Related Research (pp. 19-34). Champaign, IL: Human Kinetics Publishers; 2002.
37. Bassett DR. Validity and reliability issues in objective monitoring of physical activity. Res Q Exerc Sport 2000;71:30-36. [Abstract]
38. Freedson PS, Miller K. Objective monitoring of physical activity using motion sensors and heart rate. Res Q Exerc Sport 2000;71:21-29. [Abstract]
39. Keim NL, Blanton CA, Kretsch MJ. America's obesity epidemic: measuring physical activity to promote an active lifestyle. J Am Diet Assoc 2004;104:1398-1409. [Abstract]
40. Welk, GJ (Ed). Physical Activity Assessments for Health-Related Research. Champaign, IL: Human Kinetics Publishers; 2002.
41. ISI Web of Knowledge, Accessed October 2005. Available: http://isi01.isiknowledge.com/portal.cgi/wos/.