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1 Introductory Session This workshop brought together expert research scientists and physi- cal activity practitioners from academia and government to explore the adequacy of evidence for physical activity guidelines development. This activity was a quick response to a request made by the U.S. Department of Health and Human Services (DHHS) to the Institute of Medicine (IOM) to organize a 2-day workshop to determine whether sufficient evidence exists for DHHS to proceed in a systematic way to develop a comprehensive set of physical activity guidelines for Americans. According to RADM Penelope Slade Royall, one of the greatest challenges at DHHS is leading the American public to be more physi- cally active. Over the past 30 years, the federal government and many organizations have issued physical activity recommendations. Although the various recommendations illustrate the scientific consensus on the health benefits of physical activity, they differ from each other with re- gard to particular details: How much physical activity? What type of ac- tivity? For whom and how often? Scientific advances may make it possible to develop comprehensive guidance targeted to children, youth, adults, and older adults. RADM Royall indicated that DHHS planned to use the information presented at this IOM workshop to determine whether to move forward on developing comprehensive physical activity guidelines for Americans. 5
6 PHYSICAL ACTIVITY WORKSHOP WORKSHOP GOALS Presenter: William L. Haskell The purpose of the workshop was twofold: (1) examine the available data that link physical activity to health, giving special emphasis on the nature and strength of the evidence; and (2) identify areas in which re- search is needed to develop evidence-informed physical activity guide- lines with confidence. The term evidence-informed refers to the accumulation of data from a wide variety of research designs and clinical experiences to reach a solid conclusion. Figure 1-1 illustrates the nature of evidence-informed guidelines for public health policy. Evidence-informed physical activity guidelines could be substan- tially more comprehensive than the physical activity guidelines contained in the Dietary Guidelines for Americans 2005 (DHHS and USDA, 2005), but they also would need to coordinate with those guidelines. This work- shop was planned to address evidence related to a broad range of health outcomes (both benefits and risks) and many subpopulations, including children and youth, adults, pregnant and postpartum women, older per- sons, and persons with disabilities. The presenters were cautioned to avoid making recommendations for physical activity guidelines. Rather, they were asked to provide scientific evidence that DHHS could use to make a decision regarding whether to move forward on developing guidelines and, if the decision was positive, that would provide a useful starting point for a future expert panel in de- veloping physical activity guidelines for Americans. Thus each partici- pant was asked to provide a list of relevant scientific references and other supporting materials for their presentations. References related specifi- cally to the presentations are listed at the end of each chapter. Additional references have been forwarded to DHHS staff in the Office of Disease Prevention and Health Promotion. Dr. Haskell provided an example of the type of evidence that would be considered if U.S. Food and Drug Administration (FDA) approval was required before physical activity could be promoted as a âmedicineâ or therapy. Such approval would require evidence on the following: â¢ Efficacy. Does physical activity cause a specific health benefit as demonstrated by adequately designed clinical trials?
7 INTRODUCTORY SESSION Large randomized Meta-analysis and controlled trials systematic reviews Prospective Evidence-Informed Small randomized observational Public Health controlled trials studies Policy Case-control studies Consecutive case series Biological mechanisms Genetic studies FIGURE 1-1 Research used to support evidence-informed public health policy. SOURCE: Haskell (2006). â¢ Effectiveness. Is the specified benefit obtained by a reason- able percentage of the persons who undertake the prescribed regimen or activity? Who will be a responder, and who will be a nonresponder? â¢ Dose. What dose of physical activity provides a meaningful benefit for a specific condition? The prescribed dose needs to be defined in terms of type, intensity, frequency, and duration or amount. â¢ Mechanisms of action. What changes in structure or function caused by the physical activity are responsible for the specific health benefit? In a therapy such as physical activity, there may be multiple mechanisms for a single health benefit. â¢ Potential adverse events. What are the medical risks associated with the prescribed dose of physical activity? What are the medical contraindications for the prescribed activity, and what adjustments in dose are needed for specific populations to maximize the benefits and reduce adverse events? Data that support each of these areas could provide the scientific evi- dence base to develop broad national physical activity guidelines for Americans.
8 PHYSICAL ACTIVITY WORKSHOP STATE OF THE NATION RELATIVE TO PHYSICAL ACTIVITY RECOMMENDATIONS FOR AMERICANS Presenter: Russell R. Pate History of Physical Activity Guidelines The first physical activity guidelines in the United States were developed in 1975. Box 1-1 lists the American College of Sports Medicineâs (ACSMâs) recommended doses of aerobic physical activity and lists key physical activity guidance statements that have been published since 1994. Guidelines for children are not separated from those for adults be- cause some statements were intended to address the physical activity needs of all Americans. BOX 1-1 Chronological Listing of Physical Activity Guidelines Published from 1975 Through 2005 Recommended Dose of Aerobic Physical Activity, American College of Sports Medicine, 1975 to 2000 For Cardiorespiratory Fitness 1975: 3 to 5 days/week for 20 to 45 minutes/day at 70 to 90 percent of heart rate range (the difference between resting and maximal heart rate, typically 70 to 200 beats per minute in a young adult). 1980 and 1986: 3 to 5 days/week for 15 to 60 minutes/day at 70 to 85 per- cent of heart rate range. 1991: lower level of intensity reduced to 60 percent of heart rate range. 1995: lower level of intensity reduced to 50 percent of heart rate range and lower level of duration changed to 20 minutes/day. For Health 2000: 7 days/week for more than 20 minutes/day at 40 to 85 percent of heart rate range. ACSMâs guidance was a gradual decrease in the lower level of the rec- ommended intensityâfrom quite an intense level of exercise (70 percent of a personâs heart rate range in 1975 to 40 percent of a personâs heart rate range beginning in 1991). ACSM (1975, 1980, 1986, 1991, 1995, 2000)
9 INTRODUCTORY SESSION BOX 1-1 Continued San Diego Consensus Physical Activity Guidelines for Adolescents â¢ All adolescents should be physically active daily, or nearly every day, as part of play, games, sports, transportation, recreation, physical educa- tion, or physical exercise, in the context of family, school, and commu- nity activities. â¢ Adolescents should engage in three or more sessions per week of ac- tivities that last 20 minutes or more at a time and that require moderate to vigorous levels of exertion. Sallis and Patrick (1994) Physical Activity and Public Health: A Recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine Every U.S. adult should accumulate 30 minutes or more of moderate- intensity physical activity on most, and preferably all days of the week. Pate et al. (1995) Physical Activity and Health: A Report from the Surgeon General â¢ People of all ages should accumulate at least 30 minutes of physical activity of moderate intensity on most if not all days of the week. â¢ Activity leading to an increase in daily expenditure of approximately 150 kilocalories/day (equivalent to approximately 1,000 kilocalories/week) is associated with substantial health benefits and the activity does not need to be vigorous to achieve benefit. DHHS (1996) NIH Consensus Development Panel on Physical Activity and Cardiovas- cular Health All Americans should engage in regular physical activity at a level appro- priate to their capacity, need, 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. NIH (1995, 1996) Health Education Authority Recommendations â¢ All children and youth should participate in physical activity that is of at least moderate intensity for an average of one hour per day. While young people should be physically active nearly every day, the amount of physical activity can appropriately vary from day to day in type, set- ting, intensity, duration, and amount. â¢ All children and youth should participate at least twice per week in physical activities that enhance and maintain strength in the muscula- ture of the trunk and upper arm girdle. Cavill et al. (2001) Continued
10 PHYSICAL ACTIVITY WORKSHOP BOX 1-1 Continued Institute of Medicine Dietary Reference Intakes In addition to the activities identified with a sedentary lifestyle, an average of 60 minutes of daily moderate-intensity physical activity or shorter peri- ods of more vigorous exertion was associated with a normal BMI and therefore is recommended for normal-weight individuals. IOM (2002/2005) Dietary Guidelines for Americans 2005 Adults â¢ To reduce the risk of chronic disease in adulthood, engage in at least 30 minutes of moderate intensity physical activity. â¢ To help manage body weight and prevent gradual unhealthy weight gain in adulthood, engage in approximately 60 minutes of moderate-to- vigorous intensity activity. Children and Adolescents â¢ At least 60 minutes of moderate to vigorous physical activity is recom- mended on most days to maintain good health and fitness and for healthy weight during growth. Increasing physical activity can lower the body mass index of overweight children. â¢ During leisure time, it is advisable for all individuals to limit sedentary behaviors, such as television watching and video viewing, and replace them with activities that require more movement. DHHS and USDA (2005) Evidence-Based Physical Activity for School-Aged Youth School-aged youth should participate every day in 60 minutes of more of moderate to vigorous physical activity that is enjoyable and developmen- tally appropriate. Strong et al. (2005) National Association for Sports & Physical Education Guidelines for Toddlers and Preschoolers â¢ Toddlers should accumulate at least 30 minutes/day and preschoolers should accumulate at least 60 minutes/day of structured physical activity. â¢ Toddlers and preschoolers should engage in at least 60 minutes and up to several hours per day of daily, unstructured physical activity and should not be sedentary for more than 60 minutes at a time except when sleeping. NASPE (2006)
11 INTRODUCTORY SESSION Adults From the early 1970s to the early 1990s, physical activity recom- mendations for the U.S. population were embodied in an exercise pre- scription that specified at least 20 minutes/day of probably structured, vigorous (or what would be perceived as vigorous) exercise 3 to 5 days a week (Box 1-1). Exercise physiology research supported the view that activity performed in that way would produce improvements in physical fitness and in some other health parameters. Over that early period, the major change in ACSMâs guidance was a gradual decrease in the lower level of the recommended intensityâfrom quite an intense level of exer- cise (70 percent of the personâs heart rate range1) in 1975 to 40 percent of the personâs heart rate range beginning in 1991 (ACSM, 1975, 1991, 1995) (Box 1-1). In 1992, the American Heart Association (AHA) took an important action by declaring that physical inactivity was a major risk factor for cardiovascular diseases (CVD) (AHA, 1992). Many investigators recog- nized an inconsistency between the recommendation that physical activ- ity should be performed and structured in vigorous ways and the evidence in the epidemiological literature, which suggested that there might be many different ways to produce important health benefits through physical activity. Subsequently, the Centers for Disease Control and Prevention (CDC) and ACSM developed and jointly released the recommendation that every U.S. adult should accumulate 30 minutes or more of moderate- intensity physical activity on most or preferably all days of the week (Pate et al., 1995). The novel elements in that guideline were its sanc- tioning of moderate-intensity physical activity and the concept that short bouts of activity could be accumulated by individuals throughout the day. The core guidance provided in Physical Activity and Health: A Re- port of the Surgeon General (DHHS, 1996) and by a National Institutes of Health consensus conference (NIH, 1995; NIH Consensus Develop- ment Panel on Physical Activity and Cardiovascular Health, 1996) was essentially the same as the CDC and ACSM recommendation. Compared with earlier guidelines, one physical activity recommen- dation that was released by IOM (IOM, 2002/2005) called for a longer duration (60 minutes) of moderate-intensity physical activity daily, in 1 The heart rate range refers to the difference between the resting and maximal heart rate. For a young adult, for example, the heart rate range typically would be about 130 beats per minute (the difference between 70 and 200 beats per minute).
12 PHYSICAL ACTIVITY WORKSHOP addition to the activities required by a sedentary lifestyle, to prevent weight gain, as well as to accrue additional weight-independent health benefits of physical activity. The recommendations introduced in the Dietary Guidelines for Americans 2005 (DHHS and USDA, 2005) were related but somewhat different from the recommendations in the IOM report. Over the 30 years since the release of the 1975 ACSM exercise recommendation, many people have appeared resistant to accepting the newer physical activity recommendations. Children and Youth The effort to develop physical activity guidelines specifically for young people began in the mid-1990s (Box 1-1). The San Diego Consen- sus Physical Activity Guidelines for Adolescents (Sallis and Patrick, 1994) and the Health Education Authority Recommendations (Cavill et al., 2001) were based on very limited data. In the publication by Strong and colleagues (2005), an expert panel conducted an extensive system- atic literature review on the evidence associating physical activity with health and other outcomes in children and youth. The panel recom- mended that school-age youth participate in 60 minutes or more of daily moderate to vigorous physical activity that is developmentally appropri- ate. The guidelines for children and youth that were included in the Die- tary Guidelines for Americans 2005 are consistent with Strong et al. (2005). A different expert group convened by the National Association for Sport & Physical Education (NASPE) developed the first physical activity guidelines for toddlers and preschoolers under the age of 5 years (NASPE, 2006) (Box 1-1). Current Adherence with Existing Guidelines The Behavioral Risk Factor Surveillance System (BRFSS) is the primary source of data that tracks the extent to which Americans are meeting established physical activity recommendations. The 2001 BRFSS determined the percentages of individuals who, by self-report, engaged either in 30 minutes per day of moderate-intensity activity on 5 or more days per week or in 20 minutes per day of vigorous-intensity activity on 3 or more days per week. The percentage of persons meeting the standard decreases from about 60 percent in the youngest group to
13 INTRODUCTORY SESSION less than 40 percent in the oldest group (Macera et al., 2005). Rates of physical activity vary by racial or ethnic background, sex, and age. Simi- lar data are available from the Youth Risk Behavior Surveillance System (YRBSS) (Eaton et al., 2006); however, Dr. Pate questioned how accu- rately YRBSS estimates the level of physical activity for children and youth. The application of accelerometry as an objective measure of physical activity is making it possible to track physical activity more accurately than by self-report. Figure 1-2, which is based on accelerometry data, shows the mean number of minutes of daily moderate to vigorous physi- cal activity, counting bouts lasting 10 minutes or more, for groups rang- ing in age from 6 years to older than 70 years. Clearly, most people are physically active for fewer than 30 minutes/day. 50 Males Females 40 Minutes per day 30 20 10 0 6 12 16 20 30 40 50 60 70 to + to to to to to to to 11 69 15 19 29 39 49 59 Age (years) FIGURE 1-2 Mean moderate to vigorous physical activity minutes per day obtained using accelerometry data from the National Health and Nutrition Ex- amination Survey, 2003â2004, and counting modified bouts of at least a 10- minute duration, by age group and sex. SOURCE: Richard Troiano, Ph.D., U.S. Department of Health and Human Ser- vices, Personal communication, October 13, 2006.
14 PHYSICAL ACTIVITY WORKSHOP Growth of the Knowledge Base Regarding Physical Activity and Health Dr. Pate used two quick methods to assess the growth of the knowl- edge base regarding physical activity and health. The first was to note the change in the number of citations of the 1995 CDC and ACSM physical activity recommendations by year. In both 2004 and 2005, the number peaked at 241 citations. The second method was to examine the results of PubMed searches that used the key terms health and exercise and health and physical activity to identify publications from 1980 through 2005. Figure 1-3 depicts the curvilinear growth in the number of published pa- pers on these topics over the past 25 years. 10,000 8,000 Number of publications 6,000 Search Terms: Health and exercise 4,000 Health and physical activity 2,000 0 1980- 1986- 1991- 1996- 2001- 1985 1990 1995 2000 2005 Years of publication FIGURE 1-3 Increase in publications identified by searching PubMed for health and exercise and health and physical activity for 5-year intervals from 1980 through 2005. NOTE: The search was conducted in 2006. SOURCE: Pate (2006).
15 INTRODUCTORY SESSION Concluding Remarks Dr. Pate emphasized that we are in a period of developing improved methods for measuring physical activity and that this issue would need to be addressed by an expert group developing physical activity guidelines for Americans. Regardless of the measurement method used, most demographic groups have low adherence to the current physical activity guidelines. Dr. Pate underscored the need for major public health initia- tives to promote physical activity. One such initiative would be the de- velopment of comprehensive physical activity guidelines for the American public. REFERENCES ACSM (American College of Sports Medicine). 1975. Guidelines for Graded Exercise Testing and Exercise Prescription. Philadelphia, PA: Lea & Febiger. ACSM. 1980. Guidelines for Graded Exercise Testing and Exercise Prescrip- tion. Philadelphia, PA: Lea & Febiger. ACSM. 1986. Guidelines for Graded Exercise Testing and Exercise Prescrip- tion. Philadelphia, PA: Lea & Febiger. ACSM. 1991. Guidelines for Graded Exercise Testing and Exercise Prescrip- tion. Philadelphia, PA: Lea & Febiger. ACSM. 1995. Guidelines for Graded Exercise Testing and Exercise Prescrip- tion. Philadelphia, PA: Lea & Febiger. ACSM. 2000. Guidelines for Graded Exercise Testing and Exercise Prescrip- tion. Philadelphia, PA: Lea & Febiger. AHA (American Heart Association). 1992. Statement on exercise. Benefits and recommendations for physical activity programs for all Americans: A state- ment for health professionals by the Committee on Exercise and Cardiac Re- habilitation of the Council on Clinical Cardiology, American Heart Association. Circulation 86(1):340â344. Cavill N, Biddle S, Sallis JF. 2001. Health enhancing physical activity for young people: Statement of the United Kingdom Expert Consensus Conference. Ped Exerc Sci 13:12â25. DHHS (U.S. Department of Health and Human Services). 1996. Physical Activ- ity and Health: A Report of the Surgeon General. Office of the Surgeon Gen- eral, Atlanta, GA: Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion. [Online]. Available: http://www.cdc.gov/nccdphp/sgr/pdf/sgrfull.pdf [accessed Novem- ber 14, 2006].
16 PHYSICAL ACTIVITY WORKSHOP DHHS and USDA (U.S. Department of Agriculture). 2005. Dietary Guidelines for Americans 2005. [Online]. Available: http://www.healthierus.gov/dietary guidelines [accessed November 14, 2006]. Eaton DK, Kann L, Kinchen S, Ross J, Hawkins J, Harris WA, Lowry R, McManus T, Chyen D, Shanklin S, Lim C, Grunbaum JA, Wechsler H. 2006. Youth risk behavior surveillanceâUnited States, 2005. MMWR 55(5):1â108. [Online]. Available: http://www.cdc.gov/mmwr/PDF/SS/SS5505.pdf [ac- cessed November 14, 2006]. Haskell WL. 2006. Research to Support Evidence-Informed Public Health Pol- icy. Opening Session. Workshop Purpose and Scope. Presentation at the Insti- tute of Medicine Workshop on Physical Activity Guidelines Development. Washington, DC. October 23. IOM (Institute of Medicine). 2002/2005. Dietary Reference Intakes: Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Ac- ids. Washington, DC: The National Academies Press. Macera CA, Ham SA, Yore MM, Jones DA, Ainsworth BE, Kimsey CD, Kohl HW. 2005. Prevalence of physical activity in the United States: Behavioral Risk Factor Surveillance System, 2001. Prev Chronic Dis 2(2):A17. NASPE (National Association for Sport & Physical Education) and AHA (American Heart Association). 2006. 2006 Shape of the Nation Report. [Online]. Available: http://www.aahperd.org/naspe/ShapeOfTheNation/ [ac- cessed November 14, 2006]. NIH (National Institutes of Health). 1995. Consensus development conference statement on physical activity and cardiovascular health. J Am Med Assoc 13(3):1â33. NIH Consensus Development Panel on Physical Activity and Cardiovascular Health. 1996. Physical activity and cardiovascular health. J Am Med Assoc 276(3):241â246. Pate RR. 2006. The Evolution of Public Health Guidelines on Physical Activity. Presentation at the Institute of Medicine Workshop on Physical Activity Guidelines Development. Washington, DC. October 23. Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchner D, Ettinger W, Heath GW, King AC, Kriska A, Leon AS, Marcus BH, Morris J, Paffenbarger RS Jr, Patrick K, Pollock ML, Rippe JM, Sallis J, Wilmore JH. 1995. Physical activity and public health. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. J Am Med Assoc 273(5):402â407. Sallis JF, Patrick K. 1994. Physical activity guidelines for adolescents: Consen- sus statement. Ped Exerc Sci 6:302â314. Strong WB, Malina RM, Blimkie CJ, Daniels SR, Dishman RK, Gutin B, Her- genroeder AC, Must A, Nixon PA, Pivarnik JM, Rowland T, Trost S, Trudeau F. 2005. Evidence based physical activity for school-age youth. J Pediatr 146(6):732â737.