Adequacy of Evidence for Physical Activity Guidelines Development Workshop Summary (2007) / Chapter Skim
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4 Physical Activity and Risk--Maximizing Benefits
4 Physical Activity and Risk--Maximizing Benefits
Pages 73-94
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From page 73... ...
Both sections of the chapter include evidence regarding reduction of the risk. The discussion section provides an overview of risk–benefit considerations and of osteoarthritis and joint injuries in relation to physical activity, and it offers a brief summary of comments raised by the workshop participants.
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Factors Affecting the Risk of Injury The factors that affect the risk of physical activity-related injury include the amount and type of current physical activity, the amount of past physical activity, other health behaviors, physical fitness level, history of previous injury, selected demographic factors, and anatomical factors. Current Physical Activity Amount of physical activity The risk of injury increases as the distance run per week increases (Koplan et al., 1982)
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. For previously sedentary individuals exercising three days per week, a threshold for elevated injury risk appeared between about 30 and 45 minutes per day of running (Pollock et al., 1977)
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Physical Fitness Levels Health-related components of fitness include endurance, muscle endurance, muscle strength, flexibility, and body composition (Caspersen et al., 1985)
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• Body composition has inconsistent associations with injury risk (Hootman et al., 2001; Jones et al., 1992, 1993a; Macera et al., 1989; Reynolds et al., 1994; Taunton et al., 2003)
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Sex During army basic training where male and female trainees do the same physical training, females are at 1.6 to 2.1 times greater risk for injury than males (Bell et al., 2000; Bensel et al., 1983; Canham et al., 1998; Jones et al., 1992; Knapik et al., 2003; Kowal, 1980)
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Because the overall effect of exercise on cardiovascular health reflects a potential balance of benefits and risks, the presentation included a review of evidence regarding the magnitude of risk, factors that modify risk, data on the balance of the risks and benefits, and implications for public health and for clinical care. Magnitude of the Problem About 10 to 15 percent of all deaths from coronary heart disease are due to sudden cardiac arrest.
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showed that there was a 9-fold increase in the risk of having a sudden cardiac arrest during vigorous exercise compared to other times and a 3.2-fold increase in risk during nonvigorous exercise. To examine the risks of the exercise in relation to the potential benefits of physical activity, Siscovick and colleagues (1984)
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The relative risk of sudden cardiac arrest during vigorous exercise compared to other times is much higher in men younger than 45 years than in older men because the absolute risk of sudden cardiac arrest that occurs during inactivity is very low in younger men. Habitual physical activity The data in Table 4-2 indicate that the magnitude of the transient increase in risk during exercise was influenced by the level of habitual vigorous exercise.
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As with the investigators above who examined increases in the risk of sudden cardiac arrest, Mittleman and colleagues (1993) found that the relative risk of nonfatal myocardial infarction for heavy exertion decreased dramatically with increased frequency of regular physical exertion, reported as numbers of bouts per week.
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Specifically, some investigators define events within 30 to 60 minutes of a bout of exertion as "during exertion." In addition, most studies have only a small number of events during exertion. In general, there is a lack of detail about prior habitual activity and the presence of prior heart disease and coronary risk factors, and current data are not yet sufficient to predict cardiac events during exertion.
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Using unadjusted data, Hootman and colleagues found that people who meet the Surgeon General's physical activity recommendation (defined as 1,000 kcal or more of physical activity-related energy expenditure per week) have a risk of injury that is about 77 percent higher than that of inactive people (zero energy expenditure from physical activity per week)
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• Maintain a normal body weight. Although it is not known if weight loss reduces the risk of injury, it improves biomechanics.
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Data are unclear regarding whether there is an association between running and OA, but moderate levels of running or of other aerobic exercise do not appear to cause OA (Konradsen et al., 1990; White et al., 1993)
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Risk factors for coronary heart disease are likely to increase the risk of sudden cardiac death both during activity and during inactivity. For persons with previously ex pressed cardiovascular disease, a supervised setting for exercise is beneficial.
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2000. High injury rates among female army trainees: A function of gender?
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1988. Prevention of lower extremity stress fractures: A controlled trial of a shock absorbent insole.
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2004b. Evaluation of Two Army Fitness Programs: The TRADOC Standardized Physical Training Pro gram for Basic Combat Training and the Fitness Assessment Program.
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Med Sci Sports Exerc 18(4)
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Med Sci Sports Exerc 36(3)
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2006. Physical exertion, exercise, and sudden cardiac death in women.
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