Physical activity levels and XXXX . Analysis of epidemiologic and supporting studies.

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@entity301 , the primary health problem in western life, is caused by the interaction of multiple factors. Absolute proof of the contributing role of physical inactivity is not possible owing to the complexity of the CHD problem and the infeasibility of a definitive clinical trial because of logistical and economic constraints. Despite limitations, existing epidemiologic studies strongly suggest, but fall short of proving, the concept that habitual physical exercise offers partial protection against primary or secondary events of CHD and associated mortality. However, experimental data support this hypothesis and provide evidence of possible mechanisms responsible for the protection. The available epidemiologic data also suggest that physical inactivity is probably not as potent an individual risk factor as elevated serum @entity165 levels, @entity101 , and cigarette smoking, and that the protective effects of exercise may be overwhelmed by high levels of these major risk factors. On the other hand, there is some evidence that exercise may attenuate other risk factors both directly and through associated weight reduction. Epidemiologic studies also suggest a dose response relationship between physical activity and rates of CHD. About 2000 kcal per week of moderate intensity, dynamic, endurance-type of exercise (such as walking or jogging about 20 miles per week) or at least one hour of intermittent hard physical labor are required to obtain the optimal effect of exercise on @entity301 rates. Experimental studies suggest that this amount of exercise should provide sufficient stimulus to favorably alter blood HDL @entity165 levels and perhaps other CHD risk factors, especially if there is an accompanying reduction in weight. Possible mechanisms for the protective effects of exercise against CHD are illustrated in Figure 1. Insistence on final experimental proof prior to prudent medical practice or public health policy on physical inactivity or other coronary risk factors indicates a lack of understanding of the nature of scientific proof and evidence required for health actions.(ABSTRACT TRUNCATED AT 400 WORDS)
