Prescribing Exercise at Varied Levels of Intensity and Frequency

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Abstract
The health benefits of engaging in regular physical activity have been well established.1-5 However, most US adults are not sufficiently active regularly, and 26% are not active at all.6 Guidelines recommended by the American Heart Association,7 the Centers for Disease Control and Prevention/American College of Sports Medicine,8 and the US Surgeon General9 suggest that the accumulation of 30 minutes of moderate-intensity (ModI) physical activity on most days of the week will produce significant health benefits. The reports supporting these guidelines also describe a dose-response relationship between physical activity and health outcomes. Moderate-intensity (45%-60% of heart rate reserve [HRres]) activities completed on as few as 3 d/wk may produce observable changes in disease risk factors, and greater benefits generally accrue from engaging in exercise of greater intensity or volume.7-9 Indeed, recent analyses10,11 of the dose-response issue affirm an inverse and generally linear relationship between physical activity and cardiovascular disease (CVD)–related morbidity and mortality. However, because of the large variability in adherence that occurs when individuals are advised to perform unsupervised exercise in their natural environments, the exercise prescription required to produce beneficial changes in CVD risk factors among free-living sedentary adults requires further research.12