How Much Physical Activity For Health?

It is clear that an unfit and sedentary way of life increases the risk of several chronic diseases and conditions, and that regular physical activity provides protection against these ailments. Regular activity reduces the risk of developing coronary heart disease, stroke, colon cancer, type 2 diabetes mellitus, obesity, and loss of functional capacity. Suggestive, but not yet compelling, evidence supports the hypothesis that activity also is inversely associated with risk of depression and other mental health issues, breast cancer, and possibly prostate and lung cancer. Most of the evidence on physical activity and health derive from prospective epidemiological investigations, although well controlled clinical trials and pathophysiological studies also provide data on the health benefits of regular physical activity. One important point is that studies on physical activity and health outcomes are likely to provide underestimates of the true effect of inactivity. This is because such studies must rely on crude and imprecise self-report of activity habits from study participants. The resulting misclassification leads to risk estimates that are lower than the true association. Some studies, such as the Aerobics Centre Longitudinal Study (ACLS), have objective measures of cardiorespiratory fitness as the exposure. Although there is a genetic component of cardiorespiratory fitness, its principal determinant is the individual’s physical activity pattern. The lower rate of misclassification in studies with cardiorespiratory fitness as the exposure leads to more accurate estimates of the true effect of a sedentary lifestyle. As a specific example, we reported a relative risk of 1.8 for the development of type 2 diabetes in sedentary men as compared with active men; whereas the relative risk for unfit men was 2.9 when compared with fit men. Our studies typically show that moderately fit women and men have about a 50% lower risk of many causes of morbidity or mortality than participants who are unfit. We further observe about a 10% additional lower risk in high fit participants as compared with their moderately fit counterparts.