Physical activity and health maintenance--exactly what is known?

Broad claims have been made regarding the health benefits of physical activity. In analyzing the data on which these claims are based, including those on the risks of exercise, 5 of 13 proposed health benefits were found to have strong support in the literature. For the remainder the evidence is less conclusive or equivocal. Data regarding the risks of exercise are similarly varied. Proponents of physical activity should evaluate the documentation of its benefits and risks so as not to dilute the power of their remedy with unsubstantiated claims.