Exercise and the primary prevention of cardiovascular disease.

Longitudinal population studies have consistently demonstrated an association between sedentary lifestyles and the incidence of coronary artery disease (CAD). Diverse lines of evidence from clinical and experimental studies further implicate physical inactivity as an important risk factor for CAD. The relation between physical inactivity and CAD appears to be curvilinear and independent of other major risk factors, but of lower magnitude. Several training-induced physiologic adaptations offer plausible mechanisms for the protective effects of physical activity. Extrapolation from available data indicates that exercise must be habitual, vigorous and continuous to provide protection from CAD. However, the observed association between inactivity and CAD could represent several hypotheses other than cause and effect. The need for an appropriately designed clinical trial is apparent, but such an endeavor is not feasible at present. Until more rigorous scientific data are available, judgment on the use of exercise in prevention of CAD must necessarily be based on the accumulation of evidence supporting the role of physical activity. The rationale for exercise in preventing the occurrence of CAD is reviewed.