Relation of physical activity and cardiovascular fitness to coronary heart disease, Part II: Cardiovascular fitness and the safety and efficacy of physical activity prescription.

BACKGROUND This paper is the second of two reports that together review the scientific evidence regarding the inverse relation between physical activity and cardiovascular fitness and coronary heart disease (CHD). METHODS Using a MEDLINE search with the key words exercise, physical fitness, coronary heart disease, and cardiovascular disease, more than 75 articles were reviewed, evaluating study design, measurement error, bias and confounding, the strength of associations, consistency of results, temporal and dose-response relation, and biologic plausibility. RESULTS The relative risk in epidemiologic studies comparing the least to the most fit categories ranges from 1.2 to 4.8, which is greater than that for physical inactivity. The differences between cardiovascular fitness (an attribute) and physical activity (a behavior) are highlighted. The range of correlation (r = 0.02 to 0.44) between cardiovascular fitness and physical activity is discussed relative to measurement error and genetic and environmental factors. Studies reporting the safety of regular physical activity suggest an injury rate as high as 35 injuries per 100 persons per year. Efficacy studies limited to secondary prevention trials report a 66 percent compliance rate and 15 percent reduction in total mortality. CONCLUSIONS The scientific evidence implying a causal relation between cardiovascular fitness and CHD is strongly positive, but the clinical and public health implications are unclear. Further research and clinical guidelines are suggested.