Usefulness of cardiorespiratory fitness to predict coronary heart disease risk independent of physical activity.

Cardiorespiratory fitness has often been interpreted as a surrogate measurement of physical activity rather than an independent coronary heart disease (CHD) risk factor per se. Fitness is also known to be highly heritable, however, and rats bred selectively for treadmill endurance have low CHD risk phenotypes even in the absence of physical activity. Therefore, I assessed whether cardiorespiratory fitness predicted CHD independent of physical activity in 29,721 men followed prospectively for 7.7 years as part of the National Runners' Health Study. Specifically, CHD deaths and incident participant-reported physician-diagnosed myocardial infarction, revascularization procedures (coronary artery bypass grafting and percutaneous coronary intervention), and angina pectoris during follow-up were compared to baseline cardiorespiratory fitness (10-km footrace performance, meters/second). Nonfatal end points for the 80% of these men who provided follow-up questionnaires included 121 nonfatal myocardial infarctions, 317 revascularization procedures, and 81 angina pectora. The National Death Index identified 44 CHD deaths. Per meter/second increment in baseline fitness, men's risks decreased 54% for nonfatal myocardial infarction (p <0.0001), 44% for combined CHD deaths and nonfatal myocardial infarction (p = 0.0003), 53% for angina pectoris (p = 0.001), and 32% for revascularizations (p = 0.002). Adjustment for physical activity (kilometer/day run) had little effect on the per meter/second risk decreases for nonfatal myocardial infarction (from 64% to 63%), combined CHD deaths and nonfatal myocardial infarction (from 34% to 33%), angina pectoris (from 53% to 47%) or revascularizations (from 32% to 26%). In conclusion, the results suggest that cardiorespiratory fitness is a CHD risk factor, largely independent of physical activity, which warrants clinical screening.