Blair and Cooper's1 informative editorial raises important issues regarding the dose of exercise and health benefits. We agree that sedentary men and women may benefit from becoming moderately active but disagree on the shape of the dose-response curve between physical activity and its health benefits.2 We also interpret prospective epidemiological data, which show fewer deaths in men who improve their fitness over time, differently; Blair and Cooper believe the lower mortality is caused by increased physical activity, and I largely attribute the lower mortality to regression to the mean.
The editorial claims that cardiorespiratory fitness (treadmill test duration) is more accurate and objective than reported physical activity. The reproducibility I have observed of self-reported weekly running distance (r=0.89)3 is as strong as treadmill test duration from previous trials (r=0.89 in 30 sedentary men4 and r=0.62 in 83 sedentary overweight men5,6). I believe this amount of