To the Editor.
—The article entitled "Leisure-Time Physical Activity Levels and Risk of Coronary Heart Disease and Death" from the Multiple Risk Factor Intervention Trial1 raises important issues. The "treatment effect" of a higher level of physical activity seems to be well supported by the data.However, prior studies have shown that physical activity that is heavy enough to produce a training effect results in an increase in left ventricular mass and a reduction of resting pulse rates. In individuals with normal coronary blood flow, these factors should be offsetting. In those with a high risk of developing a coronary event, blood flow might not be adequate for an increase in left ventricular mass.Was the level of physical activity as estimated in this trial in the high-activity group sufficient to produce a training effect and therefore to potentially increase left ventricular mass? Were any measurements taken that might
Haywood LJ. Activity and Risk of Coronary Heart Disease. JAMA. 1988;259(9):1328. doi:10.1001/jama.1988.03720090020021