Noninvasive assessment of seasonal variations in cardiac structure and function in cyclists.

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Abstract
Noninvasive studies were performed in 12 male bicyclists in the competitive season (CS) and in the resting season (RS), and in 12 matched control subjects to determine seasonal variations in cardiac structure and function in athletes, and to compare the data with those of nonathletes. In athletes, peak O2 uptake was 6% lower in the RS than the CS; the RS value was 40% higher than in nonathletes. The echocardiograms of athletes showed a higher left ventricular total diameter at end-diastole in the CS than in the RS; this difference was due to a greater septal and posterior wall thickness, with unchanged internal diameter. On the ECG, R-wave voltages were larger in the CS in leads I, V5 and V6. Athletes had greater left ventricular dimension and wall thickness than nonathletes, and their ratio of wall thickness to internal radius of the left ventricle was higher. Various echo- and mechanocardiographic indexes of left ventricular function were determined. During the RS, the athletes had a lower percent shortening and maximal velocity of left ventricular internal diameter, lower maximal and minimal velocities of the endocardium of the posterior wall, a longer preejection period and a larger ratio of preejection period to left ventricular ejection time. These findings are probably related to a greater left ventricular end-systolic stress, an index of myocardial afterload, in the RS. Apparently, cyclists in the CS, compared with nonathletes, have greater left ventricular internal dimension and increased wall thickness, with similar left ventricular function. During the RS, internal dimension does not change from the level in the CS, but wall thickness is somewhat reduced and left ventricular function is slightly depressed, most likely because of a higher afterload in RS.