LEFT-VENTRICULAR FUNCTION IN ENDURANCE RUNNERS DURING EXERCISE

Left ventricular function in elite runners and controls was compared b y means of nuclear angiocardiography. Fifteen middle- or long-distance runners and a control group of 19 sedentary to moderately physically active subjects were studied at rest and during semi-sitting increment al exercise. Ejection fraction was higher in the runners than the cont rols both at rest and during exercise. At the transition from rest to exercise left ventricular end-diastolic volume initially increased sim ilarly in runners and controls by an average of 14 and 12%, respective ly, with an increase in stroke volume by approximate to 25 and 23%. Th e parallel increase in stroke volume and left ventricular end-diastoli c volume could a least partly be because of the Frank-Starling mechani sm. With increasing workloads. left ventricular end-diastolic volume a nd ejection fraction remained fairly constant, resulting in an unchang ed stroke volume from the lowest to the highest exercise intensity. Th is was in the runners accomplished by a 41% increase in peak filling r ate and a 38% increase in peak emptying rate with similar changes obse rved in the controls. This has to be due to increased myocardial contr actility paralleling the systolic shortening with increasing heart rat e. We conclude that endurance-trained athletes have a better systolic function expressed as higher ejection fraction both at rest and during exercise than untrained subjects reflecting an enhanced myocardial co ntractility contributing to the maintenance of a large stroke volume d uring exercise. The regulatory mechanisms however, appear to be simila r for athletes and healthy controls.