EFFECTS OF PHYSICAL TRAINING BY RUNNING OR SWIMMING ON VENTRICULAR PERFORMANCE OF RAT HEARTS

Male rats were conditioned by swimming (Sw) or running (R) programs of 8-10 wk in duration at intensities estimated to be similar in the two groups. Resting heart rates and body weights were less (P < 0.01) in Sw and R than in age-matched sedentary controls (Sd). Hearts were studied in an isolated working heart apparatus at similar heart rates and aortic pressures, and over a range of 5-10 cmH2O atrial filling pressure (AP). Both groups of conditioned hearts showed greater pump performance compared with Sd as evidenced by increased stroke volume, stroke work, and maximum power. In addition, at similar end-diastolic volumes, Sw and R had significantly increased (P < 0.01) ejection fractions and extents and velocities of circumferential fiber shortening. Thus, the enhanced pump performance in both sets of conditioned hearts could be explained by improved myocardial contractile function. The differences between hearts from conditioned and Sd animals became more pronounced as AP dP/dt tended to be greater in Sw than either R or Sd. Maximal negative dP/dt was greater (P < 0.05) in Sw than Sd but was similar in R and Sd. These results indicate that chronic swimming and running programs lead to enhanced contractile performance of the left ventricle. The trend for Sw to develop greater pressures and have faster rates of relaxation than R suggests that adaptations to swimming and running may be qualitatively different.