Cardiovascular adaptations to 10 days of cycle exercise.

We hypothesized that 10 days of training would enhance cardiac output (CO) and stroke volume (SV) during peak exercise and increase the inotropic response to beta-adrenergic stimulation. Ten subjects [age 26 +/- 2 (SE) yr] trained on a cycle ergometer for 10 days. At peak exercise, training increased O2 uptake, CO, and SV (P < 0.001). Left ventricular (LV) size and function at rest were assessed with two-dimensional echocardiography before (baseline) and after atropine injection (1.0 mg) and during four graded doses of dobutamine. LV end-diastolic diameter increased with training (P < 0.02), whereas LV wall thickness was unchanged. LV contractile performance was assessed by relating fractional shortening (FS) to the estimated end-systolic wall stress (sigmaES). Training increased the slope of the FS-sigmaES relationship (P < 0.05), indicating enhanced systolic function. The increase in slope correlated with increases in CO (r = -0.71, P < 0.05) and SV (r = -0.70, P < 0.05). The increase in blood volume also correlated with increases in CO (r = 0.80, P < 0.01) and SV (r = 0.85, P < 0.004). These data show that 10 days of training enhance the inotropic response to beta-adrenergic stimulation, associated with increases in CO and SV during peak exercise.