Effects of chronic exercise on cardiac output and its determinants

A protocol which combines the noninvasive measurement of cardiac output (Q), systolic time intervals (STIs), and blood pressure was used to evaluate the effects of jogging on cardiac function. Studies were conducted during levels of steady-state cycle ergometer exercise which represented approximately 35, 55, and 75% of aerobic capacity. Subjects were 15 healthy men (mean age = 37.2 years) and 13 healthy controls. Predicted aerobic capacity (pred VO2max) increased 15 and 17% in the training group after 3 and 6 months of training; the control group displayed a small detraining effect. Changes in the training group versus control group included significant increases in exercise Q, stroke volume (SV), mean systolic ejection rate (MSER), and systolic blood pressure (SBP). Changes in STIs were small and usually nonsignificant. The findings, considered in relation to echocardiographic measurements from the same subjects (L. A. Wolfe, D. A. Cunningham, P. A. Rechnitzer, and P. M. Nichol. 1979 J. Appl. Physiol. 47: 207-212.), suggested that changes in cardiac output were due to an increased preload, rather than a change in exercise heart rate, reduced afterload, enhanced contractile state, or myocardial enlargement.