PURPOSE: To test the hypothesis that in males aged 65 to 75 yr when the total amount of work completed is similar in endurance training three times per week for 12 wk at either 50% or 70% peak oxygen uptake (VO2peak), there will be no significant difference in time course and amplitude of selected responses. METHODS: Subjects were randomly assigned to three groups: 70% VO2peak, N = 19; 50% VO2peak, N = 16; or control group, N = 19. Subjects underwent a maximal cycle exercise test and blood volume (Evans Blue) determination at 0, 4, 8, and 12 wk. A submaximal exercise test (50 W) was conducted at weeks 0 and 12 where cardiac output was determined. The exercise groups maintained the same exercise relative intensity throughout the 12 wk and completed a similar total amount of work. RESULTS: There were significant and similar increases in peak VO2, power and heart rate (HR) for both exercise groups. Linear models best described the time course for peak power and HR in both exercise groups. In the 70% VO2peak group, a quadratic model for VO2 and a linear model for VE were the best fit. There were no significant changes in blood or plasma volume for any groups over the 12 wk. Significant increases in stroke volume and significant decreases in HR at 50 W were found in both exercise groups after training. CONCLUSION: Moderate-intensity cycle exercise (50% VO2peak) to achieve 180 to 200 kJ per session, three times a week for 12 wk is a safe and effective stimulus for healthy asymptomatic men aged 65 to 75 yr to improve functional capacity in a primarily linear manner.

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