Mechanisms of adaptations in cardiorespiratory fitness with exercise prescriptions differing in volume and intensity in middle-age men

Abstract

Background: To examine the mechanisms of adaptations in cardiorespiratory fitness with different dose of amount and intensity exercise training in middle-aged men. Methods: A total of 67 sedentary subjects aged 40-49 yr were assigned to participate for 12 weeks in a control group or in one of three exercise groups: 1) low volume/moderate intensity 2) low volume/vigorous intensity and 3) high volume/vigorous intensity. They were tested for VO2max, cardiac output (Q) and stroke volume (SV) before and after training and maximal arterial-venous oxygen difference (a-vO2diff) calculated by the Fick Equation. Results: Contrasted to control group, VO2max increased similar in both LVVI and HVVI groups after 12 weeks; It indicated that the intensity of exercise appears to make a greater benefit than the amount of exercise on VO2max. However, Maximal cardiac output (Qmax) and a-vO2diff contributed to increase VO2max were differences in both of vigorous intensity groups. In LVVI group, Qmax together with maximal a-vO2diff contributed to the greater VO2max; in HVVI group, the majority of the increment in VO2max was relied on larger Qmax whereas a widened a-vO2diff. Conclusion: It is appropriate to recommend vigorous intensity exercise to improve cardiorespiratory fitness and encourage higher amount to confer additional benefit for Qmax.