Abstract
AIMS: The kinetics of recovery-period oxygen uptake (VO(2) ) are affected by the O(2) deficit generated during exercise. However, studies using ramp tests (RTs) and constant work rate tests (CT) have differently characterized VO(2) responses to increased exercise intensity differently. We used these two types of loading patterns to investigate the effects of low-intensity, medium-intensity, and high-intensity exercises on the half time (T(1/2) ) of recovery-period VO(2) and the mechanism. METHODS AND RESULTS: Ten healthy men aged 21.2 ± 0.9 years underwent symptom-limited cardiopulmonary exercise tests with the ramp protocol to determine their anaerobic threshold. All subjects subsequently underwent three submaximal RT and CT at low, moderate, and high intensities. In all RTs, subjects began exercise by warming up (20 W). In CT, T(1/2) was significantly lengthened as exercise intensity increased (CT-low: 34.0 ± 3.9 s, CT-moderate: 39.5 ± 3.5 s, CT-high:44.6 ± 4.2 s; P < 0.01, ANOVA), whereas no significant change was observed in RT, which began with the same work rate (RT-low: 46.0 ± 5.7 s, RT-moderate: 45.7 ± 4.8 s, RT-high: 44.6 ± 3.5 s, RT-max: 44.8 ± 3.2 s; P = 0.868, ANOVA). Only high-intensity exercise resulted in two components (the fast and slow components) of VO(2) decay, reflecting the increased O(2) deficit by anaerobic metabolism. CONCLUSIONS: The exercise intensity at the beginning of an exercise affects early recovery-period VO(2) , which is a fast component. The T(1/2) of recovery-period VO(2) occurs during the fast component, and an increase in O(2) deficit affects both the fast and slow components, lengthening the T(1/2) . The T(1/2) of recovery-period VO(2) in CT at moderate or high intensities, even if not symptom limited, can be used to evaluate exercise intolerance and early occurrence of anaerobic metabolism. Submaximal exercise tests may be considered as convenient methods for evaluating exercise tolerance in patients with cardiac failure.