Vo2 'overshoot' during moderate-intensity exercise in endurance-trained athletes:: The influence of exercise modality

The purpose of this study was to investigate the influence of exercise modality on the 'overshoot' in VO2 that has been reported following the onset of moderate-intensity (below the gas exchange threshold, GET) exercise in endurance athletes. Seven trained endurance cyclists and seven trained endurance runners completed six square-wave transitions to a work-rate or running speed requiring 80% of mode-specific GET during both cycle and treadmill running exercise. The kinetics of VO2 was assessed using non-linear regression and any overshoot in VO2 was quantified as the integrated volume (IV) Of O-2 Consumed above the steady-state requirement. During cycling, an overshoot in VO2 was evident in all seven cyclists (IV = 136 +/- 41 ml) and in four runners (IV = 81 +/- 94 ml). During running, an overshoot in VO2 was evident in four runners (IV = 72 +/- 61 ml) but no cyclists. These data challenge the notion that VO2 always rises towards a steady-state with near-exponential kinetics in this exercise intensity domain. The greater incidence of the VO2 overshoot during cycling (11/14 subjects) compared to running (4/14 subjects) indicates that the overshoot phenomenon is related to an interaction between high levels of aerobic fitness and exercise modality. We speculate that a transient loss in muscle efficiency as a consequence of a non-constant ATP requirement following the onset of constant-work-rate exercise or an initially excessive recruitment of motor units (relative to the work-rate) might contribute to the overshoot phenomenon. (c) 2007 Elsevier B.V.. All rights reserved.