V˙O2 ‘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 V˙O2 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 V˙O2 was assessed using non-linear regression and any overshoot in V˙O2 was quantified as the integrated volume (IV) of O2 consumed above the steady-state requirement. During cycling, an overshoot in V˙O2 was evident in all seven cyclists (IV = 136 ± 41 ml) and in four runners (IV = 81 ± 94 ml). During running, an overshoot in V˙O2 was evident in four runners (IV = 72 ± 61 ml) but no cyclists. These data challenge the notion that V˙O2 always rises towards a steady-state with near-exponential kinetics in this exercise intensity domain. The greater incidence of the V˙O2 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.