Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans
- 29 December 2010
- journal article
- research article
- Published by Springer Science and Business Media LLC in European Journal of Applied Physiology
- Vol. 111 (7), 1517-1527
- https://doi.org/10.1007/s00421-010-1786-y
Abstract
\( \dot{V}{\text{O}}_{2} \) , \( \dot{Q} \) and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%VT) and at 120% of \( \dot{V}{\text{O}}_{2\max } \) (120%Wmax). An innovative approach was applied to calculate the time constant (τ2) of the primary phase of \( \dot{V}{\text{O}}_{2} \) and \( \dot{Q} \) kinetics at 120%Wmax. Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, \( \dot{V}{\text{O}}_{2} \) , \( \mathop Q\limits^{ \cdot } \) and HHb data were fitted with traditional exponential models. τ2 of \( \dot{V}{\text{O}}_{2} \) kinetics was longer (62.5 ± 20.9 s) at 120%Wmax than at 80%VT (27.8 ± 10.4 s). The τ2 of \( \dot{Q} \) kinetics was unaffected by exercise intensity and, at 120% of \( \dot{V}{\text{O}}_{2\max } , \) it was significantly faster (τ2 = 35.7 ± 28.4 s) than that of \( \dot{V}{\text{O}}_{2} \) response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%Wmax than at 80%VT (8.5 ± 2.6 s) suggesting a larger mismatch between O2 uptake and delivery at 120%Wmax. These results suggest that \( \dot{V}{\text{O}}_{2} \) at the onset of exercise is not regulated/limited by muscle’s O2 utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of \( \dot{V}{\text{O}}_{2} \) kinetics observed during supramaximal exercise.
Keywords
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