Abstract
Introduction: Prolonged cycling exercise in normoxia (N) induces fatigue due to both peripheral and central alterations. Interestingly, it has been reported that cerebral perturbations are greater during short-duration isolated exercise in hypoxia (H) compared to N1. The purpose of this study was to test the hypothesis that central alterations are accentuated in H compared to N during prolonged whole-body exercise.
Methods: Ten subjects performed two sessions consisting of 3 80-min cycling bouts at 45% of their relative maximal aerobic power in N and H (FIO2 = 12%). Before exercise and after each bout, transcranial magnetic stimulation was used to assess corticospinal excitability (motor evoked potential; MEP) and intracortical inhibition (cortical silent period; CSP) of knee extensors. Femoral nerve electrical stimulation was used to measure muscle characteristics. Voluntary activation was also assessed with both types of stimulation.
Results: A significant but similar torque reduction was observed at the end of the exercise in N and H. With the exception of CSP, a significant time effect was observed for all parameters. CSP was longer and the reduction of twitch peak torque was lower in H than in N. No other significant differences were observed between N and H.
Discussion: Fatigue level was found to be similar between N and H when exercise is performed at the same relative intensity. Even if the brain is importantly affected by hypoxia2 as shown by the greater intracortical inhibition, this does not appear to further affect central motor drive.
References:
1 Goodall et al, J Appl Physiol 109: 1842–1851 (2010); 2 Verges et al. Am J Physiol Regul Integr Comp Physiol (In press).
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