This study examined the effects of hypoxia severity on peripheral versus central determinants of exercise performance. Eight cyclists performed constant-load exercise to exhaustion at various fractions of inspired O2 fraction. At task failure arterial hypoxaemia was surreptitiously reversed via acute O2 supplementation and subjects were encouraged to continue exercising. Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force as measured pre- versus post-exercise in response to supramaximal femoral nerve stimulation. The results showed that at task failure in normoxia and moderate hypoxia, hyperoxygenation had no significant effect on prolonging endurance time. However, following task failure in severe hypoxia, hyperoxygenation elicited a significant prolongation of time to exhaustion. Following further investigation the authors were able to conclude that across the range of normoxia to severe hypoxia, the major determinants of central motor output and exercise performance switches from a predominantly peripheral origin of fatigue to a hypoxia-sensitive central component of fatigue, probably involving brain hypoxic effects on effort perception.
Journal of Physiology, 2007, 581, 1, 389-404.