Influence of hypoxia on the power-duration relationship during high-intensity exercise.

We investigated the influence of hypoxia on the asymptote (critical power, CP) and the curvature constant (W') of the hyperbolic power-duration relationship, as measured by both conventional and all-out testing procedures. 13 females completed 5 constant-power prediction trials and a 3-min all-out test to estimate CP and W', in both normoxia (N) and moderate hypoxia (H; FiO2=0.13). CP was significantly reduced in hypoxia compared to normoxia when estimated by conventional (H:132±17 vs. N:175±25 W; P<0.001) and all-out methods (H:134±23 vs. N:172±30 W; P<0.01). The W' was not significantly different in hypoxia compared to normoxia when established by conventional (H:12.3±2.7 vs. N:13.2±2.2 kJ) and all-out methods (H:12.0±2.6 vs. N:12.5±1.4 kJ). Estimates of CP and W' obtained with conventional and all-out methods were not significantly different either in normoxia or hypoxia. There was a significant relationship between the % change in CP relative to V̇(O2peak) and the % change in W' in normoxia compared to hypoxia (r=0.83, P<0.001; conventional test). Changes in the W' in hypoxia are related to changes in the CP relative to V̇(O2peak), suggesting that the W' may not be defined simply as an 'anaerobic' energy store.