Maximal oxygen uptake is achieved in hypoxia but not normoxia during an exhaustive severe intensity run

Highly aerobically trained individuals are unable to achieve maximal oxygen uptake (V̇O_2max) during exhaustive running lasting ~2 min, instead V̇O₂ plateaus below V̇O_2max after ~1 min. Hypoxia offers the opportunity to study the (V̇O₂) response to an exhaustive run relative to a hypoxia induced reduction in V̇O_2max. The aim of this study was to explore whether there is a difference in the percentage of V̇O_2max achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic V̇O_2max 67.0 ± 5.2 ml.kg⁻¹.min⁻¹) completed exhaustive treadmill ramp tests and constant work rate (CWR) tests in normoxia and hypoxia (F_iO₂ 0.13). The V̇O₂ data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR V̇O₂ was less than normoxic V̇O_2max (86 ± 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic V̇O_2max was achieved (102 ± 8% ramp, P = 0.490). The phase II time constant was greater in hypoxia (12.7 ± 2.8 s) relative to normoxia (10.4 ± 2.6 s) (P = 0.029). The results demonstrate that highly aerobically trained individuals cannot achieve V̇O_2max during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower V̇O_2max in hypoxia despite a slightly slower V̇O₂ response.