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 (VO2max) during exhaustive running lasting similar to 2 min, instead VO2 plateaus below VO2max after similar to 1 min. Hypoxia offers the opportunity to study the (VO2) response to an exhaustive run relative to a hypoxia induced reduction in VO2max. The aim of this study was to explore whether there is a difference in the percentage of VO2max achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic VO2max 67.0 +/- 5.2 ml.kg(-1).min(-1)) completed exhaustive treadmill ramp tests and constant work rate (CWR) tests in normoxia and hypoxia (FO2 0.13). The VO2 data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR VO2 was less than normoxic VO2max (86 +/- 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic VO2max 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 VO2max during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower VO2max in hypoxia despite a slightly slower VO2 response.