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 ([Formula: see text]) during exhaustive running lasting ~2 min, instead [Formula: see text] plateaus below [Formula: see text] after ~1 min. Hypoxia offers the opportunity to study the ([Formula: see text]) response to an exhaustive run relative to a hypoxia induced reduction in [Formula: see text]. The aim of this study was to explore whether there is a difference in the percentage of [Formula: see text] achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic [Formula: see text] 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(i)O(2) 0.13). The [Formula: see text] data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR [Formula: see text] was less than normoxic [Formula: see text] (86 ± 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic [Formula: see text] 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 [Formula: see text] during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower [Formula: see text] in hypoxia despite a slightly slower [Formula: see text] response.