‘Oxygen uptake efficiency slope’ in trained and untrained subjects exposed to hypoxia

We assessed the ability of the oxygen uptake efficiency slope, whether calculated on 100 and 80% of maximal exercise test duration (OUES100 and OUES80), to identify the change in cardiorespiratory capacities in response to hypoxia in subjects with a broad range of V˙O2 peak. Four maximal exercise tests were performed in trained (T) and untrained subjects (UT) in normoxia and at 1000, 2500 and 4500 m. The mean reductions in maximal exercise capacities at 4500 m were the same in T subjects for V˙O2 peak (−30%), OUES80 (−26%) and OUES100 (−26%) whereas in UT subjects only OUES100 (−14%), but not OUES80 (−20%), was lower compared with V˙O2 peak (−21%, p < 0.05). OUES100 and OUES80 were correlated with V˙O2 peak and the ventilatory anaerobic threshold in both groups. Multiple regression analyses showed that V˙O2 peak, OUES100 and OUES80 were significantly linked to O2 arterial-venous difference. The OUES80 could be considered as an interesting sub-maximal index of cardiorespiratory fitness in normal or hypoxemic subjects unable to reach V˙O2 peak.