Effects of Inhaled Oxygen Levels on Training Intensity and Subsequent Exercise Performance in Acute Hypoxia

Abstract

In many cases, athletes and soldiers must travel to high-altitude environments without adequate time for pre-acclimation. Many may utilize intermittent hypoxia training as part of their normal conditioning program in an attempt to be better prepared for vigorous tasks at altitude. While prolonged exposure to hypoxia has been shown to increase hemoglobin mass, absolute training intensity is reduced in hypoxia and may lead to peripheral detraining. Training in hyperoxia has been shown to increased absolute training load and may improve training response. PURPOSE: We sought to compare the effects of 3 weeks of high intensity interval training in hypoxia or hyperoxia on exercise performance in acute hypoxia. METHODS: Sixteen aerobically trained males (20 ± 2 yr, 72.6 ± 9.8 kg, 49.4 ± 7.4 mL-1 • kg-1 • min-1) completed a progressive exercise test to exhaustion in normoxia (PIO2 = 142 Torr) to determine VO2 max and ventilatory threshold (VT). Subjects were then matched by fitness but otherwise randomly assigned to either a hypoxic (HYPO) or hyperoxic (HYPER) training group. Each then completed a pre-training time trial test (TT) of 2 kJ · kg bm-1 as fast as possible in hypoxia (PIO2 = 88 Torr). Subjects then underwent 3 wks of 3x/wk interval training in hypoxia (PIO2 = 88 Torr) (HYPO) or hyperoxia (PIO2 = 400 Torr) (HYPER). Training consisted of 6 x 0.48 kJ · kg bm-1 efforts per session performed as quickly as possible. After the training period, subjects completed a second hypoxic TT. All exercise was performed on an electronically braked ergometer. Training intensity relative to normoxic VT, SaO2 during training sessions, and percent improvement hypoxic TT completion time were used as dependent variables. Data were analyzed using independent t-tests. RESULTS: HYPER subjects trained at a significantly higher percentage of their normoxic VT power output (103 ± 10%) compared to HYPO (85 ± 9%) (P = 0.002) and maintained significantly higher SaO2 (100 ± 1% HYPER, 83 ± 3%, P<0.001) during training. Mean improvement for the TT was significantly greater in HYPER (12 ± 6%) vs HYPO (6 ± 5%) (P=0.047). CONCLUSION: The results suggest that in comparison to training in hypoxia, performing identical training in hyperoxia results in superior exercise performance in acute hypoxia.