Purpose: The effects of hypoxic training on exercise performance remain controversial. Here we tested the hypotheses that i) hypoxic training possesses ergogenic effects at sea-level and altitude, and ii) the benefits are primarily mediated by improved mitochondrial function of skeletal muscle.
Methods: We determined aerobic performance (incremental test to exhaustion and time trial for a set amount of work) in moderately-trained subjects undergoing six weeks of endurance training (3-4 times/week, 60 min/session) in normoxia (placebo, n=8) or normobaric hypoxia (FIO2=0.15; n=9) using a double blind and randomized design. Exercise tests were performed in normoxia and acute hypoxia (FIO2=0.15). Skeletal muscle mitochondrial respiratory capacities and electron coupling efficiencies were measured via high-resolution respirometry. Total hemoglobin mass (Hbmass) was assessed by carbon-monoxide rebreathing.
Results: Skeletal muscle respiratory capacity was not altered by training or hypoxia, however electron coupling control respective to fat oxidation slightly diminished with hypoxic training. Hypoxic training did increase Hbmass more than placebo (8.4 vs 3.3%, p=0.02). In normoxia, hypoxic training had no additive effect on maximal measures of oxygen uptake (VO2peak) or time trial performance. In acute hypoxia, hypoxic training conferred no advantage on VO2peak, but tended to enhance time trial performance more than normoxic training (52 versus 32%, p=0.09).
Conclusion: Our data suggest that, in moderately-trained subjects, six weeks of hypoxic training possess no ergogenic effect at sea-level. It is not excluded that hypoxic training might facilitate endurance capacity at moderate altitude, however this issue is still open and needs to be further examined.
(C) 2014 American College of Sports Medicine