Effects of low-resistance/high-repetition strength training in hypoxia on muscle structure and gene expression

To test the hypothesis that severe hypoxia during low-resistance/high-repetition strength training promotes muscle hypertrophy, 19 untrained males were assigned randomly to 4 weeks of low-resistance/high-repetition knee extension exercise in either normoxia or in normobaric hypoxia ( FiO(2) 0.12) with recovery in normoxia. Before and after the training period, isokinetic strength tests were performed, muscle cross-sectional area (MCSA) measured (magnetic resonance imaging) and muscle biopsies taken. The significant increase in strength endurance capacity observed in both training groups was not matched by changes in MCSA, fibre type distribution or fibre cross-sectional area. RT-PCR revealed considerable inter-individual variations with no significant differences in the mRNA levels of hypoxia markers, glycolytic enzymes and myosin heavy chain isoforms. We found significant correlations, in the hypoxia group only, for those hypoxia marker and glycolytic enzyme mRNAs that have previously been linked to hypoxia-specific muscle adaptations. This is interpreted as a small, otherwise undetectable adaptation to the hypoxia training condition. In terms of strength parameters, there were, however, no indications that low-resistance/high-repetition training in severe hypoxia is superior to equivalent normoxic training.