Optimal degree of hypoxia combined with low-load resistance training for muscle strength and thickness in athletes

The benefit of resistance training under hypoxic conditions continues to draw considerable debate. This research explored the optimal degree of hypoxia combined with low-load resistance training which mimics the high-load traditional resistance training under normoxic condition. Thirty-seven male team sport athletes were divided into 3 resistance training groups; 1) normoxic high-load (NRT), 2) hypoxic low-load (HRT13.6, FiO₂ = 13.6%), and 3) hypoxic low-load (HRT15.8, FiO₂ = 15.8%). Training included 3 sets of 15 reps at either 80%1RM (high-load) or 50%1RM (low-load), 3 days per week. Muscle thickness (via ultrasonography) along with strength and muscular endurance were measured pre (1-2 days prior) and post (2-3 days post) a 5-week training period. Rectus femoris muscle thickness significantly increased in all groups, but was greater in the HRT13.6 group (18.3 ± 7.6%, mean ± SD) compared to the NRT group (9.1 ± 7.3%, p = 0.02). Similarly, muscle strength increased in all groups, but the HRT13.6 group showed a significantly larger improvement in isometric knee extension MVC (33.5 ± 12.7%) compared to the NRT group (19.8 ± 6.5%, p = 0.04). Finally, rectus femoris fat layer thickness was significantly reduced after training, particularly in the HRT13.6 group (-55.8 ± 5.5%) compared to NRT (-32.8 ± 9.6%, p = 0.01) and HRT15.8 groups (-38.2 ± 12.5%, p = 0.01). Low-load resistance training particularly in 13.6% oxygen, produced more muscle thickness, fat loss, and bigger strength gains compared to traditional high-load resistance training. This training strategy may be a useful alternative to traditional high-load resistance training