Effects of different oxygen concentrations during intermittent hyperoxic training on endurance capacity in...

While training under intermittent hyperoxia (INT) enhances endurance capacity, the effects of specific oxygen concentrations remain unclear. This study compared 50% O₂ (INT50) and 75% O₂ (INT75) in well-trained male mice, which had increased maximal work values by 7.7-fold through a 7-week voluntary running program, during a 4-week treadmill program. Results showed that INT75, but not INT50, significantly improved endurance capacity compared to the normoxic-trained (ET) group (Bayes factor, BF ≥3). The enhanced exercise capacity in the INT75 group was linked to higher levels of metabolic enzymes (citrate synthase, 3-hydroxyacyl-CoA-dehydrogenase, carnitine palmitoyl transferase-2, and phosphofructokinase) in the diaphragm and increased pyruvate dehydrogenase complex activity in the red gastrocnemius (Gr) and plantaris (PL) muscles (BF ≥3). Glutathione peroxidase-1 protein levels in the PL muscle were significantly lower in INT75 (vs ET, 0.76-fold, BF ≥3). Additionally, INT75 mice exhibited increased PGC1α levels in the left ventricle, despite decreased cytochrome-c oxidase activity. In contrast, the INT50 group showed a shift toward fast-twitch muscle fibers in the Gr. In conclusion, the ergogenic effects of intermittent hyperoxia depend on oxygen concentration. INT at 75% O₂ significantly enhances endurance capacity in well-trained mice by optimizing metabolic enzyme activity across skeletal and respiratory muscles.