Effects of hyperbaric environment on endurance and metabolism are exposure time-dependent in well-trained mice

Hyperbaric exposure (1.3 atmospheres absolute with 20.9% O 2 ) for 1 h a day was shown to improve exercise capacity. The present study was designed to reveal whether the daily exposure time affects exercise performance and metabolism in skeletal and cardiac muscles. Male mice in the training group were housed in a cage with a wheel activity device for 7 weeks from 5 weeks old. Trained mice were then subjected to hybrid training (HT, endurance exercise for 30 min followed by sprint interval exercise for 30 min). Hyperbaric exposure was applied following daily HT for 15 min (15HT), 30 min (30HT), or 60 min (60HT) for 4 weeks (each group, n = 10). In the endurance capacity test, maximal work values were significantly increased by 30HT and 60HT. In the left ventricle (LV), activity levels of 3-hydroxyacyl-CoA-dehydrogenase, citrate synthase, and carnitine palmitoyl transferase (CPT) 2 were significantly increased by 60HT. CPT2 activity levels were markedly increased by 60HT in the plantaris muscle (PL). Pyruvate dehydrogenase complex (PDHc) activity values in PL were enhanced more by 30HT and 60HT than by HT. In both 30HT and 60HT groups, lactate dehydrogenase activity levels were significantly increased and decreased, respectively, in the gastrocnemius muscle and LV. These results indicate that hyperbaric exposure for 30 min or longer has beneficial effects on endurance, and 60-min exposure has the potential to further increase performance by facilitating fatty acid metabolism in skeletal and cardiac muscles in highly-trained mice.