Peripheral Fatigue and Recovery Effects of Mild Hyperbaric Oxygen Therapy Following Exhaustive Exercise in Hot and Humid Conditions

Objective: To investigate the effects of a hot and humid environment on peripheral fatigue following incremental exercise to exhaustion in endurance athletes and to further evaluate the effects of mild hyperbaric oxygen therapy (mHBT) on post-exercise recovery under hot and humid versus temperate environmental conditions. Methods: Eighteen endurance athletes were recruited for a randomized incomplete crossover trial with a 2 (environment: hot and humid vs. temperate) × 2 (recovery modality: mHBT vs. passive recovery PR) factorial design. Each participant randomly completed two out of the four test protocols, with nine participants assigned to each protocol. Participants performed incremental exercise to exhaustion under either hot and humid or temperate conditions, followed by either mHBT or PR. Subjective fatigue ratings, core temperature, blood biomarkers of inflammation and oxidative stress were sampled, and neuromuscular function was assessed via countermovement jump (CMJ) tests before exercise, immediately after exercise, and after recovery. Results: Regarding the environmental effects, time to exhaustion was shorter and core temperature was higher during exercise in the hot and humid environment than under temperate conditions (P<0.05). Regarding the recovery effects, malondialdehyde (MDA) levels increased after PR compared with pre-exercise values (P<0.05), whereas no significant increase was observed after mHBT (P>0.05). Under hot and humid conditions, glutathione peroxidase (GSH-Px) levels were lower following PR than following mHBT (P<0.05). Creatine kinase (CK) and lactate dehydrogenase (LDH) levels were elevated after recovery compared with pre-exercise values (P<0.05). Conclusion: A hot and humid environment shortens the time to exhaustion during incremental exercise and increases core temperature, suggesting that greater thermal strain contributes to the accelerated development of exercise-induced fatigue. Within the short-term recovery period examined, biomarkers of oxidative stress, inflammation, and skeletal muscle damage predominantly reflected exercise-induced responses, with no consistent evidence of additional exacerbation attributable specifically to the hot and humid environment. A single session of mHBT may partially attenuate the post-exercise increase in MDA, suggesting a potential role in mitigating exercise-induced lipid peroxidation. However, its immediate effects on CMJ-derived neuromuscular function, inflammatory responses, and biomarkers of skeletal muscle damage appear to be limited.