Endocrine and Metabolic Responses to Endurance Exercise Under Hot and Hypoxic Conditions

Abstract

Purpose: We explored the effect of heat stress during an acute endurance exercise session in hypoxia on endocrine and metabolic responses. Methods: A total of 12 healthy males cycled at a constant workload (60% of the power output associated with their maximal oxygen uptake under each respective condition) for 60 min in three different environments: exercise under hot and hypoxia (H+H; fraction of inspiratory oxygen or FiO 2 : 14.5%, 32 • C), exercise under hypoxia (HYP; FiO 2 : 14.5%, 23 • C), and exercise under normoxia (NOR; FiO 2 : 20.9%, 23 • C). After completing the exercise, participants remained in the chamber for 3 h to evaluate metabolic and endocrine responses under each environment. Changes in muscle oxygenation (only during exercise), blood variables, arterial oxygen saturation, and muscle temperature were determined up to 3 h after exercise. Results: Serum erythropoietin (EPO) level was increased to similar levels in both H+H and HYP at 3 h after exercise compared with before exercise (P < 0.05), whereas no significant increase was found under NOR. No significant difference between H+H and HYP was observed in the serum EPO level, blood lactate level, or muscle oxygenation at any time (P > 0.05). Exercise-induced serum growth hormone (GH) elevation was significantly greater in H+H compared with HYP (P < 0.05) and HYP showed significantly lower value than NOR (P < 0.05). Arterial oxygen saturation during exercise was significantly lower in H+H and HYP compared with NOR (P < 0.05). Furthermore, H+H showed higher value compared with HYP (P < 0.05). Conclusion: The serum EPO level increased significantly with endurance exercise in hypoxia. However, the addition of heat stress during endurance exercise in hypoxia did not augment the EPO response up to 3 h after completion of exercise. Exercise-induced GH elevation was significantly augmented when the hot exposure was combined during endurance exercise in hypoxia. Muscle oxygenation levels during endurance

A Combined Hot and Hypoxic Environment during Maximal Cycling Sprints Reduced Muscle Oxygen Saturation: A Pilot Study

“…In the present study, the lower ΔTSI in the HH condition suggested enhanced muscle deoxygenation. This is in line with a study demonstrating that a combined hot and hypoxic environment while cycling at moderate intensity for 60 min tended to produce a lower TSI than thermoneutral normoxic or hypoxic environments (Yatsutani et al, 2020). Hot and hypoxic environments were reported to independently enhance muscle deoxygenation during exercise (Periard et al, 2013;Yamaguchi et al, 2019).…”

“…A few studies examined this hypothesis, but no consensus was obtained for the effect of combined hot and hypoxic environments on muscle oxygenation during exercise. Yatsutani et al (2020) reported that the tissue saturation index (TSI) during 60-min moderate-intensity cycling tended to be lower in hot hypoxic than thermoneutral hypoxic environments. On the other hand, Yamaguchi et al (2021) failed to observe larger deoxygenation during repeated cycling sprints in a hot hypoxic environment compared with a thermoneutral hypoxic environment.…”

Augmented muscle deoxygenation during repeated sprint exercise with post‐exercise blood flow restriction

“…An inconsistency between TSI and SpO 2 reflects that lowered oxygen saturation was caused in working muscles (local hypoxia), not in blood circulation (systemic hypoxia). Previous studies reported that exercise in normobaric hypoxic conditions elicited lower SpO 2 and TSI compared with normoxia (Willis et al, 2017Yatsutani et al, 2020). Furthermore, the transient reduction in O 2 partial pressure in the muscles during sprint exercise plays a key role in muscular adaptations (Hoppeler et al, 2008).…”

The effects of peripheral hormone responses to exercise on adult hippocampal neurogenesis

“…They reported mild, transient increases in EPO with training over the 8 weeks. A recent study compared circulating EPO levels in men cycling at 60% of power output at VO 2 max in an environmental chamber under either hot-hypoxic, hypoxic, or normoxic conditions ( 234 ). They reported increases in EPO after the hot-hypoxic and hypoxic conditions, but not under normoxic conditions.…”