EFFECTS OF VARIOUS HYPOBARIC HYPOXIA ON METABOLIC RESPONSE, SKELETAL MUSCLE OXYGENATION, AND EXERCISE PERFORMANCE IN HEALTHY MALES

Abstract

Objective This study aimed to evaluate the effect of various levels of hypoxia versus normoxia on exercise perfor-mance, measured by metabolic parameters and skeletal muscle oxygenation profiles during graded exercise test (GXT) in healthy men. Methods In this randomized crossover trial, 11 healthy male participants (age 21.5 ± 2.3 years) performed the GXT using a cycle ergometer at sea-level (760 torr) and at various hypobaric hypoxia: 633, 526, and 433 torr, corresponding to simulated altitudes of 1500, 3000, and 4500 m, respectively. The GXT was started at 50 W and increased by 25 W every 2 min until the participants were exhausted. The pedal frequency was set to 60 rpm. Metabolic parameters (heart rate, HR; minute ventilation, VE; carbon dioxide excretion, VCO2; respiratory exchange ratio, RER; peripheral capillary saturation, SpO2; oxygen consumption, VO2; and blood lactate, O2 pulse) and skeletal muscle oxygen profiles (oxygenated hemoglobin and myoglobin, OxyHb; deoxygenated hemoglobin and myoglobin, DeoxyHb; and tissue oxygen saturation, StO2) were measured for every 2 min during the GXT. Exercise performance was evaluated by maximal oxygen con-sumption, peak power, and duration of exercise time obtained through GXT. Results Regarding metabolic parameters, HR (P < 0.05), VE, (P < 0.05), VCO2 (P < 0.05), RER (P < 0.05), and blood lactate (P < 0.05) showed significant increase under hypoxia compared to normoxia. Moreover, the increase was more pronounced as hypoxia became more severe. However, the SPO2 (P < 0.05) and O2 pulse (P < 0.05) presented a significant decrease under hypoxia compared to normoxia. Similarly, the decrease was more pronounced as hypoxia became more severe. VO2 (P > 0.05) did not show significant difference under different environmental conditions. In skeletal muscle oxygen profiles, none of the param-eters showed noticeable changes. Regarding exercise performance, VO2max (P < 0.05) and exercise time (P < 0.05) decreased significantly as hypoxia became more severe, and peak power (P < 0.05) decreased significantly at simulated altitudes of 3000 and 4500 m compared to normoxia. Conclusion A decrease in exercise performance is due to a decrease in metabolic function under various hypoxia compared to normoxia and the decrease was more pronounced as hypoxia became more severe.