Metabolic and endocrine responses to graded exercise under acute hypoxia

Summary

Eight male subjects (24±1 years old) performed graded ergocycle exercises in normoxic (N) and acute hypoxic (H) conditions (14.5% O₂).$\dot V_{O_{_2 max} }$ decreased from 55.5±1.3 to 45.8±1.4 ml · kg⁻¹ · min⁻¹ in H condition. Plasma glucose and free fatty acid concentrations remained unchanged throughout exercise in both conditions. Increase in blood lactate concentration was associated with relative workload in both conditions. At$\dot V_{O_{_2 max} }$ lactate concentrations were similar in the two conditions, plasma insulin, glucagon, and LH concentrations did not significantly change in either. Plasma δ4-androstenedione and testosterone increased in a similar manner in both conditions. Finally plasma norepinephrine concentration reached at$\dot V_{O_{_2 max} }$ was significantly lower in hypoxia. These results suggest that acute moderate hypoxia does not affect metabolic and hormonal responses to short exercise performed at similar relative workloads, i.e. when the reduction of$\dot V_{O_{_2 max} }$ due to hypoxia is taken into consideration. The lower catecholamine response to maximal exercise under acute hypoxia might suggest that the sympathetic response could be related to relative as well as absolute workloads.