Effect of acute hypoxia on the hormonal response to exercise.

The hormonal responses to submaximal exercise under normoxic and hypoxic conditions were studied in eight fit males, aged 22--28 yr, with mean maximal oxygen uptake of 4.4 +/- 0.7 l/min. Studies were performed in a hypobaric chamber, decompressed to a simulated altitude of 4,550 m (PIO2 = 83 Torr). The subjects exercised for 20 min at 750 kpm/min on a cycle ergometer. Venous blood samples were obtained at rest, during exercise and for 60 min after exercise. Plasma glucose, free fatty acids, lactate, cortisol, and serum growth hormone concentrations all increased more during hypoxic exercise than under normoxic conditions. Serum insulin concentration showed a small decrease under normoxic conditions, but decreased by 50% during hypoxic exercise, and was followed by marked rebound when exercise stopped. These changes suggest that energy substrate-hormone interrelationships are altered by hypoxic exercise, resulting in increased fat mobilization and increased gluconeogenesis.