Aim: Physical exercise in recreational mountain sports is frequently performed without acclimatization to hypoxic conditions. Hypoxia may modify the hormonal and metabolic adaptive response to exercise depending on the type of exercise and on the physical fitness of the subject. This study aims at investigating the growth hormone (GH) response to submaximal exercise after acute exposure to moderate high altitude.
Methods: Ten trained (T) and 10 untrained (UT) male volunteers (mean age 23.8+/-3.2 y) underwent, in random order, 2 submaximal exercise (ergocycle) tests of the same absolute intensity. One test was performed at their habitual living altitude (690 m above sea level); the other, after acute exposure to 2325 m above sea level. Plasma levels of GH, Insulin-like growth factor-1 (IGF-1) and lactate were measured before and immediately after the exercise tests.
Results: Plasma GH levels increased after exercise (p<0.05) in both experimental conditions, and for both T and UT subjects. Hypoxia decreased the GH-IGF-1 response to exercise in the UT group. By contrast, the GH-IGF-1 response to exercise was not modified in the T group. The increase in plasma lactate levels induced by exercise was much higher in the UT than in the T group, and it was not affected by hypoxia.
Conclusion: Acute exposure to hypoxia blunts the GH response to submaximal physical exercise in untrained individuals.