Continuous and intermittent exposure to the hypoxia of altitude: implications for glutamine metabolism and exercise performance.

Although most elite athletes invest a considerable amount of time and resources training at altitude, the practical benefits gained remain to be clearly established despite almost half a century of investigation. Elucidating the potential factors that aVect physical performance after return to sea level has been the subject of much interest and controversy. The time spent exposed to the hypoxia of altitude would appear to be an important mediator of sea level performance. A combination of physical exercise and intermittent hypoxia (defined as an exposure time of 30 minutes to 12 hours a day) has been shown to accelerate the normal adaptations invoked by a comparable programme of normoxic training with cardioprotective and performance enhancing benefits. In contrast, increased free radical mediated oxidative stress, decreased cell mediated immunity, and increased incidence of infectious episodes have been reported in continuous hypoxia (defined as an exposure time of 24 hours a day). We have previously reported two cases of infectious mononucleosis following chronic exposure to 1500–2000 m. Glutamine has been identified as a conditionally essential amino acid required for lymphocyte proliferation and macrophage phagocytosis, and it has been suggested that any physiological decrease in plasma glutamine may impair the host’s defence against opportunistic infections. In the light of these findings, we examined changes in plasma glutamine, the incidence of overt physical illness, and maximal exercise performance as a function of continuous and intermittent hypoxic training at comparable inspiratory partial pressures of oxygen (PIO2) or simulated altitudes.