Muscle tissue adaptations of high-altitude natives to training in chronic hypoxia or acute normoxia

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Desplanches, D., H. Hoppeler, L. Tüscher, M. H. Mayet, H. Spielvogel, G. Ferretti, B. Kayser, M. Leuenberger, A. Grünenfelder, and R. Favier. Muscle tissue adaptations of high-altitude natives to training in chronic hypoxia or acute normoxia. J. Appl. Physiol. 81(5): 1946–1951, 1996.—Twenty healthy high-altitude natives, residents of La Paz, Bolivia (3,600 m), participated in 6 wk of endurance exercise training on bicycle ergometers, 5 times/wk, 30 min/session, as previously described in normoxia-trained sea-level natives (H. Hoppeler, H. Howald, K. E. Conley, S. L. Lindstedt, H. Claassen, P. Vock, and E. R. Weibel. J. Appl. Physiol. 59: 320–327, 1985). A first group of 10 subjects was trained in chronic hypoxia (HT; barometric pressure = 500 mmHg; inspired O2fraction = 0.209); a second group of 10 subjects was trained in acute normoxia (NT; barometric pressure = 500 mmHg; inspired O2fraction = 0.314). The workloads were adjusted to ∼70% of peak O2consumption (V˙o2 peak) measured either in hypoxia for the HT group or in normoxia for the NT group.V˙o2 peakdetermination and biopsies of the vastus lateralis muscle were taken before and after the training program.V˙o2 peakin the HT group was increased (14%) in a way similar to that in NT sea-level natives with the same protocol. Moreover,V˙o2 peakin the NT group was not further increased by additional O2delivery during the training session. HT or NT induced similar increases in muscle capillary-to-fiber ratio (26%) and capillary density (19%) as well as in the volume density of total mitochondria and citrate synthase activity (45%). It is concluded that high-altitude natives have a reduced capillarity and muscle tissue oxidative capacity; however, their training response is similar to that of sea-level residents, independent of whether training is carried out in hypobaric hypoxia or hypobaric normoxia.

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