The effect of high-altitude on human skeletal muscle energetics: 31P-MRS results from the Caudwell Xtreme Everest expedition

Many disease states are associated with regional or systemic hypoxia. The study of healthy individuals exposed to high-altitude hypoxia offers a way to explore hypoxic adaptation without the confounding effects of disease and therapeutic interventions. Using ³¹P magnetic resonance spectroscopy and imaging, we investigated skeletal muscle energetics and morphology after exposure to hypobaric hypoxia in seven altitude-naïve subjects (trekkers) and seven experienced climbers. The trekkers ascended to 5300 m while the climbers ascended above 7950 m. Before the study, climbers had better mitochondrial function (evidenced by shorter phosphocreatine recovery halftime) than trekkers: 16 ± 1 vs. 22 ± 2 s (mean ± SE, p < 0.01). Climbers had higher resting [Pi] than trekkers before the expedition and resting [Pi] was raised across both groups on their return (PRE: 2.6 ± 0.2 vs. POST: 3.0 ± 0.2 mM, p < 0.05). There was significant muscle atrophy post-CXE (PRE: 4.7 ± 0.2 vs. POST: 4.5 ± 0.2 cm², p < 0.05), yet exercising metabolites were unchanged. These results suggest that, in response to high altitude hypoxia, skeletal muscle function is maintained in humans, despite significant atrophy.