Muscle enzymatic composition and metabolic regulation in high altitude adapted natives.

Quechuas and Sherpas have long attracted the interest of high altitude biology and medicine. From our current knowledge, it appears that three of their most impressive high altitude adaptations are (i) high efficiency performance even in hypobaric hypoxia, (ii) low maximum (aerobic and anaerobic) capacities, and (iii) high endurance (the latter being less well documented, but widely accepted). Muscle biopsy and enzyme activity measurements clarify the basis for at least some of these adaptations. Firstly, low activity levels of enzymes in oxidative metabolism (comparable to power athletes) predict low VO2max capacities, as previously observed. Secondly, anaerobic glycolytic capacities also are low (comparable to endurance athletes) which explains low anaerobic work capacities. Thirdly, the glycolytic pathway is seemingly organized for carbohydrate oxidation, not fermentation. Because glucose (glycogen) metabolism uses O2 efficiently, the endurance characteristic may arise from coupling carbohydrate-based adenosine triphosphate (ATP) synthesis with efficient pathways of ATP utilization (for high yield of muscle work/ATP).