Samples of muscle extracted before reaching high altitude and after returning to sea-level showed that maximal activities of enzymes, such as those representative of beta-oxidation, were unchanged. However, after exposure to extremely high altitude hypoxic conditions, reductions were observed in succinic dehydrogenase, citrate synthetase and hexokinase. The findings of this study did not support the researchers' hypothesis that extremely hypoxic conditions elicit changes that are adaptive toward maximizing oxidative function at the intracellular level (Green et al., 1989).
Reference
Donoghue, S., Fatemian, M., Balanos, G.M., Crosby, A., Liu, C., O'Connor, D., Talbot, N.P., Robbins, P.A. "Ventilatory Acclimatization in Response to Very Small Changes in PO2 in Humans." Journal of Applied Physiology 98 (2005): 1587-91.
Green, H.J., Sutton, J.R., Cymerman, A., Young, P.M., Houston, C.S. "Operation Everest II: Adaptations in Human Skeletal Muscle." Journal of Applied Physiology 66.5 (1989): 2454-61.
"Muscle Tissue Adaptations to Hypoxia." The Journal of Experimental Biology 204 (2001): 3133-9.
Hoppeler, H., Vogt, M., Weibel, E.R., Fluck, M. "Response of Skeletal Muscle Mirochondria to Hypoxia." Experimental Physiology 88.1 (2003): 109-19.
Lundby, C., Pilegaard, H., Andersen, J., Hall, G., Sander, M., Calbet, J.A.L. "Acclimatization to 4100 m Does Not Change Capillary Density or mRNA Expression of Potential Angiogenesis Regulatory Factors in Human Skeletal Muscle." Journal of Experimental Biology 207 (2004): 3865-71.
Norcliffe, L.J., Rivera-Ch, M., Claydon, V.E., Moore, J.P., Leon-Velarde, F., Appenzeller, O., Hainsworth, R. "Cerebrovascular Responses to Hypoxia and Hypocapnia in High-Altitude Dwellers." Journal of Physiology 566.1 (2005): 287-94.
Wyatt, F.B. "Physiological Responses to Altitude." The Center For Exercise Physiology Online (2002) retrieved December 15, 2006 http://www.exercisephysiologists.com/Altitude/index.html.
