Human skeletal muscle exercise metabolism following an expedition to MountDenali

Chronic exposure to high altitude is known to result in changes in the mech anisms regulating O-2 delivery to the contracting muscle. However, the effe cts of acclimatization on metabolism in the contracting muscle cell remain unclear. In this study, we have investigated the hypothesis that acclimatiz ation would result in a closer coupling between ATP utilization and ATP pro duction and that the improved energy state would be accompanied by a reorga nization of the metabolic pathways consisting of an increased oxidative and decreased glycolytic potential. Five men, mean age of 28 +/- 2 (SE) yr, pe rformed a standardized, two-stage submaximal cycling task in normoxia for 2 0 min at each of 59 and 74% peak O-2 consumption before and 3-4 days after returning from a 21-day expedition to Mount Denali (6,194 m). Acclimatizati on was without effect in altering the resting values of the adenine nucleot ides (ATP, ADP, AMP), inosine monophosphate (IMP), or phosphocreatine (PCr) in the vastus lateralis. During exercise (40 min) after acclimatization co mpared with preacclimatization, PCr was not as depressed (33.2 +/- 7.1 vs. 40.6 +/- 5.4 mmol/kg dry wt) and IMP (0.289 +/- 0.11 vs. 0.131 +/- 0.03 mmo l/kg dry wt) and lactate (26.1 +/- 6.2 vs. 18.6 +/- 8.8 mmol/kg dry wt) in contracting muscle were not as elevated (P < 0.05). Although no effect of a cclimatization was observed for the maximal activity (mol.kg protein(-1.)h( -1)) of citrate synthase (4.76 +/- 0.44 vs. 4.94 +/- 0.45), lactate dehydro genase was increased by 13% (36.5 +/- 2.6 vs. 41.2 +/- 3.1, P < 0.05). It i s concluded that acclimatization results in an improved energy state in the contracting muscle when tested under normoxic conditions; however, these e ffects are not associated with a higher oxidative potential or a lower glyc olytic potential as hypothesized.