부산대학교 도서관

This study investigates the role of central vs. peripheral factors in the limitation of maximal oxygen uptake ([[??]o.sub.2max]) with moderate hypoxia [inspired fraction [MATHEMATICAL. Fifteen endurance-trained athletes performed maximal, cycle incremental tests to assess [[??]o.sub.2max], maximal cardiac output ([Q.sub.max]), and maximal arteriovenous oxygen (a-v[O.sub.2]) difference in normoxia and hypoxia. Muscle biopsies of vastus lateralis were taken 1 wk before the cycling tests to evaluate maximal muscle oxidative capacity ([V.sub.max] ) and sensitivity of mitochondrial respiration to ADP ([K.sub.m]) on permeabilized muscle fibers in situ. Those athletes exhibiting the largest reduction of [[??]o.sub.2max] in moderate hypoxia (Severe Loss group: - 18 [+ or -] 2%) suffered from significant reductions in [Q.sub.max] (-4 [+ or -] 1%) and maximal a-v[O.sub.2] difference (- 14 [+ or -] 2%). Athletes who well tolerated hypoxia, as attested by a significantly smaller drop of [[??]o.sub.2max] with hypoxia (Moderate Loss group: -7 [+ or -] 1%), also display a blunted [Q.sub.max] (-9 [+ or -] 2%) but, conversely, were able to maintain maximal a-v[O.sub.2] difference (+1 [+ or -] 2%). Though [V.sub.max] was similar in the two experimental groups, the smallest reduction of [[??]o.sub.2max] with moderate hypoxia was observed in those athletes presenting the lowest apparent Km for ADP in the presence of creatine ([K.sub.m+Cr]). In already-trained athletes with high muscular oxidative capacities, the qualitative, rather than quantitative, aspects of the mitochondrial function may constitute a limiting factor to aerobic ATP turnover when exercising at low [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], presumably through the functional coupling between the mitochondrial creatine kinase and ATP production. This study suggests a potential role for peripheral factors, including the alteration of cellular homeostasis in active muscles, in determining the tolerance to hypoxia in maximally exercising endurance-trained athletes. exercise; cardiac output doi:10.1152/ajpregu.00216.2009