Determinants of maximal oxygen uptake in moderate acute hypoxia in endurance athletes

摘要

The factors determining maximal oxygen consumption were explored in eight endurance trained subjects (TS) and eight untrained subjects (US) exposed to moderate acute normobaric hypoxia. Subjects performed maximal incremental tests at sea level and simulated altitudes (1,000, 2,500, 4,500 m). Heart rate (HR), stroke volume (SV), cardiac output ${(dot{{Q}})},$ arterialized oxygen saturation ${(hbox{Sa}^{prime}hbox{O}_2)},$ oxygen uptake ${(dot{{V}}hbox{O}_{rm 2max})},$ ventilation ( ${dot{{V}}{E}},$ expressed in normobaric conditions) were measured. At maximal exercise, ventilatory equivalent ${(dot{{V}}{E}/dot{{V}}hbox{O}_{rm 2max}),, hbox{O}_2}$ transport ${(dot{{Q}}hbox{aO}_{rm 2max})}$ and O2 extraction (O2ERmax) were calculated. In TS, ${dot{{Q}}_{rm max}}$ remained unchanged despite a significant reduction in ${hbox{HR}_{rm max}}$ at 4,500 m. SVmax remained unchanged. ${dot{{V}}{E}_{rm max}}$ decreased in TS at 4,500 m, ${dot{{V}}{E}/dot{{V}}hbox{O}_{rm 2max}}$ was lower in TS and greater at 4,500 m vs. sea level in both groups. Sa′O2max decreased at and above 1,000 m in TS and 2,500 m in US, O2ERmax increased at 4,500 m in both groups. ${dot{{Q}}hbox{aO}_{rm 2max}}$ decreased with altitude and was greater in TS than US up to 2,500 m but not at 4,500 m. ${dot{{V}}hbox{O}_{rm 2max}}$ decreased with altitude but the decrement ${(Delta dot{{V}}hbox{O}_{rm 2max})}$ was larger in TS at 4,500 m. In both groups ${Delta dot{{V}}hbox{O}_{rm 2max}}$ in moderate hypoxia was correlated with ${Delta dot{{Q}}hbox{aO}_{rm 2max}}.$ Several differences between the two groups are probably responsible for the greater ${Delta dot{{V}}hbox{O}_{rm 2max}}$ in TS at 4,500 m : (1) the relative hypoventilation in TS as shown by the decrement in ${dot{{V}}{E}_{rm max}}$ at 4,500 m (2) the greater ${dot{{Q}}hbox{aO}_{rm 2max}}$ decrement in TS due to a lower Sa′O2max and unchanged ${dot{{Q}}_{rm max}}$ 3) the smaller increase in O2ERmax in TS, insufficient to compensate the decrease in ${dot{{Q}}ahbox{O}_{rm 2max}}.$