Aerobic capacity during acute exposure to simulated altitude, 914 to 2286 meters

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Abstract
To systematically assess the effects of acute exposure to moderate hypoxia on aerobic capacity (.ovrhdot.VO2 max [maximum O2 uptake]), 12 men (regular participants in recreational distance running) performed 6 treadmill-graded exercise tests (GXT) in a hypobaric chamber. GXT 1 and 6 were performed at ambient (control) altitude (362 m, barometric pressure = 730 mm Hg). GXT 2-5 were administered during 1-2 h of exposure to barometric pressures of 681, 656, 632 and 574 mm Hg; simulating altitudes of 914, 1219, 1524 and 2286 m, respectively, with the order of presentation randomized and blinded for each subject. The mean .ovrhdot.VO2 max for GXT 1 and 6 (control altitude) were essentially identical with a test-retest correlation of r = 0.92. During peak exercise, HR max [maximum heart rate] was unchanged by hypoxia, while .ovrhdot.VO2 max was significantly lower than the control by 4.8, 6.9 and 11.9% at 1219, 1524 and 2286 m, respectively. SaO2(a) max percent [arterial O2 saturation during maximum exercise] during maximal exercise was significantly reduced from the control by 3.5, 3.6, 7.0 and 11.6% at 914, 1219, 1524 and 2286 m, respectively. .ovrhdot.VO2 max, in physically well-conditioned persons living at 362 m, is reduced during acute exposure to .gtoreq. 1219 m.