Maximal cardiorespiratory responses to one- and two-legged cycling during acute and long-term exposure to 4300 meters altitude.

During exposure to altitudes greater than about 2200 m, maximal oxygen uptake (VO2max) is immediately diminished in proportion to the reduction in the partial pressure of oxygen in the inspired air. If the exposure lasts longer than a couple of days, an increase in arterial oxygen content (CaO2), due to a hemoconcentration and an increase in arterial oxygen saturation, occurs. However, there is also a reduction in maximal cardiac output (Qmax) at altitude which offsets the increase in CaO2 and, therefore, VO2max does not improve. The purpose of this investigation was to study the contribution of the increase in CaO2 to the working muscles without the potentially confounding problem of a reduced Qmax. The approach used was to have seven male subjects (aged 17 to 24 years) perform one- and two-legged VO2max tests on a cycle ergometer at sea level (SL, PIO2 = 159 Torr), after 1 h at 4300 m simulated altitude (SA, PIO2 = 94 Torr) and during two weeks of residence on the summit of Pikes Peak, CO. (PP, 4300 m, PIO2 = 94 Torr). Cardiac output limits maximal performance during two-legged cycling but does not limit performance during one-legged cycling. During the study, CaO2 changed from 189 +/- 3 (mean +/- SE) at SL to 161 +/- 4 ml.L-1 during SA (SL vs. SA, p less than 0.01) and to 200 +/- 6 ml.L-1 at PP (SL vs. PP, p less than 0.05; SA vs. PP, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)