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

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Summary

During exposure to altitudes greater than about 2200 m, maximal oxygen uptake (\(\dot V_{O_{2max} } \)) 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 (\(\dot Q_{\max }\)) at altitude which offsets the increase in CaO2 and, therefore,\(\dot V_{O_{2max} } \) 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\(\dot Q_{\max }\). The approach used was to have seven male subjects (aged 17 to 24 years) perform one- and two-legged\(\dot V_{O_{2max} } \) 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<0.01) and to 200±6 ml·L−1 at PP (SL vs. PP,p<0.05; SA vs. PP,p<0.01). Two-legged\(\dot V_{O_{2max} } \) decreased from 3.64±0.26 L·min−1 at SL to 2.70±0.14 L·min−1 during SA (p<0.01) to 2.86±0.16 L·min−1 at PP (p<0.01). One-legged\(\dot V_{O_{2max} } \) decreased from 2.95±0.22 at SL to 2.25±0.17 L·min−1 during SA (SL vs. SA,p<0.01) but improved to 2.66±0.18 L·min−1 at PP (SA vs. PP,p<0.05). Since only one-legged\(\dot V_{O_{2max} } \) increased as more oxygen was made available to the working muscles, the altitude-induced reduction in\(\dot Q_{\max }\) can be implicated as being responsible for the reduction in\(\dot V_{O_{2max} } \) during two-legged cycling.

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Correspondence to Charles S. Fulco.

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Fulco, C.S., Rock, P.B., Trad, L. et al. Maximal cardiorespiratory responses to one- and two-legged cycling during acute and long-term exposure to 4300 meters altitude. Europ. J. Appl. Physiol. 57, 761–766 (1988). https://doi.org/10.1007/BF01076000

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Key words

  • One-legged cycling
  • Altitude acclimatization
  • Cardiac output
  • Maximal oxygen consumption