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Am J Physiol Regul Integr Comp Physiol 292: R598-R606, 2007. First published September 7, 2006; doi:10.1152/ajpregu.00269.2006
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SLEEP AND TEMPERATURE REGULATION

Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans

Lee M. Romer,1,2 Hans C. Haverkamp,2,3 Markus Amann,2 Andrew T. Lovering,2 David F. Pegelow,2 and Jerome A. Dempsey2

1Centre for Sports Medicine and Human Performance, Brunel University, Middlesex, United Kingdom; 2John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin, Madison, Wisconsin; and 3Vermont Lung Center, College of Medicine, University of Vermont, Burlington, Vermont

Submitted 20 April 2006 ; accepted in final form 26 August 2006

We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects [mean ± SE maximum O2 uptake (VO2 max) = 56.5 ± 2.7 ml·kg–1·min–1] cycled at ≥90% VO2 max to exhaustion in normoxia [NORM-EXH; inspired O2 fraction (FIO2) = 0.21, arterial O2 saturation (SpO2) = 93 ± 1%] and hypoxia (HYPOX-EXH; FIO2 = 0.13, SpO2 = 76 ± 1%). The subjects also exercised in normoxia for a time equal to that achieved in hypoxia (NORM-CTRL; SpO2 = 96 ± 1%). Quadriceps twitch force, in response to supramaximal single (nonpotentiated and potentiated 1 Hz) and paired magnetic stimuli of the femoral nerve (10–100 Hz), was assessed pre- and at 2.5, 35, and 70 min postexercise. Hypoxia exacerbated exercise-induced peripheral fatigue, as evidenced by a greater decrease in potentiated twitch force in HYPOX-EXH vs. NORM-CTRL (–39 ± 4 vs. –24 ± 3%, P < 0.01). Time to exhaustion was reduced by more than two-thirds in HYPOX-EXH vs. NORM-EXH (4.2 ± 0.5 vs. 13.4 ± 0.8 min, P < 0.01); however, peripheral fatigue was not different in HYPOX-EXH vs. NORM-EXH (–34 ± 4 vs. –39 ± 4%, P > 0.05). Blood lactate concentration and perceptions of limb discomfort were higher throughout HYPOX-EXH vs. NORM-CTRL but were not different at end-exercise in HYPOX-EXH vs. NORM-EXH. We conclude that severe hypoxia exacerbates peripheral fatigue of limb locomotor muscles and that this effect may contribute, in part, to the early termination of exercise.

hypoxemia; muscle fatigue; exercise performance


Address for reprint requests and other correspondence: L. M. Romer, Centre for Sports Medicine and Human Performance, Brunel Univ., Middlesex, UB8 3PH, UK (e-mail: lee.romer{at}brunel.ac.uk)




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