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Am J Physiol Regul Integr Comp Physiol (September 7, 2006). doi:10.1152/ajpregu.00269.2006
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Submitted on April 20, 2006
Accepted on August 26, 2006

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

Lee M Romer1*, Hans Christian Haverkamp2, Markus Amann3, Andrew T. Lovering3, David F Pegelow3, and Jerome A. Dempsey3

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

* To whom correspondence should be addressed. E-mail: lee.romer{at}brunel.ac.uk.

We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects (mean ± SEM maximum oxygen uptake [VO2max] = 56.5 ± 2.7 ml kg-1 min-1) cycled at ≥90% VO2max 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 (non-potentiated 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 post-exercise. 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.




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