Effect of acute severe hypoxia on peripheral
fatigue and endurance capacity in healthy humans. Am J Physiol
Regul Integr Comp Physiol 292: R598–R606, 2007. First published
September 7, 2006; doi:10.1152/ajpregu.00269.2006.—We hypothesized
that severe hypoxia limits exercise performance via decreased
contractility of limb locomotor muscles. Nine male subjects [mean
SE maximum O2 uptake (V˙ O2 max) 56.5 2.7 ml kg 1 min 1]
cycled at 90% V˙ O2 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
