title: Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans.
abstract: We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects [mean +/- SE maximum O(2) uptake (Vo(2 max)) = 56.5 +/- 2.7 ml x kg(-1) x min(-1)] cycled at > or =90% Vo(2 max) to exhaustion in normoxia [NORM-EXH; inspired O(2) fraction (Fi(O(2))) = 0.21, arterial O(2) saturation (Sp(O(2))) = 93 +/- 1%] and hypoxia (HYPOX-EXH; Fi(O(2)) = 0.13, Sp(O(2)) = 76 +/- 1%). The subjects also exercised in normoxia for a time equal to that achieved in hypoxia (NORM-CTRL; Sp(O(2)) = 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.
authors.affiliation: Centre for Sports Medicine and Human Performance, Brunel University, Middlesex, UB8 3PH, UK. lee.romer@brunel.ac.uk
authors.forename: Lee M
authors.initials: LM
authors.lastname: Romer
authors.forename: Hans C
authors.initials: HC
authors.lastname: Haverkamp
authors.forename: Markus
authors.initials: M
authors.lastname: Amann
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Lovering
authors.forename: David F
authors.initials: DF
authors.lastname: Pegelow
authors.forename: Jerome A
authors.initials: JA
authors.lastname: Dempsey
mesh_terms: D000328:Adult; D004417:Dyspnea / Q000209:etiology; D004574:Electromagnetic Fields; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology
chemical_list: D019344:Lactic Acid; D010100:Oxygen