title: Effect of exercise-induced arterial hypoxemia on quadriceps muscle fatigue in healthy humans.
abstract: The effect of exercise-induced arterial hypoxemia (EIAH) on quadriceps muscle fatigue was assessed in 11 male endurance-trained subjects [peak O2 uptake (VO2 peak) = 56.4 +/- 2.8 ml x kg(-1) x min(-1); mean +/- SE]. Subjects exercised on a cycle ergometer at >or=90% VO2 peak) to exhaustion (13.2 +/- 0.8 min), during which time arterial O2 saturation (Sa(O2)) fell from 97.7 +/- 0.1% at rest to 91.9 +/- 0.9% (range 84-94%) at end exercise, primarily because of changes in blood pH (7.183 +/- 0.017) and body temperature (38.9 +/- 0.2 degrees C). On a separate occasion, subjects repeated the exercise, for the same duration and at the same power output as before, but breathed gas mixtures [inspired O2 fraction (Fi(O2)) = 0.25-0.31] that prevented EIAH (Sa(O2) = 97-99%). Quadriceps muscle fatigue was assessed via supramaximal paired magnetic stimuli of the femoral nerve (1-100 Hz). Immediately after exercise at Fi(O2) 0.21, the mean force response across 1-100 Hz decreased 33 +/- 5% compared with only 15 +/- 5% when EIAH was prevented (P < 0.05). In a subgroup of four less fit subjects, who showed minimal EIAH at Fi(O2) 0.21 (Sa(O2) = 95.3 +/- 0.7%), the decrease in evoked force was exacerbated by 35% (P < 0.05) in response to further desaturation induced via Fi(O2) 0.17 (Sa(O2) = 87.8 +/- 0.5%) for the same duration and intensity of exercise. We conclude that the arterial O2 desaturation that occurs in fit subjects during high-intensity exercise in normoxia (-6 +/- 1% DeltaSa(O2) from rest) contributes significantly toward quadriceps muscle fatigue via a peripheral mechanism.
authors.affiliation: Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, 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: 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; D001784:Blood Gas Analysis; D015444:Exercise / Q000502:physiology*; D006262:Health; D006801:Humans; D000860:Hypoxia / Q000097:blood*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D010101:Oxygen Consumption; D052097:Quadriceps Muscle / Q000502:physiology*; D013997:Time Factors