title: Endurance exercise performance in acute hypoxia is influenced by expiratory flow limitation.
abstract: OBJECTIVE
  We sought to determine if expiratory flow limitation influences intensive aerobic exercise performance in mild hypoxia.
  
  
  METHODS
  Fourteen trained male cyclists were separated into flow-limited (FL, n = 7) and non-FL (n = 7) groups based on the extent of expiratory flow limitation exhibited during maximal exercise in normoxia. Participants performed two self-paced 5-km cycling time trials, one in normoxic (F IO2 = 0.21) and one in mild hypoxic (F IO2 = 0.17) conditions in a randomized, balanced order with the subjects blinded to composition of the inspirate. Percent change from normoxia to hypoxia in average power output (%ΔP TT) and time to completion (%ΔT TT) were used to assess performance.
  
  
  RESULTS
  Hypoxia resulted in a significant decline in estimated arterial O2 saturation and decrements in performance in both groups, although FL had a significantly smaller %ΔP TT (-4.0 ± 0.5 vs. -9.0 ± 1.8 %) and %ΔT TT (1.3 ± 0.3 vs. 3.7 ± 0.9 %) compared to non-FL. At the 5th km of the time trial, minute ventilation did not change from normoxia to hypoxia in FL (3.4 ± 3.1 %) or non-FL (2.3 ± 3.7 %), but only the non-FL reported a significantly increased dyspnea rating in hypoxia compared to normoxia (~9 %). Non-FL athletes did not utilize their ventilatory reserve to defend arterial oxygen saturation in hypoxia, which may have been due to an increased measure of dyspnea in the hypoxic trial.
  
  
  CONCLUSIONS
  FL athletes experience less hypoxia-related aerobic exercise performance impairment as compared to non-FL athletes, despite having less ventilatory reserve.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology, Indiana University, Bloomington, IN, 47405, USA, J.Weavil@utah.edu.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Weavil
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Duke
authors.forename: Jonathon L
authors.initials: JL
authors.lastname: Stickford
authors.forename: Joel M
authors.initials: JM
authors.lastname: Stager
authors.forename: Robert F
authors.initials: RF
authors.lastname: Chapman
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Mickleborough
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D054874:Athletic Performance / Q000502:physiology*; D001642:Bicycling / Q000502:physiology; D004417:Dyspnea / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D005105:Expiratory Reserve Volume / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010366:Peak Expiratory Flow Rate; D010807:Physical Endurance / Q000502:physiology*; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult