title: Cycling Time Trial Is More Altered in Hypobaric than Normobaric Hypoxia.
abstract: OBJECTIVE
  Slight physiological differences between acute exposure in normobaric hypoxia (NH) and hypobaric hypoxia (HH) have been reported. Taken together, these differences suggest different physiological responses to hypoxic exposure to a simulated altitude (NH) versus a terrestrial altitude (HH). For this purpose, in the present study, we aimed to directly compare the time-trial performance after acute hypoxia exposure (26 h, 3450 min) by the same subjects under three different conditions: NH, HH, and normobaric normoxia (NN). Based on all of the preceding studies examining the differences among these hypoxic conditions, we hypothesized greater performance impairment in HH than in NH.
  
  
  METHODS
  The experimental design consisted of three sessions: NN (Sion: FiO2, 20.93), NH (Sion, hypoxic room: FiO2, 13.6%; barometric pressure, 716 mm Hg), and HH (Jungfraujoch: FiO2, 20.93; barometric pressure, 481 mm Hg). The performance was evaluated at the end of each session with a cycle time trial of 250 kJ.
  
  
  RESULTS
  The mean time trial duration in NN was significantly shorter than under the two hypoxic conditions (P < 0.001). In addition, the mean duration in NH was significantly shorter than that in HH (P < 0.01). The mean pulse oxygen saturation during the time trial was significantly lower for HH than for NH (P < 0.05), and it was significantly higher in NN than for the two other sessions (P < 0.001).
  
  
  CONCLUSIONS
  As previously suggested, HH seems to be a more stressful stimulus, and NH and HH should not be used interchangeability when endurance performance is the main objective. The principal factor in this performance difference between hypoxic conditions seemed to be the lower peripheral oxygen saturation in HH at rest, as well as during exercise.
authors.affiliation: 1ISSUL, Institute of Sport Sciences, Faculty of Biology and Medicine, University of Lausanne, SWITZERLAND; 2Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, SWITZERLAND; 3Exercise Physiology Laboratory, Savoie Mont Blanc University, Chambery, FRANCE.
authors.forename: Jonas J
authors.initials: JJ
authors.lastname: Saugy
authors.forename: Thomas
authors.initials: T
authors.lastname: Rupp
authors.forename: Raphael
authors.initials: R
authors.lastname: Faiss
authors.forename: Alexandre
authors.initials: A
authors.lastname: Lamon
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bourdillon
authors.forename: Grégoire P
authors.initials: GP
authors.lastname: Millet
mesh_terms: D000328:Adult; D000531:Altitude; D054874:Athletic Performance / Q000502:physiology*; D001274:Atmospheric Pressure; D001642:Bicycling / Q000502:physiology*; D004311:Double-Blind Method; D004576:Electromyography; D005080:Exercise Test; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption
chemical_list: D010100:Oxygen