title: Hypoxic training: effect on mitochondrial function and aerobic performance in hypoxia.
abstract: OBJECTIVE
  The effects of hypoxic training on exercise performance remain controversial. Here, we tested the hypotheses that i) hypoxic training possesses ergogenic effects at sea level and altitude and ii) the benefits are primarily mediated by improved mitochondrial function of the skeletal muscle.
  
  
  METHODS
  We determined aerobic performance (incremental test to exhaustion and time trial for a set amount of work) in moderately trained subjects undergoing 6 wk of endurance training (3-4 times per week, 60 min per session) in normoxia (placebo, n = 8) or normobaric hypoxia (FIO2 = 0.15, n = 9) using a double-blind and randomized design. Exercise tests were performed in normoxia and acute hypoxia (FIO2 = 0.15). Skeletal muscle mitochondrial respiratory capacities and electron coupling efficiencies were measured via high-resolution respirometry. Total hemoglobin mass was assessed by carbon monoxide rebreathing.
  
  
  RESULTS
  Skeletal muscle respiratory capacity was not altered by training or hypoxia; however, electron coupling control respective to fat oxidation slightly diminished with hypoxic training. Hypoxic training did increase total hemoglobin mass more than the placebo (8.4% vs 3.3%, P = 0.02). In normoxia, hypoxic training had no additive effect on maximal measures of oxygen uptake or time trial performance. In acute hypoxia, hypoxic training conferred no advantage on maximal oxygen uptake but tended to enhance time trial performance more than normoxic training (52% vs 32%, P = 0.09).
  
  
  CONCLUSIONS
  Our data suggest that, in moderately trained subjects, 6 wk of hypoxic training possesses no ergogenic effect at sea level. It is not excluded that hypoxic training might facilitate endurance capacity at moderate altitude; however, this issue is still open and needs to be further examined.
authors.affiliation: 1Ecole Nationale des Sports de Montagne, site de l'Ecole Nationale de Ski et d'Alpinisme, Chamonix, FRANCE; 2Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, DENMARK; 3Zürich Center for Integrative Human Physiology, University of Zürich, Zürich, SWITZERLAND; 4Institute of Physiology, University of Zürich, Zürich, SWITZERLAND; and 5Exercise Physiology, Institute of Human Movement Sciences, Eidgenössische Technische Hochschule Zürich, Zürich, SWITZERLAND.
authors.forename: Paul
authors.initials: P
authors.lastname: Robach
authors.forename: Thomas
authors.initials: T
authors.lastname: Bonne
authors.forename: Daniela
authors.initials: D
authors.lastname: Flück
authors.forename: Simon
authors.initials: S
authors.lastname: Bürgi
authors.forename: Marco
authors.initials: M
authors.lastname: Toigo
authors.forename: Robert A
authors.initials: RA
authors.lastname: Jacobs
authors.forename: Carsten
authors.initials: C
authors.lastname: Lundby
mesh_terms: D000328:Adult; D000531:Altitude; D056352:Athletes; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D010101:Oxygen Consumption; D010807:Physical Endurance; D052097:Quadriceps Muscle / Q000378:metabolism