title: Nitrate Intake Promotes Shift in Muscle Fiber Type Composition during Sprint Interval Training in Hypoxia.
abstract: OBJECTIVE
  We investigated the effect of sprint interval training (SIT) in normoxia, vs. SIT in hypoxia alone or in conjunction with oral nitrate intake, on buffering capacity of homogenized muscle (βhm) and fiber type distribution, as well as on sprint and endurance performance.
  
  
  METHODS
  Twenty-seven moderately-trained participants were allocated to one of three experimental groups: SIT in normoxia (20.9% FiO2) + placebo (N), SIT in hypoxia (15% FiO2) + placebo (H), or SIT in hypoxia + nitrate supplementation (HN). All participated in 5 weeks of SIT on a cycle ergometer (30-s sprints interspersed by 4.5 min recovery-intervals, 3 weekly sessions, 4-6 sprints per session). Nitrate (6.45 mmol NaNO3) or placebo capsules were administered 3 h before each session. Before and after SIT participants performed an incremental VO2max-test, a 30-min simulated cycling time-trial, as well as a 30-s cycling sprint test. Muscle biopsies were taken from m. vastus lateralis.
  
  
  RESULTS
  SIT decreased the proportion of type IIx muscle fibers in all groups (P < 0.05). The relative number of type IIa fibers increased (P < 0.05) in HN (P < 0.05 vs. H), but not in the other groups. SIT had no significant effect on βhm. Compared with H, SIT tended to enhance 30-s sprint performance more in HN than in H (P = 0.085). VO2max and 30-min time-trial performance increased in all groups to a similar extent.
  
  
  CONCLUSIONS
  SIT in hypoxia combined with nitrate supplementation increases the proportion of type IIa fibers in muscle, which may be associated with enhanced performance in short maximal exercise. Compared with normoxic training, hypoxic SIT does not alter βhm or endurance and sprinting exercise performance.
authors.affiliation: Exercise Physiology Research Group, Department of Kinesiology, Katholieke Universiteit Leuven Leuven, Belgium.
authors.forename: Stefan
authors.initials: S
authors.lastname: De Smet
authors.affiliation: Exercise Physiology Research Group, Department of Kinesiology, Katholieke Universiteit Leuven Leuven, Belgium.
authors.forename: Ruud
authors.initials: R
authors.lastname: Van Thienen
authors.affiliation: Exercise Physiology Research Group, Department of Kinesiology, Katholieke Universiteit LeuvenLeuven, Belgium; Institute of Neuroscience, Université Catholique de LouvainLouvain-la-Neuve, Belgium.
authors.forename: Louise
authors.initials: L
authors.lastname: Deldicque
authors.affiliation: Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, School of Science and Technology, Nottingham Trent University Nottingham, UK.
authors.forename: Ruth
authors.initials: R
authors.lastname: James
authors.affiliation: Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, School of Science and Technology, Nottingham Trent University Nottingham, UK.
authors.forename: Craig
authors.initials: C
authors.lastname: Sale
authors.affiliation: Institute of Sport, Exercise and Active Living, Victoria University Melbourne, VIC, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Bishop
authors.affiliation: Exercise Physiology Research Group, Department of Kinesiology, Katholieke Universiteit LeuvenLeuven, Belgium; Department of Kinesiology, Bakala Academy-Athletic Performance Center, KU LeuvenLeuven, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Hespel
keywords: carnosine; citrate synthase; hypoxia; intermittent hypoxic training; muscle buffering capacity; muscle fiber type composition; nitrate; sprint interval training