title: Sprint interval training in hypoxia stimulates glycolytic enzyme activity.
abstract: OBJECTIVE
  In this study, we compared the effect of sprint interval training (SIT) in normoxia versus hypoxia on muscle glycolytic and oxidative capacity, monocarboxylate transporter content, and endurance exercise performance.
  
  
  METHODS
  Healthy male volunteers (18-30 yr) performed 6 wk of SIT on a cycling ergometer (30-s sprints vs 4.5-min rest intervals; 3 d · wk(-1)) in either normobaric hypoxia (HYP, FiO2 = 14.4%, n = 10) or normoxia (NOR, FiO2 = 20.9%, n = 9). The control group did not train (CON, n = 10). Training load was increased from four sprints per session in week 1 to nine sprints in week 6. Before and after SIT, subjects performed a maximal incremental exercise test plus a 10-min simulated time trial on a cycle ergometer in both normoxia (MAX nor and TT nor) and hypoxia (MAX hyp and TT hyp). A needle biopsy was taken from musculus vastus lateralis at rest 5-6 d after the last exercise session.
  
  
  RESULTS
  SIT increased muscle phosphofructokinase activity more in HYP (+59%, P < 0.05) than that in NOR (+17%), whereas citrate synthase activity was similar between groups. Compared with the pretest, power outputs corresponding to 4 mmol blood lactate in HYP during MAX nor (+7%) and MAX hyp (+9%) were slightly increased (P < 0.05), whereas values were constant in NOR. V·O 2max in MAX nor and TT performance in TT nor and TT hyp were increased by ≈ 6%-8% (P < 0.05) in either group. The training elevated monocarboxylate transporter 1 protein content by ≈ 70% (P < 0.05). In CON, all measurements were constant throughout the study.
  
  
  CONCLUSIONS
  SIT in hypoxia up-regulated muscle phosphofructokinase activity and the anaerobic threshold more than SIT in normoxia but did not enhance endurance exercise performance.
authors.affiliation: 1Exercise Physiology Research Group, Department of Kinesiology, KU Leuven, Leuven, BELGIUM; and 2Institute of Neuroscience, Université catholique de Louvain, Brussels, BELGIUM.
authors.forename: Joke
authors.initials: J
authors.lastname: Puype
authors.forename: Karen
authors.initials: K
authors.lastname: Van Proeyen
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Raymackers
authors.forename: Louise
authors.initials: L
authors.lastname: Deldicque
authors.forename: Peter
authors.initials: P
authors.lastname: Hespel
mesh_terms: D000293:Adolescent; D000328:Adult; D015308:Anaerobic Threshold; D001642:Bicycling / Q000502:physiology; D002950:Citrate (si)-Synthase / Q000378:metabolism; D005080:Exercise Test; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000201:enzymology* / Q000503:physiopathology; D008297:Male; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D010101:Oxygen Consumption; D025221:Phosphofructokinases / Q000378:metabolism; D064797:Physical Conditioning, Human / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D052097:Quadriceps Muscle / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism; D055815:Young Adult; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D002950:Citrate (si)-Synthase; D006003:Glycogen; D027501:Monocarboxylic Acid Transporters; D009124:Muscle Proteins; D025221:Phosphofructokinases; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1; C406962:SLC16A4 protein, human