title: Training with low muscle glycogen enhances fat metabolism in well-trained cyclists.
abstract: OBJECTIVE
  To determine the effects of training with low muscle glycogen on exercise performance, substrate metabolism, and skeletal muscle adaptation.
  
  
  METHODS
  Fourteen well-trained cyclists were pair-matched and randomly assigned to HIGH- or LOW-glycogen training groups. Subjects performed nine aerobic training (AT; 90 min at 70% VO2max) and nine high-intensity interval training sessions (HIT; 8 × 5-min efforts, 1-min recovery) during a 3-wk period. HIGH trained once daily, alternating between AT on day 1 and HIT the following day, whereas LOW trained twice every second day, first performing AT and then, 1 h later, performing HIT. Pretraining and posttraining measures were a resting muscle biopsy, metabolic measures during steady-state cycling, and a time trial.
  
  
  RESULTS
  Power output during HIT was 297 ± 8 W in LOW compared with 323 ± 9 W in HIGH (P < 0.05); however, time trial performance improved by ∼10% in both groups (P < 0.05). Fat oxidation during steady-state cycling increased after training in LOW (from 26 ± 2 to 34 ± 2 μmol·kg−¹·min−¹, P < 0.01). Plasma free fatty acid oxidation was similar before and after training in both groups, but muscle-derived triacylglycerol oxidation increased after training in LOW (from 16 ± 1 to 23 ± 1 μmol·kg−¹·min−¹, P < 0.05). Training with low muscle glycogen also increased β-hydroxyacyl-CoA-dehydrogenase protein content (P < 0.01).
  
  
  CONCLUSIONS
  Training with low muscle glycogen reduced training intensity and, in performance, was no more effective than training with high muscle glycogen. However, fat oxidation was increased after training with low muscle glycogen, which may have been due to the enhanced metabolic adaptations in skeletal muscle.
authors.affiliation: School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Hulston
authors.forename: Michelle C
authors.initials: MC
authors.lastname: Venables
authors.forename: Chris H
authors.initials: CH
authors.lastname: Mann
authors.forename: Cara
authors.initials: C
authors.lastname: Martin
authors.forename: Andrew
authors.initials: A
authors.lastname: Philp
authors.forename: Keith
authors.initials: K
authors.lastname: Baar
authors.forename: Asker E
authors.initials: AE
authors.lastname: Jeukendrup
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D006003:Glycogen / Q000172:deficiency*; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011506:Proteins / Q000032:analysis; D055815:Young Adult
chemical_list: D011506:Proteins; D006003:Glycogen