title: Impact of Muscle Glycogen Availability on the Capacity for Repeated Exercise in Man.
abstract: OBJECTIVE
  This study aims to examine whether muscle glycogen availability is associated with fatigue in a repeated exercise bout following short-term recovery.
  
  
  METHODS
  Ten endurance-trained individuals underwent two trials in a repeated-measures experimental design, each involving an initial run to exhaustion at 70% of VO2max (Run 1) followed by a 4-h recovery and a subsequent run to exhaustion at 70% of VO2max (Run 2). A low-carbohydrate (L-CHO; 0.3 g · kg body mass(-1) · h(-1)) or high-carbohydrate (H-CHO; 1.2 g · kg body mass(-1) · h(-1)) beverage was ingested at 30-min intervals during recovery. Muscle biopsies were taken upon cessation of Run 1, after recovery, and at exhaustion during Run 2 in L-CHO (F2). In H-CHO, muscle biopsies were obtained after recovery, at the time point coincident with fatigue in L-CHO (F2), and at the point of fatigue during the subsequent exercise bout (F3).
  
  
  RESULTS
  Run 2 was more prolonged for participants on H-CHO (80 ± 16 min) than for participants on L-CHO (48 ± 11 min; P < 0.001). Muscle glycogen concentrations were higher at the end of recovery for participants on H-CHO (269 ± 84 mmol · kg dry mass(-1)) than for participants on L-CHO (157 ± 37 mmol · kg dry mass(-1); P = 0.001). The rate of muscle glycogen degradation during Run 2 was higher with H-CHO (3.1 ± 1.5 mmol · kg dry mass(-1) · min(-1)) than with L-CHO (1.6 ± 1.3 mmol · kg dry mass(-1) · min(-1); P = 0.05). The concentration of muscle glycogen was higher with H-CHO than with L-CHO at F2 (123 ± 28 mmol · kg dry mass(-1); P < 0.01), but no differences were observed between treatments at the respective points of exhaustion (78 ± 22 mmol · kg dry mass(-1) · min(-1 )for H-CHO vs 72 ± 21 mmol · kg dry mass(-1) · min(-1) for L-CHO).
  
  
  CONCLUSIONS
  Increasing carbohydrate intake during short-term recovery accelerates glycogen repletion in previously exercised muscles and thus improves the capacity for repeated exercise. The availability of skeletal muscle glycogen is therefore an important factor in the restoration of endurance capacity because fatigue during repeated exercise is associated with a critically low absolute muscle glycogen concentration.
authors.affiliation: 1Human Physiology Research Group, Department for Health, University of Bath, Bath, UNITED KINGDOM; and 2School of Life Sciences, Queen's Medical Center, Nottingham, UNITED KINGDOM.
authors.forename: Abdullah F
authors.initials: AF
authors.lastname: Alghannam
authors.forename: Dawid
authors.initials: D
authors.lastname: Jedrzejewski
authors.forename: Mark G
authors.initials: MG
authors.lastname: Tweddle
authors.forename: Hannah
authors.initials: H
authors.lastname: Gribble
authors.forename: James
authors.initials: J
authors.lastname: Bilzon
authors.forename: Dylan
authors.initials: D
authors.lastname: Thompson
authors.forename: Kostas
authors.initials: K
authors.lastname: Tsintzas
authors.forename: James A
authors.initials: JA
authors.lastname: Betts
mesh_terms: D001628:Beverages; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D015444:Exercise / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology; D014508:Urea / Q000097:blood; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D014508:Urea; D006003:Glycogen