title: Cardiorespiratory and metabolic responses after exercise-induced muscle damage: the influence of lowered glycogen.
abstract: BACKGROUND
  We examined the effect of early-onset of muscle damage and low muscle glycogen on cardiorespiratory and metabolic responses to low-intensity exercise.
  
  
  METHODS
  Twelve men cycled for 10 min at 50% maximal oxygen uptake before, and 12 h after a morning downhill run (five, 8 min bouts at -12% gradient, with 2 min rests) under normal (NORM) and lowered glycogen (LOW) conditions, following a cross-over design with conditions separated by six weeks. Cardiorespiratory responses were recorded, with oxidation measures derived from stoichiometry equations.
  
  
  RESULTS
  Muscle damage symptoms post-downhill (0 h) were similar between conditions. Carbon dioxide ventilatory equivalent increased 12 h post-downhill for LOW (P<0.05), but not NORM (P=0.7). A trend towards decreased respiratory exchange ratio (RER) was shown 12 h post-downhill for LOW (1.00±0.07 to 0.89±0.12, P=0.06), but not NORM (0.94±0.11 to 0.94±0.08; P=0.6). Twelve hours after LOW downhill running fat oxidation increased (0.21±0.18 g·min-1 to 0.36±0.27 g·min-1; P<0.05) and carbohydrate oxidation decreased (2.68±0.52 g·min-1 to 1.98±0.75 g·min-1; P<0.05); NORM oxidation rates were unchanged (fat: 0.26±0.18 g·min-1 to 0.33±0.18 g·min-1; P=0.5; carbohydrate: 2.51±0.49 g·min-1 to 2.29±0.47 g·min-1; P=0.3).
  
  
  CONCLUSIONS
  Cycling at low-intensity 12 h post-downhill running with lowered muscle glycogen increased fat oxidation, decreased carbohydrate oxidation and elevated carbon dioxide ventilation. Damaging exercise with reduced glycogen availability increases fat utilization during subsequent low-intensity exercise as little as 12 h later.
authors.affiliation: Department of Sport and Exercise Sciences, University of Chichester, Chichester, UK - jgavin@bournemouth.ac.uk.|Department of Sport and Physical Activity, Bournemouth University, Bournemouth, UK - jgavin@bournemouth.ac.uk.
authors.forename: James P
authors.initials: JP
authors.lastname: Gavin
authors.affiliation: Department of Sport and Exercise Sciences, University of Chichester, Chichester, UK.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Myers
authors.affiliation: Department of Sport and Exercise Sciences, University of Chichester, Chichester, UK.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Willems
mesh_terms: D000328:Adult; D056352:Athletes / Q000706:statistics & numerical data; D001265:Athletic Injuries / Q000378:metabolism* / Q000503:physiopathology; D001786:Blood Glucose / Q000378:metabolism; D000072599:Cardiorespiratory Fitness; D015444:Exercise / Q000502:physiology; D005223:Fats / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000293:injuries* / Q000378:metabolism / Q000503:physiopathology; D010101:Oxygen Consumption; D012420:Running / Q000502:physiology; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D005223:Fats; D006003:Glycogen