title: Creatine supplementation reduces muscle inosine monophosphate during endurance exercise in humans.
abstract: BACKGROUND
  Creatine (Cr) supplementation has been shown to attenuate increases in plasma ammonia and hypoxanthine during intense endurance exercise lasting 1 h, suggesting that Cr supplementation may improve muscle energy balance (matching of ATP resynthesis to ATP demand) during such exercise. We hypothesized that Cr supplementation would improve muscle energy balance (as assessed by muscle inosine monophosphate (IMP) accumulation) during intense endurance exercise.
  
  
  METHODS
  Seven well-trained men completed two experimental trials involving approximately 1 h of intense endurance exercise (cycling 45 min at 78+/-1% & OV0312;O2 peak followed by completion of 251+/-6 kJ as quickly as possible (performance ride)). Subjects ingested approximately 42 g.d dextrose for 5 d before the first experimental trial (CON), then approximately 21 g Cr monohydrate plus approximately 21 g.d dextrose for 5 d before the second experimental trial (CREAT). Trials were ordered because of the long washout time for Cr. Subjects were blinded to the order of the trials.
  
  
  RESULTS
  Creatine supplementation significantly (P< 0.05) increased muscle total Cr (resting values: CREAT: 138.1+/-7.9; CON: 117.7+/- 6.5 mmol.kg dm). No difference was seen between treatments in any measured muscle or blood metabolite after the first 45 min of exercise. Despite the performance ride completion time being similar in the two treatments ( approximately 13.5 min, approximately 86% & OV0312;O2 peak), IMP at the end of the performance ride was significantly (P<0.05) lower in CREAT than in CON (CREAT: 1.2+/- 0.6; CON: 2.0+/- 0.7 mmol.kg dm).
  
  
  CONCLUSIONS
  Raising muscle total Cr content before exercise appears to improve the ability of the muscle to maintain energy balance during intense aerobic exercise, but not during more moderate exercise intensities.
authors.affiliation: Department of Physiology, Monash University, Clayton, Victoria, AUSTRALIA.
authors.forename: Glenn K
authors.initials: GK
authors.lastname: McConell
authors.forename: Joanna
authors.initials: J
authors.lastname: Shinewell
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Stephens
authors.forename: Christos G
authors.initials: CG
authors.lastname: Stathis
authors.forename: Benedict J
authors.initials: BJ
authors.lastname: Canny
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Snow
mesh_terms: D000328:Adult; D003401:Creatine / Q000494:pharmacology*; D019587:Dietary Supplements; D017079:Exercise Tolerance; D006801:Humans; D007291:Inosine Monophosphate / Q000037:antagonists & inhibitors*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D010101:Oxygen Consumption; D010807:Physical Endurance / Q000187:drug effects* / Q000502:physiology; D011446:Prospective Studies; D013997:Time Factors
chemical_list: D007291:Inosine Monophosphate; D003401:Creatine