title: Creatine enhances oxygen uptake and performance during alternating intensity exercise.
abstract: OBJECTIVE
  The main purpose of the present study was to measure the total oxygen consumed, accumulation of blood metabolites, and performance during alternating intensity exercise before and after a period of creatine (Cr) loading in well-trained humans.
  
  
  METHODS
  Fourteen males were randomly assigned to two groups of seven males and were tested before and after 5 d of placebo (PL) or Cr monohydrate (CR) loading (20 g x d(-1)). Oxygen uptake was measured using a breath-by-breath system during bicycle exercise alternating every 3 min between bouts at 30%(-30%) and 90% (-90%) of the maximal power output to exhaustion. Blood samples were also obtained at rest, before the end of each cycling load, at exhaustion, and 5-min postexercise.
  
  
  RESULTS
  The oxygen consumed during 1-90% (5.08 +/- 0.39 L) and 2-90% (5.32 +/- 0.30 L) was larger after CR (5.67 +/- 0.34 and 5.78 +/- 0.35 L, P < 0.01 and P < 0.05, respectively). Blood ammonia accumulation at the end of 1-90% (23.1 +/- 6.5 micromol x L(-1)) and 3-30% (64.7 +/- 15.2 micromol x L(-1)) was lower after CR (P < 0.05), whereas plasma uric acid accumulation was lower at exhaustion (P < 0.05) and 5-min postexercise (P < 0.01). Time to exhaustion increased (P < 0.05) from 29.9 +/- 3.8 to 36.5 +/- 5.7 min after CR, whereas it remained the same after PL.
  
  
  CONCLUSIONS
  The results indicate that Cr feeding increases the capacity of human muscle to perform work during alternating intensity contraction, possibly as a consequence of increased aerobic phosphorylation and flux through the creatine kinase system.
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Sciences, University Autonoma of Barcelona, Spain. j.rico-sanz@proton.uab.es
authors.forename: J
authors.initials: J
authors.lastname: Rico-Sanz
authors.forename: M T
authors.initials: MT
authors.lastname: Mendez Marco
mesh_terms: D000328:Adult; D003401:Creatine / Q000494:pharmacology*; D019587:Dietary Supplements; D015444:Exercise / Q000502:physiology; D017079:Exercise Tolerance / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue; D010101:Oxygen Consumption
chemical_list: D003401:Creatine