title: Impact of creatine on muscle performance and phosphagen stores after immobilization.
abstract: OBJECTIVE
  This study investigated the effect of creatine (CR) supplementation during cast-immobilization to preserve skeletal muscle total work, power and intramuscular phosphocreatine (PCr) kinetics during dynamic exercise.
  
  
  METHODS
  Twenty-five active individuals (24 ± 4 years,) performed wrist flexion exercise within a 1.9 Tesla superconducting magnet before and after 1 week of cast-immobilization. An incremental protocol to fatigue and two constant load (CL1 and CL2) exercise bouts were performed. While casted, participants consumed either 20 g day(-1) of CR or a placebo (PLA). (31)P magnetic resonance spectroscopy was used to quantify in vivo intramuscular PCr levels.
  
  
  RESULTS
  No significant group × time interaction effects were found for work or power throughout all exercise bouts. Total work was significantly reduced over time in both groups (p = 0.049) during the incremental exercise bout. Work production in CL1 tended (p = 0.073) to attenuate in the CR group, compared to PLA. No changes were observed in CL2. Baseline PCr significantly decreased with casting in PLA (PRE: 26.6 ± 6.3 vs. POST: 22.5 ± 5.6 mM kg(-1) wet muscle, p = 0.003). No change (p = 0.31) was observed in the CR group. Changes in work production were significantly correlated with changes in resting PCr in CR (r = -0.63, p = 0.021) but not PLA (r = -0.36, p = 0.26) group.
  
  
  CONCLUSIONS
  Results suggest decreases in short-term endurance may be due to alternations of PCr status and/or metabolism. More research is needed to fully determine the efficacy of CR supplementation during short-term immobilization.
authors.affiliation: Exercise Science Program, Marcella Niehoff School of Nursing, Loyola University Chicago, 1032 W. Sheridan Road, BVM Hall 8th Floor, Chicago, IL, 60660, USA, jfransen@luc.edu.
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Fransen
authors.forename: Micah
authors.initials: M
authors.lastname: Zuhl
authors.forename: Chad M
authors.initials: CM
authors.lastname: Kerksick
authors.forename: Nathan
authors.initials: N
authors.lastname: Cole
authors.forename: Steve
authors.initials: S
authors.lastname: Altobelli
authors.forename: Dean O
authors.initials: DO
authors.lastname: Kuethe
authors.forename: Suzanne
authors.initials: S
authors.lastname: Schneider
mesh_terms: D003401:Creatine / Q000008:administration & dosage*; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D007103:Immobilization; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D053580:Muscle Strength / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism*; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D010725:Phosphocreatine; D003401:Creatine