title: Muscle metabolism during exercise with carbohydrate or protein-carbohydrate ingestion.
abstract: BACKGROUND
  Ingesting protein (PRO) with CHO during prolonged exercise is purported to improve performance compared with CHO alone by altering the regulation of skeletal muscle energy provision. However, no study has directly investigated this issue. We tested the hypothesis that compared with CHO alone, coingestion of PRO would alter markers of metabolic control, including the magnitude of glycogen use and the net expansion of the tricarboxylic acid cycle intermediate pool, which has been linked to the capacity for oxidative energy delivery.
  
  
  METHODS
  Eight trained men (mean +/- SE: age = 29 +/- 2 yr; VO2peak = 55 +/- 2 mL x kg(-1) x min(-1)) cycled at 69% +/- 1% VO2peak for 90 min on two occasions, and biopsy samples (vastus lateralis) were obtained before and after exercise. In a randomized, double-blind manner, subjects ingested one of two drinks during exercise that contained either 6% CHO or 6% CHO + 2% PRO (CHO + PRO) at a rate of 1 L x h(-1) to deliver 60 g x h(-1) CHO +/- 20 g x h(-1) PRO.
  
  
  RESULTS
  CHO + PRO ingestion increased the plasma concentration of branched chain (561 +/- 46 vs 301 +/- 32 micromol x L(-1)) and essential amino acids (1071 +/- 98 vs 670 +/- 71 micromol x L(-1)) after exercise versus CHO (both P values <or=0.05). However, net muscle glycogen use (CHO + PRO = 223 +/- 31 vs CHO = 185 +/- 38 mmol x kg(-1) dry weight) and tricarboxylic acid cycle intermediate expansion (CHO + PRO = 2.3 +/- 0.7 vs CHO = 2.1 +/- 0.2 mmol x kg(-1) dry weight) were similar between trials. Blood creatine kinase activity and 20-km time trial performance measured approximately 24 h after the first exercise bout were not different between treatments.
  
  
  CONCLUSIONS
  When trained men ingest CHO at a rate on the upper end of the range generally recommended to improve endurance performance, coingestion of PRO does not alter specific markers proposed to reflect an enhanced capacity for skeletal muscle energy delivery.
authors.affiliation: Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Ontario, Canada.
authors.forename: Naomi M
authors.initials: NM
authors.lastname: Cermak
authors.forename: Amy S
authors.initials: AS
authors.lastname: Solheim
authors.forename: Melanie S
authors.initials: MS
authors.lastname: Gardner
authors.forename: Mark A
authors.initials: MA
authors.lastname: Tarnopolsky
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Gibala
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000008:administration & dosage*; D004311:Double-Blind Method; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009864:Ontario; D010807:Physical Endurance / Q000187:drug effects; D011506:Proteins / Q000008:administration & dosage* / Q000378:metabolism; D013177:Sports
chemical_list: D015415:Biomarkers; D002241:Carbohydrates; D011506:Proteins