Muscle Metabolism during Exercise with Carbohydrate or Protein-Carbohydrate Ingestion

INTRODUCTION: 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