Article Text

Protein ingestion increases muscle protein synthesis after, but not during, endurance exercise
  1. C Hulston,
  2. E Wolsk,
  3. T Grøndahl,
  4. C Yfanti,
  5. G van Hall
  1. Copenhagen Muscle Research Centre, Copenhagen, Denmark


The purpose of this study was to determine muscle protein turnover and fractional synthetic rates during endurance exercise and recovery with carbohydrate (CHO) or CHO plus protein (CHO+P) ingestion. On two occasions, eight healthy males were studied at rest and during 3 h cycling and 3 h recovery. Leg muscle protein turnover was determined from stable isotope infusion (L-[ring-13C6]phenylalanine), arterial femoral-venous blood sampling and plasma flow measurements. Fractional synthetic rates (FSR) of the vastus lateralis were determined from the incorporation of L-[ring-13C6]phenylalanine into bound protein. Leg phenylalanine release, which is indicative of muscle protein breakdown, was ∼twofold higher during exercise than at rest (p<0.05), and was not different between CHO and CHO+P (p>0.05). CHO+P ingestion increased leg phenylalanine uptake during exercise (p<0.05) and increased muscle intracellular phenylalanine concentration (p<0.05). However, FSR were not different between CHO and CHO+P (0.029±0.004 and 0.030±0.003%/h respectively, p=0.88). During the recovery period, FSR were 0.070±0.003 and 0.105±0.013%/h for CHO and CHO+P, respectively (p<0.01). Furthermore, ingesting CHO+P during recovery resulted in a net phenylalanine uptake, compared with a net phenylalanine release in the CHO trial. The authors conclude: (1) that endurance exercise increases muscle protein breakdown, (2) protein ingestion does not reduce muscle protein breakdown or increase muscle protein synthesis during exercise, (3) protein ingestion augments post-exercise muscle protein synthesis and (4) protein ingestion is essential to achieve positive muscle protein balance during recovery from endurance exercise.

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