It is generally understood that resistance exercise alone has a positive effect on protein synthesis and that consuming protein after exercise can enhance the effect further. However the magnitude of the effect and the details of how protein synthesis is upregulated are less clear. The amino acid Leucine is known to play a critical role in turning on the protein synthethic machinery in muscle. A study just published in the American Journal of Physiology examined the effect of a supplement containing essential amino acid and carbohydrate on regulators of protein synthesis in skeletal muscle. The supplement was specifically designed to be high in leucine in order to maximize the effects on protein synthesis. Healthy men performed resistance exercise with and without supplementation. During the supplementation trial, they consumed 22 g of essential amino acids (8 g leucine) plus 31 g of sugar consumed 1 hr after resistance exercise. As expected resistance exercise alone increased muscle protein synthesis by 41%. The leucine-rich amino acid mixture however had a dramatically greater effect increasing muscle protein synthesis by 145%. Supplementation also increased key signaling proteins including mTOR in muscle, which turn on protein synthesis. This study highlights the importance of high leucine content of a supplement in optimizing the anabolic response to resistance exercise.

Dreyer HC, Drummond MJ, Pennings B, Fujita S, Glynn EL, Chinkes DL, Dhanani S, Volpi E, Rasmussen BB. Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle. Am J Physiol Endocrinol Metab. 2008 Feb;294(2):E392-400. Epub 2007 Dec 4.