Leucine And Muscle Synthesis

A beautiful woman exercising with dumb bells.
by Ambro. Courtesy of FreeDigitalPhotos.net

One of the most important amino-acids in sports nutrition is leucine which was found recently in a study to increase muscle protein synthesis (MPS) by 33% in a US Army clinical study (Pasiakos et al., 2011). Muscle protein is constantly being remodelled by the synthesis of new proteins and breakdown of existing proteins. Supplements of branched chain amino-acids (BCAA) are shown to improve net muscle protein balances, increase the factors for muscle signalling that are believed to regulate protein synthesis and reduce those markers associated with protein breakdown. The branched chain amino-acids are also understood to reduce muscle tiredness and associated soreness, and improve recovery after exercise. It was unclear though if the BCAA helped improve the net muscle protein balance seen with supplementation by increasing protein synthesis or its breakdown.

One specific study found that consuming BCAA (5g) 15 minutes before a bout of exercise in the form of squats helped to reduce the subjective feelings of muscle soreness and fatigue experienced over a number of days (Shimomura et al., 2006). It was suspected then that BCAA such as leucine might stimulate protein synthesis and attenuate exercise induced breakdown. The same group (Shimomura et al., 2010) repeated their findings with volunteers performing similar exercises. There was a statistically significant reduction in muscle soreness for women in the days after the exercise and also for men but this was not statistically significant for them.

A number of other studies have looked at the role of essential amino-acids including BCAAs which have promoted metabolism of muscle protein, focussing especially on improving muscle protein synthesis (Rasmussen et al., 2000; Tipton et al., 2001; Glynn et al., 2010). Another study reports that ingestion of BCAAs to a high level could improve muscle recovery and reduce muscle damage between exercise bouts (Skillen et al., 2008).

This latest study supports the view that muscle protein synthesis is influenced rather than its breakdown. Eight volunteers participated in a randomised crossover study consumed 10 grams of drinks with two different levels of leucine during exercise. These resistance exercises took the form of cycling. The researchers looked at protein turnover and intracellular signalling associated with the mammalian target for rapamycin 1(mTORC1). The study showed muscle protein synthesis to increase by 33% when the concentration of leucine also increased in the supplement compared to the control. What remains to be studied is the molecular mechanisms and the role that the level and duration of exercise has on supplementation with leucine. It also has implications for other protein related conditions.

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References

Glynn, E.L., Fry, C.S., Drummond, M.J., Dreyer, H.C., Dhanani, S., Volpi, E., Rasmussen, B.B. (2010) Muscle protein breakdown has a minor role in the protein anabolic response to essential amino acid and carbohydrate intake following resistance exercise. Am. J. Physiol. – Regulative, Integrative and Comparative Physiology, 299, pp. 533-540.
Pasiakos, S.M., McClung, H.L., McClung, J.P., Margolis, L.M., Andersden, N.E., Cloutier, G.J., Pikosky, M.A., Rood, J.C., Fielding, R.A., Young, A.J. (2011) Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis. Amer. J. Clin. Nutr. 94(3) pp. 809-818
Rasmussen, B.B., Tipton, K.D., Miller, S.L., Wolf, S.E., Wolfe, R.R. (2000) An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise. J. Appl. Physiol. 88 pp. 386–392.
Shimomura, Y. Yamamoto, Y. Bajotto, G. Sato, J. Murakami, T. Shimomura, N. Kobayashi, H. Mawatan, K. (2006) Nutraceutical effects of branched-chain amino acids on skeletal muscle. J. Nutr 136: 529S–532S,
Shimomura, Y., Inaguma, A., Watanabe, S., Yamamoto, Y., Muramatsu, Y., Bajotto, G., Sato, J., Shimomura, N., Kobayashi, H., Mawatari, K. (2010) Branched-Chain Amino Acid supplementation before squat exercise and Delayed-Onset Muscle Soreness. Int. J. Sport Nutr. Exercise Met. 20(3), pp. 236-44.
Skillen, RA., Testa, M., Applegate, EA., Heiden, EA., Fascetti, AJ., & Casazza, GA. (2008) Effects of an amino acid-carbohydrate drink on exercise performance after consecutive-day exercise bouts. Int. J. Sport Nutr. Exercise Met., 18,pp. 473–492.
Tipton, KD., Rasmussen, BB., Miller, SL., Wolf, SE., Owens-Stovall, SK., Petrini, BE., & Wolfe, RR. (2001) Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Am. J. Physiol., 281, E197–E206.

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