Nutrition and Protein Synthesis
Ellen Coleman, RD, MA, MPH © 2004

Athletes in strength and power sports constantly seek nutritional strategies to enhance the effect of resistance training on muscle protein synthesis. Skeletal muscle growth is possible only when muscle protein synthesis exceeds muscle protein breakdown. The most potent initiator of muscle protein synthesis is the combination of resistance exercise and the availability of amino acids (see Tipton and Wolfe, 2001).

Muscle protein synthesis and breakdown are elevated for more than 24 hours following resistance exercise. If no food is consumed, the rate of muscle protein breakdown exceeds synthesis and the net muscle protein balance becomes negative. Conversely, an abundant supply of amino acids increases muscle protein synthesis and the net muscle protein balance becomes positive.

Biolo and colleagues found that infusing amino acids intravenously (40 g total) following resistance exercise dramatically increased muscle protein synthesis and net muscle protein balance. The anabolic effect of the amino acids following exercise was greater than at rest, suggesting an additive effect (see Biolo et al, 1997). However, intravenous infusion is not a practical way of delivering amino acids to athletes. This study also does not address whether the ingestion of amino acids is as effective in stimulating muscle protein synthesis.

Tipton and colleagues examined the effect of orally administered amino acids (one liter solution with 40 g of amino acids) following resistance exercise on muscle protein synthesis. The researchers found that net muscle protein synthesis from amino acid ingestion was similar to that seen following amino acid infusion (see Tipton et al, 1999). Since amino acid availability can be increased as effectively with oral intake as with infusion, consuming a source of amino acids following resistance exercise (food or a supplement) should promote muscle anabolism.

The muscle protein breakdown that normally occurs following resistance exercise may be reduced by the increase in insulin levels associated with carbohydrate ingestion. Since amino acids increase muscle protein synthesis and insulin blunts muscle protein breakdown, the combination of amino acids and carbohydrates (to stimulate insulin secretion) may be a powerful anabolic mixture.

Rasmussen and colleagues examined the effects of ingesting a drink containing 6 g of essential amino acids and 35 g of carbohydrate (sucrose) on muscle protein metabolism following resistance exercise (see Rasmussen et al, 2000). The carbohydrate-amino acid drink increased both serum insulin and amino acid levels and changed the net muscle protein balance from negative to positive. Muscle protein synthesis was stimulated without the expected, associated rise in muscle protein breakdown. The anabolic response was the same whether the drink was consumed one hour or three hours following resistance exercise.

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