Independent and combined effects of amino acids and glucose after resistance exercise

Purpose: This study was designed to assess the independent and combined effects of a dose of amino acids (similar to6 g) and/or carbohydrate (similar to35 g) consumed at I and 2 h after resistance exercise on muscle protein metabolism. Methods: Following initiation of a primed constant infusion of H-2(5)-phenylalanine and N-15-urea, volunteers performed leg resistance exercise and then ingested one of three drinks (amino acids (AA), carbohydrate (CHO), or AA and CHO (MIX)) at 1- and 2-h postexercise. Results: Total net uptake of phenylalanine across the leg over 3 h was greatest in response to MIX and least in CHO. The individual values for CHO, MIX, and AA were 53 6, 114 +/- 38, and 71 +/- 13 mg(.)leg(-1.)3 h(-1). Stimulation of net uptake in MIX was due to increased muscle protein synthesis. Conclusions: These findings indicate that the combined effect on net muscle protein synthesis of carbohydrate and amino acids given together after resistance exercise is roughly equivalent to the sum of the independent effects of either given alone. The individual effects of carbohydrate and amino acids are likely dependent on the amount of each that is ingested. Further, prior intake of amino acids and carbohydrate does not diminish the metabolic response to a second comparable dose ingested 1 h later.