ESSENTIAL AMINO ACIDS AND MUSCLE PROTEIN RECOVERY FROM RESISTANCE EXERCISE

Abstract

Although net muscle protein balance is generally improved after resistance exercise, nutrient intake is necessary to achieve positive net muscle protein balance. Muscle protein synthesis (PS) has been shown to increase 3.5-fold when a small amount (6 g) of a mixture of essential amino acids (EAAs) was given along with 35 g of carbohydrate after resistance exercise, but the independent effect of EAAs is not known. PURPOSE: To determine the independent effect of ingestion of a bolus of 6 g of EAA on net muscle PS after resistance exercise, and to determine if the response of net muscle PS to a second dose of EAA is affected by the ingestion of an initial dose one hour earlier. METHODS: Three men and three women (23 ± 2 (SD) yr), participated in the study. Each subject was studied once. Subjects performed a resistance exercise bout consisting of 10 sets of 10 repetitions of leg presses, and 8 sets of 8 repetitions of leg extensions at 80% of the one-repetitions maximum. Before and after exercise, they rested in bed. At one and two hours post-exercise, they were given an oral supplement of 0.087 g of EAAs (in proportion to composition of muscle protein) per kg body weight. Amino acid metabolism was measured by combining a primed constant infusion of the stable isotopes L-[2H5]-phenylalanine and L-[1-13C]-leucine, with blood samples from the femoral artery and vein, and muscle biopsies from vastus lateralis. RESULTS: Arterial EAA concentrations increased several-fold following drink consumption. Net muscle protein balance increased proportionally more than the increase in arterial AA concentrations in response to the drinks, and returned rapidly to basal values when AA concentrations started to decrease again (20–30 min after drinks). The area under the curve (AUC) for net uptake of phenylalanine above the basal value was similar for the hour after the first drink (67 ± 17 (SE) mg/leg) vs. the hour after the second drink (77 ± 20 mg/leg). Corresponding AUC values for net uptake of leucine above the basal value were 159 ± 36 and 165 ± 32 mg/leg, respectively (NS between drinks). CONCLUSION: Ingestion of 6 g of EAAs stimulates muscle protein synthesis following exercise, and the response to a second dose is not affected by ingestion of a previous dose.