Effect of BCAA Intake During Exercise on Skeletal Muscle Protein Metabolism in Young Individuals

Abstract

1372 PURPOSE: To determine the effect of branched-chain amino acids (BCAA) intake during cycling exercise on the net balance of amino acid concentrations across the working muscles in young individuals. METHODS: Eight healthy young volunteers (4 males and 4 females, means ± SD, 26 ± 2 yrs, 178 ± 10 cm, 73 ± 11 kg) were studied by a double blind placebo-controlled cross-over trial. The subjects performed 3 bouts of 20-min cycling exercise (5-min break between each bout) at intensity of 126 ± 37 W corresponding to 50% of maximal work intensity. Either a BCAA drink (2000 mg BCAA and 20 g carbohydrate, 500 mL) or an iso-calorie placebo drink (500 mL) was given at 10 min of the 1st exercise bout. Arterial and venous blood samples st were taken from arteria radialis and vena femoralis. Blood flow in arteria femoralis was determined by ultrasound Doppler technique. Blood sampling and blood flow measurements were performed at rest, every 10 min during each exercise bout, and every 15 min during 60-min recovery period. Net balance of plasma phenylalanine concentration [Phe] (μmol/min) as an index for skeletal muscle protein metabolism, was calculated by the use of the following formula: Net balance of [Phe] = ([Phe]artery − [Phe]vein) × blood flow × (1-hematocrit). RESULTS: No difference in blood flow was observed between BCAA and placebo group at rest (0.43 ± 0.19 vs. 0.55 ± 0.25 L/min) and the end of 3rd exercise bout (3.60 ± 1.37 rd vs. 3.48 ± 1.58 L/min). Plasma BCAA concentration increased from 10 min, and peaked at 25 min (75.8 % increase compared to rest), and remained significant increase until 75 min (41.7 %) after BCAA ingestion. In placebo group, the arterial plasma BCAA concentration remained constant throughout the experiment. Negative balance of [Phe] across leg muscles was observed during the exercise bouts in both groups. Cumulative [Phe] release from the leg muscles during the exercise bouts after BCAA ingestion tended to be lower than that after placebo ingestion (−33.5 ± 27.1 vs. −60.6 ± 51.3μmol/60 min, P < 0.10). The cumulative [Phe] release during 3rd exercise bout in BCAA group was less than that rd in placebo group (−5.0 ± 21.0 vs. −35.9 ± 37.4μmol/25 min, P < 0.05). CONCLUSION: These results suggest that BCAA intake at onset of exercise is effective to suppress skeletal muscle proteolysis induced by dynamic exercise.