The purpose of this study was to examine the effects of oral branched-chain amino acid (BCAA) supplementation before resistance exercise on plasma levels of amino acids, cortisol, insulin, and serum creatine kinase and lactate dehydrogenase. Ten active female students in a double-blind crossover design randomly were assigned to a BCAA supplement or a placebo group. Both groups performed 5 sets of 12 to 15 repetitions at 50% of the 1-repetition maximum. Plasma leucine and isoleucine levels were increased whereas glutamine and phenylalanine were decreased at the end of exercise in the S group. BCAA supplementation did not affect plasma insulin, cortisol, serum creatine kinase and lactate dehydrogenase levels. These results suggest that in resistance exercise, BCAAs may support an insulin-independent anabolic state, but it cannot prevent muscle damage.
