Purpose: The purpose of this study was to examine the effect of branched-chain amino acid (BCAA) supplementation on leukocyte subset before single bout of moderate exercise. Methods: Twelve healthy active college students participated in a double-blinded crossover study. The subjects ingested either 92 mg/kg BW of BCAA (BCAA) or placebo (PLA) capsules 60 minutes before exercise respectively. They exercised at 60% VO2 max on cycle ergometer for 30 minutes. Blood samples were collected prior to supplementation, immediately prior to exercise, and 0, 15, 60 minutes after cycling (P0, P15, P60) for analysis of leukocyte subset counts and their classified percentage. The data were analyzed by two-way ANOVA with repeated measures and significance was accepted at α=.05. Results: No interactions between treatment and timing were found. Significant main effect was found for timing on total leukocyte, phagocyte and lymphocyte counts. At P0, there were significant increases (p＜.05) above preexercise values in total leukocyte (52%), phagocyte (41%) and lymphocyte (76%) counts. At P60, total leukocyte and phagocyte counts were still above preexercise values, but lymphocyte counts were significantly lower (-9%) than preexercise values. Significant main effect was found for timing on phagocyte and lymphocyte percentage. At P60, phagocyte percentage was significantly greater than prexercise value, but lymphocyte percentage changed inversely. There was no significant difference between BCAA and PLA treatment on leukocyte subset counts. Conclusion: These results indicate that BCAA supplementation has no effect on changes of leukocyte subset counts after single bout of exercise (30 minutes 60% VO2 max) which is according to American College of Sports Medicine's exercise prescription. Further, we need to reevaluate the effect of BCAA supplementation before similar exercise which is performed 3-5 days a week.
