We have previously reported the preventive effects of light resistance exercise (voluntary tower climbing exercise) after ingestion of a high-protein snack (HPS) on muscle loss in glucocorticoid-injected rats. However, such studies have not been performed in humans. In this cross-over study, we examined the effect of light resistance exercise after ingestion of HPS on plasma branched-chain amino acid (BCAA) concentrations in humans. Seven healthy young adult females (aged 22.1 +/- 1.2 y) participated in this study. They were assigned to either an exercise group or a control group. Seven days after the first experiment. they were crossed over to the opposite intervention. The subjects ingested RPS (15 g protein, 18 g sugar) 3 h after breakfast (basal meal). The plasma BCAA concentrations increased at 30 min after HPS ingestion. The subjects in the exercise group performed light resistance exercise (15 min dumbbell exercise using 300 g brown-rice-filled fabric dumbbells) when the plasma BCAA concentrations were increased (60 min after the snack ingestion). The control group maintained a resting position during the experiment. Changes in the plasma BCAA concentrations between 60 and 90 min after HPS ingestion increased continuously in the control group (+27 mu mol/L) but decreased in the exercise group (-37 mu mol/L. Therefore. light resistance exercise after HPS ingestion may be effective for utilization of plasma BCAA in humans.