Basic nutritional investigationDistinct effects of leucine or a mixture of the branched-chain amino acids (leucine, isoleucine, and valine) supplementation on resistance to fatigue, and muscle and liver-glycogen degradation, in trained rats

ObjectiveThe aim of this study was to evaluate the effects of the mixture of branched-chain amino acids (BCAAs) supplementation compared with leucine administered orally on muscle biochemical parameters of trained rats submitted to an exercise-induced protocol of glycogen depletion.MethodsAfter 6 wk of swimming exercise, 8 wk-old (250 g, adult) male Wistar rats were randomly divided into three experimental groups (n = 8 per group): the mixture of BCAAs (BCAAs), leucine (LEU), and placebo (PLA). All groups were submitted to swimming exercise for 6 wk and supplemented with either the mixture of BCAAs, leucine, or placebo during the last week of training. At week 7 of the protocol, the rats were submitted to an intermittent, progressive swimming test until exhaustion and sacrificed. Muscle gastrocnemius and liver were depicted to determine total glycogen, tricarboxylic acid cycle (TCA) intermediates, and enzymatic activities. Statistical evaluation was performed by one-way analysis of variance with Tukey post hoc test.ResultsBoth muscle and liver glycogen degradation ratio were significantly higher in the mixture of BCAAs group compared to the PLA group (P < 0.05) and the LEU group presented decreased liver glycogen degradation ratio compared with the mixture of BCAAs group (P < 0.05). Both muscle and liver glycogen content were significantly spared in the mixture of BCAAs and LEU groups compared to the PLA group (P < 0.01). A performance test demonstrated that LEU supplementation enhanced resistance to exhaustion compared to the mixture of BCAAs (P < 0.001), however, no difference was found when LEU supplementation was compared to PLA (P > 0.05) Muscle citrate content was significantly higher in the mixture of BCAAs group compared with the PLA group (P < 0.001). Muscle malate content was significantly elevated in the mixture of BCAAs group compared with both the PLA (P < 0.001) and LEU groups (P < 0.001). BCAT activity was significantly reduced in the mixture of BCAAs supplementation group compared with the LEU group (P < 0.001).ConclusionLeucine supplementation improved performance compared with the mixture of BCAAs supplementation, sparing muscle glycogen stores despite the augmentation of some TCA intermediate concentrations on the left side of the TCA cycle.