Effects of ingesting branched chain amino acids and carbohydrate on myostatin signaling and markers of myogenesis in response to a bout of heavy resistance exercise.

Purpose: To determine if co-ingestion of carbohydrate (CHO) with branchedchain amino acids (BCAA) or leucine (Leu) downregulates the myostatin signaling pathway and upregulates the makers of myogenesis to a extent greater than that which resistance exercise elicits alone; to explore a possible mechanism for a CHO-BCAA or CHO-Leu induced the modification of myostatin pathway and the activation of myogenesis. Methods: 31 males (22.5yrs; 81.1kg) were randomly assigned to 1 of 3 groups: CHO-BCAA (maltodextrin 1.5 g/kg/bw, BCAA 120mg/kg/bw), CHO-Leucine (maltodextrin 1.5 g/kg/bw, Leu 60mg/kg/bw) and CHO alone (maltodextrin 1.5 g/kg/bw). A control group ingesting placebo (450 ml Crystal Light®) was employed from the previous study using the same study design in the same lab. Subjects performed 4 sets of leg press and leg extension at 80% 1RM to failure. Supplementation was ingested at 3 time points: 30 minutes prior to RE, and immediately pre- and post-RE. Venous blood was sampled at baseline; 30min later, immediate postexercise, 30min post-exercise; 2hr post-exercise, and 6hr post-exercise for serum glucose, insulin, IGF-1, myostatin, myostatin propeptide, follistatin and FLRG. Muscle biopsies were sampled at baseline, and 30min post, 2hr post, and 6hr post-exercise for myostatin, ActRIIB, p21cip, p27kip, myoD, myf-5, myogenin and MRF-4 mRNA expression. Serum variables were expressed in delta values as percent change and analyzed via a 4 (group) × 6 (time points) repeated measures MANOVA. Muscle variables were analyzed as CT ratio for relative mRNA expression via a 4 (group) × 4 (time points) repeated measures MANOVA. Univariate ANOVAs (Bonferroni adjusted) were conducted as follow-up tests to the MANOVA. Post-hoc tests of the interaction effects demonstrated in the ANOVA were investigated via an independent sample T-test. Results: CHO-BCAA, CHO-Leu and CHO alone significantly increased blood glucose and serum insulin levels combined with resistance exercise. Either CHO-BCAA or CHO-Leu enhanced serum insulin to a greater extent compared with CHO alone, nonetheless no statistically significance indicated. None of the CHO-BCAA, CHO-Leu or CHO alone, compared with placebo, modified serum IGF-1, myostatin and its inhibitors. Regarding muscle samples, a univariate group × time interaction relative to myogenin mRNA expression indicated that the CHO-Leu group was significantly upregulated at the 6hr post time point in comparison with the Placebo group (p < .05). No group × time interactions were observed for the myostain signaling molecules and other myogenic regulatory factors except myogenin. Summary: CHO-Leu supplementation upregulated the myogenin mRNA expression in conjunction with resistance exercise at 6hr post-exercise. Co-ingestion of BCAA or Leu had no effect on the inhibition of myostatin signaling at pre- and post-translational level.