Effects of ingesting carbohydrate and branched-chain amino acids on markers of skeletal muscle protein synthesis of the insulin-PI3K-mTOR signal transduction pathways in response to a bout of heavy resistance exercise.

Purpose: To determine if activity of the MAPK-ERK or PI3K-mTOR insulin signaling pathway is increased in response to an acute lower body resistance exercise (RE) bout and supplemental BCAA + CHO or CHO ingestion. Methods: 27 recreationally trained males (20.9 y; 81.8 kg) were randomly assigned to a group: BCAA (30 g) + CHO (350 g), CHO (350 g) or placebo CON. Participants performed 4 sets of leg press and extensions at 80% 1RM to failure. Supplements were ingested at 3 time points: 30 min prior to RE, and immediately pre- and post-RE. Venous blood was sampled at baseline (Pre); 30 min post-exercise; 2 h post-exercise, and 6 h post-exercise for serum glucose and insulin. Blood variables were transformed to percent change values and analyzed by a 3 x 4 repeated measures MANOVA. Muscle biopsies were obtained at baseline, 30 min post-exercise, 2 h post-exercise and 6 h post-exercise for ERK1/2, IRS, Akt/PKB, GSK, mTOR, 4E-BP1, and P70S6K. Skeletal muscle variables were transformed to percent change values and analyzed by 3 x 4 repeated measures MANOVA. Univariate ANOVAs were utilized as follow-up tests to the MANOVA for select variables. Results: MANOVA results demonstrate a significant group x time interaction for insulin and glucose (P<.05). Despite a nearly 3 fold-increase of insulin over fasting baseline measures in the CHO groups as compared to the placebo group, neither BCAA + CHO or CHO significantly increased any of the muscle variables. Univariate analysis demonstrated significant group x time interaction for Akt/PKB phosphorylation (p=0.039) suggestive of a group effect. The following muscle variables demonstrated by MANOVA a significant time effect: IRS (p=.054); Akt/PKB (p=0.011); ERK1/2 (p=0.026); p70S6K (p=0.038). A time trend for mTOR (p=0.089) was noted. No significant effects were found for GSK and 4E-BP above baseline or among groups. Summary: The results indicate that RE but not BCAA + CHO or CHO increased the phosphorylation status of IRS, AKT/PKB, p70S6K and ERK above baseline levels (p<.05) with trends for group x time interaction for Akt/PKB and trend for mTOR activation. Phosphorylation of GSK and 4E-BP was not influenced by the RE and supplementation protocol.