Mason C. McIntosh, Casey L. Sexton, Joshua L. Godwin, Bradley A. Ruple, Shelby C. Osburn, John M. Michel, Daniel L. Plotkin, Christopher B. Mobley, Michael D. Roberts. Auburn University, Auburn, AL.

BACKGROUND: The myostatin (MSTN) gene has been heavily researched for its role in repressing skeletal muscle hypertrophy and the anabolic mTORC1 signaling pathway. Preliminary data from our laboratory has shown a significant hypermethylation of cytosine phosphate guanine sites within the MSTN gene as well as a significant downregulation of MSTN mRNA following acute bouts of resistance exercise to failure (i.e., training at 30% one repetition maximum versus 80% one repetition maximum). This study sought to determine the changes of MSTN-related and mTORC1 signaling proteins following two bouts of resistance exercise to failure. We hypothesized there to be significant time-effects of assayed markers in response to each bout of resistance training. METHODS: Eleven previously-trained college-aged men (age: 23 ± 4 years, 11.4 ± 6.4 percent fat, 4 ± 3 years training experience) participated in this study. Each participant performed two resistance training sessions (spaced one week apart) involving either: i) 30FAIL training; 4 sets of back squats and 4 sets of leg extensors to failure at 30% of one-repetition maximum (1RM), or: ii) 80FAIL training; 4 sets of both exercises at 80% of 1RM. Vastus lateralis muscle biopsies were obtained prior to each training session (PRE), 3 hours following training (3hPOST), and 6 hours following training (6hPOST). Western blots were performed on biopsied muscle to determine the relative expression of phosphorylated (p)-mTOR (Ser2448), p-p70S6K (Thr389), p-AKT (Ser473), p-rpS6 (Ser235/236), follistatin (FST), and MSTN. RESULTS: There were no significant bout*time interactions for any of the assayed markers. There were significant differences observed for p-p70S6K (p=0.001; PRE to 3hPOST) and FST (p=0.021; PRE to 6hPOST). There were no significant main time effects observed for p-mTOR, p-AKT, or p-rps6. CONCLUSIONS: The two modes of resistance training elicited similar effects on p-p70S6K and FST protein expression. These results suggest, regardless of training load, mTORC1 markers and MTSN-related protein expression respond similarly in previously-trained college-aged men.

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