Influence of Myosin Heavy Chain Protein Isoforms on Akt/mTOR Signaling and mRNA Expression Following Resistance Exercise in Trained Men

Abstract

The purpose of this study was to investigate anabolic signaling responses in resistance-trained men, and to examine the influence of myosin heavy chain (MHC) isoform composition on the magnitude of anabolic signaling. Eight resistance-trained men (24.9±4.3y; 91.2±12.4kg; 176.7±8.0cm) performed a whole body, high-volume resistance exercise protocol (REX) and a control protocol (CTL) in a balanced, randomized order. Participants were provided standardized meals during each protocol. Muscle biopsies were completed at baseline (BL), 2- (2H) and 6-hours post-exercise (6H). BL biopsies were analyzed for MHC isoform composition. Phosphorylation of proteins specific to the Akt/mTOR signaling pathway and MHC mRNA expression were quantified. Phosphorylation of p70S6k was significantly greater in REX compared to CTL at 2H (p=0.04). MHC mRNA expression and other targets in the Akt/mTOR pathway were not significantly influenced by REX. The percentage of type IIX isoform was inversely correlated (p<0.05) with type I and type IIA MHC mRNA expression (r=-0.69- -0.93). Maximal strength was also observed to be inversely correlated (p<0.05) with Type I and Type IIA MHC mRNA expression (r=-0.75– -0.77) and p70S6k phosphorylation (r=-0.75). Results indicate that activation of p70S6k occurs within 2-h following REX in resistance-trained men. Results also suggest that highly trained, stronger individuals have an attenuated acute anabolic response.