Effect of an Acute Bout of Eccentric Exercise at Different Velocities on Muscle Hypertrophy Signaling

Abstract

Recently, many studies have focused on the effects of strength training variables manipulation on the activation of intracellular signaling pathways for skeletal muscle hypertrophy. It has been suggested that muscle tension plays a major role in such process via activation of hypertrophy signaling pathways through increase in mechano growth factor (MGF). Eccentric muscle actions (EE) are notorious for imposing a greater amount of tension on the active muscle. In particular, EE performed at high velocities seems to exert an additional effect on muscle tension and thus, on muscle hypertrophy. However, little is known about the effect of EE velocity manipulation on hypertrophy pathways signaling. PURPOSE: To determine the acute effect of low and high velocity EE on muscle hypertrophy signaling proteins (Akt and p70S6K) phosphorylation and MGF mRNA expression. METHODS: Twenty subjects were randomly assigned to either a slow velocity group - 20o/s (ECC20) or fast group - 210o/s (ECC210). Muscle biopsy samples were taken before, immediately after and two hours after the completion of five sets of eight maximal repetitions of knee extension exercise at the designated velocity. Proteins phosphorylation and mRNA expression comparisons were made using two-way ANOVA with repeated measures. RESULTS: Akt and p70S6K protein analysis did not reveal any between or intra groups differences. Akt and p70S6K protein phosphorylation results indicated a main effect for time (p<0.05), with increased phosphorylation values for immediately after and two hours after time points in comparison to baseline values. MGF mRNA analysis did not show any between groups differences but were significantly higher at the two hours post intervention time point when compared to baseline in group ECC20. CONCLUSIONS: The acute manipulation of EE velocity does not seem to differently influence the phosphorylation or expression of the proteins studied.