Plateau effects of resistance exercise result from over-expression of eIF4E-BP1
Resistance exercise (RE) training may lead to a ‘plateau effect’; whereby muscle protein synthesis is not elevated post exercise. We observed during previous studies in our lab (unpublished) that 15 RE sessions over 5 weeks leads to muscle hypertrophy in rats, without an elevation of muscle protein synthesis (PS). The purpose of this study was to determine if this anabolic plateau after training resulted from altered mRNA translation signaling. Eight male S-D rats were operantly conditioned to engage in ‘squat-like’ exercise and assigned to either a RE or control group. Resistance was progressively increased from 80g (50 repetitions) during session 1 to 410g during session 15, and repetitions were adjusted to maintain a constant volume of work (repetitions x resistance). Sixteen hours post session 15, rates of muscle protein synthesis and signaling intermediates in mixed gastrocnemius were assessed using flooding dose and immunoblotting, respectively. PS was not different between RE or control rats (p>0.05). Protein levels of p70S6k and eIF2B-epsilon, key regulators of PS, were not different between groups (p>0.05). However, protein levels of eIF4E-BP1, a protein that acts as a ‘brake’ on mRNA translation, was significantly higher in RE compared to control (p<0.05). These results suggest that over-expression of eIF4E-BP1 may, in part, limit levels of PS with resistance exercise training.
