Activation of mTOR signalling in young and old human skeletal muscle in response to combined resistance exercise and whey protein ingestion

Abstract

Purpose: To investigate the impact of whey protein ingestion and resistance exercise training on the phosphorylation of mRNA translational signalling proteins in the skeletal muscle of young and old men. Methods: Sixteen healthy young (aged 18–25 years) and 15 healthy older men (aged 60–75 years) completed 12 weeks of resistance exercise and were randomly assigned to consume a whey protein (WPI) or placebo drink after each session. Muscle biopsies were collected before and 2 h after an acute exercise bout at the beginning and the end of training. Results: All subjects significantly increased strength after following strength training. Phosphorylation of mTOR was significantly greater in the WPI groups compared with placebo for both younger and older subjects. Phosphorylation of p70S6K, eIF4G, and 4EBP1 was greater for older subjects consuming WPI. Phosphorylation of rpS6, eIF4G, and 4EBP1 tended to increase in the younger subjects that had consumed WPI. Post-training, younger subjects demonstrated a similar pattern of mTOR phosphorylation as seen pre-training. In contrast, the initial heightened phosphorylation of mTOR, p70S6K, rpS6, and eIF4G in older muscle to combined resistance exercise and WPI ingestion became less pronounced after repeated training sessions. Conclusions: In the untrained state, resistance exercise coupled with WPI increases the phosphorylation of proteins involved in mRNA translation compared with exercise alone. Post-training, WPI- and exercise-induced protein phosphorylation was reduced in older men, but not in younger men. Thus, strategies to induce hypertrophy should utilize protein and resistance training concurrently. Further investigations should delineate interventions that will maintain sensitivity to anabolic stimuli in older populations.