Abstract
The effect of resistance exercise with the ingestion of supplementary protein on the activation of the mTOR cascade, in human skeletal muscle has not been fully elucidated. In this study, the impact of a single bout of resistance exercise, immediately followed by a single dose of whey protein isolate (WPI) or placebo supplement, on the activation of mTOR signalling was analyzed. Young untrained men completed a maximal single-legged knee extension exercise bout and were randomized to ingest either WPI supplement (n = 7) or the placebo (n = 7). Muscle biopsies were taken from the vastus lateralis before, and 2, 4 and 24 h post-exercise. WPI or placebo ingestion consumed immediately post-exercise had no impact on the phosphorylation of Akt (Ser473). However, WPI significantly enhanced phosphorylation of mTOR (Ser2448), 4E-BP1 (Thr37/46) and p70S6K (Thr389) at 2 h post-exercise. This study demonstrates that a single dose of WPI, when consumed in modest quantities, taken immediately after resistance exercise elicits an acute and transient activation of translation initiation within the exercised skeletal muscle.
Highlights
Resistance exercise is a potent stimulus of muscle hypertrophy, with net increases in skeletal muscle protein synthesis persisting during recovery [1,2]
Necessary for the enhanced rate of protein synthesis is the activation of kinases in the IGF-1/Akt/mTOR pathway [3,4]. mTOR exerts a critical role in mediating the signaling necessary for mRNA translation initiation, an important regulatory site in cellular protein synthesis [5]
The activation of translation initiation by amino acids is independent of upstream components of IGF-1 signalling, with mTOR acting as a convergence point for the separate actions of amino acids and resistance exercise [5,8]
Summary
Resistance exercise is a potent stimulus of muscle hypertrophy, with net increases in skeletal muscle protein synthesis persisting during recovery [1,2]. Evidence has accumulated such that when a resistance exercise stimuli is combined with a large ingested dose of amino acids, there is synergistic activation of mTOR and downstream kinases necessary for translation initiation [6,7]. In these studies, branch-chain amino acids (BCAA; total dose 100 g) consumed prior, during and in the early recovery phase, resulted in markedly greater mTOR, p70S6K and rpS6 phosphorylation, than was observed with exercise alone. The present study aimed to measure the phosphorylation status of Akt, mTOR, 4E-BP1, p70S6K and rpS6 in human skeletal muscle following either a single bout of resistance exercise alone (placebo) or when supplemented with a comparable dose of whey protein isolate (WPI)
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