Resistance Exercise Sustains p70S6K1 Activity in Response to Protein Ingestion at 4 hours

Abstract

The additive effect of protein feeding and resistance exercise on the stimulation of muscle protein synthesis is well established. However, it is unclear whether the activity of the signalling protein p70S6K1 is enhanced when protein feeding is combined with resistance exercise compared with protein feeding alone. PURPOSE:To directly compare the response of p70S6K1 activity to protein feeding alone vs protein feeding combined with resistance exercise. METHODS:Retrospective signalling analysis was carried out on muscle tissue from a previously published study. Twenty-three resistance trained males consumed a high protein breakfast before resting for 3 h. Following a bout of unilateral resistance exercise (8 × 10 leg press and leg extension exercises; 80% 1 RM) participants consumed a whey protein isolate drink (containing 10, 20 or 40 g protein). The activity of p70S6K1 was measured at 0 and 4 h in rested and exercised legs using a [γ-32P] ATP kinase assay. Statistical analysis of the fold change (0-4 h) in p70S6K1 activity between rested and exercised legs was conducted using a paired samples t-test (protein doses were pooled). Linear regression analysis was performed on the difference in fold change of p70S6K1 between rested and exercised (x-axis) against the previously published myofibrillar muscle protein synthesis data (y-axis). Effect sizes were calculated and reported as Cohen’s d with confidence intervals (CI). RESULTS:The fold change in p70S6K1 activity in response to protein ingestion from 0-4 h was 62% higher (p=0.004; d=0.61; CI=0.14 to 1.08) in the exercised leg (1.8 ± 1.3 fold; mean ± SD) compared with the rested leg (1.1 ± 0.8 fold). Regression analysis revealed a significant linear relationship between the difference in p70S6K1 activity fold change between rested and exercised legs and previously published myofibrillar muscle protein synthesis data (p=0.031; r2=0.204; y=1.28+0.11*x). CONCLUSIONS: Resistance exercise enhances the response of p70S6K1 activity to protein feeding and likely contributes to the enhanced response of myofibrillar muscle protein synthesis when protein feeding and resistance exercise are combined. Partially funded by GSK Consumer Healthcare.