Protein Ingestion Further Augments S6K1 Phosphorylation in Skeletal Muscle Following Resistance Type Exercise in Males

Abstract

Our objective was to determine the impact of carbohydrate and/or protein ingestion before and after exercise on ribosomal protein S6 kinase (S6K1) and S6 phosphorylation status in human skeletal muscle tissue. Seven healthy, untrained men (22.5 α 0.9 y) were randomly assigned to 2 cross-over experiments. Before, immediately after, and 1 h after a single bout of resistance exercise, subjects consumed 0.3 gηkg−1 carbohydrate with or without 0.3 gηkg−1 protein hydrolysate (CHO+PRO and CHO, respectively). Muscle biopsies were taken before and immediately after exercise and after 1 and 4 h of postexercise recovery to determine 4E-BP1, S6K1 (both T421/S424 and T389), and S6 phosphorylation status. Following resistance exercise, 4E-BP1 phosphorylation was reduced to a greater extent in the CHO treatment (−48 α 7%) than in the CHO+PRO treatment (–15 α 14%, P < 0.01). During recovery, 4E-BP1 phosphorylation increased in both experiments (P < 0.01), and tended to be higher in the CHO+PRO test (P = 0.08). S6K1 phosphorylation at T421/S424 substantially increased following exercise and remained elevated during recovery with no differences between treatments. In contrast to the CHO treatment (−4 α 2%), S6K1 phosphorylation at T389 was higher following exercise in the CHO+PRO treatment only (+78 α 2%, P < 0.01). During recovery, S6K1 phosphorylation at T389 remained higher in CHO+PRO than in CHO (P < 0.05). S6 phosphorylation was substantially higher following exercise in the CHO+PRO (1.69 α 0.35) than in the CHO experiment (0.45 α 0.07, P < 0.01) and remained elevated during recovery (P < 0.05). We conclude that the availability of dietary protein further enhances phosphorylation of S6K1 during recovery from resistance type exercise.