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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Protein Ingestion Further Augments S6K1 Phosphorylation in Skeletal Muscle Following Resistance Type Exercise in Males¹

Departments of ² Movement Sciences and ³ Human Biology, Nutrition and Toxicology Research Institute Maastricht (NUTRIM), Maastricht University, Maastricht 6200 MD, The Netherlands

^* To whom correspondence should be addressed. E-mail: r.koopman{at}hb.unimaas.nl.

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 ± 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 g·kg^–1 carbohydrate with or without 0.3 g·kg^–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 ± 7%) than in the CHO+PRO treatment (–15 ± 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 ± 2%), S6K1 phosphorylation at T³⁸⁹ was higher following exercise in the CHO+PRO treatment only (+78 ± 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 ± 0.35) than in the CHO experiment (0.45 ± 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.

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