Purpose: We examined the impact of an acute bout of resistance-type exercise on mixed muscle protein synthesis in the fed state.
Methods: After a standardized breakfast, 10 untrained males completed a single, unilateral lower-limb resistance-type exercise session. A primed, continuous infusion of l-[ring-13C6]phenylalanine was combined with muscle biopsy collection from both the exercised (Ex) and the nonexercised (NEx) leg to assess the impact of local muscle contractions on muscle protein synthesis rates after food intake. Western blotting with phosphospecific and pan antibodies was used to determine the phosphorylation status of AMP-activated kinase (AMPK), 4E-binding protein (4E-BP1), mammalian target of rapamycin (mTOR), and p70 ribosomal protein S6 kinase (S6K1).
Results: Muscle protein synthesis rates were approximately 20% higher in Ex compared with NEx (0.098% ± 0.005% vs 0.083% ± 0.002%·h−1, respectively, P < 0.01). In the fed state, resistance-type exercise did not elevate AMPK phosphorylation. However, the phosphorylation status of 4E-BP1 was approximately 20% lower after cessation of exercise in Ex compared with NEx (P < 0.05). Conversely, 4E-BP1 phosphorylation was significantly higher in Ex compared with NEx after 6 h of recovery (P < 0.05) with no changes in mTOR phosphorylation. S6 phosphorylation was greater in Ex versus NEx after cessation of exercise (P < 0.05), although S6K1 phosphorylation at T389 was not up-regulated (P > 0.05).
Conclusion: We conclude that resistance-type exercise performed in a fed state further elevates postprandial muscle protein synthesis rates, which is accompanied by an increase in S6 and 4E-BP1 phosphorylation state.