Cumulative responses of muscle protein synthesis are augmented with chronic resistance exercise training

Aim: The purpose of this study was to determine the anabolic response of a single bout of high intensity resistance exercise (RE) following 5 weeks of RE training. Methods: To complete these studies, Sprague-Dawley rats were assigned by body mass to RE, exercise control (EC), or sedentary cage control (CC) groups and studied over 36 h after 5 weeks of RE (squat-like) training. Cumulative (final 36 h) fractional rates of muscle protein synthesis (FSR) were determined by 2H(2)O, and acute (16 h post-RE) rates of muscle protein synthesis (RPS) were determined by flooding with l-[2,3,4,5,6-3H]phenylalanine. Regulators of peptide-chain initiation, 4E-BP1, eIF4E and the association of the two were determined by Western blotting and immunoprecipitation respectively. Results: No differences were observed with acute measures of RPS obtained 16 h following the final exercise bout in the plantaris or soleus muscles (P > 0.05). Consistent with this observation, 4E-BP1 was similarly phosphorylated and bound to eIF4E among all groups. However, upon determination of the cumulative response, FSR was significantly increased in the plantaris of RE vs. EC and CC (0.929 +/- 0.094, 0.384 +/- 0.039, 0.300 +/- 0.022% h-1 respectively; P < 0.001), but not the soleus. Conclusion: With the advantage of determining cumulative FSR, the present study demonstrates that anabolic responses to RE are still evident after chronic RE training, primarily in muscle composed of fast-twitch fibres.