Co-ingestion of protein or a protein hydrolysate with carbohydrate enhances anabolic signaling, but not glycogen resynthesis, following recovery from prolonged aerobic exercise in trained cyclists

Purpose The effect of carbohydrate (CHO), or CHO supplemented with either sodium caseinate protein (CHO-C) or a sodium caseinate protein hydrolysate (CHO-H) on the recovery of skeletal muscle glycogen and anabolic signaling following prolonged aerobic exercise was determined in trained male cyclists [n = 11, mean +/- SEM age 28.8 +/- 2.3 years; body mass (BM) 75.0 +/- 2.3 kg; VO2peak 61.3 +/- 1.6 ml kg(-1) min(-1)]. Methods On three separate occasions, participants cycled for 2 h at similar to 70% VO2peak followed by a 4-h recovery period. Isoenergetic drinks were consumed at + 0 and + 2 h of recovery containing either (1) CHO (1.2 g kg (-1) BM), (2) CHO-C, or (3) CHO-H (1.04 and 0.16 g kg(-1) BM, respectively) in a randomized, double-blind, cross-over design. Muscle biopsies from the vastus lateralis were taken prior to commencement of each trial, and at + 0 and + 4 h of recovery for determination of skeletal muscle glycogen, and intracellular signaling associated with protein synthesis. Results Despite an augmented insulin response following CHO-H ingestion, there was no significant difference in skeletal muscle glycogen resynthesis following recovery between trials. CHO-C and CHO-H co-ingestion significantly increased phospho-mTOR Ser(2448) and 4EBP1 Thr(37/46) versus CHO, with CHO-H displaying the greatest change in phospho-4EBP1 Thr(37/46). Protein co-ingestion, compared to CHO alone, during recovery did not augment glycogen resynthesis. Conclusion Supplementing CHO with intact sodium caseinate or an insulinotropic hydrolysate derivative augmented intracellular signaling associated with skeletal muscle protein synthesis following prolonged aerobic exercise.