Chocolate Milk Consumption Following Endurance Exercise Affects Skeletal Muscle Protein Fractional Synthetic Rate and Intracellular Signaling

Abstract

PURPOSE: The aim was to determine the effects of fat-free chocolate milk consumption during recovery from endurance exercise on skeletal muscle protein fractional synthetic rate (FSR) and phosphorylation of intracellular signaling proteins (ISP) specific to synthesis. METHODS: Moderately trained male runners (N=8, 23.7 ± 1.6 y, 76.0 ± 3.8 kg, BMI = 24.0 ± 0.9, body fat = 14.4 ± 2.0%, VO2peak = 53.1 ± 1.6 mL·kg-1·min-1) participated in a randomized, crossover-design study during which they consumed a eucaloric diet for which protein intake was 1.5 g·kg-1 for two weeks. At the end of each week, participants performed a 45-min run at 65% of VO2peak after which 16 oz. of either fat-free chocolate milk (MILK) or a non-nitrogenous, isocaloric control beverage (CON) was consumed. A primed, continuous infusion of l-[ring-(2)H(5)]phenylalanine was administered to measure FSR. Vastus lateralis muscle biopsy samples and arterialized blood draws were taken during a 3-h recovery interval following the run. Relative phosphorylation of eEF2, mTOR, eIF4E-BP1, and rpS6 was determined to assess translational activity specific to skeletal muscle protein synthesis. RESULTS: FSR and ISP activity were enhanced from 0 to 3 h of recovery (p ≤ 0.05; means ± SE). Post-exercise FSR was higher after MILK than after CON (0.11 ± 0.01 vs. 0.08 ± 0.01 %h-1, N=6). MILK increased relative eIF4E-BP1 (Thr37/46) (0.63 ± 0.03 to 0.88 ± 0.08 AU), while CON had no effect (0.76 ± 0.09 to 0.81 ± 0.06 AU). Neither MILK nor CON affected mTOR (Ser2448) (0.89 ± 0.10 to 0.97 ± 0.11 AU and 0.88 ± 0.11 to 0.97 ± 0.10 AU), rpS6 (Ser235/236) (0.31 ± 0.08 to 0.34 ± 0.07 AU and 0.27 ± 0.10 to 0.29 ± 0.16 AU), or eEF2 (Thr56) (1.46 ± 0.10 to 1.58 ± 0.10 AU and 1.39 ± 0.10 to 1.45 ± 0.06 AU). CONCLUSION: Chocolate milk consumption after an endurance exercise bout enhanced kinetic and translational outcomes of skeletal muscle protein synthesis during recovery. Athletes can consider fat-free chocolate milk as an economic nutritional alternative to other sports nutrition beverages to support post-endurance exercise skeletal muscle repair. Supported in part by Dairy Management, Inc.