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We tested the thesis that CHO and protein coingestion would augment muscle protein synthesis (MPS) and inhibit muscle protein breakdown (MPB) at rest and after resistance exercise.Nine men (age = 23.0 ± 1.9 yr, body mass index = 24.2 ± 2.1 kg·m−2) performed two unilateral knee extension trials (four sets × 8-12 repetitions to failure) followed by consumption of 25 g of whey protein (PRO) or 25 g of whey protein plus 50 g of maltodextrin (PRO + CARB). Muscle biopsies and stable isotope methodology were used to measure MPS and MPB.The areas under the glucose and insulin curves were 17.5-fold (P < 0.05) and 5-fold (P < 0.05) greater, respectively, for PRO + CARB than for PRO. Exercise increased MPS and MPB (both P < 0.05), but there were no differences between PRO and PRO + CARB in the rested or exercised legs. Phosphorylation of Akt was greater in the PRO + CARB than in the PRO trial (P < 0.05); phosphorylations of Akt (P = 0.05) and acetyl coA carboxylase-β (P < 0.05) were greater after exercise than at rest. The concurrent ingestion of 50 g of CHO with 25 g of protein did not stimulate mixed MPS or inhibit MPB more than 25 g of protein alone either at rest or after resistance exercise.Our data suggest that insulin is not additive or synergistic to rates of MPS or MPB when CHO is coingested with a dose of protein that maximally stimulates rates of MPS.