Seven young men (age: 22±1 y) will undergo repeated blood and biopsy sampling during primed continuous L-[ring-2H5]phenylalanine and L-[1-13C]leucine tracer infusions, and ingested 38 g of L-[1-13C]phenylalanine- and L-[1-13C]leucine-labeled milk protein concentrate

The macronutrient composition and energy of the milk protein beverage provided to participants is 38 g protein (3.46 g leucine), 4.17 g carbohydrate, and 1.4 g fat. The milk protein met all chemical and bacteriologic specifications for human consumption. The L-[1-13C]phenylalanine and L-[1-13C]leucine enrichments in the milk protein concentrate averaged 38.3 and 10.8 mole percent excess (MPE), respectively.

Myofibrillar protein synthesis rates will be assessed during the postabsorptive period for 3 hours, and every 1-2 hours during the 5 hours after protein ingestion. This will allow us assess the timecourse of muscle protein synthesis after eating.

Phosphorylation of anabolic signaling pathways (mTORC1, AKT, and P70S6K) involved in the stimulation of myofibrillar protein synthesis rates will be assessed during the postabsorptive period for 3 hours, and every 1-2 hours during the 5 hours after protein ingestion.