A low-protein (6.25 g) mixed macronutrient beverage can be as effective as a high-protein dose (25 g) at stimulating increased MPS rates when supplemented with a high (5.0 g total leucine) amount of leucine. These results have important implications for formulations of protein beverages designed to enhance muscle anabolism. This trial was registered at clinicaltrials.gov as NCT 1530646.

Di Donato DM, West DW, Churchward-Venne TA, Breen L, Baker SK, Phillips SM. Influence of aerobic exercise intensity on myofibrillar and mitochondrial protein synthesis in young men during early and late postexercise recovery. Am J Physiol Endocrinol Metab 306: E1025-E1032, 2014. First published March 3, 2014 doi:10.1152/ajpendo.00487.2013.-Aerobic exercise is typically associated with expansion of the mitochondrial protein pool and improvements in muscle oxidative capacity. The impact of aerobic exercise intensity on the synthesis of specific skeletal muscle protein subfractions is not known. We aimed to study the effect of aerobic exercise intensity on rates of myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis over an early (0.5-4.5 h) and late (24 -28 h) period during postexercise recovery. Using a within-subject crossover design, eight males (21 Ϯ 1 yr, V O2peak 46.7 Ϯ 2.0 ml·kg Ϫ1 ·min Ϫ1 ) performed two work-matched cycle ergometry exercise trials (LOW: 60 min at 30% W max; HIGH: 30 min at 60% W max) in the fasted state while undergoing a primed constant infusion of L-[ring-13 C6]phenylalanine. Muscle biopsies were obtained at rest and 0.5, 4.5, 24, and 28 h postexercise to determine both the "early" and "late" response of MyoPS and MitoPS and the phosphorylation status of selected proteins within both the Akt/mTOR and MAPK pathways. Over 24 -28 h postexercise, MitoPS was significantly greater after the HIGH vs. LOW exercise trial (P Ͻ 0.05). Rates of MyoPS were increased equivalently over 0.5-4.5 h postexercise recovery (P Ͻ 0.05) but remained elevated at 24 -28 h postexercise only following the HIGH trial. In conclusion, an acute bout of high-but not low-intensity aerobic exercise in the fasted state resulted in a sustained elevation of both MitoPS and MyoPS at 24 -28 h postexercise recovery.Aerobic exercise intensity; myofibrillar and mitochondrial protein synthesis ADAPTATIONS TO AEROBIC-BASED EXERCISE include increases in mitochondrial protein content (both size and number of mitochondria) and subsequent improvements in muscle oxidative capacity and resistance to fatigue (20). Additionally, traditional aerobic exercise (16, 18) as well as high-intensity "sprint" training (19, 33) can also enhance skeletal muscle hypertrophy, an adaptation that would be contingent upon stimulation of myofibrillar protein synthesis (MyoPS) and expansion of the myofibrillar protein pool (31). Specific phenotypic outcomes (i.e., improved oxidative capacity and muscle hypertrophy) in response to divergent exercise stimuli must relate to changes in the synthesis of specific muscle protein subfractions and may be altered by the intensity of exercise (35). For example, workmatched performance of high-intensity resistance exercise results in greater rates of MyoPS than low-intensity resistance exercise (6,22). An increase in the rate of mixed muscle protein synthesis has been reported after an acute bout of aerobic-based exercise (8,17,27); however, such measures preclude insight into the synthetic response of ...