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ORIGINAL RESEARCH COMMUNICATION |
1 From the Exercise Metabolism Research Group, Department of Kinesiology (DRM, MJR, JLF, JET, EIG, SBW, TP, and SMP), and Departments of Neurology and Pediatrics (MAT), McMaster University, Hamilton, Canada.
2 Supported by a grant from the Natural Sciences and Engineering Research Council (NSERC) of Canada. DRM and SBW were supported by Canada Graduate Scholarships from the Canadian Institutes for Health Research (CIHR). MJR was supported by an NSERC Undergraduate Student Research Award. JLF was supported by a McMaster University Undergraduate Student Research Award. JET and EIG were supported by CIHR Doctoral Research Awards. SMP was the recipient of a CIHR New Investigator career award. 3 Reprints not available. Address correspondence to SM Phillips, Department of Kinesiology, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1. E-mail: phillis{at}mcmaster.ca.
Background: The anabolic effect of resistance exercise is enhanced by the provision of dietary protein.
Objectives: We aimed to determine the ingested protein dose response of muscle (MPS) and albumin protein synthesis (APS) after resistance exercise. In addition, we measured the phosphorylation of candidate signaling proteins thought to regulate acute changes in MPS.
Design: Six healthy young men reported to the laboratory on 5 separate occasions to perform an intense bout of leg-based resistance exercise. After exercise, participants consumed, in a randomized order, drinks containing 0, 5, 10, 20, or 40 g whole egg protein. Protein synthesis and whole-body leucine oxidation were measured over 4 h after exercise by a primed constant infusion of [1-13C]leucine.
Results: MPS displayed a dose response to dietary protein ingestion and was maximally stimulated at 20 g. The phosphorylation of ribosomal protein S6 kinase (Thr389), ribosomal protein S6 (Ser240/244), and the 
-subunit of eukaryotic initiation factor 2B (Ser539) were unaffected by protein ingestion. APS increased in a dose-dependent manner and also reached a plateau at 20 g ingested protein. Leucine oxidation was significantly increased after 20 and 40 g protein were ingested.
Conclusions: Ingestion of 20 g intact protein is sufficient to maximally stimulate MPS and APS after resistance exercise. Phosphorylation of candidate signaling proteins was not enhanced with any dose of protein ingested, which suggested that the stimulation of MPS after resistance exercise may be related to amino acid availability. Finally, dietary protein consumed after exercise in excess of the rate at which it can be incorporated into tissue protein stimulates irreversible oxidation.
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