Factors That Influence the Amount of Protein Necessary to Maximize the Anabolic Response of Muscle following Resistance Exercise

• The metabolic basis for changes in muscle mass is net muscle protein balance, i.e., the balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Changes in MPS are responsible for a much greater proportion of the change in net muscle protein balance than are changes in MPB. • Many factors influence the response of MPS to protein ingestion following resistance exercise. However, the amount of protein consumed in a single serving following exercise is the most important factor that determines the magnitude of the MPS response. • The increase in MPS with increasing amounts of ingested protein is not infinite and plateaus at some optimal amount of ingested protein. • The optimal amount of protein to consume following exercise varies depending on a number of factors, including the characteristics of the exercise bout (i.e., leg-only vs. whole-body), the age of the individual, type of protein ingested and possibly the amount of muscle mass an individual possesses. • The ingestion of 20-25 g of high-quality protein seems to be sufficient to maximally stimulate MPS in healthy young males following leg-only resistance exercise. However, it is clear that ingesting 20 g of protein does not maximally stimulate MPS under all circumstances. • The amount of protein necessary to maximally stimulate MPS increases when exercising with greater amounts of muscle, increasing age and ingestion of proteins with inferior amino acid compositions.