The importance of an improved response of skeletal muscle protein synthesis to the ingestion of amino acids is obvious for individuals across the age spectrum, and particularly the elderly, because skeletal muscle mass declines with advancing age.

Ingestion of extra leucine may be particularly important for the stimulation of skeletal muscle protein synthesis in the elderly, because evidence from animal studies indicates that skeletal muscle protein synthesis becomes less responsive to the stimulatory effects of leucine with aging.

The purpose of this study was to determine the acute effects of two different EAA mixtures on skeletal muscle protein metabolism in elderly and young subjects, a mixture that is based on the distribution of EAAs in whey protein (~26% leucine) and a similar mixture that is enriched in leucine (41% leucine). We determined muscle protein synthesis by calculating the incorporation rate of L-[ring-2H5]phenylalanine in the skeletal mixed muscle protein pool and muscle protein retention by measuring the leg arteriovenous net balance of phenylalanine.

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