This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Many adults experience a progressive loss of skeletal muscle mass with increasing age. This concomitant loss of contractile tissue and functional capacity (i.e., sarcopenia) contributes to increased risk of falls, bone fracture and may substantially impair many activities of daily living. Given the fact that net muscle protein synthesis is a major metabolic determinant of muscular strength and functional capacity, the goal of this study is to determine if a leucine enhanced amino acid drink will stimulate net muscle protein synthesis to a greater extent compared to an equivalent (same weight in terms of amino acid composition) amino acid drink containing only the essential amino acids. The direct comparison of those two drinks will provide new information on the effects of including a larger amount of leucine (compared to the other essential amino acids) in a drink, which will serve as important preliminary data for subsequent investigations looking at optimizing amino acid supplementation in elderly individuals. To achieve the goals of this research, a total of 8 healthy patients with no prior cardiovascular or peripheral vascular disease will participate in this research study. Subjects will be normal healthy males and females between the ages of 60 and 85. The study will consist of two 8-hour trials performed on separate days. The study will examine muscle protein kinetics prior to and following the ingestion of the amino acids containing drinks. Muscle protein kinetics will be determined using established stable isotope tracer methodology, arterial-venous sampling and muscle biopsies.