Major Accomplishments This project represents a combination of two NASA-funded protocols, which investigated nutritional countermeasures to activity-induced sarcopenia. Our previous NASA project demonstrated that essential amino acid supplementation (EAA) throughout bed rest preserved lean body mass and reduced the loss of muscle function. However, the supplement we utilized was not feasible for delivery during space flight. The general goal of the current proposal is to reduce the amount of supplement required by optimizing the composition, the amount, and the timing of ingestion in order to effectively minimize the loss of lean body mass and function. Since the protocols of Drs. Wolfe and Ferrando were designed to be complementary, we have included them under one institutional review board (IRB) protocol at University of Arkansas for Medical Sciences (UAMS). Thus, this report will detail progress in both grant projects. Since our move to UAMS, we have completed three important study groups related to the goals of this project. The aims we focused upon represented the testing of a more practical approach to the delivery of EAA in an astronaut population. We have completed the following specific aims: 1. Determine if the addition of 3 g of leucine to meals results in a stimulation of muscle protein synthesis over a 24 hr period. Two groups of subjects were studied during short-term bed rest; a control and a leucine group. In the control group, we enrolled 12 subjects and studied 8, while in the leucine group, we enrolled 8 and studied 8. While analyses are currently underway, preliminary data indicates that muscle protein synthesis was greater during the first day of bed rest with the leucine supplementation. It does not appear; however, that leucine supplementation was effective in stimulating muscle protein synthesis on subsequent days of inactivity. 2. Determine if ingestion of 7.5 g of EAA three times per day between meals will efficiently (gm protein synthesized/gm ingested) stimulate muscle protein synthesis. This group will be compared to a control group consisting of 2-day bed rest alone. We hypothesize that 7.5 g EAA will preserve muscle protein synthesis during bed rest. While 8 control subjects were studied, we also enrolled 10 and studied 7 subjects given 7.5 g of EAA TID (three times a day) throughout bed rest. Based upon our previous work, we anticipate that the addition of 7.5 g of EAA TID will result in an increase synthetic response. While these analyses are ongoing, this dosage allows us to ascertain a dose-response of EAA, given our previous results with the maximal response of 15 g.