For the tracer study, a forearm catheter will be placed for tracer infusion, and a retrograde catheter will be placed in the opposite hand for arterialized blood sampling, with the hand heated thereafter. After collecting a background blood sample, a primed-continuous infusion of L-[ring-13C6] Phenylalanine (priming dose=2 umol/kg; infusion rate = 0.05 umol/kg/min) will be started to measure muscle protein synthesis and boluses of [methyl d3] methionine (17.5umol/kg) and [methyl d3] 3-methylhistidine (0.5umol/kg) will be infused to measure myofibrillar protein synthesis and breakdown using the pulse-bolus method when the leucine is taken. At t=2 the first muscle biopsy will be taken from the vastus lateralis using aseptic procedure and local anesthesia with lidocaine to measure basal muscle protein synthesis rate with the precursor-product model (see E. Human Subjects for details on protections against risks), cell signaling, and redox homeostasis (reduced and total glutathione). Between t=5 and t=7, frequent arterialized blood samples will be taken from the hand vein to measure phenylalanine, methylhistidine and methionine enrichments and concentrations; additionally, blood flow and muscle perfusion will be measured by real-time Doppler and CEU (see Methods). At the end of basal period (t=5) a second, muscle biopsy will be taken to measure muscle protein synthesis.