The study will use a two-arm parallel design to determine the effect of EAA supplementation on post-TKA muscle cell structure and function, and quality of life in the shorter term (6 months post-TKA) and long term (1 yr post-TKA) vs. Placebo. Subjects will be 80 older male and female adults having primary TKA at the Slocum Center for Orthopedics and Sports Medicine, Eugene, Oregon. Slocum study staff will pre-screen/identify potential subjects for recruitment based on inclusion/exclusion criteria. Eligible patients will be invited to join the study. After the completion of informed consent procedures, participants will be assigned a unique patient identification number, and randomly assigned to either EAA or Placebo on a 1:1 allocation ratio, with blinding of treatment condition to subject and research staff/statisticians collecting data. Twice-daily ingestion of 20 g of supplement will begin 7 days prior to TKA and end at 6 wks post. EAA subjects will receive EAA and Placebo subjects will receive the non-essential amino acid Alinine. Subjects will document compliance with the supplement protocol in a log book and will return empty vials. Subjects will be followed for 1 yr.