Key research questions are: (a) Does EAA prevent shorter-term (6 wks post-TKA) bilateral muscle atrophy, preserve quadriceps strength, and accelerate the return of functional mobility vs. Placebo? (b) Are there shorter-term sex differences on outcome measures? (c) Will EAA increase longer-term (6 mo post-TKA) quadriceps strength and functional mobility vs. Placebo? (d) Does EAA improve long-term (1 yr post-TKA) functional mobility and measures of quality of life vs. Placebo? (e) Are there long-term sex differences in functional mobility or measures of quality of life? Assessment points will be at 6 wks, 4 wks, and 1 wk prior to surgery, and 1 wk, 2 wks, 6 wks, 6 mos, and 1 yr post-TKA. At different assessment points, we will collect demographic, medical (e.g., length of hospital stay, tourniquet use), physiological (e.g., muscle biopsy, MRI, DEXA, strength; blood tests), pharmacologic, functional mobility, physical activity (accelerometer), psychometric (e.g., quality of life; Veterans RAND 12-item Health Survey [VR-12]), food intake (3-day diary), physical therapy, and perceived pain data. The following schedule of assessments will be followed: no more than 6 mo pre-TKA (enrollment and screening), 6 wks pre-TKA (screening, surveys, DEXA scan, MRI test, physical activity and food recording), 4 weeks pre-TKA (blood draw, strength and functional mobility testing, muscle and fat biopsy); 1 wk pre-TKA and in hospital (physical activity and food recording); 1 wk post-TKA (physical activity and food recording); 2 wks post-TKA (blood draw, physical activity and food recording); 6 wks post-TKA (blood draw, MRI test, strength and functional mobility testing, physical activity and food recording, muscle and fat biopsy); 3 mos post-TKA (surveys, strength and functional mobility testing, physical activity and food recording); 6 mos post-TKA (surveys, DEXA scan, MRI test, strength and functional mobility testing, physical activity and food recording, muscle and fat biopsy), and 1 yr (surveys, DEXA scan, MRI test, strength and functional mobility testing, physical activity and food recording, muscle and fat biopsy).