Power analyses indicated that a sample size of 80 subjects would be sufficient to detect anticipated effects on primary outcomes: operative leg quadriceps volume (MRI), non-operative leg quadriceps volume (MRI), isometric strength, Get Up And Go test, stair climb up test, stair climb down test, and six-minute walk test. The mean effect size across these outcomes, based on baseline- to 6-week percent change in pilot data) was d = 1.01, reflecting large effects. For a sample size of 30/group, this study can detect ESs of d > .79 with 85% power, and the minimally detectable ES drops to 0.68 or 0.52 with pretest covariates of r = .50 or .75. Every effort will be made to reduce attrition and obtain data on all participants at all assessment points. However, attrition is expected. Because this study will have power to detect anticipated physiological and functional effects with 30 subjects per condition, we will enroll 80 total subjects (40/condition) to account for possible attrition.