A total of 200 subjects will participate in this study. Functional and strength testing provides information for the patients’ clinical treatment and allow us to monitor their progress. This information will also help in the design of a training program for individuals following a total knee replacement that optimizes the return to full level of function after surgery. MRI screening will provide information regarding the size of the thigh muscle at various periods throughout rehabilitation. It will enable us to assess the impact of post-operative treatment on increasing the size of the thigh muscle. Patients will be asked to participate in functional and strength testing sessions, lasting about 1½ hours, at the following times: 0-2 weeks before surgery, 3-4 weeks, 6-7 weeks, 10-12 weeks, 6 months, 1 year, and 2 years after surgery. MRI testing will last about 30 minutes per session and will be performed 0-2 weeks before surgery, and 3-4 weeks, 10-12 weeks, and 1 year after surgery.