Reduced muscle strength from illness or injuries often leads to loss of function and independence in the elderly. The recovery of muscle strength and function in disabled elderly individuals is a major challenge in rehabilitation. The etiology of the muscle weakness with injury or age is not fully elucidated. Training programs designed to maximize strength gains in young individuals may not be optimal in the elderly because the cause of the weakness and the morphology of the muscle may be different for young vs. old people. The overall goal of this work is to determine if physiologically and morphologically based rehabilitation programs are more effective than traditional rehabilitation to counter changes in muscle strength and function in older individuals. Neuromuscular electrical stimulation (NMES) may be used to improve strength and function following injury or surgery. This study provides motivation for exploring the use of NMES with the elderly. We posit that using NMES to augment a traditional rehabilitation program for elderly patients with osteoarthritis following total knee arthroplasties (TKA) will result in greater strength and functional gains than using only traditional rehabilitation. Elderly patients with osteoarthritis who undergo TKAs serve as ideal subjects for testing the effectiveness of rehabilitation programs become those patients almost always exhibit marked quadriceps weakness that is resistant to traditional physical rehabilitation. More than 300,000 TKAs are performed each year in the United States to treat osteoarthritis of the knee in older individuals. So, the successful rehabilitation of elder patients following TKA is an important and challenging problem. The specific aims of this proposal are: 1) To assess the effectiveness of high-level neuromuscular electrical stimulation is an adjunct to ongoing intensive, early rehabilitation in restoring quadriceps strength and improving the functional outcome after primary TKA, and 2) To identify the physiological and morphological bases for improvements in quadriceps strength and functional outcome