2. Physical Performance Testing. There is a risk of the participant losing their balance and falling associated with the physical performance-based testing (e.g., the fast 400-meter walk test, balance tests, rising from a chair, muscle strength and power testing). In rare instances persons doing the fast 400-meter walk test will experience leg or chest pain, heart palpitations, shortness of breath. In very rare situations exercise can result in heart attack or sudden death. We will minimize this risk by: (1) safely escorting participants to chairs located along the walking course should they become unsteady; (2) following them at a close distance; and, (3) being at their side should they need assistance. There is a risk that participants may experience muscle soreness, strains, pulls, falls or joint injury or discomfort as a result of the physical performance testing procedures. A warm-up and range of motion practice will be conducted before maximal strength testing. In addition, if a participant reports pain, dizziness, lightheadedness or other medical problem during the test, the test will be terminated.