 All participants will complete questionnaires before beginning their assigned training programs and then every 3 months till Month 24. The questionnaires will take between 30 and 60 minutes to complete. At various times during the study, participants will measure their activity levels with a pedometer or an accelerometer. Prior to starting the training programs, at Month 9, and after completing the training programs, participants will complete several tests to measure their physical capabilities and muscle strength. Upon completing the training programs, participants will receive a follow-up x-ray of their knees at an assigned radiology clinic. They will also be asked to provide feedback on their study experiences via a mailer questionnaire, and they may be asked to provide feedback in a short telephone interview. 