 This study will last 1 year. All participants will visit the hospital 3 times, at study entry and Months 6 and 12. At each visit, height and weight will be measured, muscle strength and balance will be tested, and bones and muscles in the spine and lower leg will be imaged with computed tomography CT, a special x-ray machine. Participants will be randomly assigned to one of two groups. For this study, all participants will be asked to stand for 10 minutes every day for 1 year. For Group 1, a vibrating platform will be used for the 10-minute standing sessions during the first half of the study but not during the second half of the study. For Group 2, this will be reversed and the vibrating platform will not be used during the first half of the study but will be used during the second half of the study. 