Sample Size To ensure that the study is properly powered to detect a difference between groups with a power = 0.90, α = 0.05, µ1 = 14 (unrestricted mobility), µ2 = 21 (immobilized), δ = 10, a total of 88 participants is required (44 to each group). To allow for attrition of sample size in the first year, we will enroll up to 100 subjects (50 in each study arm).