Statistical Considerations The primary analysis will compare difference in changes in study outcomes from 0 to 12 weeks between the two treatment arms InterWalk vs control. For the primary outcome, VO2peak, assuming a standard deviation of 2 ml/kg/min, 16 patients in each group will provide 80% power to detect a between group difference of +2 ml/kg/min in. To account for a potential attrition-rate of up to 20%, 20 patients will be included in each group.