 This study will use these load-sensing platforms in patients with neuromuscular conditions. Successful completion of this pilot study will assist in the development of a future multicenter clinical trial to definitively determine relationships, if any, between passive standing and measures of BMD, fracture incidence, pulmonary function, and health-related quality-of-life measures in children with a variety of neuromuscular disabilities e.g., spinal muscular atrophy, cerebral palsy, muscular dystrophy, spina bifida, Rett syndrome. 