Acute Intermittent Hypoxia on Leg Function Following Spinal Cord Injury

Inclusion Criteria: * 18 to 75 years old (the latter to reduce likelihood of heart disease); * medically stable with clearance from physician to participate; * motor---incomplete SCI at C2---L5 with non---progressive etiology; * \>6 months since SCI to ensure minimal confounds of spontaneous neurological recovery; * those classified as ambulatory must have the ability to advance one step overground without human assistance. Exclusion Criteria: * concurrent illness, including unhealed decubiti, severe neuropathic or chronic pain syndrome, infection, cardiovascular disease, osteoporosis (history of fractures), active heterotopic ossification, or known history of peripheral nerve injury to legs; * less than 24 on the Mini-mental Exam; * recurrent autonomic dysreflexia * cardiopulmonary complications * concurrent physical therapy * pregnancy because of unknown effects of AIH on a fetus, although women will not otherwise be excluded