Inclusion Criteria:  Male or female 18-75 years. > 1 year post-injury. Non-progressive SCI at C2-C7. Motor Complete ASIA Impairment Scale (A, B). Ventilator dependency with less than 5 cm H20 maximal inspiratory and expiration pressure. Able to attend weekly testing sessions for up to 21 months. Have intact chest/lung, upper and lower extremity anatomy. The neuromuscular connections between the spinal cord and its effector muscles (respiratory and extremity) are required to be intact. Have intact cognitive ability, able to follow commands/voice concerns, and give consent.  Exclusion Criteria:  History of severe autonomic dysreflexia Phrenic nerve or diaphragm pacer Phrenic nerve paralysis Musculoskeletal dysfunction, unhealed fracture, pressure ulcer, active infection Clinically significant depression or ongoing drug abuse Received lung surgery or intrinsic lung disease (COPD, acute or chronic lung infection, asthma, emphysema, cystic fibrosis, etc)