Pairing Intermittent Hypoxia and Transcutaneous Electrical Spinal Cord Stimulation to Promote Arm Use After Cervical SCI

Inclusion Criteria: * 18 to 65 years old * medically stable with medical clearance from physician to participate * SCI at or below C3 and at or above C7 * non-progressive etiology of spinal injury * American Spinal Injury Association Impairment Scale (AIS) C-D at initial screen * at least 1 year post-injury (chronic) * difficulty independently performing hand functions in activities of daily living Exclusion Criteria: * dependence on ventilation support * implanted stimulator (e.g. diaphragm pacing by phrenic nerve stimulation, vagus nerve stimulator, pacemaker, cochlear implant, epidural stimulator, baclofen pump, etc.) * spinal cord injury related complications including unhealed pressure sore, severe neuropathic or chronic pain syndrome, history of frequent autonomic dysreflexia, infection (e.g. urinary tract), cardiovascular disease (e.g. deep vein thrombosis), pulmonary disease, heterotopic ossification in the upper extremities, severe osteoporosis, unhealed fracture, contracture of the upper extremity joints * received botulinum toxin injections in upper extremity muscles in the prior 6 months * history of tendon or nerve transfer surgery in the upper extremity * history of additional neurologic disease, such as stroke, multiple sclerosis, traumatic brain injury, peripheral neuropathy (diabetic polyneuropathy, entrapment neuropathy, etc.) or peripheral nerve injury in the upper extremity * history of concomitant diseases that would prevent full participation in intensive exercise therapy, such as uncontrolled hypertension, rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus, etc.), pulmonary disease, active cancer, chronic contagious disease, etc. * anticoagulation medication * pregnancy * history of allergic reaction or any skin reaction to use of adhesive electrodes