Our goal is to enhance repeated exposure to acute intermittent hypoxia (rAIH)/training-induced aftereffects on upper and lower limb function recovery in humans with chronic spinal cord injury (SCI).

The experiments in this study will test the following: Hypothesis 1.1(Experiment 1) that rAIH will enhance corticospinal excitability and upper and lower limb function in humans with incomplete SCI. Hypothesis 1.2 (Experiment 2) that enhancing the aftereffects of rAIH with exercise training will further enhance upper and lower limb motor function in humans with incomplete SCI. Measurements of corticospinal, cortical, and motoneuron excitability will be tested to further understand the mechanisms of this induced-plasticity. Persons with chronic (>6 months) spinal cord injury between the levels of C2 and T2. SCI subjects must possess either the ability to produce a visible precision grip force with one hand, and/or the ability to perform some small wrist flexion and extension. Additionally, subject must possess the ability to perform a small visible contraction with dorsiflexion and hip flexor muscles. Controls must be right handed due to potential differences in the organization of the brain in right handed and left handed individuals.

Inclusion criteria for SCI:

1. Males and females between 18-85 years
2. Chronic SCI (≥ 6 months post injury)
3. SCI at or above L2
4. ASIA A, B, C, or D, complete or incomplete
5. Possess the following: The ability to produce a visible precision grip force with one hand, and/or the ability to perform some small wrist flexion and extension. The ability to perform a small visible contraction with dorsiflexion and hip flexor muscles.

Inclusion criteria for controls:

1. Males and females between 18-85 years
2. Right-handed (Only right-handed individuals will be accepted into this group because of the potential differences in the organization of the brain in right handed and left handed individuals)

Exclusion criteria for SCI and for controls:

1. Uncontrolled medical problems including pulmonary, cardiovascular or orthopedic disease
2. Any debilitating disease prior to the SCI that caused exercise intolerance
3. Premorbid, ongoing major depression or psychosis, altered cognitive status
4. History of head injury or stroke
5. Metal plate in skull
6. History of seizures
7. Receiving drugs acting primarily on the central nervous system, which lower the seizure threshold such as antipsychotic drugs (chlorpromazine, clozapine) or tricyclic antidepressant
8. Pregnant females
9. Ongoing cord compression or a syrinx in the spinal cord or a spinal cord disease as spinal stenosis, spina bifida or herniated cervical disk.

AIH exclusion criteria (in addition to the above listed exclusion criteria)

1. Resting heart rate ≥120 BPM
2. Resting systolic blood pressure >180 mm Hg
3. Resting diastolic Blood Pressure >100 mmHg
4. Self-reported history of unstable angina or myocardial infarction within the previous month
5. Resting SpO2 ≥ 95%
6. Cardiopulmonary complications such as COPD