High Intensity Exercise in Incomplete SCI

Inclusion criteria * Individuals with motor incomplete SCI (AIS C or D) \> 12 mo. duration will be recruited to participate in the study, with further criteria including anatomical lesions between C1-T10.. * Participants will be between 18 and 75 years of age (note: while participants \> 50 yrs with subacute SCI have a reduced probability of functional ambulation 79, participants will already be ambulatory with only minimal or no assistance and in the chronic phase of rehabilitation, and prediction rules using age will not necessarily apply in this study). * All participants must be able to perform walking training with passive range of motion within the limits of normal locomotor function, including: 0-30 degrees ankle plantarflexion, knee flexion from 0 to 90 degrees, hip flexion to 0-90 degrees. Exclusion criteria: * Participants with body mass \> 400 lbs will be excluded, which is the highest limit for use of our motorized treadmill and safety harness systems. * Participants will be medically stable with medical clearance to participate, with absence of concurrent severe medical illness including: unhealed decubiti, existing infection, significant cardiovascular or metabolic disease which limits exercise participation, significant osteoporosis (as indicated by history of fractures following injury), active heterotrophic ossification in the lower extremities, known history of peripheral nerve injury in lower legs, history of traumatic brain injury, and history of pulmonary complications that limits exercise capacity, including significant obstructive and/or restrictive lung diseases. * Participants who are ventilator-dependent will be excluded secondary to severely impaired respiratory capacity. * Participants with substantial orthopedic bracing to stabilize the cervical or thoracic vertebral column are not eligible due to safety concerns with harness supported ambulation training.. * Patients will also be excluded if they are unable to tolerate 10 minutes of standing without orthostasis (decrease in blood pressure by 20 mmHg systolic and 10 mmHg diastolic); previous experience in the sub-acute population suggests that 10 minutes of standing is more than sufficient for tolerating 45 minutes of walking secondary to increased activity/muscle pump minimizing risk for orthostasis. * Individuals who are undergoing concurrent physical therapy will be excluded from the study population to eliminate confounding effects of additional physical interventions, Other therapies, such as occupational or speech therapies, will be allowed as prescribed by their physician. Individuals will be allowed and encouraged to continue their normal exercise routines during the course of the intervention, with activity monitors measuring stepping activity in all participants * Women of childbearing potential will not be excluded, although women who are pregnant or who are considering becoming pregnant will be excluded due to the trunk and pelvis restraints required for use during locomotion. * All subjects prescribed oral anti-spastic medications will not be excluded, although patients with intrathecal baclofen pumps or history of recent (\< 3 months) botulinum toxin injection in the lower extremities will be excluded due to potential increases in weakness interfering with the effects of stepping training performance. * Patients with a known history of autonomic dysreflexia will not be excluded, although specific signs and symptoms of all patients with history of injury \> T6 anatomical level will be closely monitored throughout training. Other criteria * Men and women will be recruited for participation in the proposed clinical trial at rates consistent with national and local average of gender disparities of SCI (80% male, 20% women). Women of childbearing potential will not be excluded, although women who are pregnant or who are considering becoming pregnant will be excluded due to the trunk and pelvis restraints required for use during locomotion. * Individuals of different ethnicities will be recruited at rates similar to the national and local ethnicity rates. Current data since 2005 indicate that of the entire population of SCI, 66.1% are Caucasian, 27.1% are African American, 6.6% are of Hispanic origin, and 2.0% Asian. These populations closely resemble those at RHI and in our previous studies in human SCI.