Inclusion Criteria:
Healthy Volunteers
* Age between 16 and 65 years old
* Healthy people with no major comorbidities of any organ system
Exclusion Criteria:
Healthy Volunteers
* Subjects younger than 16 or older than 65 years old
* Subjects not providing consent or not able to consent
* Subjects with any acute or chronic pain condition
* Subjects with any acute or chronic disease of a major organ system
* Use of analgesics within 24 hours prior to study period
* Use of caffeine with 3 hours of study appointment
Inclusion criteria:
Participants with spinal cord injury (SCI)
* Age between 16-65 years old
* Traumatic SCI C4-T9 level, incomplete (ASIA C or D)
* at least 1 year post injury
* Stable medical condition
* difficulty independently performing leg movements in routine activities
* able to follow simple commands
* able to speak and respond to questions
Exclusion criteria:
Participants with spinal cord injury (SCI)
* Subjects younger than 16 or older than 65 years old
* Not willing or able to provide consent
* Any acute or chronic pain condition
* Any acute or chronic disease of a major organ system
* Use of analgesics within 24 hours prior to study appointment
* Use of caffeine with 3 hours of study appointment
* Presence of tremors, spasms and other significant involuntary movements
* Etiology of SCI other than trauma
* Concomitant neurologic disease traumatic brain injury (TBI) that will significantly impact the ability to follow through on study directions, multiple sclerosis (MS), stroke or peripheral neuropathy)
* History of significant medical illness (cardiovascular disease, uncontrolled diabetes, uncontrolled hypertension, osteoporosis, cancer, chronic obstructive pulmonary disease, severe asthma requiring hospitalization for treatment, renal insufficiency requiring dialysis, autonomic dysreflexia, etc).
* Severe joint contractures disabling or restricting lower limb movements.
* Unhealed fracture, contracture, pressure sore, urinary tract infection or other uncontrolled infections, other illnesses that might interfere with lower extremity exercises or testing activities
* Depression, anxiety, or cognitive impairment
* Deficit of visuospatial orientation
* Sitting tolerance less than 1 hour
* Severe hearing or visual deficiency
* Miss more than 3 appointments without notification
* Unable to comply with any of the procedures in the protocol
* Botulinum toxin injection in lower extremity muscles in the prior six months
* Any passive implants (osteosynthesis material, metallic plates or screws) below T9.
* Any implanted stimulator in the body (pacemaker, vagus nerve stimulator, etc.)
* History of alcoholism or another drug abuse
* Pregnancy (or possible pregnancy)
* Having an Intrathecal Baclofen Therapy Pump (ITB pump)
* History of epilepsy
