The specific aims of this study are listed below: 1a) Evaluate the ergonomics of the wearable device that will be used to record and detect spasms, then to deliver vibration to tendons to dampen spasms. 1. b) Determine the vibration parameters that best reduce spasms in leg muscles paralyzed by spinal cord injury (SCI) in the laboratory using the wearable device. 2. a) Examine the efficacy of tendon vibration in altering muscle spasms by treating spasms as they occur in real world environments using 24-hour electromyographic (EMG) recordings. Hypothesis 2a: Achilles tendon vibration will dampen spasms acutely, and may alter their distribution Assess excitatory and/or inhibitory mechanisms that underlie spasms, and changes induced with vibration, by recording physiological, clinical, functional and self-reported measures of different aspects of spasticity, and health-related quality of life, before and after conditioning spasms with vibration. These data will provide insight into the site(s), magnitude, and time-course of changes with vibration; and user perspective on the effects of the therapy. Achilles tendon vibration will dampen spasms by reconfiguring circuits generating 6-13 Hz shared drive to motoneurons.
Inclusion Criteria: - Male and females between ages 18-85 years of age - SCI ( ≥1 month of injury) - ASIA A, B,C and D - SCI above L5 - Able to perform a visible contraction with dorsiflexor and hip flexor muscles (allowing testing of largely impaired patients) - Able to ambulate a few steps with or without an assistive device. Inclusion criteria for healthy controls: - Male and females between ages 18-85 years - Able to complete precision grips with both hands - Able to complete full elbow flexion-extension with both arms. - Able to walk and complete lower-limb tests with both legs. Exclusion Criteria: - Uncontrolled medical problems including pulmonary, cardiovascular or orthopedic disease, - Any debilitating disease prior to the SCI that caused exercise intolerance - Premorbid, ongoing major depression or psychosis, altered cognitive status - History of head injury or stroke, - Metal plate in skull - History of seizures - Receiving drugs acting primarily on the central nervous system, which lower the seizure threshold such as antipsychotic drugs (chlorpromazine, clozapine) or tricyclic antidepressants. - Pregnant females, and - Ongoing cord compression or a syrinx in the spinal cord or who suffer from a spinal cord disease such as spinal stenosis, spina bifida or herniated cervical disk. This information will be obtained by self-report.