Neural Prostheses and Gait Performance: Model-Based Strategies

Inclusion Criteria: This study includes stroke survivors greater than 18 years of age, \>180 days from first clinical hemorrhagic or nonhemorrhagic stroke with: * Unilateral hemiparesis with sufficient endurance and motor ability to ambulate \>30 feet continuously without an AFO requiring no more than 25% physical help * Berg Balance Scale score \>23 without assistive devices * Standing ankle dorsiflexion strength of \<4/5 * Foot-drop during ambulation with gait instability or inefficient gait defined as supervision need * Possible use of physical assistance or assistive device (cane, walker) * Evidence of foot-drop as seen by "dragging" or "catching" of affected toes during limb swing or circumducting affected limb * Vaulting of the unaffected limb or hiking the affected hip to clear toes. * Intact and electrically ex-citable lower motor neurons * Ankle dorsiflexion to at least neutral while standing with electrical stimulation of common peroneal and tibial nerves without painful hypersensitivity to stimulation * Adequate social support and stability * Medically stable with intact skin in affected lower limb * Willingness to comply during research procedures * No systemic co-morbidities * No history of potentially fatal cardiac arrhythmias i.e. ventricular tachycardia, supraventricular tachycardia and rapid ventricular response atrial fibrillation with hemodynamic instability * No psychological problems or chemical dependency * No acute medical complications such as depression or chronic anxiety requiring long term pharmacological therapy. Able-bodied controls must be of similar age, body mass and stature as those with hemiparesis and must be free of any medical and disabling orthopedic problems. Exclusion Criteria: In addition to failure to meet the inclusion criteria, participants will be excluded from the study for the following: * Requires an ankle foot orthosis (AFO) to prevent knee flexion collapse in stance * Excessive edema of affected extremity * Absent sensation in affected limb * History of potentially fatal cardiac arrhythmias such as ventricular tachycardia, supraventricular tachycardia, and rapid ventricular response, atrial fibrillation with hemodynamic instability * Demand pacemakers or any implanted electronic systems * Pregnancy * Uncontrolled seizure disorder * Ipsilateral lower limb lower motor neuron lesion * Parkinson's disease * Spinal cord injury * Traumatic brain injury * Multiple sclerosis * Ankle plantar flexor contraction * Severely impaired cognition and communication * Painful hypersensitivity to neuromuscular stimulation of common peroneal nerve * Knee hyperextension (genu recurvatum) that cannot be adequately corrected with peroneal nerve stimulation * History of botulinum toxin to the lower extremity within the prior three months.