The purpose of this research is to find the optimal patterns of functional electrical stimulation (FES) of muscles in the lower legs that will improve walking ability in those who have had a stroke and at the same time ensure walking stability. FES involves applying small electric currents to the nerves, which cause the muscles to contract.

FES research projects vary from simple investigations of the therapeutic effects of exercise on muscle function and skin health, to more complex studies of functional movements such as standing or walking.

The study aims to find the optimal patterns of functional electrical stimulation (FES) of muscles in the lower legs that will improve walking ability in those who have had a stroke and at the same time ensure walking stability will be achieved through an analytical approach comprised of computational models and gait simulations to objectively determine patient-specific patterns of muscle activation. The investigators will develop a computer simulation of the dynamics of hemiplegic gait characterized by unilateral plantarflexor weakness. Then, the investigators will relate the results of the computer model results to real data collected from subjects with known plantarflexor weakness to provide a theoretical basis for improving gait efficiency and stability with FES.

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.

The able-bodied participant was only used to develop the computational optimization and was not considered to be enrolled in the study.