Effect of Transcutaneous Electrical Nerve Stimulation on Post-stroke Patients

Post Stroke Cohort: Inclusion Criteria: * History of single unilateral stroke with subsequent lower limb hemiparesis on either side (\> 6 months since onset) * Ability to walk as part of activities of daily living * Age between 18 and 80 Exclusion Criteria: * Presence of concurrent severe medical illness including unhealed pressure sore, active or untreated infection, thromboembolic disease, severe contracture, osteoporosis, heterotropic classification, lower limb fracture, severe pulmonary disease or cardiovascular instability, uncontrolled seizure, uncontrolled diabetes * History of any neurological injury other than a single stroke * Has received a Botox injection in the lower extremity within the last 4 months * Any cognitive deficit that would prevent informed consent or ability to perform the experiment * History of prior injury or surgery to the hip or knee * Presence of significant lower extremity edema - Presence of cardiac pacemaker or any other electrically implanted device - Use of braces limiting harness/Lokomat fit (Any spinal orthoses such as TLSO, HALO) * Weight greater than 300 pounds * Adults unable to consent, infants, children, teenagers, pregnant women and prisoners will not be included in the study * Clinically significant depression, psychiatric disorders, or ongoing drug abuse * Actively taking medications with agents known to increase (e.g. amphetamines) or decrease motor system excitability * Suffered a concussion in the last 6 months. * Unexplained headaches Healthy Cohort: Inclusion Criteria: * No history of stroke, cerebral palsy, injury or surgery to the lower limb. * Currently not taking any central nervous system (CNS) affecting medication. * Ability to walk as part of activities of daily living * Age between 18 and 80 Exclusion Criteria: * Presence of concurrent severe medical illness including unhealed pressure sore, active or untreated infection, thromboembolic disease, severe contracture, osteoporosis, heterotropic classification, lower limb fracture, severe pulmonary disease or cardiovascular instability, uncontrolled seizure, uncontrolled diabetes * History of any neurological injury * Taking any medication affecting change in CNS * Any cognitive deficit that would prevent informed consent or ability to perform the experiment * History of prior injury or surgery to the hip or knee * Presence of significant lower extremity edema - Presence of cardiac pacemaker or any other electrically implanted device - Use of braces limiting harness/Lokomat fit (Any spinal orthoses such as TLSO, HALO) * Weight greater than 300 pounds * Adults unable to consent, infants, children, teenagers, pregnant women and prisoners will not be included in the study * Clinically significant depression, psychiatric disorders, or ongoing drug abuse * Actively taking medications with agents known to increase (e.g. amphetamines) or decrease motor system excitability * Suffered a concussion in the last 6 months. * Unexplained headaches * Has received a Botox injection in the lower extremity within the last 4 months