Muscle Delay Characterization

Eligibility Details: Inclusion Criteria: - healthy normal individuals aged 18-65 and individuals with movement disorders (e.g., spinal cord injury, Parkinson's disease, stroke) - capable to perform the cycling exercises either voluntarily or under controlled electrical stimulation - all participants have to be medically stable (i.e., do not exhibit asymptomatic osteoporosis, cardiopulmonary disease, pain, or other significant medical complications that would prohibit or interfere with testing or training) - for neurologically impaired individuals, they should have a single neurologic condition - under all situations the body size and weight of participant has to be compatible with the testing apparatus to ensure safety at all times Exclusion Criteria: - participants who are unresponsive to surface FES are not considered eligible for the study - a history of significant cardiovascular disorders, chronic arterial diseases or congestive cardiac failure, including being medicated for hypertension and/or have an implanted pacemaker - have a history of major musculoskeletal problems that limit hip and knee extension such as orthopedic surgery, including ACL reconstruction and/or joint replacements - participants with denervated muscle, severe osteoporosis or abnormal bone formation in hip/knee joints, bone fractures, acute hernia, severe muscle spasticity, infection in the lower extremities, epilepsy, diabetes, severe angina, pressure ulcers, vein thrombosis, and any ailments causing high fever, high blood pressure or high heart rate - pregnant women, children/minors, adults with diminished decision-making capacity, and non-English speakers - under all situations the body size and weight of participant has to be compatible with the testing apparatus to ensure safety at all times