Inclusion Criteria:  I1: Diagnosis of hemiplegic cerebral palsy I2: Gait pattern in hemiplegic limb: deficit of knee extension during late swing phase/initial contact I3: Age 7 to 17 years I4: Able to walk on a treadmill without assistive devices  I5: Able to understand spoken English at the level needed to:  understand and follow instructions for equipment setup, testing and task performance answer questions related to effort and preference be able to understand consent document and provide informed consent  Exclusion Criteria:  E1: Significant injury (such as fracture) in legs or feet that interferes with their ability to walk E2: Known risk factor for stroke or heart attack while exercising E3: Lower extremity orthopaedic surgery less than 12 months prior to study start E4: Other significant health conditions that may interfere with the participant's ability to complete the study or could interfere with interpretation of the study results.