 Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The risk of CAREN based gait analysis is negligible. A safety harness provides protection against falling. It will avoid subject falling on or off the treadmill while performing training. The safety harness is secured with a life line to the ceiling. The burden of the children or adolescents is minimal. Participants will visit the MUMC once, where the Harris Hip Score, Borg CR10 Score, physical examination and gait analysis will be performed. The whole session will take 2 hours. Due to the nature of the study, this study can only be done using this specific patient group. 