The proposed research seeks to develop technology for improving mobility, fitness, productivity and independence in children, especially those with impaired mobility. The broad goal is to improve public health, starting with development of healthy habits and fitness at a young age. The objective in this proposal is to design and develop an affordable rehabilitation device to promote intensive practice of a gait-like movement pattern for 4 to 12 year olds with physical disabilities and chronic conditions. This is based on preliminary data that shows improved function in adults who used a motorized elliptical device for rehabilitation. The central hypothesis is that the device developed will provide an affordable, biomechanically correct and ergonomically accessible tool for children with different heights/leg lengths to use for intensive gait rehabilitation. The rationale is that this research will bridge gps in: (1) usability of elliptical trainers or similar devices in attaining gaits similar to overgroun walking, and (2) creating affordable techniques for gait rehabilitation of young children living wih physical disabilities and chronic conditions. Specific Aim 1: Develop and validate a foot-guidance linkage system that promotes a movement pattern similar to normal gait for 4-12 year olds. According to the central hypothesis, and based upon strong preliminary work, the developed device will promote a movement pattern of the trunk, pelvis and lower extremities that is highly similar to that of overground walking regardless of height variation typical of the target population. The movement pattern will be validated initially through computer modeling and subsequently through biomechanical comparisons (kinematics and stride characteristics recorded during device and gait conditions) in 4-12 year olds without known disability. Specific Aim 2: Develop the ergonomic infrastructure that will enable children with physical disabilities and chronic conditions to access and use the foot-guidance linkage system for gait retraining and exercise. If the device is to be readily incorporated into use for rehabilitation then it must e easily accessible for use in therapy and school settings. A set of ergonomic adaptations (i.e., an assistive drive mechanism for advancing the feet, stairs, platforms and ramps for access) will be developed, integrated and refined that enable children with weakness, movement control problems, and balance deficits to access and train for sustained periods. This infrastructure will be validated in children with disabilities.