Project Summary Walking promotes independence, participation, fitness, and exploration in daily life. Like other activities, walking requires metabolic energy from the food we eat, which is ultimately used by our muscles to power movement. Experimentally, we can measure this energy using indirect calorimetry, which monitors oxygen and carbon dioxide as the body converts stored energy into the form used by muscles during activities of daily living. Decades of energetics research has demonstrated that human walking is incredibly efficient. However, for people with cerebral palsy the energetic cost of walking is significantly increased, on average over two times higher than typically-developing individuals. This means that for people with cerebral palsy, walking is as tiring as jogging or climbing stairs. An energetic cost of this magnitude restricts activities of daily living and causes exhaustion. While our team and many others have sought to reduce these costs through surgical interventions, rehabilitation, orthotics, or other assistive devices, these strategies have failed to result in meaningful reductions in energy. To design strategies that successfully reduce walking costs, we must first understand the underlying mechanisms contributing to elevated cost in people with cerebral palsy. The proposed research seeks to fill this knowledge gap by examining biomechanical factors that contribute to elevated energy for people with cerebral palsy. Specifically, we will evaluate the energetic cost of supporting the body (Aim-1) and stabilizing the body (Aim-2) during walking for children with cerebral palsy, and compare these costs to typically-developing peers. These tasks require very little energy during unimpaired walking (e.g., <10% of total walking cost), but their costs remain unknown for people with cerebral palsy and have direct implications for treatment decisions and assistive device design. Building upon decades of energetics research of unimpaired walking, this research will use a mechatronic device to precisely provide support and stabilization assistance during walking and quantify the impact of this assistance on walking cost. In unimpaired adults, similar methods have led to the design of exoskeletons and training programs that effectively reduce walking and running energy. This research will provide the foundation to create evidence-based strategies to decrease energy costs, minimize fatigue, and increase quality of life for people with cerebral palsy and other neurologic injuries.