The influence of lever-propelled wheelchair parameters on locomotion performance: a predictive simulation study using a new equivalent muscle approach

Lever-propelled wheelchairs constitute a promising alternative to their handrim-propelled counterparts as they are associated with more favorable upper extremity biomechanics during propulsion. This can potentially reduce the large incidence of upper extremity pain and injury among long-term users of handrim-propelled wheelchairs. However, the effects of wheelchair design parameters on locomotion performance are poorly understood. Here, we propose a modeling approach and an optimal control framework to investigate the influence of parameters such as lever length, gear ratio, and position of the lever pivot on steady-state locomotion performance. We propose using a pair of equivalent antagonistic muscle units, called Equivalent Muscle Actuators (EMAs), acting directly on the propulsion levers and representing the intrinsic properties of the musculoskeletal system and its interaction with the device. This approach reduces the model dimension and promotes a straightforward analysis of the biomechanical advantage considering the human-device interaction. The predictive simulations of wheelchair locomotion are generated for various gear ratios and lever pivot positions at different average velocities, slope angles, and hand positions along the lever. ... mehrThe results reveal that a posterior pivot position requires consistently less effort due to a biomechanically more favorable configuration and gravity’s beneficial effect during the propulsion phase. The results also indicate the most appropriate gear ratios depending on speed and slope angle. This study provides guidelines for the design of lever-propelled wheelchairs and a modeling and computational framework that can be extended to investigate different assistive technologies or other mechanical devices interacting with the human body.