Colloquia

Samenvatting

Standing wheelchairs introduce significant physical and psychosocial benefits by enabling users to alternate between seated and upright postures. The Ezer is a standing wheelchair that incorporates a standing-propelling mechanism, presenting new biomechanical and ergonomic challenges that have not been addressed in the existing literature. 

This thesis examines the impact of handrim positioning and geometry on propulsion efficiency and joint safety, aiming to optimize the biomechanical interaction between the user and a manual standing wheelchair. The research employs a dual-pathway methodology. First, Part I develops a biomechanical model of upper-limb motion during the pushing cycle, accounting for ergonomic and biomechanical factors to determine the optimal handrim position in standing mode. Then, Part II develops the handrim geometry, focusing on ergonomic grip, hand coupling, and effective force application. Both pathways converge in an integrated user test to evaluate propulsion performance, effort, comfort, and usability.

Quantitative results demonstrate that implementing an optimized handrim configuration significantly improves propelling efficiency compared to the current Ezer configuration, up to 28.8% as measured by the transmitted force indicator. The optimized configuration resulted in a longer effective push phase, reduced peak force, and lower perceived joint effort across participants. However, the biomechanical analysis showed that the shoulder and wrist exceeded the safe active range of motion, with the wrist as the most critical joint, as it can experience strain at the limit position. Other measurements showed improvements in ergonomic alignment and enhanced overall propulsion effectiveness, as reflected in higher usability and comfort ratings of 4.6/5 for the new configuration, compared with 2.6/5 for the current configuration.

Moreover, the results lead to concrete design recommendations for the Ezer, including the implementation of the optimized handrim geometry, as it can already be assembled to the chassis. Besides this, as the change in handrim position requires a significant modification, implementing the standardized footrest position of the biomechanical model, which can improve arm alignment during standing propelling.