Investigating the effects of manual wheelchair adjustments on locomotion stability through multi-factorial numerical simulations

Introduction/Background Manual wheelchair (MWC) enables people with certain disabilities to recover mobility at the expense of higher energy expenditure for the upper limbs. To reduce the risk of musculoskeletal disorders, MWC configuration has to be adapted to the user, meanwhile considering MWC stability to reduce the risk of fall. The aim of this study was to investigate the effect of various adjustments on MWC stability during locomotion. Material and method A numerical representation of the MWC was developed, allowing several tasks of daily life (start-up, propulsion, turning, etc.) to be simulated from various MWC configurations. The inputs of the model were the mechanical actions of the user on both the frame and the two handrims, and the kinematics, which enabled the computation of ground reaction forces on the wheels. Subsequently, the proportion of the normal component on both the rear and front wheels allowed calculating a locomotion index of stability, which revealed either backwards, balanced or frontwards loading of the MWC. Results Simulation allowed investigating multiple adjustments, altering the rear wheel axle position with respect to the seat (−10 to +10 cm) and the wheelbase (20 to 50 cm). The different combinations from these two parameters resulted in important changes in stability, ranging from −18% backward to +59% forward with respect to the balance position ( Fig. 1 ). Conclusion MWC settings are multiple and interdependent, and affect both mobility and stability. Multi-factorial simulations could then help to design suitable MWC configurations for users. In this study, we focused on stability but other parameters could have been studied because trade-offs have to be made between stability, mobility and energy expenditure. For that purpose, optimization procedures could be used to assist clinician in finding the most suitable MWC settings.