Force direction in manual wheel chair propulsion: balance between effect and cost

Objective. To evaluate the relationship between mechanical effect and musculoskeletal cost in wheelchair propulsion. Design. Simulation of force direction, based on experimental data from wheelchair users. Method's. For nine wheelchair users driving at 20 W, 1.39 mis, the force direction was compared to simulation results based on a criterion defined as the ratio of mechanical effect and musculoskeletal cost. Results. Simulation data compare well to the actual force direction for the middle and final parts of the push. Conclusions. The musculoskeletal cost of the exerted force must be taken into account to explain the observed propulsion pattern. Experienced users appear to optimize the force pattern by balancing mechanical effect and musculoskeletal cost of the pushing action.