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

Objective. To evaluate the relationship between mechanical effect and muscu loskeletal cost in wheelchair propulsion. Design. Simulation of force direction, based on experimental data from whee lchair users. Method's. For nine wheelchair users driving at 20 W, 1.39 mis, the force di rection 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 in to account to explain the observed propulsion pattern. Experienced users ap pear to optimize the force pattern by balancing mechanical effect and muscu loskeletal cost of the pushing action.