The effect of seat position on manual wheelchair propulsion biomechanics: a quasi-static model-based approach

The position of the seat relative to the rear wheels is generally adjusted to modify the rearward stability of the wheelchair. Recent studies have shown that seat position also has an effect on propulsion biomechanics and suggest that seat position can be optimized. A quasi-static wheelchair propulsion model was developed to investigate the mechanism by which seat position affects propulsion biomechanics. Inputs to the model include the length of the user's arm segments, the position of the user's shoulder, the size of handrim used and the force profile on the handrim. Outputs from the model include joint kinematics, joint torques, push angle, and push frequency. Handrim force profile was determined by averaging the force profile of five wheelchair users. Force profiles were measured using the SMARTWheel. The effect of seat position on push angle was found to be directly affected by the length of the position vector from the hub of the wheel to the shoulder and indirectly affected by the angular orientation of the vector. Decreasing hub to shoulder length was found to increase push angle, decrease push frequency, decrease shoulder torque and increase elbow extension torque. It is suggested that future research investigating the role of seat position on propulsion biomechanics include both the kinematics and kinetics of the upper extremity.