Effect of backrest height on wheelchair propulsion biomechanics for level and uphill conditions.

OBJECTIVE To evaluate the effect of backrest height on wheelchair propulsion kinematics and kinetics. DESIGN An intervention study with repeated measures. SETTING University laboratory. PARTICIPANTS Convenience sample included manual wheelchair users (N=36; 26 men and 10 women) with spinal cord injuries ranging from T8 to L2. INTERVENTION Participants propelled on a motor-driven treadmill for 2 conditions (level and slope of 3°) at a constant speed of 0.9 m/s while using in turn a sling backrest fixed at 40.6 cm (16 in) high (high backrest) and a lower height set at 50% trunk length (low backrest). MAIN OUTCOME MEASURES Cadence, stroke angle, peak shoulder extension angle, shoulder flexion/extension range of motion, and mechanical effective force. RESULTS Pushing with the low backrest height enabled greater range of shoulder motion (P<.01), increased stroke angle (P<.01), push time (P<.01), and reduced cadence (P=.01) regardless of whether the treadmill was level or sloped. CONCLUSIONS A lower cadence can be achieved when pushing with a lower backrest, which decreases the risk of developing upper-limb overuse related injuries. However, postural support, comfort, and other activities of daily living must also be considered when selecting a backrest height for active, long-term wheelchair users. The improvements found when using the low backrest were found regardless of slope type. Pushing uphill demanded significantly higher resultant and tangential force, torque, mechanical effective force, and cadence.