Biomechanics of manual wheelchair propulsion in elderly: system tilt and back recline angles.

OBJECTIVE To investigate the effects of the system tilt and back recline angles on the biomechanics of wheelchair propulsion for a group of older, disabled patients. It was hypothesized that increasing both the system tilt and backrest recline angles would have a positive effect on the biomechanical efficiency of manual wheelchair propulsion. DESIGN Three kinetic variables were estimated during a 10-m, steady-state propulsion between 0.96 m/sec and 1.01 m/sec. The fraction of the mechanical effective force is defined by the ratio between the tangential and the total force applied to the pushrim: It expresses the directionality of force application. The mechanical use is defined as the ratio between the total force generated during wheelchair propulsion and that generated during maximal isometric contraction. The biomechanical efficiency is defined as the product of mechanical effective force and the mechanical use. RESULTS On average, the fraction of the mechanical effective force was found to be low when compared with other studies. Tilting the system by 10 degrees and reclining the back by 10 degrees increase significantly the biomechanical efficiency of the subject by 10%. The biomechanical efficiency variable was more sensitive to the system tilt than to the back recline adjustment. CONCLUSIONS The results of this study confirm the hypothesis that system tilt angle but not back recline significantly affects biomechanical efficiency. The findings of this study will help in designing and adjusting a wheelchair intended for self-propelled, older people.