The Influence of Inertial Forces on Manual Wheelchair Propulsion

Both experimental and computational studies have contributed to the understanding of the loads during wheelchair propulsion and the factors leading to the incidence of musculoskeletal disorders. However, few studies have addressed the influence of inertial forces on wheelchair propulsion, which are potentially large as upper limb segments undergo large accelerations along the different phases of the propulsion cycle. This study determines and investigates the influence of inertial forces during manual wheelchair propulsion for a subject at two different locomotion velocities. The isolated influence of inertial as well as gravitational forces is determined using a planar model of the upper extremity and an inverse-dynamics approach. The results show that the inertial forces are preponderant even at lower speeds. These findings evidence that quasi-static models are inappropriate to investigate wheelchair propulsion and show the importance of accurate estimation of anthropometric parameters such as segment masses and moments of inertia, which directly affect inertial force estimations in inverse dynamics-based studies of wheelchair propulsion. The results can also help guide investigations on efficient propulsion techniques, as they show that the radial component of the pushrim forces are, to a large extent, determined by inertial effects rather than by an inefficient propulsion technique.