Abstract
The ratio of tangential to total pushrim force, the so-called Fraction Effective Force (FEF), has been used to evaluate wheelchair propulsion efficiency based on the fact that only the tangential component of the force on the pushrim contributes to actual wheelchair propulsion. Experimental studies, however, consistently show low FEF values and recent experimental as well as modelling investigations have conclusively shown that a more tangential pushrim force direction can lead to a decrease and not increase in propulsion efficiency. This study aims at quantifying the contributions of active, inertial and gravitational forces to the normal pushrim component. In order to achieve this goal, an inverse dynamics-based framework is proposed to estimate individual contributions to the pushrim forces using a model of the wheelchair-user system. The results show that the radial pushrim force component arise to a great extent due to purely mechanical effects, including inertial and gravitational forces. These results corroborate previous findings according to which radial pushrim force components are not necessarily a result of inefficient propulsion strategies or hand-rim friction requirements. This study proposes a novel framework to quantify the individual contributions of active, inertial and gravitational forces to pushrim forces during wheelchair propulsion.
Highlights
In spite of the large number of users worldwide, locomotion with manual wheelchairs is associated with upper-extremity injuries, shoulder pain, large energy demand and low efficiency [1,2,3]
The inefficiency of wheelchair locomotion has been linked to the radial component of the push force during the propulsion phase [4,5], based on the fact that only the tangential component of the force on the rim contributes to the moment applied to wheel and, to actual wheelchair propulsion
The Fraction Effective Force (FEF), defined in [6] as the ratio of the pushrim tangent component to the pushrim total force is shown on the left-hand side of Fig. 3
Summary
In spite of the large number of users worldwide, locomotion with manual wheelchairs is associated with upper-extremity injuries, shoulder pain, large energy demand and low efficiency [1,2,3]. The inefficiency of wheelchair locomotion has been linked to the radial component of the push force during the propulsion phase [4,5], based on the fact that only the tangential component of the force on the rim contributes to the moment applied to wheel and, to actual wheelchair propulsion. Many experimental studies have shown low ratios of tangential force to total pushrim force, the so-called Fraction Effective Force (FEF), during wheelchair propulsion even for experienced users [6,7]. This indicates large FEF with a more tangential pushrim force direction is not necessarily associated with higher efficiency. In the latter study authors conclude that the observed force direction, with relatively large radial component in wheelchair propulsion, is a compromise between efficiency and the constraints imposed by the wheelchair-user system
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