An Investigation of Bilateral Symmetry During Manual Wheelchair Propulsion

Abstract

Studies of manual wheelchair propulsion often assume bilateral symmetry to simplify data collection, processing, and analysis. However, the validity of this assumption is unclear. Most investigations of wheelchair propulsion symmetry have been limited by a relatively small sample size and a focus on a single propulsion condition (e.g., level propulsion at self-selected speed). The purpose of this study was to evaluate bilateral symmetry during manual wheelchair propulsion in a large group of subjects across different propulsion conditions. Three-dimensional kinematics and handrim kinetics along with spatiotemporal variables were collected and processed from 80 subjects with paraplegia while propelling their wheelchairs on a stationary ergometer during three different conditions: level propulsion at their self-selected speed (free), level propulsion at their fastest comfortable speed (fast), and propulsion on an 8% grade at their level, self-selected speed (graded). All kinematic variables had significant side-to-side differences, primarily in the graded condition. Push angle was the only spatiotemporal variable with a significant side-to-side difference, and only during the graded condition. No kinetic variables had significant side-to-side differences. The magnitudes of the kinematic differences were low, with only one difference exceeding 5°. With differences of such small magnitude, the bilateral symmetry assumption appears to be reasonable during manual wheelchair propulsion in subjects without significant upper-extremity pain or impairment. However, larger asymmetries may exist in individuals with secondary injuries and pain in their upper extremity and different etiologies of their neurological impairment.

Keywords: asymmetry; biomechanics; graded; hand dominance; side-to-side differences; speed.

Figure 1

Experimental setup: (A) Manual wheelchair ergometer consisting of supporting frame, controlling computer and split rollers. (B) Subject on ergometer with markers affixed to the body and wheel.

Figure 2

Hand pattern variable definitions. The solid line denotes the hand path during push phase, while the dashed line denotes the hand path during recovery phase. The handrim radius is denoted by the variable r and push angle is denoted by θ.