Influence of Leg Support Elevation on Horizontal Force Acting on the Buttocks in a Reclining Wheelchair in Different Rotational Axis Positions of the Back Support

Purpose: The purpose of this study was to investigate how the influences of leg support elevation on the horizontal force acting on the buttocks in a reclining wheelchair changes in various rotational axis positions of the back support. Materials and methods: The participants were 13 healthy men. The horizontal force was measured using a force plate on the experimental chair. Four experimental conditions were tested: the leg-down condition in the rearaxis and trochanteraxis positions of back support and the leg-up condition in the rear-axis and the trochanteraxis positions. The back support was reclined at increasing angles, beginning with the initial upright position (IUP) and proceeding to the fully reclined position (FRP). We calculated the variation rate of the forces acting on the buttocks between the FRP and the IUP (FRP/IUP*100: %). Results: In the trochanter-axis position, the variation rate of the leg-down and the leg-up conditions was 155.6 ± 29.1% and 119.3 ± 10.7%, respectively. In the rear-axis position, the variation rate of the leg-down and the leg-up condition were 100.7 ± 16.7% and 96.3 ± 10.2%, respectively. There were significant differences in the variation rate between the leg-down and leg-up conditions in the trochanter-axis position, but there were not significant differences in the rear-axis position. Conclusion: The extent of the influence of leg support elevation on the horizontal force acting on the buttocks in a reclining wheelchair decreases when the rotational axis of the back support is placed close to the trochanter.