Effect of Rotational Axis Position of Wheelchair Back Support on Shear Force when Reclining

[Purpose] The purpose of this study was to investigate the influence of the rotational axis position of a reclining wheelchair’s back support on fluctuations in the shear force applied to the buttocks while the back support is reclined. [Subjects] The subjects were 12 healthy adult men. [Methods] The shear force applied to the buttocks was measured using a force plate. This study used two different experimental conditions. The rotational axis of the back support was positioned at the joint between the seat and the back support for the rear-axis condition, and was moved 13 cm forward for the front-axis condition. [Results] With the back support fully reclined, the shear forces were 11.2 ± 0.8%BW and 14.1 ± 2.5%BW under the rear-axis and front-axis conditions, respectively. When returned to an upright position, the shear forces were 17.1 ± 3.1%BW and 13.8 ± 1.7%BW under the rear-axis and front-axis conditions, respectively. Significant differences appeared between the two experimental conditions (p < 0.01). [Conclusion] These results suggest that the shear force value could be changed by altering the position of the back support’s rotational axis during reclining.