Relationship between the fluctuation of the shear force applied to the buttocks and the timing just before sliding the trunk upward on the back-support during back-support inclination

Abstract

The purpose of this study was to investigate the relationship between the fluctuation of the shear force applied to the buttocks and the timing just before sliding the trunk upward on the back-support, during upward back-support inclination. The participants included 16 healthy persons. A force plate was used to measure the shear force. The inclination angle of back-support just before sliding the trunk was measured based on the videos taken during the experiment. The experiment was conducted under three conditions: the buttocks were positioned at distances of 3 cm, 6 cm, and 9 cm from the back-support in order to investigate the influence of the buttocks’ position. The results revealed that the shear force just before sliding the trunk on the back-support was maximum during upward back-support inclination under all conditions. The inclination angle of the back-support at that time was approximately 26° from the vertical line as the middle range of the back-support inclination under all conditions. This result suggested that even if the buttocks are at different positions, and if the angle just before sliding the trunk upward on the back-support is the same, the fluctuation of the shear force applied to the buttocks is equal.