椅子上安楽座位におけるずれ力発生のメカニズム―座圧分布変位の時間的要素による検証―

Abstract

ABSTRACT:The purpose of this study was to verify the initial mechanism of shear force in comfortable sitting position on chair. With 10 healthy men as subjects, we measured the displacement width of sitting pressure distribution with trunk backward inclining and the time difference from contact with the backrest until the beginning of the shift of the sitting pressure center position under two conditions of "with" and "without" backrest using a pressure distribution meter. The results show that the sitting pressure center position gradually moves backwards with trunk backward inclining, and in the case of "with" backrest turned forward just after the inclining (0.2 ± 0.1 sec). The displacement width was a shift forward from the base sitting position of 0.5 ± 1.2 cm "with" backrest and a shift backward of 2.0 ± 1.1 cm "without" backrest, showing a significant difference between them (p<0.01). These results suggest the intervention of backrest is indispensable in the initiation of shear force.

The influence of the distance between the backrest of a chair and the position of the pelvis on the maximum pressure on the ischium and estimated shear force

“…In a previous study, we investigated the temporal elements of the changes in sitting pressure distribution while leaning against a backrest to verify the onset mechanism of shear force in a comfortable sitting posture 20 . Results showed that in the central position of sitting, the pressure gradually displaced in a posterior direction as the trunk leaned backward, which was reversed to the anterior direction as the back leaned against the backrest.…”

Influence of sacral sitting in a wheelchair on the distribution of contact pressure on the buttocks and back and shear force on the ischial region

“…The back support converts backward angular momentum of the trunk produced by posterior pelvic tilt to shear force in the forward direction13, 14 ) . In this study, posterior pelvic tilt markedly increased in sacral sitting compared with that in basic sitting, which may have increased the force pressing the trunk against the back support and shear force generated by sliding the ischial region forward, compared to basic sitting.…”

Influence of rotational axis height of back support on horizontal force applied to buttocks in a reclining wheelchair

“…As a result, the force applied to the back support causes the buttocks to slide forward, producing horizontal force to the buttocks. 31 Under the upward-axis condition, which is presumed to generate the lowest static friction force on the back support, the reaction force can be released without restricting the relatively easy upward slide of the trunk. Thus, the horizontal force applied to the buttocks was significantly lower under the upward-axis condition.…”