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.
