Atsuko Eguchi

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

Purpose. For some people with leg disorders, the alternative to becoming bedridden is sitting in a wheelchair for long periods of time. The purpose of this study was to investigate the relation between the backrest of a chair and the position of the pelvis on the maximum pressure at the ischium and the estimated shear force encountered while sitting in a chair. Methods. Ten healthy males aged 22.4 ± 2.3 years without pathologies in the leg and/or trunk participated in this study. The subjects were instructed to sit in a chair and the pressure and shear forces were measured under three sitting conditions: In the standard position, a 5 cm forward position and a 10 cm forward position. The effects of the positions of the pelvis on the maximum pressure at the ischium were measured by an instrument for measuring pressure distribution and the shear forces were estimated using an experimental model proposed by us. Results. Comparisons were made among the three sitting positions; the range of displacement of the maximum pressure point was not significant. The estimated shear force on the seat was 15.5 ± 12.4 N in the standard position, 34.4 ± 8.5 N in the 5-cm forward position, and 53.2 ± 16.7 N in the 10 cm forward position. There were significant differences among the three values (p < 0.01). Conclusions. Displacing the pelvis forward and leaning against the backrest tends to increase the shear force and raise the risk of decubitus ulcers.

Investigation of validity of model for estimating shear force applied to buttocks in elderly people with kyphosis while sitting comfortably on a chair

Purpose. The purpose of the present study was to investigate the validity of a model for estimating shear force on the buttocks of elderly people with kyphosis. Method. The subjects with kyphosis were 10 elderly people in a facility providing health care services for the elderly. The shear force was measured using a force plate and, simultaneously, the position of the resultant centre of mass of the upper body and the inclination angle of the trunk were measured. The estimated shear force was calculated by substituting these values in the model. Results. The average value of the measured shear force was 8.4 SD 1.4 [%BW], and the average value of the estimated shear force was 5.8 SD 1.0 [%BW]. Although there was a significant difference between these two values (p < 0.01), there was a strong positive correlation between them (r = 0.786, p < 0.01). The regression line between the two values was y = 1.097x + 1.96, where x = estimated value, y = measured value. Conclusions. These results suggest that the estimated shear force was close to the measured shear force and thus is approximately known by substituting the calculated values for the linear regression.