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.