SOME OBSERVATIONS OF HUMAN BUTTOCKS MOTION IN WALKING

An accurate information of instantaneous positions of walking human buttocks, if it is known, will be very useful for developing a walking simulator for the clothing research. The two-dimensional swinging motion of human buttocks when walking at an ordinary speed was measured by taking moving pictures of the testee's back. Following results were obtained. 1. The mean amplitudes of the vertical and horizontal buttocks swinging motions were about 1.72cm and 1.08cm, respectively. The tops of buttocks rotated horizontally inward and outward by an angle of ca. 2°-5° and ca. 1°-4°, respectively, about an vertical axis through the intersection point of the short and long axes of the horizontal hip cross-section. 2. An amplitude ratio λr of vertical to horizontal swinging motion of the buttock tops of various testees was dispersed between 0.8 and 2.8. An inclination angle of the line between the right and left buttock tops was also estimated to be ±7°-10°. 3. A vertically projected track of the swinging buttock tops in walking was made. It is found that each track exhibits a very complicated pattern, but some of them resemble long ellipses and the others circles. 4. From these results, gaits of the testees can be classified into two groups. One is an elliptical track, of which the long axis is perpendicular to the vertical direction or a circle, having λr2.