2007 年 17 巻 2 号 p. 13-23
The objective of this study was to measure ball deformation and impact force during the ball impact phase in side-foot soccer kicking, using a three-dimensional analysis technique. Firstly, to examine the method for measuring the three-dimensional position of the center of the ball while the kicking foot contacted the ball, the motion of ball rolling on the ground was captured three-dimensionally at 250fps. The position of the center of the ball was calculated as the point located at 11cm (=radius of the ball) from three markers fixed on the ball surface. It was suggested that in cases when the distances between each marker were more than 8cm, the position of the center of the ball was validly calculated. Also, five experienced male university soccer players performed side-foot kicks using a one-step approach. The kicking motions were captured three-dimensionally by two high-speed cameras at 2500fps. The contact point between the kicking foot and ball was calculated as the intersection point of the perpendicular line dropped from the center of the ball to the medial aspect of the kicking foot. The ball deformation was calculated by subtracting the distance between the center of the ball and the contact point from the radius of the ball. Furthermore, the impact force was calculated from the ball deformation, based on the Hertz contact theory. It was considered that the ball deformation and the impact force measured with these approaches were valid.