抄録
The purpose of this study was to investigate relationships between the velocity of the center of gravity (CGV) and the ground reaction force in side step and cross step cutting. The subjects were five university students belonging to the American football club. In the experimental trials, subjects changed their running direction by 45, 90 and 135 degrees in both side step and cross step. These were videotaped at 60 fields/s with two VTR cameras and the ground reaction force data of the support leg were measured using a force platform. Twenty-five body landmarks were digitized and their three- dimensional coordinate data were reconstructed using the DLT method. The horizontal component of the ground reaction force was divided into two directions: parallel, and normal to CGV.
There was positive correlation between the angle of direction change of CGV and the impulse normal to CGV. The angle of changing direction of CGV in the second half of the support was larger, and CGV at mid-support was smaller in side step than cross step. However, there was no significant difference in the impulse normal to CGV in the second half of the support between side and cross step. These results suggested that although the ground reaction forces normal to CGV changed the direction of CGV, the amount of direction change of CGV was affected not only by the magnitude of the ground reaction force acting normal to CGV direction but also by the magnitude of CGV.
