Development and validation of fingertip contact analysis method for throwing in American football

Abstract

In this study, our purpose was to develop a method to analyze the presence or absence of contact between the ball and the fingertip during the ball release phase of the throwing motion in American football, and verify its validity. Further, using the fingertip contact analysis method developed in this study for the throwing motion analysis, we tried to analyze the contact between the ball and the fingertip during the release phase. In the developed method, the presence or absence of contact is analyzed using only the position coordinates acquired by the motion capture system. The fingertip contact analysis boundary positioned at a distance of each fingertip thickness from the ball surface is formulated into a mathematical expression. If the marker attached to the fingertip is located closer to the ball surface than the boundary, it is judged as contact. The validity of the developed method is verified by simultaneously measuring the simple action of touching the ball with the fingertips and releasing it using a motion capture system and a high-speed camera, and comparing the contact frame analyzed by the developed fingertip contact analysis method with the contact frame visually judged from the image of the high-speed camera. Since the difference was within two frames before or after, the developed method is considered appropriate as a method of performing fingertip contact analysis. When using the developed method in the throwing motion analysis, since the order in which the fingers left the ball was the same, and the intervals between the fingers’ departure from the ball showed a similar tendency in all the four throwing attempts by the same subject, it is suggested that this method is valid as a method to obtain the fingertip contact analysis characteristics in the release phase of throwing motion.