The first objective of this study was to clarify the impact point that produced the greatest ball velocity immediately after impact in instep soccer kicking. The second objective was to calculate the impact force during the ball impact phase.
Five experienced male university soccer players performed maximal instep kicks using a one-step approach in varying the impact point. The kicking motions were captured two-dimensionally by a high-speed video camera at 2,500 fps. The impact point was calculated as the distance from the center of mass of the foot (projected onto the dorsal aspect of the foot) to the contact point. The influence of the impact point on the ball-foot velocity ratio (ball velocity immediately after impact/foot velocity immediately before impact) was examined. The impact force was calculated from ball deformation based on the Hertz contact theory.
Impact on the surrounding area of the center of mass of the foot produced the greatest ball velocity and little angular displacement of the ankle. As an example, in a trial with a ball velocity of approximately 24 m/s, the peak ball deformation was approximately 4.5 cm and the peak impact force was over 2,000 N. Time-series of the impact force calculated in this study can be used in kinetic analysis during the ball impact phase.
