Biomechanical Differences Between Toe and Instep Kicking - Influence of Contact Area on the Coefficient of Restitution

Abstract

The coefficient of restitution (COR) was determined for toe and instep soccer kicks. Furthermore, experiments were performed with a pendulum that modeled the different impact areas in toe and instep kicking. Six sub-elite soccer players performed 20 toe and 20 instep kicks with no run-up at a range of velocities. The path of the foot and ball were recorded using a high-speed video camera (240 Hz) and manually digitized. The velocity of the pendulum and the velocity of the ball were determined using an opto-electrical system (500 Hz). The COR is the ratio between the foot/pendulum and ball velocity before and after impact. In the pendulum experiments the COR was larger for the small area (Toe) at all velocities, whereas this only was found at the lower velocities (< ~15 m s^-1) in the human experiments. In both experiments the COR dropped with increased impact velocity. The different impact areas in the two types of kicks might explain why it is advantageous to perform a toe kick if aiming at producing the highest possible ball velocity. However, this advantage is lost at higher velocities, possibly because, in toe kicks, it is not possible to keep the foot aligned.