3D Link-Segment Model for Kinematics and Kinetics of Lower Limbs in Soccer Free Kick: Protocol Design

Soccer is one of the most popular sports in the world, and the direct free kick is a defining instance in the result of a game. In this work, a soccer free kick recording protocol has been developed. A 3D link segment model is proposed and the kinematics of both lower limbs and kinetics and power in each joint of the kicking leg are evaluated. The results of the energy transferred to the ball in relation to the energy transferred in every joint of the kicking leg are analyzed. The results suggest that power generated to perform the shot comes mainly from the hip, and that the other two joints are responsible for fine control of the kick, absorbing power during the cycle, allowing greater precision in the kick. An average of the sum of linear and angular energy transfers in the proximal to distal direction, plus the energy generated by the muscles was calculated for the right lower limb. However, the variable of interest was the energy that the ball acquired from the impact with the foot. This estimation showed, in average, that the linear energy transferred to the ball was approximately 89% of the energy generated during the movement. This is consistent, considering that the energy generated and transferred between segments, by the muscles of the lower limb, during the kick cycle, was slightly greater than the energy received by the ball during the contact with the foot.