Pelvic Rotation Mechanism in Soccer Instep Kicking Toward Angled Directions.

The purpose of the present study was to clarify the dynamic factors that induce pelvic rotation when soccer players kick a ball toward angled directions using an instep kick. Nine experienced, right-footed, male soccer players instep kicked a stationary ball in 3 different angled directions, 15°, 45°, and 75° relative to the run-up direction, and a motion capture system with a force plate recorded the kicking data. Kinematic and kinetic variables of the support leg, associated with pelvic rotation about the vertical axis, were compared among the kicking conditions. The pelvic rotation significantly increased in response to larger kicking angles, and it coincided with increase of the support leg hip joint and foot segment rotation about the vertical axis. The joint torque at the support leg hip joint significantly increased with the kicking angles. Additionally, the interaction torque due to the ground reaction force was the primary factor driving foot segment rotation relative to the force plate in angled kicking conditions, whereas no remarkable action of the free moment existed. Instep kicks toward angled directions involve a mechanism that increases the pelvic rotation about the support leg's hip joint and foot segment, which differs from the mechanism involved in straight kicks.