The present study aimed to clarify the differences in interaction torques acting on the kicking limb by expressing them as functions of the relative linear accelerations in a linked lower leg system. Twenty experienced male university-level soccer players (19.5 ± 1.1 years, 1.75 ± 0.06 m, 69.2 ± 5.5 kg) were instructed to perform the side-volley and instep kicks as forcefully as possible. The kicking motions were captured using a 12-camera optoelectronic motion capture system at 500 Hz. To describe the differences in the detailed mechanics of the interaction torques between the two kicks, the acceleration of the lower leg centre of gravity was decomposed into the relative accelerations of adjacent body landmarks from the support leg`s hip joint, which allowed us to calculate the interaction torques due to accelerative actions of these body landmarks. The side-volley kick generated significantly smaller total interaction torque and the interaction torque due to the support leg`s hip in the final phase of kicking than the instep kick. There was a distinctive difference between the two kicks in the practical accelerative actions at the support leg`s hip. In the side-volley kick, while the interaction torque due to the vertical acceleration of the support leg`s hip was negligible during kicking, that due to the horizontal acceleration (towards the left from the back-view of right-footed players) had the most considerable magnitude. The horizontal acceleration is most likely derived from the support leg`s hip adduction joint torque, apparent in the latter part of kicking.
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