For simplifying interpretation of results, the kicking motion was divided into three phases by these four key moments (Fig. 2). The forward swing of the kicking leg was started from right toe off (RTO), with the hip joint reaching its maximum extension angle (MHE) while the knee flexion motion was occurring. The knee joint subsequently reached its maximum flexion angle (MKF) and then continuously extended until ball impact. The back-swing phase was defined as a time period from RTO to MHE. The leg-cocking phase followed and ended at MKF. The leg-acceleration phase subsequently occurred and ended at ball impact.