chapter  11
Coefficient of Restitution (COR) in Toe and Instep Soccer Kicks
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In all soccer kicks, the velocity of the ball after impact is determined by the velocity of the foot before impact, the effective striking mass of the foot and the coefficient of restitution (COR) of the impact (Plagenhoef, 1971, Bull Andersen et al., 1999). The COR in soccer kicking describes the transfer of velocity from the foot to the ball during the impact phase and is the ratio between the relative velocity (Vball−Vfoot) after impact and the relative velocity before impact The factors determining the COR are the mechanical properties of the foot and ball, i.e. stiffness, contact area and contact point. Furthermore, the COR in two-dimensional analyses is affected by the direction of the path of the foot before impact and the path of the ball after impact.