Myth and fact of ball impact dynamics in football codes

Abstract

Kicking is important in all the football codes and impact is the most crucial component of the skill. However, only a few studies have documented the foot to ball impact phase adequately due to low sample rates and methodological issues. This paper reviews these studies in an attempt to better understand foot-ball impact and explores the veracity of impact-related coaching cues. In soccer, the use of ultrahigh-speed video, a new smoothing procedure and ball modelling to calculate the centre of mass of the ball during deformation has allowed for detailed analysis of impact. A number of studies have identified four phases during foot-ball contact. First the foot acts to deform the ball (phase I), followed by ball acceleration until foot and ball speeds are similar (phase II). The ball then begins to reform while still accelerating (phase III). The last phase shows little interaction between foot and ball suggesting no influence on ball speed. Also using ultrahigh-speed video in the punt kick, but with methods largely focusing on average rather than instantaneous analyses of impact, differences in impact characteristics have been found between seniors and juniors, preferred and non-preferred legs, and kick distances and kick types. The four phases evident in soccer kicking were also present in the punt kick and might have similar underlying mechanisms. Differences exist between player perceptions of what is happening at impact and what actually occurs. Coaching advice to extend the time in contact to produce greater ball velocity was not correct but maintaining a firm foot in the punt kick for distance is an appropriate cue. Further, impact phase analysis has been shown to have useful practical applications. A unique impact location on the foot was found in producing a knuckle ball, and using the difference between this and the instep kick as a cue, the technique was successfully learned by a university level player. Finally footwear design to improve resultant ball performance was explored, looking at existing footwear products, application of ball to foot impact research and potential theories applicable to footwear.