The bi-pedal ape: plasticity and asymmetry in footedness.

A strong preference for using the right foot for skilled activities parallels a similar side bias for hand use. However, many neuropsychologists, sports scientists and sports commentators argue that right-foot bias in soccer is reduced or even eliminated by practice. This sort of plasticity is an important component of the principle genetic theories of handedness, yet very little is known about the relative asymmetries in the many unipedal skills required in soccer at amateur or professional levels. The first study examined self-report of hand and foot bias in a sample (n=400) of amateur soccer players, in addition to information about their practice with the non-preferred foot. A second study quantified foot use on the pitch in a large sample (n=426) of professional soccer players. The majority of the amateurs reported a right-foot bias that is very similar to that seen in the general population ( approximately 80%). However they only endorse strong biases for "closed" (self-paced) soccer actions like penalty and other free kicks, which give players unlimited time and space for preparation and execution. Although there was a very slight tendency for less right-foot bias in the professionals ( approximately 75%), as assessed by actual foot use rather than questionnaire, few players show anything like what could be described as two-footed play. This bias, unlike in the reports of amateurs, were for all of the behaviours investigated, not just so-called "skilled" behaviours. Finally, when outcomes of preferred and non-preferred foot behaviours were contrasted, the professionals were remarkably adept on those rare occasions when they use their non-preferred foot, suggesting that skill cannot explain asymmetry of choice. These results are discussed in terms of 1) limitations of self-report on questionnaires for predicting actual on the field behaviour, 2) the surprising absence of plasticity in foot use, given the importance of learning, experience and culture in models of handedness and footedness, and 3) a left hemisphere lateralised intentional system as important for the selection of movements as for their execution.