This weekend, as athletes face off in the semi-finals of the World Rugby Cup, Grant Trewartha will be watching the kickers. In research published in the journal Sports Biomechanics, Trewartha and colleagues at the University of Bath analyzed the role of the upper body in the kick. He reports, "We found that systematic motions of the arms and quite liberal actions helped kickers in terms of the length of the kick and also the accuracy of the kick."

The scientists videotaped skilled players and then reconstructed 3D images of their movements. The same motions have been observed in star kickers like England's Johnny Wilkinson. The arm opposite the kicking leg is thrown vigorously across the chest as the player's foot impacts the ball. Trewartha explains that this action not only gives velocity to the kick, but gets the whole body involved. "[It] also control[s] the rotations of the body to make sure that the rest of the body, the trunk, the hips and the shoulders are all facing the target and therefore increasing the chance of success."

Trewartha says the analysis can help players and coaches on any level. "The next time that you are going to kick a ball," he advises, "[think] about what you are doing with your whole body, rather than just where your kicking foot is going."

But Trewartha admits that there's more than the mechanics of an arm swing in the secret to a good kick. "It's about putting it all together and getting your timing right."

The semi-finals in the Rugby World Cup continue this weekend with France facing England and South Africa against Argentina.