One of the greatest kickers in the history of rugby, England's Jonny Wilkinson owes his phenomenal success less to his "praying mantis" style of preparation than a barely-noticed movement of his right arm, scientists say.
Players who swing their non-kicking-side arm across their chest as they make contact with the ball are nearly twice as accurate as those who use this arm less or not at all, they say.
Researchers at the University of Bath, western England, asked five experienced kickers at university first-team level to take part in an experiment in biomechanics - the study of body movement and posture.
Using a standard size-five rugby ball and wearing reflective markers, the guinea pigs carried out seven trials for kicking accuracy and seven trials for kicking distance in a large indoor sports hall.
They were filmed simultaneously by a network of 11 cameras. These transferred the data to motion analysis software, which transcribed in three dimensions every movement of the torso, head and limbs in all phases of the kick.
The most successful kickers by far were the ones who swung the arm, on their non-kicking side, across their chest as their toe smacked into the ball. For left-footer Wilkinson, the swinging arm is on his right side.
"In taking a kick, players try to have their torso facing the target at the point of impact with the ball," said researcher Grant Trewartha in the Sport and Exercise Science Department at the university's School for Health.
"Swinging their non-kicking-side arm helps players to maintain this position for longer."
As a result, the player has a more powerful followthrough - a 'J'-shaped kicking action, rather than the weaker 'C'-shaped one.
There is also a gain in accuracy, added Trewartha.
"When you examine their action from the front, it is clear that this action also helps counteract the swing of the leg, enabling the players to remain more upright at ball contact. This should increase their error of margin and increase their overall accuracy."
Trewartha, who worked with PhD student Neil Bezodis, said the swinging-arm technique was used by the most successful kickers in the World Cup so far.
Wilkinson's signature two-armed stance as he prepares for the kicks is also important, as it is a pre-performance ritual that helps to steady him, says Trewartha.
"A lot of effort goes in to helping players prepare psychologically for key moments in games. For those that need it, biomechanical analysis of their technique could really help."
The study appears in a specialist journal, Sports Biomechanics.
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