In the split second before foot meets ball, a striker's body betrays whether a penalty kick will go left or right, according to latest research whose findings were released during the ongoing World Cup.
The findings could explain how some top goalkeepers are able to head off a penalty kick, diving in the correct direction in advance of the kick. It could also point the way to changes in how players kick, and goalies react.
The research, performed by Gabriel J Diaz, doctoral student at Rensselaer Polytechnic Institute, employed motion capture technology and computer analysis to identify five early indicators of the direction a ball would ultimately be kicked.
Diaz said his research stemmed from an observation of real-world penalty kicks, in which players aim for the left or right side of the goal while hiding their choice from the goalkeeper.
"When a goalkeeper is in a penalty situation, they can't wait until the ball is in the air before choosing whether to jump left or right - a well-placed penalty kick will get past them," Diaz said.
"As a consequence, you see goalkeepers jumping before the foot hits the ball. My question is: Are they making a choice better than chance (50/50), and if so, what kind of information might they be using to make their choice?"
Diaz tested potential indicators of kick direction, drawn from sports literature and derived from a computer analysis of the kicks - and identified reliable indicators of the direction the ball will go.
In the second part of his work, Diaz also showed that reliable indicators he identified are used by people who are able to predict the direction of the kick before the foot strikes the ball, said a Rensselaer release.
Diaz used motion capture technology - cameras, sensors, and software - in Rensselaer associate professor Brett Fajen's Perception and Action (PandA) motion capture lab to record the movements of three college-level penalty kickers.
The technology is similar to that used to create realistic movement in computer-generated graphics.