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"Purposeful heading does not seem to be an issue [because] the impacts are so low," says Donald Kirkendall, an orthopaedics specialist at the University of North Carolina and a co-author of a study reported in the May issue of Sports Medicine. The conclusion is based on a review of some 50 previous studies of sports-related head trauma.
Much of the fear that heading was a danger to the brain stems from Norwegian studies linking neurological defects to soccer players. But those studies didn't control for factors other than heading that could have explained the connection, such as drug or alcohol use and learning disabilities, say the researchers.
The force sufficient to cause a concussion is about 22 Newton per second (a Newton is the force required to accelerate a one-kilogram mass one metre per second). A soccer ball travelling 40 miles an hour generates only 12 to 13 Newton, Kirkendall says.
Moreover, he says when players head the ball, they typically don't do so with the mass of their noggin alone. At the very least, they tense their neck muscles and throw the weight of their upper body into the oncoming ball. If they're on the ground, they've got their entire body weight behind their bean. Simply put, even the smallest player overwhelms a soccer ball, which range in weight from 11 ounces on a pee-wee field to nearly a pound in high school and the pro games.
So while some soccer players do suffer memory problems and other evidence of head trauma later in life, that's the result of concussions, "not the fact that they headed a ball in a game," Kirkendall says.
Trey Crisco, a sports medicine expert at Brown University, says soccer players may still run the risk of concussion, but so do athletes in other contact sports. "Although people associate heading with concussions, it's mostly due to running into other players," a goal post or the ground, he says.
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