"In terms of heading the soccer ball, we found that really only at the highest [ball] speed did it make any difference, and it was a very small difference," says Dr. Rosanne Naunheim, the study's lead author and assistant professor of emergency medicine at Washington University in St Louis.
There's increasing concern that repeated blows to the head from soccer balls may cause mental impairment. That's a potentially major health issue because there are about 200 million people playing soccer worldwide.
Naunheim and her colleagues tested four models of soccer headgear available in the United States -- Kangaroo, Head Blast, Soccer Docs, and Head'r.
Each headband was mounted on a magnesium head form equipped with sensors. The head form was attached to a semi-flexible rubber neck. Impact tests were done using regulation soccer balls at various inflation levels propelled at the head form at three different speeds -- 20, 26, and 34 miles per hour.
Those speeds are slower than the typical maximum speed encountered by high school soccer players heading the ball, the study says.
Measuring peak acceleration, the researchers concluded that the headgear shows little ability to weaken a soccer ball's impact. They found the headgear only eased impact slightly at the highest speeds and ball pressures tested.
Naunheim says the results of the study, which appears in the January issue of the journal Academic Emergency Medicine, aren't a surprise.
"The surprise, I think, comes to other people who aren't really familiar with helmet testing," she says.
Naunheim says a soccer ball and the headgear are about equal in terms of softness. As a result, there's not much change in soccer ball force and acceleration when the ball hits the headgear.
"In order to cause a measurable difference in the protection, you'd have to have a measurable increase in the thickness of the headband. It isn't clear how much thicker, but maybe 6 to 8 inches, which would make it impossible to wear during a game," Naunheim says.
Changing soccer ball pressure may help protect players heading the ball.
"In our study, we found that if the ball pressure was lower, the impact was less. So, if you didn't inflate the ball to the maximum pressure, it would make a difference," Naunheim says.
The potential effect of the study's findings is unclear. Naunheim says not many soccer players use the headgear because it's considered to be on the low end of the cool scale.
That point is echoed by Eric H. Chudler, a neuroscience researcher at the University of Washington, Seattle, who created a Web site for children about soccer and the brain. In his years of coaching, playing and watching soccer, he's never seen anyone wear soccer headgear.
As for the study, Chudler notes that it doesn't address the issue of repeated soccer-related blows to the head.
It also doesn't include any data about the possibility that the headgear may reduce soccer-related concussions caused by player-player, player-ground, or player-goalpost contact. He notes that these kinds of hits may be responsible for soccer head injuries, not heading of the ball.
Chudler also says there's no discussion in the study about whether soccer players might change their style of play if they wore headgear. For example, players may feel much safer wearing the headgear and become more aggressive on the field and in the way they go after the ball.
Naunheim notes that current studies don't provide conclusive evidence that heading the soccer ball over the course of many seasons causes long-term mental impairment.
"The word isn't in on that. We're going to have to follow people long-term over a career, from when they're young till when they're through college and do comparisons over time to see if there's a decrease in IQ or cognitive scores," she says.
"All we can say at this point is that we'd recommend that children don't head the soccer ball. In terms of long-term damage, there may be some, but it's not been demonstrated yet," Naunheim says.