Force and Frequency of Hits Likely a Factor, but Genetics, Even Diet, May Play Roles, Too
By Matt McMillen
WebMD Health News
Reviewed by Louise Chang, MD
May 16, 2012 -- College football and hockey players sustain numerous blows to the head every season. Those hits, according to a new study published in the online edition of the journal Neurology, may add up to brain injuries that impact learning for some players.
The authors of the study followed football players at three schools: Dartmouth College, Brown University, and Virginia Tech. They also tracked ice hockey players -- both male and female -- at two of those schools. Altogether, they studied 214 athletes over the course of a season, comparing them to 45 players in non-contact sports such as track, crew, and Nordic skiing.
At the beginning and end of the season, all of the study participants took a 20-minute computer test to measure memory and reaction time, while a smaller number also took a comprehensive battery of mental tests. The preseason test results showed few differences between the contact and the non-contact players. For researcher Thomas McAllister, MD, that was encouraging.
"They are all Division I level and have been playing for many years, and the contact players have been hitting their heads for many years, so we thought we might see a difference between them and the non-contact players, but both looked pretty similar," says McAllister, a professor of psychiatry and neurology at Dartmouth Medical School.
The players' postseason scores, however, told a somewhat different story.
While the researchers found that a season's worth of head impacts do not have a measurable effect on all athletes, some players do appear susceptible. On one of the tests, which is used to measure a person's ability to learn and remember new things, 22% of the football and hockey players performed at a level that many clinicians would find "worrisome," says McAllister. Only 4% of the non-contact players showed a similar negative result.
The football and hockey players each wore helmets rigged with the HIT System, which monitors and measures the impacts of blows to the head during both games and practice. The helmets recorded an average of 469 hits per player over the course of the season.
According to the study, those who suffered the heaviest blows in the last week of play did worse on two of the mental tests. This, McAllister says, suggests "a modest correlation" between both the number of hits and the force of the hits and brain performance.
Reactions to the Study
"This study provides some objective evidence that may eventually allow us to know what is a reasonable number of hits," says neurosurgeon and sports medicine specialist Robert Cantu, MD, who was not involved in the research.
The researchers excluded athletes who suffered a concussion during the season, so that they could focus on the consequences of sub-concussive hits. Cantu, who co-directs Boston University's Center for the Study of Traumatic Encephalopathy, says that such an exclusion might not have been possible.
"The difficulty with this study is that many concussions are missed," says Cantu. "Did the lower scores happen because of sub-concussive blows to the head or did it happen because recent concussions were missed? The bottom line is that performance is down."
Cantu says much more research is needed before we'll understand all the risks and all the factors at play. Michael Bergeron, PhD, agrees.
"My suspicion is that we will see more definitive detrimental effects as this issue is examined further -- not fewer," Bergeron, executive director of the National Institute for Athletic Health & Performance and the National Youth Sports Health & Safety Institute, tells WebMD in an email. He was not involved with the study.
Bergeron says many factors influence a player's susceptibility to injury, including genetics, the angle, severity, and frequency of hits, prior history of concussion, neck strength, and diet.
"It's hard to pinpoint the reason some are affected and others not so much," he says.
Study Is 'Potentially Reassuring'
UCLA neurologist Chris Giza, MD, cautions people from overreacting to the study's negative results and overlooking the positive outcomes. He points out that while some of the players did do worse on a small number of the measures, on many of the tests, they showed no signs of impairment compared to those who play non-contact sports.
"The study is potentially reassuring," says Giza, who reviewed the study for WebMD. "There doesn't seem to be some pervasive effect across all contact sports participants."
McAllister also describes his study as reassuring, though he points out it does not disprove that there are risks involved in contact sports.
"It raises the possibility that a small but significant group of folks is more susceptible to repetitive impacts," he says. "There's an awful lot to learn about the short- and long-term effects of being hit over and over again. If I was a parent of a kid playing contact sports I would be very vigilant about any signs or symptoms of concussion. Pay attention to the signs, but don't panic."
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