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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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