Dartmouth defenders sandwich a New Hampshire wide receiver during a game in Durham, N.H., in 2009.
Concussions have deservedly gotten most of the attention in efforts to reduce the risk of head injuries in sports.
But scientists increasingly think that hits too small to cause concussions also affect the brain, and that those effects add up. And it looks like some athletes may be more vulnerable than others.
"Maybe we should be asking a different question," says Dr. Thomas McAllister, chair of the department of psychiatry at the Indiana University School of Medicine. "Not 'Is hitting your head bad?', but for whom it's bad."
To figure that out, McAllister and colleagues put sensors in the helmets of varsity football and hockey players at Dartmouth University, to measure when and how hard they got hit over the course of a season.
They also had the athletes take cognitive tests at the beginning and end of the season, along with athletes in non-contact sports like Nordic skiing and track and field.
They didn't find the dramatic differences in brain performance at the end of the season that they were expecting in the contact-sport players.
But when they looked at the athletes who didn't do well on the cognitive tests at the end of the season, more of them were playing contact sports. All told, 20 percent of the 80 football and ice hockey players scored 1.5 standard deviations lower than would be expected, compared to 11 percent of the 79 athletes in non-contact sports.
That group of contact-sport athletes also had more changes in their brain's white matter in MRI scans.The more often they got hit and the more intense the hits, the more the white matter changed.
The study was published online Wednesday in the journal Neurology.
White matter is the brain's communications network, and changes in white matter are a hallmark of brain injury. But the changes seen here were subtle, and the study can't prove that those changes came as a result of hits.
This may even end up being good news for contact sports players, McAllister speculates, because at the beginning of the season their brains were looking pretty good. And that's in people who had been playing these sports for years.
"It's sort of reassuring," he told Shots. "But we don't know if these kinds of changes are long-lasting and progressive, or whether it's just a subset of people who might be vulnerable to these repetitive impacts."
If that turns out to be true, and if researchers could figure out a way to identify people whose brains are more vulnerable, then perhaps that could be factored in when children choose sports.