Even mild hits in contact sports changing brain

Suffering a concussion can cause serious and often lasting damage in the brain. For athletes, it could be one strong blow to the head during a tackle or an aggressive head-first check into the boards.

But what about all of those minor hits to the head in everyday practices?

Western-led research now shows that those mild impacts are causing subtle brain changes even in the brains of otherwise healthy, symptom-free athletes. These are changes, according to researchers, that may not reveal their true damage until decades later.

“Even with no concussions, the repetitive impacts experienced by players clearly had effects on the brain,” said Ravi Menon, a Schulich School of Medicine & Dentistry professor and principal investigator on the study. “We were able to show – quite strikingly – a very obvious trend in athletes who play contact sports over multiple seasons.”

The study, Longitudinal changes of brain microstructure and function in nonconcussed female rugby players, was published June 17 in Neurology, the medical journal of the American Academy of Neurology.

The study followed 101 female varsity athletes at Western – 70 who played rugby and 31 who participated in either rowing or swimming. The idea was to compare the brains of athletes who played contact sports with age- and sex-matched controls involved in the same level of intense exercise without the contact.

It is the first study of its kind to use another group of athletes as the control rather than using baseline pre-season measures.

The athletes wore devices to record head impacts during practices and games to provide insight into the amount of impact they were experiencing in a regular season. Researchers also used high-field magnetic resonance imaging (MRI) brain scans to look for changes in the structure of the white matter in the brain and how the different brain regions communicate with each other.

The study showed that rowers experienced zero impacts while 70 per cent of rugby players experienced an average of three impacts during two practices and one pre-season game.

The research team found changes to the microstructure of the white matter in the brains of rugby players. In some, those changes increased over time. While they also seemed to recover slightly in the off season, there was evidence they worsened over multiple seasons.

Those same changes were not evident in the brains of swimmers or rowers.

“These white matter tracts connect all the areas of the brain. They are the highways along which information travels. When you damage them, you have difficulty moving information around,” Menon said. “Your brain finds ways to reroute the information along a different route, which is why you won’t be able to find any difference behaviourally.”

Researchers don’t yet understand what happens when all of those routes are exhausted. The data shows there are also compensatory changes in the brain along the other routes; the brain is working hard to compensate for this damage.

“But we suspect that if something else happens late in life, like a stroke or dementia, you’ve now used every available pathway – and there are only so many roads you can take. We may not see the impact of this damage for another 50 years.”

Further work needs to study the impact of these contact sports over a longer period of time, researchers stressed.

“It’s clear that even sub-clinical impacts have an effect on the brain,” said Kathryn Manning, PhD’18, study author and a postdoctoral scholar at the University of Calgary. “These findings have immediate implications for concussion research. Though the long-term effects of sub-clinical impacts remains unclear, an effort to limit the number of impacts athletes experience in practice could be beneficial.”

This is important information for athletes, parents and coaches to understand when designing practices.

“When you’re 20, you probably feel like you’re invincible. But your brain is demonstrably showing changes when you have these multiple impacts – even if you don’t get obviously hurt on the field,” Menon said.

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