Generally, people have believed if a hit to the head didn’t cause a concussion, there was no brain injury either. Now, physicians are learning that even hard hits that do not cause concussion – called subconcussive hits – can still lead to changes in the brain.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
“Many impacts in sports are not mild,” says neurologist Andrew Russman, DO. “They are significant hits, hard enough to be jarring, but they do not result in obvious concussion symptoms.”
Subjective symptoms, often underreported
What’s tricky about a concussion is that it’s so subjective. A hit that causes a concussion in one person might not in another because of differences in body structure, such as neck musculature from person to person. And there is no definitive test for concussion – it is diagnosed based on what symptoms the patient reports, and it is notoriously underreported.
Based on a recent study of 120 high school football players conducted by Cincinnati Children’s Hospital Medical Center, fewer than half of the players would tell their coach or athletic trainer if they had concussion symptoms.
So reducing the risk of hits that do not cause symptoms presents a significant challenge.
Repetitive hits have ‘cumulative effect’
“Repetitive impacts to the head which do not cause concussion may still cause brain-related changes,” Dr. Russman says. “Evidence suggests subconcussive impacts may have a cumulative effect, but the degree varies between individuals.”
Chronic traumatic encephalopathy (CTE), which can only be diagnosed during an autopsy, is the most worrisome potential effect of multiple concussive and subconcussive impacts over time, he says.
CTE can cause memory loss, aggression, confusion and depression. While it has been linked to boxing and football, a recently published study conducted by researchers from the Gruss Magnetic Resonance Research Center found that soccer, too, can lead to diminished neurocognitive performance among athletes who frequently head the ball.
“We regularly see concussions from soccer headers,” he says. “I would be reluctant to encourage a child to do headers in youth soccer. The lifetime accumulation of impacts is a concern,” he adds.
Subconcussive hits and future concussions
Another concern is whether subconcussive hits make an athlete more vulnerable to concussion. Regular subconcussive hits could have a priming process for concussions from other, possibly less forceful impacts, Dr. Russman says.
Other than avoiding impacts to the head, there is no other way to protect kids. “While participating in sports may have physical and social advantages during child development, parents may wish to consider excluding children from participating in sports with a high risk of concussion,” he says.
The Institute of Medicine and National Research Council recently reported on a “culture of resistance” among young athletes to report concussion symptoms.
“In addition to informing people about the signs and symptoms of concussion,” Dr. Russman says. “We need to educate parents and athletes about the dangers of repetitive head trauma with or without concussion in sports.”
Free online concussion course for youth and parents
Suspect a Concussion? What You Need to Know