The sub-concussive impact

Image Credit: Wikimedia Commons

In 2002, Jeff Astle passed away at the age of 59 after suffering years of slowly declining mental health. Astle was a professional English soccer player in the 1960s and 70s. Prior to his death, doctors and family members thought he was suffering from early-onset Alzheimer’s disease, but the coroner found a different cause of death – chronic traumatic encephalopathy (CTE). Astle’s death raised many questions. CTE is most commonly associated with high-contact sports, such as football or boxing, where serious head traumas and concussions occur frequently. How could someone without a history of concussions or major head injuries die from a disease like CTE? Nicknamed “The King,” Astle was a prolific player known for his skill at heading the soccer ball. Could years of heading the ball be to blame?

Since 2002, concussions have quickly risen to the forefront of sports research. Gone are the days when a severe blow to the head during a football game could be brushed off as part of the game. With an expanding pool of knowledge and research, concussions are now considered a major public health issue.

But what about cases like Jeff Astle’s? What about when doctors find posthumous brain injuries in people who haven’t had a series of concussions? As more and more professional athletes are diagnosed with neurodegenerative diseases, the long-term consequences of repeated head impacts are becoming clearer.

Recent findings indicate that a newly identified threat, called sub-concussive head impacts, may be doing more damage than previously thought. Researchers are finding positive correlations between CTE and the amount of time spent playing sports with long-term exposure to sub-clinical head trauma. “This indicates that the cumulative head impacts or sub-concussive hits may be more important than concussions” says Peter Kiernan, a research assistant at Boston University’s CTE Center, which performed the definitive studies on CTE.

A doctor can diagnose a concussion based on any number of symptoms that appear as a result of an impact to the head. Symptoms may include headaches, vision problems, balance issues, as well as possible changes in hearing, speech, or smell. Sub-concussions differ in that they do not present any signs or symptoms. Doctors define a sub-concussive impact as any impact or force to the head that does not result in a concussion diagnosis. Yet sub-concussions may have major consequences. Anthony Petraglia, a neurosurgeon at Rochester Regional Health, NY, and expert in sports related neurological injuries says, “This concept of sub-concussion is a significant emerging one that definitely requires thorough consideration.”

Several studies show that athletes at college, high school, and youth levels can sustain anywhere from several hundred to over a thousand head impacts during a single season of football. A 2016 study out of Wake Forest School of Medicine examined structural changes in the brains of 25 youth football players (ages 8-13) following a full season. Researchers performed brain imaging scans prior to the start of season and after the season ended. The scientists kept detailed data measuring both number and severity of head impacts for each individual player. They only measured sub-concussive events; if a player sustained a concussion, the researchers excluded him from the study. At the conclusion of the football season, researchers found a significant relationship between the number and severity of head impacts and structural changes in certain areas of the athletes’ brains. For these participants, stronger and more frequent head impacts corresponded with larger physical brain changes.

Specifically, researchers noted changes in the way water flowed through the white matter of the brain. White matter is full of nerve fibers, or axons, encased in a fatty insulating substance. Joel Stitzel, a professor of biomedical engineering and co-author of the study, describes these axons as similar to insulated wires connecting and transmitting information. “Water generally moves in the same direction that the white matter ‘tracks’ are,” says Stitzel, “when you get a little bit of inflammation or when there’s an injury, we view in the MRI an abnormality; the water flows in other directions.” Researchers worry about the change in water flow found in this study because similar changes appear in brains that undergo more traumatic brain injuries.

Jeff Astle’s untimely death is a reminder that sub-concussive impacts extend beyond high-contact sports such as football, rugby, or hockey. One recent study, published in 2016, showed changes in brain function after a single soccer ball-heading drill. Researchers at the University of Stirling, Scotland, took a group of 23 adult soccer players and measured brain activity and cognitive ability prior to participating in a heading drill considered ‘routine’ in a soccer practice. The participants each headed 20 soccer balls during a 10-minute period.

To measure cognitive ability, the participants completed a standard computer-based test before and after the drill to measure mental tasks such as memory, reaction time, and sustained attention. Following the heading drill, they displayed decreases in memory performance by 41 to 67 percent.

The results of this experiment also show that the players had an increase in brain inhibition after the ball heading drill. Brain inhibition relates to the way the brain responds to stimulation. Some signals to the brain are “excitatory” and cause neurons to fire quickly, while other signals are “inhibitory” and block neurons from firing. These two types of signals need to be balanced in order for the brain to function properly: If excitatory signals win out, it can cause seizures. If inhibitory signals increase, as was the case in the soccer heading drill, it can result in blocked learning and decreased memory function. Though the changes in brain function returned to normal approximately 24 hours after the test, researchers still see these results as evidence that more work needs to be done to fully understand the consequences of sub-concussive head impacts.

These examples represent only two studies of what is now a growing field of research. Petraglia describes the findings as, “just phenomenal when you think about it. We’re talking about asymptomatic players that are showing changes on advanced functional tasks.”

The solution is not to simply remove children and young adults from athletic competition. “There’s too many benefits to participation in sports,” says Stitzel. Instead, people should use this information as a means to increase the safety of sports equipment or change the rules to better protect players. In January 2016, U.S. Soccer released new rules for youth soccer players that reflect concerns about concussive and sub-concussive impacts. Children 11 and under are no longer allowed to head the ball during games or practices and children aged 12 &13 are limited to 15-20 headers per week. Some football coaches are banning full-contact during practices; others talk of adding helmets to sports such as soccer as a preventative measure.

The next step to understand sub-concussive impacts will involve more long-term studies. Experts don’t know if young people’s brains are more susceptible to this type of head trauma than older, more developed brains. The human brain undergoes significant anatomical, functional, and structural changes until the mid-twenties and may be more vulnerable to damage. This is especially concerning as athletes participate in sports such as soccer as young as 4 or 5. Many youth athletes also engage in multiple sports year-round, which translates to potentially thousands of head impacts from childhood to adulthood.


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