Collective force of head hits increases odds of CTE, study says

When Jeffrey Valk started out as a running back in high school and then a safety in college in the 1990s, he made and made countless tackles during full-contact football practices. Hitting was a mainstay, as were injuries, including injuries.

When he became the coach at Buffalo Grove High School outside Chicago in 2005, Vlk did what he had been taught: He hit and tackled his players in drills to “toughen them up.”

By the time he became head coach in 2016, however, he noticed that many of his players were so tired from a week’s worth of hitting practice that they missed games or were more likely to be injured in those games.

Therefore, starting in 2019, Vlk eliminated full-contact practices. The players wore shoulder pads once a week, on Wednesdays, which they called contact days. Only then did he hit the tackle bag and crash pad, and wrap up teammates but not throw them to the ground. Vlk said that no starting player has been injured in his practice in four years.

“These types of injuries can stay with you for a long time,” he said, “and knowing that I am keeping kids safe is reason enough to go this route, not only in our program, but beyond the program. Is.”

VLK’s approach to limiting the number of hits players have is slowly spreading in the football world, where most efforts have focused on avoiding and treating concussions, which are often observable symptoms and tracked by sports leagues. are done.

But researchers have assumed for years that the more injuries a player sustains to the head — even subconscious ones that usually aren’t tracked — the more likely they are to have cognitive and neurological problems later in life. more likely to develop.

A new study published Tuesday in the scientific journal Nature Communications adds an important wrinkle: A football player’s chances of developing chronic traumatic encephalopathy, or CTE, are not related to the number of head impacts absorbed, but to the cumulative effect of all those hits. are also related to ,

The study, the largest to date to look at the causes of CTE, used published data from 34 studies that tracked the number and magnitude of head hits as measured by football helmet sensors. Using data that went back 20 years, scientists estimated the number and force of head hits absorbed by 631 former football players who donated their brains for a study overseen by Boston University researchers.

The paper sought to address one of the most persistent challenges for brain trauma researchers: identifying which aspects of head hits contribute most to CTE. They looked at the number of hits to the head, the number of years played football, The strength of those hits and other factors.

The best predictor of brain disease later in life, the study found, was the cumulative power of head hits absorbed by players during their careers, not the number of diagnoses.

“We’re now getting a better understanding of what causes CTE pathology, but we’re also getting a better understanding of what doesn’t cause CTE pathology,” said Dr. Daniel Daneshwar, assistant professor at Harvard Medical School and lead author of the research. Is.” the study. “And in this case, this is the largest study of CTE pathology ever done, and the findings were basically noise.”

Of the 631 brains examined, 451 players, or 71 percent, were found to have CTE, while 180 were not. The players who were estimated to have absorbed the greatest cumulative power had the worst form of CTE, which is associated with symptoms including memory loss, impulsive behavior, depression and suicidal thoughts.

Eric Naumann, a biomedical engineering professor at the University of Cincinnati who was not involved in the study, said the results reinforce the idea that accumulation of subclinical hits, rather than coalescence, is the driving force behind long-term cognitive decline. Was.

The latest data “seem to support the idea that, yes, all these hits matter, they all add up,” Dr. Nauman said. “If you accumulate damage faster than the body can repair it, now you have a problem.”

He said the analysis pointed to clear changes that could make football safer, such as the elimination of hitting in practices and the development of helmets that absorb more impact, especially at the back of the head.

Dr. Naumann said the new study included the brains of players with and without the disease, deflecting the common concern that the researchers only looked at the most damaged brains.

It also found a correlation between the estimated number and type of hits players hit during their careers and their health several years later, a factor Dr. Nauman said that it would be more difficult for opponents to argue that the players had suffered possibly undiagnosed injuries in later decades. He stopped playing football which could later lead to his cognitive problems.

Dr. Nauman said that the new research is still bound by limitations. The study calculated all head impacts detected by the helmet sensors, except those caused by shock or accidental movement. But previous research has suggested that the most significant hits appear above a certain threshold, a distinction the study was not able to make.

Because the NFL does not publish its helmet sensor data, the study used college sensor data as a proxy for professional players.

Helmets have improved in recent years, and it is likely that players who have improved in their careers absorb more impact than any hit. But football players decades ago were smaller and slower on average than those playing today, making any hit less forceful, Dr. Nauman said.

“It’s definitely a caveat, but it’s not something that makes me think the basic findings are wrong,” he said.

Joseph J., a professor at Brown University who helped design the sensors used in the Riddell helmet. Crisco said the study sought to address a fundamental challenge — that the researchers had not tracked how many hits the brain donors had accumulated over the course of their careers.

Instead, the study used helmet sensor data from a more recent set of players, who played at what level of play and for how long, to estimate the number and force of impacts to the head of older players. Based on the positions taken.

While the actual lifetime head impacts of players were needed to be studied, he said, the findings suggest that “players who are hitting hardest and most often on the road are more likely to have CTE.”

Steve Rawson, who studies the effects of helmets and injury risk at Virginia Tech, said the study emphasizes the force and number of hits players take to stay fit in how scientists understand brain injuries.

“Every time you hit your head, your brain goes through some load, and there’s going to be a pressure response and a brain stress response — a stretching of the brain tissue,” he said. “And if you cross some threshold, you would expect some injury response, and the severity of that injury response is going to depend on the acceleration values.”

The researchers have managed to pinpoint a few factors that explain how different players are exposed to head impacts, he said. For example, he said, linemen are often hit on the fronts of their helmets, while quarterbacks suffer severe impacts to the backs of theirs.

But, Dr. Rossen said, it would be a mistake for people to think they can use the findings now to predict someone’s likelihood of long-term cognitive problems.

“I don’t think what we can do right now is look at one person and really get a good idea of ​​their head impact risk relative to another,” he said, “because there’s such a huge difference from person to person.” is that we cannot count enough.

The study adds that future research should investigate different thresholds for counting hits, Dr. Rossen said a progression was important. Some head impacts, he said, are mild enough that the brain can probably tolerate them. But exactly at what point the effects become harmful is not clear, he said.

“Not all effects are created equal,” he said. “Trying to figure out which effects are most important is what I think can really help with this kind of analysis.”