A CHOP researcher and the NFL studied 5,100 player collisions. Here’s what they found.

For decades, NFL highlight reels have used a magic formula — a rush of swelling music here, some hypnotic slow motion there — to transform footage of the violent collisions that unfold in every football game into an almost weightless ballet.

The reality is often uglier.

Stan Walters, a Pro Bowl left tackle on the 1980 Philadelphia Eagles — the first team in franchise history to play in a Super Bowl — once compared the head impacts that offensive and defensive lineman routinely absorb to boxing.

“A thousand jabs,” Walters, 76, previously told The Inquirer, “instead of one knockout punch.”

The NFL has spent much of the last 25 years reckoning with the long shadow of traumatic brain injuries that generations of football players sustained during their careers. The league has simultaneously sought to better understand concussions and to reduce their prevalence in the sport, a quest that led to Children’s Hospital of Philadelphia.

Kristy Arbogast, the scientific director of CHOP’s Center for Injury Research and Prevention, is the lead author of a study, presented last September at the International Research Council on Biomechanics of Injury, that examined NFL players’ head kinematics, or head motions.

For four seasons, 98 players wore mouth guards equipped with electronic sensors, which recorded 5,104 head acceleration events.

Arbogast and the study’s coauthors focused on 10% of those collisions, which represented the highest accelerations that players experienced.

The researchers found that 59% of high-severity impacts struck players’ face masks.

Among the players who participated in the study, 66% of offensive and defensive lineman absorbed high acceleration impacts to their face masks, along with 56% of running backs, tight ends, and linebackers, and 46% of wide receivers and defensive backs.

None of the impacts that were measured by the mouth guards resulted in diagnosed concussions, Arbogast said.

“We looked at the severity and the magnitude of the linear acceleration and angular acceleration, which are the two parameters that the mouth guard measures,” she said. “They were relatively high. But there is no absolute threshold value above which an injury conclusively occurs.”

Past research into football and traumatic brain injuries has attempted to lend some sense of context to the collisions that players experience.

Dan Daneshvar, the chief of brain injury rehabilitation at Harvard Medical School, was the lead author of a 2023 study that explored a link between chronic traumatic encephalopathy (CTE) and the cumulative effect of head impacts that players absorb.

He uses gravitational force to describe different types of head accelerations. A boxer’s punch to an opponent’s head is the equivalent of about 50G, said Daneshvar, who was not involved in the mouth guard study.

“The average concussion,” he said, “occurs around 80G.”

The NFL — which helped fund Arbogast’s study — has said that newer generations of helmets have contributed to an ongoing reduction in brain injuries. The league recorded 182 concussions during the 2024 season, a 17% decrease from 2023 and the fewest overall in the last decade.

Face masks, though, have changed little over time, said Allen Sills, the league’s chief medical officer and a coauthor of the mouth guard study.

The study’s findings might result in new face mask designs and changes to playing technique that would be meant to further reduce head impacts.

“We never want to portray that the helmet alone is going to be the solution,” Sills said. “Because, again, the best way to avoid these injuries is to avoid striking the head in the first place.”

Arbogast began collaborating on research with the NFL and the players’ union in 2015, a fraught moment in the league’s history.

That year, a judge in Philadelphia federal court finalized an agreement to settle lawsuits that thousands of former players had filed against the NFL, accusing the league of minimizing the risks of repeated brain injuries.

The league denied the players’ allegations but committed to funding, for 65 years, a settlement program to compensate ex-players who developed neurocognitive impairment, Alzheimer’s disease, Parkinson’s disease, or amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease).

The NFL was also reeling from the suicide deaths of several notable retired players, including Andre Waters, a fearsome Philadelphia Eagles safety.

Those stories led parents of young athletes across the country to question whether it was safe for their children to strap on a helmet and step onto a football field, the sort of creeping doubt that could have blossomed into an existential crisis for the sport.

“I think it was a public narrative that needed science and rigor and study, like any other disease that we may study here at Children’s Hospital,” said Arbogast, who also serves as the codirector of the hospital’s Minds Matter Concussion Program.

The NFL and the players’ union, she said, “knew they had to bring resources, expertise, and knowledge to that discussion.”

Arbogast reviewed NFL footage of every diagnosed concussion of a player, for a better sense of how and when brain injuries occurred on the field. (The league has about 40 cameras at each regular season game, and nearly 100 cameras at playoffs.)

In 2017, the NFL hired Sills, a neurosurgeon from Vanderbilt University Medical Center, for the newly created position of chief medical officer.

That same year, the league had 281 concussions, and retired players started to submit claims to the concussion settlement program. (The program has since paid out $1.4 billion, but some ex-players still struggle to receive compensation.)

In 2018, Arbogast and the NFL began to plan for a new concussion study.

Some researchers had used helmet sensors to glean insights into head injuries, but those devices had a shortcoming, Sills said: “They’re not really measuring the force that’s going to the brain, which is our organ of interest.”

Arbogast and the NFL instead developed custom mouth guards that could collect data from within players’ bodies.

Players who volunteered to participate in the study began using the devices in 2019, though some elected to wear them only during practices.

“Prior to this study, we had no [mouth guard sensor] data at the professional level,” Arbogast said. “So we were really thrilled to get whatever data the players were willing to let us collect.”

While the study emphasizes the potential for equipment and rule changes that could make football safer, it also raises concerns about the long-term health of offensive and defensive linemen.

Previous research found that a third of the concussions that linemen suffer are from impacts to their face masks. The mouth guard study showed that those same players are also sustaining “frequent and relatively high severity — and in particular high angular severity — face mask impacts that do not result in a concussion,” reads one passage.

The cumulative impact of those impacts, the study continues, “must be further studied.”

Sills said it’s possible that mouth guard sensors will be used more widely by NFL players in the future, and he noted that World Rugby, the governing body for the international rugby union, requires its 7,500 players to wear similar sensors to detect head injuries.

The NFL already uses radio frequency identification chips to track which helmets are used in games; GPS devices in players’ shoulder pads document their speed and movement across the field. The league also has a “vision system” that can quantify head impacts.

“It’s a major focus of ours,” Sills said. “How do we get the head out of the game? And how do we avoid avoidable head contact?

“Step one of changing behaviors is being able to measure the behavior. So I think that’s where it becomes useful to be able to quantify this.”

The sport is still confronted by reminders of the grim fates that await some players.

Last month, researchers at Boston University’s Chronic Traumatic Encephalopathy Center said that Frank Wycheck, the Northeast Philly native and onetime Tennessee Titans star, had Stage 3 CTE when he died in 2023 at age 52.

More than 345 former players have been found to have had the degenerative disease.

A survey of nearly 2,000 retired NFL players, conducted by Harvard University’s Football Players Health Study, found last fall that 34% of those athletes felt certain that they had CTE.

Arbogast said that protocols for identifying concussions and ensuring that athletes are healthy before they can return to play have both improved dramatically during the last decade.

“I think it will be interesting to see the experience of the players who are playing now, when they’re 50 or 60,” she said, “and whether they’ll have better outcomes.”