College football players beware: Linebackers and linemen suffer more head impacts during a game than players in other positions, but running backs and quarterbacks endure the hardest and most severe blows to the head, a new study reports.
The findings may not come as a surprise to ardent football fans familiar with the skirmishes between linemen and the devastating sacks that can lay quarterbacks flat on their backs. But for neurologists, the research — based on direct measurements of nearly 300,000 head impacts during three college football seasons — is a step toward understanding the subtle factors in collisions that can result in chronic brain injury and concussions, the causes of which are still very much a mystery.
As the risks of long-term damage from concussions have become more evident, head impacts in football and other sports have become the subject of deep concern, much study and even Congressional hearings in recent years. Spurred by alarming research, the National Football League has introduced new rules on managing concussions and tried to eliminate particularly dangerous tackles, and colleges and high schools have instituted protocols to try to protect student athletes, like taking players out of games after worrisome impacts.
The new data, collected over three seasons of college football at Brown University, Dartmouth College and Virginia Tech, have already led to further changes. After looking at the early findings, Ivy League officials moved this year to limit full-contact football practices to no more than twice a week. According to research on Division I teams, college players sustain more total hits to the head in practices than in games.
The new study was published in the latest issue of the Journal of Biomechanics and was financed in part by the National Institutes of Health. The researchers measured impacts with standard football helmets outfitted with sophisticated sensors that recorded such data as head acceleration and impact location. The technology was wireless and non-intrusive, allowing each player on the three teams to go about normal play without any obstructions. Over the course of three seasons beginning in 2007, 314 players took part, and 286,636 head impacts were recorded.
The data allowed researchers to quantify the severity and frequency of blows to the head by player position. The magnitude of a head impact is not the only predictor of the likelihood of a concussion or other brain injury. Studies have shown that other factors can play a role: repetitive but less forceful head impacts, even those with no acute symptoms or signs, are called “sub-concussive impacts” and may be a cause of chronic brain injury. Studies have also shown that rotational acceleration — think of the whiplash a quarterback suffers when tackled from behind — can cause the most tissue damage. It is thought that concussions generally occur when the head accelerates rapidly and then is stopped, or when the head is turned rapidly.
It’s also known that having one concussion raises the likelihood of another.
“But what we don’t know is whether it’s because you’re always sticking your head in the wrong place at the wrong time, or because getting hit lowers your tolerance,” said Dr. Joseph J. Crisco, a professor of orthopedics at the Warren Alpert Medical School at Brown University and an author of the new study.
To get a better idea of how these factors contribute to concussions, the researchers combined the data on head acceleration and impact location to come up with a measure called HITsp, which they believe is a good indicator of concussions. On average, the running backs had the highest HITsp scores, at 36.1. Quarterbacks fell just behind, at 34.5, and linebackers followed closely with scores of 32.6. The data showed that offensive and defensive linemen had the lowest scores, at roughly 29. But that was not necessarily good news, as they also suffered the most frequent hits to the head.
“There’s a concern that linemen, for example, may not get concussions, but because they take so many hits, that may lead to chronic problems further down the road,” Dr. Crisco said.
The study did not identify which hits resulted in concussions. But Dr. Crisco said he and his co-authors are now going through the data and linking the hits with concussions, which will allow them to assess to what extent head impact exposure is associated with injury.
Dr. Crisco said the data could help equipment manufacturers design safer helmets for specific positions. A former college football player himself, he also noted that the data showed the importance of instructing players to avoid intentionally using their heads to tackle or strike other players.
“I love hitting as much as any football fan does,” he said. “But lowering your head into somebody is not part of the game. And I think you can get a great, hard-hitting game without intentional use of your head.”
“Whether or not that can be done is a different issue,” he added. “That would involve rule management and coaching technique.”
