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Analyzing Hard Hits on the Football Field

New data on the frequency and location of head impacts could shed light on the causes of brain injury.

New research on head injuries in football–data gathered from a large study of players in action–might reinforce the growing suspicion that brain trauma is caused not only by knock-out hits that leave a player woozy, but also by the accumulation of smaller hits. The findings could eventually support the creation of something like the pitch limits in youth baseball: after a certain threshold of blows to the head, a football player would come out of a game.

Taking hits: This Riddell football helmet is equipped with six accelerometers in its liner. The red circles show where the accelerometers go. The sensors measure the acceleration of the head and transmit the data to a computer for analysis.

The research comes from a federally funded study that was designed to improve the understanding of the biomechanics of brain injury among athletes. The study is especially timely given two recent cases that raised questions about whether football causes more extensive brain damage than most fans and players realize.

Owen Thomas, a 21-year-old University of Pennsylvania football player who committed suicide, and Chris Henry, a 26-year-old Cincinnati Bengals wide receiver who died during a domestic dispute, were both found to have chronic traumatic encephalopathy. That is a degenerative brain disease caused by head trauma. It’s been found in more than 20 deceased NFL players. It cannot be diagnosed in a living person because physicians have to take microscopic examinations of brain tissue to identify the protein and abnormalities that mark the disease.

In the new study, funded by the National Institutes of Health, researchers outfitted football teams from Virginia Tech, Brown University, and Dartmouth College with sensor-equipped helmets that measure the magnitude, location, and direction of a hit and send the data to a computer. The researchers could then focus on the frequency and location of blows to the head that individual players received during practices and games.

The researchers discovered that some players receive 1,400 to 1,500 hits to the head (the study calls them “head impact exposures”) in a season–on average about six per practice and 14 per game, but typically more for linemen and linebackers who absorb the most; running backs get hit less often, but the magnitude of the impacts was generally higher, says Rick Greenwald, president of Simbex, a research and product development company in Lebanon, New Hampshire. Greenwald is principal investigator of the research team and was due to present the data Friday at the Head Trauma and the Athlete Conference in Waltham, Massachusetts. The full study is being published in the Journal of Athletic Training in December, and Greenwald hopes the data will be used by helmet manufacturers to design better equipment and by the organizations that set standards for helmet testing.

The study, now in its fourth year, has yet to take the next step and correlate the number of hits a given player received to the condition of his brain. Even so, specialists in the field say the data offer important insights into the toll football takes. “Players are receiving thousands of hits in one season,” says Robert Cantu, clinical professor in the department of neurosurgery and codirector of the Center for the Study of Traumatic Encephalopathy at Boston University School of Medicine. “Add that up over the years and you have many thousands of head impacts.”

The helmet sensors measure the force of the impact by measuring both the linear and rotational acceleration of the head. The resulting linear acceleration is expressed in g-force, with 1 g being equal to the force of gravity. NFL research has determined that 98 g is a threshold for concussions. But Chris Nowinski, president of the Sports Legacy Institute, a nonprofit organization based in Waltham that studies brain injury in athletes, said the study data indicates that football players are enduring numerous blows that are beneath the concussion threshold but still are serious.

“Ninety percent of concussions on the football field go undiagnosed because the impact was relatively minor and a player was able to play through it,” Nowinski says. “When you line up this data–so hits that are 30 g’s and 40 g’s are next to impacts of 120 g’s–you start to see the damage. It seems insane that football players take repetitive hard hits to the head and this is applauded for making them tougher.”

The data for the study came from a system originally developed by Simbex, which specializes in biomechanical feedback systems, and Joseph Crisco, an engineering professor at Dartmouth. In 2004, Riddell, a sporting-equipment manufacturer based in Rosemont, Illinois, acquired the technology and developed a helmet called Revolution IQ Hit. Individual helmets are $1,000, while the equipment that continuously and wirelessly transmits data to a sideline laptop is sold to teams for roughly $60,000 to $70,000. (A less-expensive version is being developed for high school and youth leagues.)

The alerts on the helmet system can be customized so sideline physicians can be notified when a player exceeds a certain number of hits per practice or game, or when his accumulated g forces are too high. Within a few years, such a system could be used in colleges and high schools for the equivalent of a pitch count for football, says Gunnar Brolinson, the physician for Virginia Tech’s football team and the associate dean for clinical research for the Virginia College of Osteopathic Medicine. “Currently, when a player sustains a high head acceleration and continues to play, we watch him carefully from the sideline. If he is acting confused and not playing appropriately, he can remove him from the game for medical evaluation,” says Brolinson. But once researchers better understand the effects of cumulative head accelerations, a player might be taken out once he has sustained a certain frequency or magnitude of collisions, even if no single blow registered at extreme levels.

Already, he says, Virginia Tech has modified its practices to reduce the number of head impacts players sustain and taught players new ways to tackle that don’t require using their heads as battering rams.

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