A quick shake of the head after a hard hit could signal that a person has a concussion, a new study suggests, based on the experiences of young athletes.
It’s an easily recognizable movement that could help significantly reduce the number of concussions that go undiagnosed if added to official evaluation guidelines, according to researchers from Mass General Brigham and the Concussion Legacy Foundation.
“We describe it in detail as a time that after a hit to the head, someone laterally shakes their head at a speed between two and eight Hertz. But that’s complicated medical terminology for something we’ve all seen,” said Dr. Dan Daneshvar, a study co-author and co-chair of sports concussion at Mass General Brigham.
Cartoons often depict a circle of birds that fly away after the character shakes their head, for example.
“There’s such a strong lay understanding of this being associated with concussions,” he said, but it’s not included in guidelines or medical literature.
To better understand this movement – dubbed a spontaneous headshake after a kinematic event, or SHAAKE – and its relationship to concussions, the researchers surveyed hundreds of young adults who had played a sport at the high school, collegiate or semiprofessional level.
They found that the vast majority of the young athletes were familiar with the gesture and had experienced it themselves, more often than once. In nearly three out of four cases, the individuals surveyed said that they got a concussion at the time of the SHAAKE.
The concussions that the survey participants reported were often self-diagnosed, but the underlying reasons they typically reported for making the head shake – such as disorientation or confusion, or changes to spatial perception – lined up with symptoms that are known to be associated with concussions.
Recognizing this head shake and its link to concussions in a more formal way is “long overdue,” said Dr. Julie Stamm, a clinical assistant professor at the University of Wisconsin-Madison who was not involved with the new study.
“Going back a few decades, we used to think that you had to lose consciousness to have a concussion,” she said. Now, the science shows that concussions very rarely result in severe symptoms like this. Instead, more subtle signs are known to be more common – and the severity of the symptoms doesn’t always line up with the severity of the injury, she said.
“People would try to shake off a ‘bell ringer’ or shake off ‘seeing stars’ and kind of reset,” Stamm said. “We didn’t always consider some of those injuries to be concussions, and now we do.”
Based on the survey responses, researchers suggest in the new study that more formal recognition of SHAAKE as a sign of a concussion could help identify up to a third of undiagnosed concussions.
“Based on our data, SHAAKE is a reliable signal that a concussion may have occurred, like an athlete clutching their head after contact, being slow to get up, or losing their balance,” said Daneshvar, who is also chief of brain injury rehabilitation at Spaulding Rehabilitation and Harvard Medical School. “Just like after these other concussion signs, if athletes exhibit a SHAAKE, they should be removed from play and evaluated for a potential concussion.”
The National Football League and the NFL Players Association agreed to update the league’s concussion protocol in October 2022 after intense scrutiny over decisions made following a hit that knocked Miami Dolphins quarterback Tua Tagovailoa to the turf.
A sideline doctor initially concluded that Tagovailoa’s fall was due to a previous injury to his back, and he was allowed to return to the game, only to be hospitalized for a concussion later. The imbalance he was experiencing was later attributed to ataxia, which describes a lack of coordination caused by a neurological issue. Under the new NFL concussion protocols, players are unable to compete if they are experiencing ataxia.
But the researchers of the new study, published Wednesday in the peer-reviewed scientific journal Diagnostics, suggest that the diagnosis and decisions for Tagovailoa may have played out differently if the head shake were part of the official concussion protocol.
“In this instance, the SHAAKE he exhibited would be difficult to attribute to a prior back injury,” the researchers wrote. “Any of the doctors that saw Tua, both on the field and in the subsequent days, may have reconsidered and, based on this additional evidence, determined that a concussion diagnosis would more appropriately cover both his imbalance and his SHAAKE.”
A board of independent and NFL-affiliated physicians and scientists developed the league’s official Game Day Concussion Diagnosis and Management Protocol in 2011, and it’s “reviewed each year to ensure players are receiving care that reflects the most up-to-date medical consensus on the identification, diagnosis, and treatment of concussions,” according to an overview on the NFL’s website.
“The NFL’s medical committees regularly review new research, and we have been in touch with the authors of this study,” NFL Chief Medical Officer Dr. Allen Sills said in a statement about the new study. “As with any new research, we will discuss these findings with our experts and look at our own data to see if these findings can be replicated.
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“Our concussion protocol, a conservative process developed from internationally accepted guidelines, is reviewed annually to ensure players are receiving care that reflects the most up-to-date medical consensus on the identification, diagnosis, and treatment of concussions.”
For the researchers of the new study and other experts, including SHAAKE as a potential sign of a concussion – in sports protocol and medical guidelines more broadly – would bring very significant benefits at very little cost.
“Our understanding of how concussions look is evolving,” Daneshvar said. “From my perspective, this is one of those things where it doesn’t cost anything to pull an athlete out and evaluate them. But the potential negative consequences of not evaluating an athlete who has a concussion could be catastrophic – for themselves, for their career and for their life.”
Concussions are frequently unreported, and recognizing more signs in official protocol could help, Stamm said.
“It really gives the clinicians the power to say, ‘No, this is real,’” she said. “It both gives the clinician more reason to take them off the field, and if the athlete understands that shaking their head is happening because they’re having symptoms, maybe they’ll actually realize it’s a concussion if they didn’t know that before.”