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.