For decades, researchers have studied how different types of head movement contribute to concussions. Now, a new Stanford Medicine study is challenging a long-standing theory about which forces may be most closely associated with these injuries.
Published in the Annals of Biomedical Engineering, the research suggests that linear acceleration, or straight-line movement of the head, may be a stronger predictor of concussion than rotational acceleration, which involves the head turning.
The findings challenge a theory dating back approximately 85 years that has emphasized rotational movement as a major contributor to brain injuries.
To investigate, researchers analyzed data collected through motion-sensing mouthguards worn by 203 athletes across seven sports, including football, lacrosse, and mixed martial arts.
The data included 47 impacts associated with concussions and 3,804 impacts that were not.
Researchers found that peak linear acceleration was the strongest individual predictor of concussion in their mathematical model. Adding rotational acceleration did not improve the model's predictive performance.
However, the researchers emphasized that their findings do not mean rotational forces are harmless.
In fact, most real-world impacts involve a combination of linear and rotational movement.
The study also raises questions about how helmets are evaluated and whether current safety standards adequately account for straight-line head acceleration.
But the authors acknowledge important limitations, including the relatively small number of concussions analyzed and the need for additional research to confirm their findings.
“I would say this is the beginning, not the end,” said senior author David Camarillo, Ph.D., associate professor of bioengineering at Stanford.
For Athletic Trainers and sports medicine professionals, the research offers another perspective on the ongoing effort to better understand concussion biomechanics.
While the findings may eventually influence protective equipment and injury prevention strategies, they do not establish new clinical guidelines or change existing concussion assessment protocols.
For now, the study adds to a growing body of research exploring how head impacts affect the brain and how athletes might be better protected in the future.
Study: Limitations of Rotational Acceleration for Predicting Concussion: A New Injury Risk Function
Journal: Annals of Biomedical Engineering (2026)