Concussion risk: Are we overlooking straight-line impacts?

Clinical takeaway: Consider that concussion risk may be more closely tied to straight-line head acceleration than rotational acceleration alone. Current helmet standards and injury thresholds may underestimate risk from impacts previously considered relatively safe.

Concussion prevention strategies and helmet ratings have largely been built around an 85-year-old theory that rotational head motion is the primary cause of brain injury. New research using instrumented mouthguards that directly measured head motion during real-world sports impacts challenges that assumption and suggests linear acceleration may play a larger role than previously appreciated.

Researchers analyzed 3,852 video-verified head impacts, including 47 concussions, across seven sports. Peak linear acceleration was substantially better at distinguishing concussive from nonconcussive impacts than peak rotational acceleration, while adding rotational acceleration provided little additional predictive value. Peak rotational velocity modestly improved prediction when combined with linear acceleration.

The team estimated that a head impact producing 100 g of linear acceleration carried about a 50% concussion risk. That threshold is far below a widely cited 192 g benchmark derived from older helmet-mounted sensor data. The model predicted that impacts around 150 g were associated with a greater than 99% risk of concussion.

Youth concussion impacts occurred at much lower acceleration levels than adult injuries. When researchers tested their model in four concussion cases involving athletes younger than 14 years, it failed to identify any of them, suggesting that concussion thresholds may be substantially lower in children than in adults.

The study pooled data from 203 male and female athletes participating in football, Australian football, rugby, mixed martial arts, lacrosse, gymnastics, and ice hockey. Custom-fitted instrumented mouthguards captured six-degree-of-freedom head kinematics, and concussion outcomes were confirmed by medical evaluation and/or video review. The primary outcome was the ability of linear and rotational head-motion measures to predict concussion risk.

The investigators say the findings need confirmation in larger datasets but may prompt reconsideration of helmet testing standards and concussion risk models. Ongoing work aims to clarify how linear acceleration injures the brain and whether mechanisms such as brain-skull contact, fluid displacement, or pressure-driven cavitation contribute to concussion.

“If linear acceleration is its own distinct mechanism of concussion and it’s very common, then we’ve been missing a lot. We haven’t tried as hard to optimize for this variable. It gives me some hope that there’s a new opportunity for preventing concussions,” said senior author David Camarillo, PhD.

Source: Towns JA, et al. (2026 Nov 9) Ann Biomed Eng. Limitations of Rotational Acceleration for Predicting Concussion: A New Injury Risk Function.