A Stanford Medicine study finds that straight-line head motion predicts concussion better than the turning motion blamed since the 1940s.

It was published on 9 November in the Annals of Biomedical Engineering.

Researchers used motion-sensing mouthguards worn by 203 male and female athletes in seven sports, including lacrosse, MMA and football.

The data covered 3,851 head impacts. Forty-seven of them caused concussions, and every impact was recorded on video.

Peak linear acceleration was the single strongest predictor of whether a hit led to concussion.

A hit of 100 g, or 100 times the pull of gravity, carried a 50% risk of concussion.

"The threshold is lower than people had previously thought," said lead author Jessica Towns, a Stanford bioengineering student.

Examples include a jab between the eyes, or a football player's lowered head taking a hit on top.

The old view came from Scottish physicist A.H.S. Holbourn, who argued from mechanics that rotation drives concussion.

The authors say rotation is still harmful. Most real hits mix both kinds of motion, and more studies are needed.

Senior author David Camarillo says helmet safety rules may be underestimating the risk from straight-line hits.

Read the full concussion study report on Trends News Stories.

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