The football helmet is perhaps the most iconic piece of safety equipment there is, but we're just now beginning to understand how helmets can — and should — protect the brain.
Blows that rotate the head are known to cause brain trauma, yet a new Stanford study (subscription required) has found that this kind of movement isn't included in the tests currently used to evaluate a football helmet's safety.
In the study, bioengineer David Camarillo, PhD, and his team investigated the types of head movements that cause concussions using computer models of the brain and data collected from Stanford football players wearing mouthguards instrumented with accelerometers (device that measures changes in velocity).
Using the computer model, they found that the brain's movement increases when the head oscillates (moves back and forth) at 15-20 hertz and it completes a single oscillation in about 50 milliseconds. The field data from the accelerometers showed that the players typically experience head oscillations around 20 hertz.
When the research team compared these results to the scenarios used to test the safety of football helmets, they found a mismatch. The standard tests used to evaluate football helmet safety (acceleration tests and a test that drops a helmet-wearing dummy head from various heights) fail to include the rotational movements known to cause concussions; they also generate faster head oscillations (100 hertz); and measure head acceleration for only 15-36 milliseconds.
"The problem with having a model that doesn't re-create what players actually experience in the field, is that you could optimize a helmet to perform well in the drop test that unintentionally performs poorly in the field," said Fidel Hernandez, a doctoral candidate in mechanical engineering and one of the study's lead authors, in a Stanford News story.
This is a big deal because roughly 70 percent of football players in the United States who rely on helmets to keep their head's precious cargo safe are under the age of 14, and they receive, on average, a whopping 240 hits to the head each season.
Camarillo and his team hope their findings can be used to make more realistic and useful helmet tests.
Previously: Stanford bioengineers and clinicians team up to shed light on how concussions affect the brain, Forces at work in concussions more complicated than previously thought, new Stanford study reveals, Now that's using your head: Bike-helmet monitor alerts emergency contacts after a crash and Study shows concussion recovery may take longer for female, younger athletes
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