Researchers at Stanford University have tested a bike helmet that comes in a soft pocket worn around the neck and pops up, like an air bag, around a person's head when it senses a potential collision.

Traditional "foam bike helmets can and have been proven to reduce the likelihood of skull fracture and other, more severe brain injury," said David Camarillo, an assistant professor of bioengineering at Stanford. "But, I think many falsely believe that a bike helmet is there to protect against a concussion. That's not true."

Given that bicycling is the leading cause of sports- and activity-related concussion and brain injury in the United States, Camarillo's lab, which works on understanding and preventing concussion, decided to test a new type of helmet that is originally designed to address the fact that people do not like to wear helmets for aesthetic reasons and is starting to be available in some European countries.

"We conducted drop tests, which are typical (U.S.) federal tests to assess bicycle helmets, and we found that air bag helmets, with the right initial pressure, can reduce head accelerations five to six times compared to a traditional bicycle helmet," Mehmet Kurt, a postdoctoral scholar in the Camarillo Lab, said in a Stanford news release.

Results of the test were published in the recent edition of Annals of Biomedical Engineering.

The drop test consisted of putting the helmets on a dummy head containing accelerometers and dropping it, neck-side up, from various heights onto a metal platform.

The head form was tilted at two different angles, simulating hits to the crown and the side of the head.

Researchers dropped the helmets from as low as 0.8 meters to as high as two meters and measured the linear acceleration of the helmet as it struck the ground.

"As our paper suggests, although air bag helmets have the potential to reduce the acceleration levels that you experience during a bicycle accident, it also suggests that the initial pressure that your air bag helmet has is very critical in reducing these acceleration levels," Kurt said.

Camarillo said the large size of the air bag helmet compared to foam bike helmets is the likely source of its success. Being larger, it can also be softer, allowing for a more cushioned fall.

However, this cushioning also has a potential downside. In the testing, the air bag helmet was pre-inflated and the researchers maximized the pressure of the air inside the helmet before each drop in order to get these results.

Without the maximum amount of air, the air bag helmet could bottom out, causing the head to hit the ground with much more force than if it were wearing a traditional foam helmet.

In current versions of the air bag helmet, a chemical process triggers expansion, which doesn't seem to guarantee maximum air pressure. Endit

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