Traumatic brain injuries are commonly associated with contact sports, such as football and lacrosse. In reality, though, bike accidents are the leading cause of such injuries in the United States, notes Mehmet Kurt, postdoctoral fellow in bioengineering at Stanford University.
This surprising statistic led Kurt and Stanford bioengineering professor David Camarillo to consider whether bike helmets could be improved, specifically to prevent concussion. Camarillo, who has himself experienced severe bike-related head injuries, was particularly interested in researching a new technology -- an airbag "helmet" -- in which variable sensors are embedded in a neck collar. The sensors detect the accident, and the airbag expands over the head to prevent injuries.
Unlike a standard foam helmet, the uninflated airbag helmet does not go on the head: It looks and works like a scarf, wrapped around the neck and shoulders.
Camarillo wanted to know how airbag helmets, such as the ones developed by Hövding, a company in Sweden, performed compared to the foam one. The results, he and his team at the university's Camarillo Lab said, were encouraging.
Standard bicycle helmets are about an inch thick and made out of polystyrene foam, Kurt explained, noting that foam helmets can absorb a lot of energy. However, after a certain amount of impact, or "deformation," the foam breaks.
"If you've ever hit your head with a foam helmet, you will see that they break -- they reach their deformation limit because they're not very thick," he said.
In comparison, the airbag helmets tested were 5 inches thick when expanded. The helmets were dropped from 0.6 meters to 1.8 meters with variable pressure -- the same method that is used by the Consumer Products Safety Commission to test bicycle helmets.
The study found that the airbag helmet, given the correct level of pressure, can reduce the acceleration of impact by five to six times that of standard foam helmets.
There is, however, still more research to be done, Camarillo noted. The test they employed was based on the government's standard test, which Camarillo described as narrow and limited. It specifically assesses skull fracture because acceleration is linked to skull fracture, but it doesn't mean that the airbag would be better in all situations. Additionally, Camarillo said, the federal test does not assess the helmet's efficacy around its full circumference.
One other important area that researchers need to investigate, Camarillo said, is whether the airbag helmet in some situations might not inflate or might be too soft, resulting in what he referred to as the risk of "bottoming out," an even more dangerous situation in which there would be no protection for the skull.
The study also found that different pressure levels are needed in different types of accidents.
"In bicycling you can hit a curb and just fall softly versus you can get hit by a car and have a severe hit, so you essentially need to have different pressure levels for different impacts," said Kurt, who soon will become an assistant professor at Steven's Institute of Technology in New Jersey.
Simply increasing the pressure in the airbag to a uniform level would not solve the problem because as the pressure is increased, the airbag becomes stiffer, at which point the advantage of the airbag -- to make the helmet softer and bigger -- is lost, Kurt explained.
"The result of this study tells us that the smart thing to do is to have an adjustable pressure level. So you need to have sensors essentially that can detect the severity of the impact before the impact," Kurt said.
There is a long way to go before American bicyclists can get excited about switching to airbag helmets, which are now available in Europe, since they do not currently comply with the federal government's safety regulations for bike helmets. According to Camarillo, those standards, based on research from the 1950s and 1960s, would need to be updated.
As it stands under the Consumer Product Safety Commission, one requirement that helmets have is that they have to pass a cost effectiveness bar. Camarillo believes it would take a significant amount of political pressure from constituencies to change the current standards by which helmets are tested and approved.