Why didn’t my bike helmet prevent my TBI?


15 per cent of the approximately 18,000 traumatic brain injuries (TBIs) that occur in a year in Ontario are a result of a cycling accident. Every year in Canada, over 11,000 people die as a result of a traumatic brain injury (TBI) – using the same 15 per cent – that’s over 1600 people in Canada who die as a result of a TBI caused by a cycling accident. 85 per cent of all cyclists’ deaths in Canada involve a brain injury.

A little over five years ago, I sustained a TBI while riding my bike. It was a beautiful spring morning, and I was riding my bike to work, as I had hundreds of times before. I remember leaving my home that morning, and then waking up in the emergency room at St. Michael’s Hospital, several hours later. I was told by the doctors in the emergency department that I had been knocked off my bike, hit the ground, passed out, and taken to the ER by ambulance. Several hours later I was diagnosed with a brain injury. To this day, I have no memory of the incident.

I was wearing a bike helmet, which I always did, but my helmet did not protect me against acquiring a TBI. I’d always wondered why, and recently I got my answer. I came across a TED Talk by bioengineer (and former football player) David Camarillo, who, along with his team at Stanford University, has been able to demonstrate what really happens to our brain during a concussion, and why bike helmets, and other sports helmets, such as football helmets are not designed to protect against concussion, but rather, they are designed and tested to determine how well they protect against skull fracture.

What happens to your brain during a concussion?

The standard thinking of what happens to your brain during a concussion is that the head moves, the brain lags behind, catches up, smashes into the skull, rebounds off the skull and then proceeds to run into the other side of the skull. This dynamic is repeated many times. This understanding of what happens to the brain during concussion suggests that the brain is damaged on the outer edges.

In his Stanford University lab, Camarillo and his team, with the aid of new technology, have looked closely at what happens to the brain when it is experiencing a concussion. Their investigations suggest that the current thinking about what occurs to the brain during a concussion is not entirely accurate. Firstly, he does not believe that the brain moves around as much as current wisdom suggests. Camarillo argues that there is very little room in our cranial cavity for movement, perhaps a few millimetres, and our cranial cavity is filled with spinal fluid, which acts as a protective layer. Secondly, he suggests that the brain does not move as a whole.

Football player with ball about to fall to the ground

Our brain is one of the softest organs in our body – the consistency of Jell-O – and as the brain moves around in our skull during a concussion, it is probably twisting and turning and contorting – the tissue is getting stretched. Concussion does not appear to be something that is happening to the outer edges of the brain, but rather it is happening somewhere much deeper, in the centre of the brain.

The Laboratory – The Stanford Football Team

To help Camarillo and his team better understand what is happening to the brain during a concussion they utilized a mouth guard equipped with sensors and a gyroscope, which most experts believe can tell us what happens to the brain during a concussion. When someone is struck in the head, the mouth guard records how the skull moves at a thousand samples per second.

The study’s laboratory is the Stanford football team, young men who regularly go out and hit their heads.  This allows for rich information to be obtained when the researchers extract the data out of the mouth guard.

When the data from the mouth guard, was combined with a finite element model of the brain, developed by Svein Kleiven in Sweden, it showed that the brain of football players, who have suffered a concussion does not smash around in the skull, as current thinking would lead us to believe, but rather twists and contorts. The data shows that the greatest amount of stretching occurs very close to the centre of the brain.

What’s there? The corpus callosum, the wiring which connects the left and right hemispheres of your brain. Camarillo believes that this might be one of the most common mechanisms of concussion, the wiring is being disrupted, which causes a disassociation between your right and left brain and could explain a lot of the symptoms one sees in concussion. This is consistent with what researchers see with Chronic Traumatic Encephalopathy (CTE) – when the corpus callosum of a middle aged, former football player is viewed, and compared to an individual who does not have CTE, his corpus callosum is greatly atrophied.

Although there is a rapid transmission of forces down to the corpus callosum when the head is struck, it does take a certain amount of time. What Camarillo and his team believe is that if we can slow the head down just enough so that the brain does not lag behind the skull, but instead moves in synchrony with the skull, then we might be able to prevent this mechanism of concussion.

How can we slow the head down?

The most currently used bicycle helmet is constructed of expanded polystyrene (EPS) foam within a thin plastic shell. The EPS liner absorbs the force of an impact by deforming, while the outer shell increases the area over which the force is dissipates. The main considerations when designing a bike helmet is the size and stiffness of the helmet, which impacts how efficiently energy is absorbed. As a result of the materials used in constructing an EPS helmet, the size of the helmet has been limited to a few inches. This does not slow down the head enough to enable the brain to move in synchrony with the skull, rather than lag behind the skull. It turns out that air, in an expandable helmet would be the ideal mechanism for slowing the head down enough during impact, so that the brain moves in synchrony with the skull, rather than lagging behind.

woman wearing a skirt standing with her bike

It turns out that a company in Sweden called Hovding, is using the principle of air to give the wearer of their ‘helmet’ some extra space to prevent concussion. Hovding has created what is essentially the world’s first airbag for cyclists. The Hovding is a collar, worn around the cyclist’s neck, that uses advanced sensors, similar to the sensors used in the mouth guards described in Camarillo’s research above, that can sense the cyclist’s movement patterns and will react in case of an accident. The airbag will then inflate, fixate your neck and provide a shock absorption. In experiments conducted by Camarillo and his team they have found that the Hovding collar can greatly reduce the risk of concussion in some scenarios, compared to a standard EPS bike helmet. The Hovding is currently for sale in Europe and Japan, and is CE labelled, which means it complies with European Union safety standards, but not for sale in the United States, and alas, Canada.

In the US, bike helmets are federally regulated by The Consumer Product Safety Commission. The Commission has jurisdiction over the type of helmets they approve. The test they use in order to grant approval to a bike helmet is testing the helmets capacity to prevent skull fractures, not whether the helmet is likely to prevent concussion. In Canada, The Canadian Standards Association accredits organizations to certify that bicycle helmets meet certain standards, such as CPSC bicycle helmet standard, which uses the tests described above by Camarillo.

I contacted Hovding and asked about the availability of their helmet in Canada – alas, it is not available here. They replied that, at this time, they have not investigated helmet certification in Canada. So it might take some time to get my head into one!

Even so, any helmet is better than no helmet, so keep wearing whatever helmet you have, and wear it properly.


Modelling and Optimization of Airbag Helmets for Preventing Head Injuries,  published in The Annals of Biomedical Engineering in September 2016.

Since her TBI in 2011, Sophia has educated herself about TBI. She is interested in making research into TBI accessible to other survivors.