James Cracknell was struck by a petrol tanker travelling at high speed in July 2010, while he was cycling in Arizona. This incident has converted Cracknell into one of the most prominent advocates of cycle helmets in Britain, apparently on the basis that the helmet he was wearing at the time ‘saved his life’.

The following extract is from Cracknell’ autobiography, Touching Distance, recounting a ‘piece to camera’ he did for the Headway brain injury charity. The words are those he used in the video.

‘Last year when I was cycling across America, a truck’s wing mirror smashed into the back of my head at seventy miles an hour, knocking me off my bike and on to the road. My brain swung against the front of my skull as it hit, causing severe damage to the frontal lobes of my brain. ‘When I came out of intensive care, I wasn’t me any more. All of my friends and family told me that my entire personality had changed. My short-term memory was gone. I couldn’t make decisions. Had no motivation. ‘But I was lucky. I was wearing a helmet. If I hadn’t been, I’d be dead. Doctors say in time I should hopefully make a good recovery. I’m already back on my bike. Some cyclists will never ride again. I make the choice to wear a helmet. If you do too, please send this one to a friend. ‘I’m nearly James Cracknell. Use your head. Use your helmet.’ I hope it was a powerful message. I wanted to do everything I could to support such a worthwhile charity. It was designed to educate people into protecting their heads or influence others to persuade their friends and family to cycle with a helmet. I also wanted to do something positive to mark the anniversary of the accident.

From this account – his own – it is clear that the injury to Cracknell’s brain was the result of it rapidly accelerating within his skull, and hitting it.

What effect did the helmet he was wearing have in lessening the effects of this injury, and indeed preventing death? Well, we have information from Cracknell himself that the helmet he was wearing at the time he was struck by the wing mirror ‘was shorn in two’. (This description of what happened to the helmet is consistent with the many other accounts given by Cracknell and his wife). So it split on impact, and did not deform.

This means it did next to nothing to lessen the acceleration his brain received within his skull – which we have been told, again by Cracknell himself, caused his brain injury. Cycle helmets are designed to deform, and so lengthen the period over which deceleration occurs – much like the crumple zone of a car.

Polystyrene-based helmets protect by absorbing the energy of the impact through compressing the polystyrene. If the polystyrene has broken into pieces but not compressed, it has failed. Yet ironically we mistakenly believe that the broken helmet saved us.

So given the nature and cause of Cracknell’s injury, there does not appear to be any reasonable basis for his claim that his helmet ‘saved his life’. His helmet split, and failed, and did not protect his brain from the acceleration that damaged it. This is not the fault of the helmet. They are – quite reasonably – not designed to protect a human head from these kinds of impacts.

The question is why Cracknell is choosing to argue that it did – and indeed using his incident as a basis for arguing that we should persuade our friends and family to always ‘protect their heads’, rather than campaigning to keep fast heavy objects away from those heads.