I'd have issue with #2 (big suprise, right?)

from my previous information about the area protected, I'm not sure 1% is much less.

From my previous question (and in response to the irony of a cycle helmet working best when not cycling e.g. no - or little - forward momentum) I'm no doctor, so please correct me if I'm off base here, but as I understand it,

Bicycle helmets are primarily designed to reduce the effect of linear forces, by providing a soft crushing layer which reduces the peak linear acceleration to the brain during impact. Linear impacts were found to cause mainly only localised (focal) injury at the point of impact. These shock waves are non-injurious as they do not cause permanent displacement of brain matter.

Head impacts from bicycle crashes do not generally involve a direct square-on impact. Most commonly there is an angled impact as the head hits the ground with forward momentum; or the windshield of a motor vehicle. Such an impact is likely to impart some degree of rotational force on the head and brain. Sudden rotation of the head was found to be the cause of most severe diffuse brain injuries. When rotational forces are applied, there is a change in the angular velocity of the brain and the skull. This results in diffuse shearing strains which can cause permanent displacement of matter throughout the entire brain.

The brain floats within the skull surrounded by cerebrospinal fluid (CSF), one of the functions of which is to protect the brain from normal light "trauma", e.g., being jostled in the skull by walking, jumping, etc., as well as mild head impacts. Concussion is considered a type of diffuse brain injury (as opposed to focal brain injury), meaning that the dysfunction occurs over a more widespread area of the brain. Diffuse axonal injury (DAI) is one of the most common and devastating types of brain injury and is one of the major causes of unconsciousness and persistent vegetative state after head trauma. Unlike brain trauma that occurs due to direct impact and deformation of the brain, DAI is the result of traumatic shearing forces. The major cause of damage in DAI is the tearing of axons, the neural processes that allow one neuron to communicate with another.


My guess is that this is what Clive Cook was referring to. It also explains why brain injury can occur with no impact at all and often does not appear after impacts.

I think the concern with focal traumatic brain injury is with a possible intracranial hemorrhage or a depressed skull fracture occuring resulting pieces of the broken skull pressing into the tissue of the brain, but the rub is this. I use the helmet while riding, and while riding I have forward momentum. This has to be the prime risk. It also might be the explanation that the measured effects of increased helmet usage (DL Robinson, published in BMJ and GB Rodgers, for the Journal of Products Liability) shows no measurable effects in head injuries. The largest study ever, Rodgers, shows a small but significant increase in risk.

I can agree with the other 4 points bragi makes.

That's a good question. I don't ask them about their helmets because I'm usually passing them while we're both travelling at 15+ MPH. So it doesn't seem like an opportune time to ask a total stranger to stop riding and endure my quizzical nature. Plus I think many folks would find that rude.

Personally I don't, I stop and talk to anybody asking me a question on the streets -- including the pan handlers who I at least have the courtesy to say 'No' politely when they ask for money. But that's me, I'm an different breed of cat, and I don't expect anyone else to live life as I do.

funny how over 100 views of the thread (I'm sure some by previous participants) since my lastpost went up, and nobody has responded to the medical explaination on how it is that helmets have limited ability to prevent brain injury, something that is fundamental to the point of wearing one.

I'm not even claiming what I've posted to be accurate, and looking for a response to see how this explaination could be incorrect, but no one is addressing it.

All threads die, but somehow, I think the helmet issue won't.

Is it possible the explanation could have killed the point of wearing a helmet making a significant impact on brain injury?

I had the same issue 10 years ago when I was hit by a car. The fall injured my knee only, but in the insurance interview, I was asked if I was wearing a helmet.

This is what I'm finding. If someone cannot explain how it is that brain injury is prevented by a helmet while cycling and when enough brain injuries occur to people who wear helmets to make any kind of conclusion of their prevention inconclusive, reasoning is the last thing I expect.