It's also not obvious that helmets are a universal help in another way:
By design, bicycle helmets are only effective only at very low speeds (< 14mph). Any deviation from this and a bicycle helmet can actually increase the severity of injury [ref]. For example, an off-center impact on the oblong surface of a helmet or having the air vents catch on something can violently twist the head and neck, leading to a potentially fatal neck injury (pp. 173-174, The Art of Urban Cycling by Robert Hurst). Recent research on brain injury adds further confusion, suggesting that the major causes of permanent intellectual disablement and death may well be torsional forces leading to diffuse axonal injury, a form of injury which helmets cannot mitigate (The efficacy of bicycle helmets against brain injury, Curnow, WJ. 2003. Accident Analysis and Prevention: 2003,35:287-292).
By design, bicycle helmets are only effective only at very low speeds (< 14mph). Any deviation from this and a bicycle helmet can actually increase the severity of injury [ref]. For example, an off-center impact on the oblong surface of a helmet or having the air vents catch on something can violently twist the head and neck, leading to a potentially fatal neck injury (pp. 173-174, The Art of Urban Cycling by Robert Hurst). Recent research on brain injury adds further confusion, suggesting that the major causes of permanent intellectual disablement and death may well be torsional forces leading to diffuse axonal injury, a form of injury which helmets cannot mitigate (The efficacy of bicycle helmets against brain injury, Curnow, WJ. 2003. Accident Analysis and Prevention: 2003,35:287-292).
- http://www.lobv.org/15reasons.html
This isn't the first place I've seen that claim, the site I was looking for had brain scan images and such as well, I think.