Thursday, 6 August 2009

Hate Cycle Helmets?

Here is a salutary lesson from one of the Province's foremost broadcasters, Noel Thompson, who swears that a cycle helmet may have saved his life a while ago.

Read, learn and inwardly digest, as my old Latin master once said.


Richard Keatinge said...

The trouble with bike helmets is that the figures don't show that they work - helmet laws have stopped a lot of people cycling and have done nothing for head injury rates, see Robinson DL. No clear evidence from countries that have enforced the wearing of helmets. BMJ. 2006 March 25; 332(7543): 722–725. doi: 10.1136/bmj.332.7543.722-a. (Robinson's work uses the best scientific methods, all available control groups and so on.) It appears that helmets break easily, but don't absorb the impact, see the engineers quoted at A broken helmet has simply failed, and the widespread anecdotes on the theme of "a helmet saved my life" seem to owe more to wishful thinking than to science. As for "a car ran over my head", see the pro-helmet site; if a car goes over your head, I'm sorry to say you won't be sitting up and praising your helmet. The only known connection is that helmets have strangled a few young children who were wearing helmets while playing off their bicycles.

I no longer wear a helmet and haven't pressed them on my children. I do check that their brakes work and that they have a good idea of the rules of the road.

At my moderately advanced age it's far too dangerous not to cycle - regular cycling, Danish style, not too far, not too fast, nearly halves the death rate, see All-Cause Mortality Associated With Physical Activity During Leisure Time, Work, Sports, and Cycling to Work. Andersen et al, Arch Intern Med. 2000;160:1621-1628. Bicycling is good for health, but helmets don't seem to be.

Timothy Belmont said...

Many thanks for your contribution. As a matter of interest, are you a cyclist yourself? Would you counsel against the wearing of cycle helmets? I've no particularly string views on the matter; I suppose you could say I'm neutral. I imagine they're better than nothing, under certain circumstances.


Richard Keatinge said...

Well, I use a bike to get around quite a lot. I used to wear a helmet - before anyone else did in the UK and before the evidence I've quoted started coming out. I don't any more, they are uncomfortable and inconvenient, and they simply don't appear to work. When my less fit patients ask me, I advise them to do whatever is most likely to make them feel comfortable getting them the exercise they need, but to rely on riding skills not protective gear.

I do strongly oppose the various attempts to make helmet use compulsory. An intervention that has been shown to fail is hard to recommend anyway. This one causes deep resentment among those who have some idea of the facts and even among people who only know that their actual level of risk on a bike is small. For people of goodwill who'd like to do something for their fellow humans, cycle helmets are not a good thing to advocate.

Timothy Belmont said...

That's fascinating. I absolutely agree that they are uncomfortable, insofar as one is always aware of the straps. The cheap ones are probably more uncomfortable!

I'm not sure whether you have read the article on the link about Noel Thompson who fell head-over-heel and broke his collar-bone. He seemed convinced; then again, under those circumstances I imagine one would. Do you think he may be misguided and that the helmet made no difference?


Richard Keatinge said...

That's exactly what I suspect. Anecdotal evidence doesn't count for much - my eldest son went over his handlebars a few days ago, fortunately without significant injuries, and might now believe that his helmet saved his life. Except that he wasn't wearing one. It doesn't amount to good evidence either way. I do tend to believe the best scientific analyses.

I also note that helmets are designed to crush in accidents. They're tested by putting them on instrumented metal headforms, sliding them a couple of metres down a wire, so that the headforms crush the expanded polystyrene, and checking that the headform's acceleration doesn't exceed a limit which is on semi-arbitrary grounds thought to be what the head can usually cope with. The trouble is that experts have seen a lot of damaged helmets from real accidents, and it seems that helmets crack a lot (which doesn't take much energy and makes the helmet unable to absorb any further impact). But in real accidents they don't seem to crush, though they often break. The senior engineer of Bell Sports, the market leader in cycle helmets, writes: “Another source of field experience is our experience with damaged helmets returned to customer service... I collected damaged infant/toddler helmets for several months in 1995. Not only did I not see bottomed out helmets, I didn’t see any helmet showing signs of crushing on the inside.” (Jim G Sundahl, Senior Engineer, Bell Sports. 19th January 1998.

In 1987, the Australian Federal Office of Road Safety found that in real accidents "very little crushing of the liner foam was usually evident... What in fact happens in a real crash impact is that the human head deforms elastically on impact. The standard impact attenuation test making use of a solid headform does not consider the effect of human head deformation with the result that all acceleration attenuation occurs in compression of the liner. Since the solid headform is more capable of crushing helmet padding, manufacturers have had to provide relatively stiff foam in the helmet so that it would pass the impact attenuation test..." (DEPARTMENT OF TRANSPORT, FEDERAL OFFICE OF ROAD SAFETY.

Real heads aren't made of metal, they're significantly more flexible, and they just don't seem to do the crushing in real accidents.

A broken helmet has simply failed, and the widespread anecdotes on the theme of "a helmet saved my life" seem to owe more to wishful thinking than to science. Heads are vulnerable, but they do survive remarkable things. I see a lot of photos of broken helmets, but so far none of helmets that have crushed as per design. I do not believe that a bicycle helmet will make any noticeable amount of difference to the chances of anyone coming out well from an accident.

John Self said...

Well, I'll continue to take my chances with a helmet if it's all the same to you, Richard. I'll stick with the recommendations of the World Health Organisation and your professional body the British Medical Association.

A quick google suggests you are a vigilant commenter on blogs and sites discussing cycle helmet safety issues. We all need a hobby.

I must however disagree with you that "regular cycling, Danish style ... nearly halves the death rate." As you, a doctor, should know, Richard, the death rate for all of us is 100%.

Richard Keatinge said...

Fourteen-year death rate, to be more exact, and only about 40% down, but in a short response it's easier to be slightly imprecise. As you say, we all need a hobby, and it's fine by me if you want to wear a helmet or many other odd items.

The BMA meeting was interesting. I wouldn't have minded if they'd taken a considered view of the evidence and disagreed with me, but I was disappointed to find that at least one sponsor of the motion didn't seem to know that there was any evidence and certainly couldn't say anything sensible about it. They haven't produced a competent review. Not one of their better-considered judgements. As for the WHO, you wouldn't be referring to Philip Graitcer's one-man initiative? There is no shortage of people pushing helmets, and we could both quote plenty more. I'd rather stick with the science, and that's fairly clear that the bicycle helmets don't have a measurable useful effect, and they put people off riding bikes. Which will do a lot more harm to their health than any protective gear could prevent.

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