Re: Helmets: Do you wear one? Why? When?
On Thu, 7 Aug 200800, surfcolorado <> wrote:
>
> Ian Smith wrote:
> >
> > Have you tested it?
>
> No, but I’ll try later. you jump to a lot of assumptions about me.
>
> Ian Smith wrote:
> >
> > Now, you will presumably say that your no-test is much more
> > accurate than my test (most people do, for no coherent reason),
> > but why would your guess be more likely to reflect reality than my
> > approximate test?
>
> Why would you assume that I will jump to the conclusion that my
> hypothesis is more accurate than your test.
For the reason stated - because most people (the vast majority, in
fact) do. I can’t state my reason any clearer than I did before -
because most people do, for no coherent reason.
> So, If I am understand what you are saying. If I’m not please
> correct me. The reduction in torsional injury from not wearing a
> helmet outways the reduction in impact from wearing helmet.
Well, for a pure tangential impact (or nearly purely tangential) I
think there is no reduction in impact - the helmet may reduce the
acceleration of the normal component, but it will probably (or at
least, I believe it would probably) increase the rotational
acceleration. Given (for now) that rotational acceleration can be at
least as damaging as linear, we have ‘safety’ gear that potentially
causes as much harm as it protects. So yes, in approximate terms, the
average increase in torsional damage from wearing a helmet may
balance the average reduction in linear damage.
It is worth noting that (so far as I am aware) none of the helmet
test standards test anything other than normal impacts, so there are
no pressures on manufacturers to mitigate the torsional behaviour.
But note - I’m not saying that this is the cause of the observation
that increasing (sometimes dramatically) the proportion of people
wearing helmets has no detectable effect on head injury rates. The
limit of what I’m suggesting is that there are reasonably plausible
mechanisms by which helmets could exacerbate injury. It happens that
the injuries in question are of the most serious class, but that is
not directly relevant. The situations in which such increase in
severity could occur are not particularly unusual - in fact, an impact
with at least some tangential component is probably more likely than a
purely normal impact. I think it is cherent (though not necesarily
right) to conclude that such a mechanism could explain why injury
statistics do not support the claims made for cycling helmets.
That is, this mechanism is suggested only as a possible cause of the
population level statistics observations that helmets have negligible
effect on head injury rate. It doesn’t need to be the true mechanism,
for purposes of coherency of the argument, in only needs to be a
coherent explanation. Given at least one possible cause, the
statistical data cannot be discarded out-of-hand.
However, there are so many confounding factors it’s not funny. In
particular, much of the information comes from data before and
after compulsion is introduced, and the behaviour of a cyclist
compelled to wear a helmet may be different from that of a cyclist
who makes a free choice to do so.
IMO, the most likely other effects are risk compensation by the rider,
risk compensation by motorists (a link suggesting this has already
been posted) and changes in the number of cyclists. The first two of
these would probably apply to both compelled and ‘free choice’
wearers, but the last would only be relevant where compulsion is
introduced.
Where the ‘true’ mechanism is relevant is in trying to decide if the
statistics from bicycling populations can be extrapolated to
unicycling. If the cause is rider risk compensation, they almost
certainly can; if the cause is torsional impacts they possibly can,
but it’s not so clear-cut because of difference in exposure to motor
vehicles, difference in typical speeds and so on; if the cause is just
change in the number of bicyclists on the roads, I would expect they
probably cannot.
> Where I believe and I have observed. That a helmet can protect you
> from cracking your head like an egg on a rock or reduce the impact
> to your skull and brain by absorbing some of the impact.
There are several assumptions in that. In particular, heads don’t
crack like eggs. Heads are remarkably good at surviving impacts.
> both of the above can be life-changing, and that outways the
> increase in torsional injury from wearing a helmet, which I believe
> to be relatively low.
Why? Why do you believe torsional injuries are of low severity? (Or is
it that you belive they are of low likelihood)? Do you have any
evidence that tangential impacts are less common or less severe than
normal impacts? It would certainly be interesting to see such a
study, but I can’t imagine any remotely reliable methodology for it.
> Plus as an added bonus, you are protected from low lying branches
> and small crashes that would give you non life-changing injuries to
> the head.
I think this is the only thing that is universally accepted - helmets
do seem to do a good job of protecting against minor, embarrassing and
sometimes painful injuries.
When I used to wear a helmet religiously, it once took a blow from a
low-hanging garage door. Had I hit the door with my unprotected head,
I expect it would have split the scalp and been painful and quite
bloody - I might even have attended A&E, because it’s difficult to
patch up your own scalp (IME). Of course, had I not had a helmet on
with a brow and peak obscuring forwards upwards visibility, I might
have seen the door and not walked into it at all.
> personally it also allows me to ride with more confidence, knowing
> that it is unlikely that I will have a head injury at all.
As I said - risk compensation is potentially another explanation.
It may be the only one necessary.
regards, Ian SMith
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