Cycle helmets - major study

[Andyp]

I promised myself that I would not get involved in this debate again but I just can't stop myself.
How can banging your head on a hard surface be safer when not wearing protection?

AndyP

"Paul Smith" <[email protected]> wrote in message
news:[email protected]...
> Hi All,
>
> The DfT have just published a major study of cycle helmets.
>
>
http://www.roads.dft.gov.uk/roadsafety/roadresearch/bicyclehelmets/index.htm
> --
> Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
> cameras cost lives

 

[Just Zis Guy]

On 22 Apr 2003 15:40:18 +0100 (BST), David Damerell <[email protected]> wrote:

>>Once you're flying through the air en route for some hard stuff it's a good idea to put your
>>helmet on.

>This is by no means proven; it seems likely that helmets have little effect on severe impacts, and
>exacerbate torsional injuries.

It is absolutely true that helmets may well have little effect in severe impacts - the "bogeyman"
impacts which the report refers to, being hit by cars, will almost invariably result in a head
impact speed greatly in excess of the parameters of any bike helmet standard, and probably well
outside the design parameters of the helmet itself. The fact that helmets often stand up to such
impacts surprisingly well is quite likely to be accidental, and is certainly not a reason for making
mandatory helmets which are fundamentally designed to protect in single vehicle accidents at speeds
below 12mph.

On the other hand, I still don't buy this "torsional injury" bit, mainly because at the point of
likely impact the radius of the helmet is very small compared with that of the head. I have seen
some studies on torsional effects, but all related to motorcycle helmets, and many to speeds well in
excess of likely bike crash speeds (unless you're Rob English of course). Motorcycle helmets are
both larger and much heavier than bike helmets, so would undoubtedly have a significant effect on
the overall behaviour of the head in a crash. Bike helmets weigh, according to a rough guess, less
than 5% of the weight of a human head.

Guy
===
** WARNING ** This posting may contain traces of irony. http://www.chapmancentral.com (BT ADSL and
dynamic DNS permitting)
NOTE: BT Openworld have now blocked port 25 (without notice), so old mail addresses may no longer
work. Apologies.

 

[Richard Burton]

"Just zis Guy, you know?" <[email protected]> wrote in message
news:[email protected]...
> On 22 Apr 2003 15:40:18 +0100 (BST), David Damerell <[email protected]> wrote:
>

> On the other hand, I still don't buy this "torsional injury" bit, mainly because at the point of
> likely impact the radius of the helmet is very small compared with that of the head. I have seen
> some studies on torsional effects, but all related to motorcycle helmets, and many to speeds well
> in excess of likely bike crash speeds (unless you're Rob English of course). Motorcycle helmets
> are both larger and much heavier than bike helmets, so would undoubtedly have a significant effect
> on the overall behaviour of the head in a crash. Bike helmets weigh, according to a rough guess,
> less than 5% of the weight of a human head.

Motorcycle helmets may be heavier, but they are no larger in diameter. The dimension to be
considered for torsional injuries must be the effective radius of the head when a force causes
rotation: the larger the diameter, the greater the effect of the force. Cycle helmets increase the
radius of the head by approximately 20-30%, and are therefore likely to have a significant effect on
rotational injuries, since any force will be effectively increased by that proportion.

Cheers

Rich

 

[Robert Goodman]

"Richard Burton" <[email protected]> wrote in message
news:[email protected]...

> > On the other hand, I still don't buy this "torsional injury" bit, mainly because at the point of
> > likely impact the radius of the
helmet
> > is very small compared with that of the head. I have seen some studies on torsional effects, but
> > all related to motorcycle helmets, and many to speeds well in excess of likely bike crash speeds
(unless
> > you're Rob English of course). Motorcycle helmets are both larger
and
> > much heavier than bike helmets, so would undoubtedly have a significant effect on the overall
> > behaviour of the head in a crash. Bike helmets weigh, according to a rough guess, less than 5%
> > of the weight of a human head.

> Motorcycle helmets may be heavier, but they are no larger in diameter.
The
> dimension to be considered for torsional injuries must be the
effective
> radius of the head when a force causes rotation: the larger the
diameter,
> the greater the effect of the force. Cycle helmets increase the
radius of
> the head by approximately 20-30%, and are therefore likely to have a significant effect on
> rotational injuries, since any force will be effectively increased by that proportion.

But it's not just the moment. It's also that the increased "head size" makes it likelier the
head-helmet combination will hit or be hit by something.

 

[Michael Macclan]

In message <[email protected]>, andyp <[email protected]> writes
>I promised myself that I would not get involved in this debate again but I just can't stop myself.
>How can banging your head on a hard surface be safer when not wearing protection?
>
>AndyP

The assertions which seek to support this view include:

1. Wearing a helmet increases the effective size of the head and therefore makes it more likely that
you'll hit something.

2. Wearing a helmet increases the effective radius of the head and therefore magnifies the
likelihood of torsional injuries caused by the head rotating in a crash.

3. Cyclists who wear helmets are supposed, on average, to ride more recklessly than if they weren't
wearing helmets.

4. Helmets may protect against minor injuries but are ineffective against major injuries because
they aren't designed for these.

But it's not all about banging heads on hard surfaces. There is a powerful argument that forcing
people to wear helmets reinforces the impression that cycling is an inherently dangerous pastime
and therefore deters people from cycling. In this case the total number of cyclists drops, which is
bad for the remaining cyclists, bad for the 'non-cyclists' who will be less healthy, bad for
society that has to bear the cost of the ill-health and bad for the cycling industry which sells
fewer bikes.

I strongly suspect that both sides in this debate (should that be 'all three sides' because the
camps appear to be 'pro', 'anti' and 'pro-choice'?) feel as if they're banging their heads against
brick walls. Do members of the 'anti' camp wear helmets when doing this? ;-)
--
Michael MacClancy

 

[David Damerell]

Just zis Guy, you know? <[email protected]> wrote:
>On the other hand, I still don't buy this "torsional injury" bit, mainly because at the point of
>likely impact the radius of the helmet is very small compared with that of the head.

Surely the radius of the helmet is strictly larger than that of the head? I suspect I am not quite
clear on what you mean.

>Bike helmets weigh, according to a rough guess, less than 5% of the weight of a human head.

I'm not sure that the weight is relevant; surely all that matters is the lever arm of the impact
point about the spine.
--
David Damerell <[email protected]> Distortion Field!

 

[Michael Macclan]

In message <Ehu*[email protected]>, David Damerell
<[email protected]> writes
>Just zis Guy, you know? <[email protected]> wrote:
>>On the other hand, I still don't buy this "torsional injury" bit, mainly because at the point of
>>likely impact the radius of the helmet is very small compared with that of the head.
>
>Surely the radius of the helmet is strictly larger than that of the head? I suspect I am not quite
>clear on what you mean.

I read Guy's comment as meaning the 'additional radius due to the helmet'.

>
>>Bike helmets weigh, according to a rough guess, less than 5% of the weight of a human head.
>
>I'm not sure that the weight is relevant; surely all that matters is the lever arm of the impact
>point about the spine.

Assuming a heavy helmet and assuming that the impact is great enough to accelerate the head to an
appreciable angular velocity then I am sure that you would agree that the deceleration forces needed
to stop the rotation would be greater than for a light helmet or that the rotation would continue
for longer. I guess that the deceleration is provided partly by bodily structures which would be
subject to greater forces or greater extensions in the case of the heavier helmet, both of which
would increase the likelihood of injury.
--
Michael MacClancy

 

[Paul Smith]

On Wed, 23 Apr 2003 12:44:03 +0000 (UTC), "W K" <[email protected]> wrote:

>> A rather more plausible risk compensation mechanism is that when perceived risk is lower less
>> attention is paid to the task at hand.

>> Since many accidents are avoided by a mechanism of early perception and planned avoidance, it
>> follows that less attention can easily lead to an increase in accidents.

>You really haven't got a clue about what it feels like to ride a bike have you?

You what?

Perhaps you would like to post your analysis or experience of risk compensation mechanisms instead
of resorting to foolish jibes.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[W K]

"Paul Smith" <[email protected]> wrote in message
news:[email protected]...
> On Tue, 22 Apr 2003 09:05:47 +0000 (UTC), Tim Woodall <[email protected]> wrote:
>
> >There may be some risk compensation occuring but I don't believe that
that
> >will be affecting the head injury rate which tends to be as the result of car/cycle collisions
> >where the extra 1mph or so that someone might risk in a given situation is unlikely to make much
> >difference to the collision rate. OTOH, for single bike accidents that 1mph might make the
> >difference between making it around a "slippy" bend and losing it. (I don't believe that much
> >more than 1mph can be involved because given
the
> >same conditions, i.e. commuter, training, racing etc, then 1mph is likely to be all that is
> >physically and reasonably available - although top
speed
> >on decents might vary by a bit more. I very nearly overcooked it on the windcheetah last week.
> >1mph may well have made all the difference between "heart stopping exhilaration on two wheels"
> >and sliding across the road on my side - and possibly hitting my head - can I claim this as a
> >serious head injury that didn't occur because I wasn't wearing a helmet? ;-P )
>
> A rather more plausible risk compensation mechanism is that when perceived risk is lower less
> attention is paid to the task at hand.
>
> Since many accidents are avoided by a mechanism of early perception and planned avoidance, it
> follows that less attention can easily lead to an increase in accidents.

You really haven't got a clue about what it feels like to ride a bike have you?

 

[Kit Wolf]

>>>Bike helmets weigh, according to a rough guess, less than 5% of the weight of a human head.
>>
>>I'm not sure that the weight is relevant; surely all that matters is the lever arm of the impact
>>point about the spine.
>
> Assuming a heavy helmet and assuming that the impact is great enough to accelerate the head to an
> appreciable angular velocity

But presumably this acceleration would require a higher impact velocity for a heavy sphere than for
a lighter one?

I can't decide - my head hurts already.

> then I am sure that you would agree that the deceleration forces needed to stop the rotation would
> be greater than for a light helmet or that the rotation would continue for longer. I guess that
> the deceleration is provided partly by bodily structures which would be subject to greater forces
> or greater extensions in the case of the heavier helmet, both of which would increase the
> likelihood of injury.

Imagine someone flying over the handlebars with a 3ft long lever attached to their forehead[*]. The
end of the lever would hit the ground first, snapping the person's head forwards 90 degrees relative
to their body which would remain roughly horizontal due to its greater mass - it doesn't bear
thinking about. I'd always assumed that it was this sort of effect (but to a lesser extent) that the
anti-helmet campaigners had in mind?

Kit

[*] A lever obviously isn't the best good model as a helmet is roughly spherical, but aiming for
simplicity rather than perfection...

 

[Tony W]

"Paul Smith" <[email protected]> wrote in message
news:[email protected]...
>
> A rather more plausible risk compensation mechanism is that when perceived risk is lower less
> attention is paid to the task at hand.

mmmm -- possible.

> Since many accidents are avoided by a mechanism of early perception and planned avoidance, it
> follows that less attention can easily lead to an increase in accidents.

See. Proof at last. That tree did jump out into my path. It was so relaxed by not having anything
more important to think about it darn well went and caused an accident.

Smith being incisive and knowledgeable as usual.

T

 

[Michael Macclan]

In message <[email protected]>, Kit Wolf
<[email protected]> writes
>>>>Bike helmets weigh, according to a rough guess, less than 5% of the weight of a human head.
>>>
>>>I'm not sure that the weight is relevant; surely all that matters is the lever arm of the impact
>>>point about the spine.
>>
>> Assuming a heavy helmet and assuming that the impact is great enough to accelerate the head to an
>> appreciable angular velocity
>
>But presumably this acceleration would require a higher impact velocity for a heavy sphere than for
>a lighter one?

I agree. I think there's a beginning and end to this process. The initial acceleration of the
lighter sphere will be higher, potentially causing more injuries during this phase. The deceleration
of the heavier sphere will be higher or spread over a longer time, potentially causing more injuries
during this phase.
>
>I can't decide - my head hurts already.

Mine too.

>
>> then I am sure that you would agree that the deceleration forces needed to stop the rotation
>> would be greater than for a light helmet or that the rotation would continue for longer. I guess
>> that the deceleration is provided partly by bodily structures which would be subject to greater
>> forces or greater extensions in the case of the heavier helmet, both of which would increase the
>> likelihood of injury.
>
>Imagine someone flying over the handlebars with a 3ft long lever attached to their forehead[*]. The
>end of the lever would hit the ground first, snapping the person's head forwards 90 degrees
>relative to their body which would remain roughly horizontal due to its greater mass - it doesn't
>bear thinking about. I'd always assumed that it was this sort of effect (but to a lesser extent)
>that the anti-helmet campaigners had in mind?
>

Good point. I was actually thinking more of rotations around the neck axis. I don't know what they
have in mind but the thought of your model worries me a bit. Plenty of helmets have squared-off rear
ends which would tend to increase the effect you describe, no?

>Kit
>
>[*] A lever obviously isn't the best good model as a helmet is roughly spherical, but aiming for
>simplicity rather than perfection...

--
Michael MacClancy

 

[Paul Smith]

On Wed, 23 Apr 2003 14:30:45 +0100, "Tony W" <[email protected]> wrote:

>> A rather more plausible risk compensation mechanism is that when perceived risk is lower less
>> attention is paid to the task at hand.

>mmmm -- possible.

>> Since many accidents are avoided by a mechanism of early perception and planned avoidance, it
>> follows that less attention can easily lead to an increase in accidents.

>See. Proof at last. That tree did jump out into my path. It was so relaxed by not having anything
>more important to think about it darn well went and caused an accident.

Your joke quite closely matches the subjective experience of many drivers involved in commonplace
accidents caused by inattention. Where a road user is inattentive it's quite "normal" for a
dangerous hazard to "suddenly appear".

And anyway, more dangerous situations obviously demand more attention; it's a continuous scale from
sleeping to live bomb disposal.

>Smith being incisive and knowledgeable as usual.

Thanks.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Tony Raven]

Paul Smith <[email protected]> wrote:
>
> Your joke quite closely matches the subjective experience of many drivers involved in commonplace
> accidents caused by inattention. Where a road user is inattentive it's quite "normal" for a
> dangerous hazard to "suddenly appear".
>

There was a fascinating piece on this in this year's Reith Lecture about concious and unconscious
pathways in the brain - people who are totally blind through brain damage who can accurately locate
the position of a light they cannot see because the vision is working through other brain pathways
not associated with conscious vision. The contention by a leading neuroscientist was that much of
driving takes place in "unconcious" circuits until something happens that requires the attention of
the concious circuits. The lecture transcipt is online at
http://www.bbc.co.uk/radio4/reith2003/reith2003_lecture2_transcript.shtml

Tony

--
http://www.raven-family.com

"The reasonable man adapts himself to the world; the unreasonable man persists in trying to
adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
Bernard Shaw

 

[Kit Wolf]

>>> then I am sure that you would agree that the deceleration forces needed to stop the rotation
>>> would be greater than for a light helmet or that the rotation would continue for longer. I guess
>>> that the deceleration is provided partly by bodily structures which would be subject to greater
>>> forces or greater extensions in the case of the heavier helmet, both of which would increase the
>>> likelihood of injury.
>>
>>Imagine someone flying over the handlebars with a 3ft long lever attached to their forehead[*].
>>The end of the lever would hit the ground first, snapping the person's head forwards 90 degrees
>>relative to their body which would remain roughly horizontal due to its greater mass - it doesn't
>>bear thinking about. I'd always assumed that it was this sort of effect (but to a lesser extent)
>>that the anti-helmet campaigners had in mind?
>>
> Good point. I was actually thinking more of rotations around the neck axis. I don't know what they
> have in mind but the thought of your model worries me a bit. Plenty of helmets have squared-off
> rear ends which would tend to increase the effect you describe, no?
>
No idea, but it may be the reason (in reverse) they make those sun visors break off easily. When
baby brother was a toddler and still smaller than me, he used to have a helmet that was far thicker
in comparison to his head than an adults would be. I really could imagine that for him the leverage
effects might have been significant.

>>Kit

>>[*] A lever obviously isn't the best model as a helmet is roughly spherical, but aiming for
>>simplicity rather than perfection...

 

[David Damerell]

Kit Wolf <[email protected]> wrote: [Whoever's deleting attribution lines, quit it! I've
reconstructed them.]
>Michael MacClancy:
>>David Damerell:
>>>Guy Chapman:
>>>>Bike helmets weigh, according to a rough guess, less than 5% of the weight of a human head.
>>>I'm not sure that the weight is relevant; surely all that matters is the lever arm of the impact
>>>point about the spine.
>>Assuming a heavy helmet and assuming that the impact is great enough to accelerate the head to an
>>appreciable angular velocity
>But presumably this acceleration would require a higher impact velocity for a heavy sphere than for
>a lighter one?

If the helmet was massive enough to change the weight of your head appreciably, there might indeed
be effects - but it's not. More or less, your head weighs the same, but the ground (or whatever
you've hit) exerts a greater lever arm about the neck.
--
David Damerell <[email protected]> Kill the tomato!

 

[Tony Raven]

David Damerell <[email protected]> wrote:
>
> If the helmet was massive enough to change the weight of your head appreciably, there might indeed
> be effects - but it's not. More or less, your head weighs the same, but the ground (or whatever
> you've hit) exerts a greater lever arm about the neck.

You need to also factor in the different frictional properties of a head and a helmet since it is
the frictional force which imparts the twisting force to the neck and the degree of decoupling
between the helmet and head that will give a slower build up of that force which itself will be
beneficial. Real life is not simple.

Tony

--
http://www.raven-family.com

"The reasonable man adapts himself to the world; the unreasonable man persists in trying to
adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
Bernard Shaw

 

[Guy Chapman]

"Richard Burton" <[email protected]> wrote in message
news:<[email protected]>...

> > I still don't buy this "torsional injury" bit

> The dimension to be considered for torsional injuries must be the effective radius of the head
> when a force causes rotation

<waves engineering degree>

I understand that perfectly well.

> Cycle helmets increase the radius of the head by approximately 20-30%

You have either a small head or a large helmet. Where the thickest part of my lid sits over the
shorter axis of my head the difference is 15%. You should also take into account the fact that heads
with hair and skin are less likely to skid than helmets with shiny plastic.

I've not seen any real evidence of torsional injuries in cyclists. I really do think it's a red
herring, like the extra height issue. A helmet increases my height on a bike by under 1% -
definitely insignificant.

The thing which the pro-lidders never quite manege to explain away is how non-wearers going over the
bars at speed (like my friend Albert, who face-planted at quite a rate recently) apparently suffer
pretty much the same levels of concussion and fractures, the only noticeable difference seeming to
be in soft-tissue injuries. I'm quite content to wear a lid to save getting road rash on my head
again, but I don't think it will stop me being concussed or killed if I'm hit by another car.

Guy

 

[Paul Smith]

On Wed, 23 Apr 2003 15:32:21 +0100, "Tony Raven" <[email protected]> wrote:

>> Your joke quite closely matches the subjective experience of many drivers involved in commonplace
>> accidents caused by inattention. Where a road user is inattentive it's quite "normal" for a
>> dangerous hazard to "suddenly appear".

>There was a fascinating piece on this in this year's Reith Lecture about concious and unconscious
>pathways in the brain - people who are totally blind through brain damage who can accurately locate
>the position of a light they cannot see because the vision is working through other brain pathways
>not associated with conscious vision. The contention by a leading neuroscientist was that much of
>driving takes place in "unconcious" circuits until something happens that requires the attention of
>the concious circuits. The lecture transcipt is online at
>http://www.bbc.co.uk/radio4/reith2003/reith2003_lecture2_transcript.shtml

I've scanned so far, and it is fascinating. I look forward to further reading later. Many thanks
for the link.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Michael Macclan]

In message <[email protected]>, Guy Chapman
<[email protected]> writes
>
>The thing which the pro-lidders never quite manege to explain away is how non-wearers going over
>the bars at speed (like my friend Albert, who face-planted at quite a rate recently)

Oh dear, what was the frequency of his face-plants? ;-) People will be calling for mandatory face
protectors next.

--
Michael MacClancy