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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 5:58 pm
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Joined: Thu Jan 01, 2004 1:40 pm
Posts: 504
Location: L.A. & Ventura Counties, CA
davesails7 wrote:
KiteschoolHolland wrote:
I don't know what torque is, but I measured the circumference of my head above the nose, without a helmet and with 3 brands kitehelmet: 59 cm, 64, 68 and 70. (Gath was the largest, Smartcap the thinnest)
If the water replacement on impact is calculated as a half sphere, it is 1,7 liters, 2.2, 2.6 and 2.9.
So the average of these 3 helmets means a 50 % increase in force on the neck in the case of headfirst collision into a wave (as was the case in the broken neck above, in the case of rotational crashes, see Johnny Rotten)

That's the third time you have posted this calculation of volume in this post and made the incorrect assumption that a 50% increase in volume = a 50% increase of force on your neck. The force on you neck is not directly proportional to the volume of your head! It is proportional to projected surface area plus lots of other things (speed, shape, angle...). It's not an easy thing to calculate.

Increase in projected area is smaller than increase in volume. Projected area is proportional to r^2 while volume is proportional to r^3

So there is an increase in projected surface area, and therefore an increase in force on the helmet at impact. Then you have the foam under the hard shell of the helmet absorbing some unknown amount of the total impact. The larger the helmet, the thicker the layer of impact energy absorbing foam! I don't have any proof of how much of the energy is absorbed, but I estimate that it is enough to make up for the increase in projected surface area.

Please do not say that wearing a helmet means an increase of 50% of force on your neck anymore.

Besides doubting the accuracy of KieschoolHoland's calculations, I doubt that extra resistance produced by the larger surface area of the helmet creates enough of a problem to be significant. Although this extra resistance could have an adverse effect, it likely would not happen unless a fall occurred which produced the MAXIMUM effect and even then the odds that this adverse effect rising to the level of being HAZARDOUS seems remote. More importantly though, the VAST majority of falls result in GLANCING blows which do not produce anywhere near the maximum effect.

As to the calculations themselves, the following is excerpted from my post at viewtopic.php?f=1&t=2373624&start=60

RichardM wrote:
KiteschoolHolland wrote:

Richard, if you ever do give the matter any thought (especially before commenting)
please continue the topic where it fits,
viewtopic.php?f=1&t=2364753&p=744011#p744011

Although I don’t think your flawed theory requires any detailed analysis to see why it is incorrect, per your request, I have given the calculations some thought.

I assume that these are the calculations upon which you are basing your theory:

“I measured the circumference of my head above the nose, without a helmet and with 3 brands kitehelmet: 59 cm, 64, 68 and 70.
If the water replacement on impact is calculated as a half sphere, it is 1,7 liters, 2.2, 2.6 and 2.9.
So the average of these 3 helmets means a 50 % increase in force on the neck.
Maybe this increase is lessened by a time delay.”

First of all, the entire theory bites the dust “If the water replacement on impact is NOT calculated as a half sphere.” I doubt that “water replacement on impact” is anywhere near a half a sphere. Please present some rational argument as to how you came up with this amount.

Second, whatever amount of force is applied to the neck is likely based upon the total amount of force which is applied to the ENTIRE head, NOT just the force applied to the area from the nose up. Therefore, any additional force which may be caused by a helmet does NOT represent the percentage of increase (in your calculations 50%). Since from the nose up probably represents no more than 50% of the head, even assuming that you are correct, the 50% increase you allege actually represents no more than a 25%-33% increase in force.

Your DESPERATE attempt to justify not wearing a helmet also concentrates on the relatively rare possibility of neck injury and ignores the protective effect of reducing the possibility of loss of control due to being stunned. And of course your attempted justification completely falls apart when protection from ANY hard obstacles (including the ground) is beneficial.

Feel free to repost this on any thread you want.

Richard M.
Malibu Kitesurfing - since 2002
(310) - 430 - KITE (5483)
http://www.MalibuKitesurfing.NET
kfRichard@MalibuKitesurfing.NET

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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 6:15 pm
 Medium Poster

Joined: Mon Mar 02, 2009 4:22 pm
Posts: 79
Location: Amsterdam area, Netherlands
Richard, you're right about the majority of glancing blows.
Still: necks have been broken.

For rational arguments, see the post just above yours.
Please also read Johnny Rottens wakeboarding info and his guideline for when he does and does not wear a helmet.

See you next week!

ps I'm not at all desperate against helmets - I do wear one sometimes, like I described somewhere in this thread.

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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 6:30 pm
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Joined: Fri Jul 16, 2010 6:27 am
Posts: 1326
Location: Ford Lake, Michigan
"Pro divers like Greg Louganis don't wear helmets, let's ask them why. Diving from 10 m. platform must get somewhere near the force to crack the neck or concuss the brain."

This is actually not a bad idea. Diving from higher and higher platforms, head first, feet first bellyflop backflop, with and without a helmet, and video taping the results.

It's a bit subjective, but as close to a scientific results as we will probably get.

My personal feeling is that diving from a 10m platform feetfirst or headfirst, since you are streamlined helmet or no helmet it will feel the same. But when you bellyflop or backflop from a 10m platform you will be begging for a helmet.

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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 6:58 pm
 Very Frequent Poster

Joined: Thu Jan 01, 2004 1:40 pm
Posts: 504
Location: L.A. & Ventura Counties, CA
davesails7 wrote:
KiteschoolHolland wrote:
I don't know what torque is, but I measured the circumference of my head above the nose, without a helmet and with 3 brands kitehelmet: 59 cm, 64, 68 and 70. (Gath was the largest, Smartcap the thinnest)
If the water replacement on impact is calculated as a half sphere, it is 1,7 liters, 2.2, 2.6 and 2.9.
So the average of these 3 helmets means a 50 % increase in force on the neck in the case of headfirst collision into a wave (as was the case in the broken neck above, in the case of rotational crashes, see Johnny Rotten)

That's the third time you have posted this calculation of volume in this post and made the incorrect assumption that a 50% increase in volume = a 50% increase of force on your neck. The force on you neck is not directly proportional to the volume of your head! It is proportional to projected surface area plus lots of other things (speed, shape, angle...). It's not an easy thing to calculate.

Increase in projected area is smaller than increase in volume. Projected area is proportional to r^2 while volume is proportional to r^3

So there is an increase in projected surface area, and therefore an increase in force on the helmet at impact. Then you have the foam under the hard shell of the helmet absorbing some unknown amount of the total impact. The larger the helmet, the thicker the layer of impact energy absorbing foam! I don't have any proof of how much of the energy is absorbed, but I estimate that it is enough to make up for the increase in projected surface area.

Please do not say that wearing a helmet means an increase of 50% of force on your neck anymore.

Besides doubting the accuracy of KieschoolHoland's calculations, I doubt that extra resistance produced by the larger surface area of the helmet creates enough of a problem to be significant. Although this extra resistance could have an adverse effect, it likely would not happen unless a fall occurred which produced the MAXIMUM effect and even then the odds that this adverse effect rising to the level of being HAZARDOUS seems remote. More importantly though, the VAST majority of falls result in GLANCING blows which do not produce anywhere near the maximum effect.

As to the calculations themselves, the following is excerpted from my post at viewtopic.php?f=1&t=2373624&start=60

RichardM wrote:
KiteschoolHolland wrote:

Richard, if you ever do give the matter any thought (especially before commenting)
please continue the topic where it fits,
viewtopic.php?f=1&t=2364753&p=744011#p744011

Although I don’t think your flawed theory requires any detailed analysis to see why it is incorrect, per your request, I have given the calculations some thought.

I assume that these are the calculations upon which you are basing your theory:

“I measured the circumference of my head above the nose, without a helmet and with 3 brands kitehelmet: 59 cm, 64, 68 and 70.
If the water replacement on impact is calculated as a half sphere, it is 1,7 liters, 2.2, 2.6 and 2.9.
So the average of these 3 helmets means a 50 % increase in force on the neck.
Maybe this increase is lessened by a time delay.”

First of all, the entire theory bites the dust “If the water replacement on impact is NOT calculated as a half sphere.” I doubt that “water replacement on impact” is anywhere near a half a sphere. Please present some rational argument as to how you came up with this amount.

Second, whatever amount of force is applied to the neck is likely based upon the total amount of force which is applied to the ENTIRE head, NOT just the force applied to the area from the nose up. Therefore, any additional force which may be caused by a helmet does NOT represent the percentage of increase (in your calculations 50%). Since from the nose up probably represents no more than 50% of the head, even assuming that you are correct, the 50% increase you allege actually represents no more than a 25%-33% increase in force.

Your DESPERATE attempt to justify not wearing a helmet also concentrates on the relatively rare possibility of neck injury and ignores the protective effect of reducing the possibility of loss of control due to being stunned. And of course your attempted justification completely falls apart when protection from ANY hard obstacles (including the ground) is beneficial.

Feel free to repost this on any thread you want.

After reading his latest post mentioning diving, it seems that his calculations assume the EXTREMELY RARE possibility of a perfectly straight impact on the top of the head. This so uncommon and injury due to COMPRESSION of the neck so much less likely than injury due to the possible WHIPLASH effect that I had thought his concern was about the whiplash effect.

Whiplash can happen if the helmet has a visor or is too big and allows excessive amounts of water to enter. However, a supposed concern about a COMPRESSION neck injury caused by any extra force which results from a larger surface are is too unlikely to be taken seriously.

Richard M.
Malibu Kitesurfing - since 2002
(310) - 430 - KITE (5483)
http://www.MalibuKitesurfing.NET
kfRichard@MalibuKitesurfing.NET

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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 7:14 pm
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Joined: Fri Jul 16, 2010 6:27 am
Posts: 1326
Location: Ford Lake, Michigan
RichardM wrote:
Whiplash can happen if the helmet has a visor or is too big and allows excessive amounts of water to enter.

Richard I don't think a big visor causes whiplash, because it's almost impossible to get whiplash if you bellyflop visor or not, the mechanics are wrong, your body slams to a stop, then your head dips forward, and with a visor it just straightens out your head in line with your body quicker. Might see stars with a big visor but not whiplash.

But a test of someone diving off a platform would be a great way to test it out, not that anyone here has time to do that . . . .

Maybe someday when it's not blowing and someone has a pool, a helmet, and a camera phone and wants to test it out.

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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 7:47 pm
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Joined: Thu Jan 01, 2004 1:40 pm
Posts: 504
Location: L.A. & Ventura Counties, CA
edt wrote:
RichardM wrote:
Whiplash can happen if the helmet has a visor or is too big and allows excessive amounts of water to enter.

Richard I don't think a big visor causes whiplash, because it's almost impossible to get whiplash if you bellyflop visor or not, the mechanics are wrong, your body slams to a stop, then your head dips forward, and with a visor it just straightens out your head in line with your body quicker. Might see stars with a big visor but not whiplash.

But a test of someone diving off a platform would be a great way to test it out, not that anyone here has time to do that . . . .

Maybe someday when it's not blowing and someone has a pool, a helmet, and a camera phone and wants to test it out.

I was thinking about when your head hits the water or when being dragged and a visor catches water. Also going THROUGH a wave or whitewater.
Richard M.
Malibu Kitesurfing - since 2002
(310) - 430 - KITE (5483)
http://www.MalibuKitesurfing.NET
kfRichard@MalibuKitesurfing.NET

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 Post subject: Re: Doctors on HelmetsPosted: Thu Apr 19, 2012 7:58 pm
 Very Frequent Poster

Joined: Fri Jul 16, 2010 6:27 am
Posts: 1326
Location: Ford Lake, Michigan
RichardM wrote:
I was thinking about when your head hits the water or when being dragged and a visor catches water. Also going THROUGH a wave or whitewater.

There is an air bubble around the face going through a wave or an impact, so no matter what I don't see how it can catch. Definitely worth experimenting with in a pool some day.

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 Post subject: Re: Doctors on HelmetsPosted: Fri Apr 20, 2012 1:05 am
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Joined: Sun May 18, 2008 5:34 pm
Posts: 567
Location: Imperial Beach, CA
I've only had 2 incidents with head wounds kiting(both in the last year). The first required 7 stitches. Below is a pic I took with my iphone a couple hours after the second one. if you look closely, you can see the scar from the first injury right above the swelling. Both injuries were within 6 months of each other and both happened on days were the wind was light and the waves were on the big side. To me, these are the most dangerous conditions for kiting. I now wear a helmet in certain conditions/terrain even though it does feel a little clunky.

 Attachments: 2-10-12 064.JPG [ 1.56 MIB | Viewed 304 times ]
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 Post subject: Re: Doctors on HelmetsPosted: Fri Apr 20, 2012 6:00 am
 Medium Poster

Joined: Thu Dec 04, 2008 1:50 am
Posts: 192
Johnny Rotten wrote:
I have taken some SAVAGE wipe out in boots, due to catching an edge when a trick went wrong,

KiteschoolHolland wrote:
So you crash harder in boots?

Yes!
If you catch an edge with boots on your horizontal speed will be translated directly to rotational speed of your body....Then BOOOM welcome to the hurt locker..
With straps you just blow your feet out of the sandals.
Reason why NO-ONE wears straps behind a boat is you`ll rip apart your knees and ankles if 1 foot comes out at boat speed 20-30 mph + whatever speed you gain edging.

Curious if any of the dutch loop fatalities involved boots....

Here`s one from your countryman`s kiteloop contest, (Not fatal) but dude got RAGDOLLED)
http://vimeo.com/37046251

Johnny Rotten wrote:
The wakeboarding world has submitted this to myth busters a number of times with no results yet.

KiteschoolHolland wrote:
I don't understand what you mean, the wakeboarders say a helmet helps?

No, the wakeboarders have gone over the same argument that we have and no one knows. Some swear by em others say they make it worse....... In North America there is a TV show called myth busters where they physically test certain urban legends scientifically(ish) ` For example if your car falls in the water you have to wait until it totally fills up with water before you can get the door open....you can`t shoot someone swimming underwater....Or if an elevator is falling and you jump up just before it hits the bottom you will live. etc....etc. Interesting show sometimes.....would love to see them do a bit on helmets and wake or kite boarding

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 Post subject: Re: Doctors on HelmetsPosted: Sun Apr 22, 2012 5:49 am
 Frequent Poster

Joined: Fri Feb 15, 2008 5:50 pm
Posts: 387
Location: On a very big sandy beach. With camels.
KiteschoolHolland wrote:
Mr_Weetabix wrote:
You're possibly looking for a rational answer where there isn't one. I know a couple of doctors who smoke. They're aware of the risks, but smoke because they like to.
...
You don't want to wear a helmet. We get it.

No you don't get it.
You know a few doctors smoking, well maybe... from how many??
I know 0 from at least 12.

.. and all the doctors I know, with the exception of a couple whose religion forbids it, drink alcohol. Quite a lot, in some cases (although thankfully not as much as they did when they were students). Once again, they do so, knowing the risks to health, because they enjoy it.

KiteschoolHolland wrote:
Anyway, your suspections about doctors' motives are less relevant than the on-topic information from doctors about why they don't (or do) wear helmets.

This post started with an article about doctors calling for kiters to wear helmets, but it's been sidetracked by an anecdote about a doctor saying that he doesn't want to wear a helmet because of the perceived risk of neck injury, and the widespread observation that most kiting medics don't wear helmets - just like most kiters don't wear helmets.

My point is this - doctors are no different from the rest of us. They do things which may be unhealthy, knowing the potential outcome. The same factors come into the choices they make as they do for the rest of us - comfort and appearance being among them.

You clearly want to find a scientific reason not to bother with a (well fitting) helmet. If you need one, it's this - any helmet will increase the chance of whiplash on impact with water. This is because it increases the mass (and therefore inertia/momentum) above the neck, thus increasing the force exerted on the neck when you get ragdolled; it also increases cross-sectional area, which will increase the rate of deceleration of your head relative to your body if you go into the water face first - again, increasing the force exerted on your neck. This is from an engineer (but hey, this is all about physics), but I hope it makes you feel better about your choice. If you need to compare the relative levels of risk between neck injuries and head trauma, you'll need a statistician.

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