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Shock horror we are all wrong about boots.....

 Poster: A snowHead
Poster: A snowHead
https://skimoves.me/2015/02/13/the-shocking-truth-about-power-straps/

I am all for the rise of science which began in the 16th century. But I get annoyed when theoretical assertion and experimental observation is confused. The piece I have put up here is a prima facie example of this confusion, in my view. It poses a theoretical problem, based on solid understanding of physiology. And then implies that this is a real problem, rather than a theoretical one. The paper is an excellent outline of what MIGHT be happening, which then should lead to a series of questions about how to design a set of observations which would determine whether this is a real problem. I can see that locking the mid-shin mechanically via a powerstrap changes the dynamic of forces between the ski edge and the acting mass (the sum of the mass above the ski including the iPhone in my pocket and my son's spare gloves in my sack). All well and good. But the piece contends that this mechanical constraint is an entirely bad thing. Not proven. Where I object to the theoretical work in this piece is it forgets the sheer complexity of the dynamics of this system of terrain-trajectory-ski-boot-leg-body in the real world. I know that when I lean forward in my boot, and twist, there's not a simple set of motions. No powerstrap clamps the boot to the shin, it just offers further stability, but stability which can be overcome by forces which occur in skiing. Note that the dynamics entirely change if you are in a stiff boot (say 110) and pressuring it properly, from being in the same boot and being in the back seat.

Subjective issues: everything being loose and wiggly between the knee and edge seems to result in a dangerous level of imprecision in the ski (hello ACL tear as the ski whips round in an uncontrolled way in Spring clag); in the intense Darwinist context of racing, professionals have adopted the powerstrap and have not abandoned it; when I leave my powerstrap inadvertently undone, I notice pretty damn quickly; higher cuff boots are a preference of some skiers seeking precision (and thus control).

I can't think of a set of circumstances in which I would like a low cuff with a poor mechanical constraint on my lower leg.

Also, I have noticed that major back problems have only occurred with me through impact - when my body is poorly positioned for an impact up from the base of the ski, or I hit a mogul hard and unbalanced (same thing?) - and I have a pretty wrecked back (L3 wedge fracture) - the key thing here is having a pliable zeppa in my boot - big help (a la Salomon 1080 and FT B&E) - it doesn't seem to be a function of the lower leg being constrained by the powerstrap. So I feel (just subjective) that this is a red herring.

This piece = all very interesting and possible, but no empirical validation.

Reactions? CEM?
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Clicked on link, saw picture of pair of 20yo boots, didn't read.
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It's all about the ability to balance. My experience is that locking out the lower leg can lead to a loss of fore\aft balance.

I'd also suggest that the racer analogy is also misleading. The forces racers are trying to manage are somewhat different to those most recreational skiers are dealing with.
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@valais2, You did notice that this was a personal blog not a peer reviewed paper in a scientific jhournal.
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I always kept them loose(dalbello panthera 130), as intermediot helped me to progress my skiing.
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@rjs, I don't think boots have changed that much (free ride/walkmode/dynafit_adapted excepted).

But, I think the article is b0ll0x.
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@johnE, indeed ... but I guess that's one of the advantages of peer-reviewed knowledge - passes some basic tests of veracity (of course peer-reviewing a fraught process in some disciplines)....
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I'm a bit torn on this topic:

1. first of all by focusing on powerstraps he rather misses the big argument which would be that OVERLY STIFF boots (through whatever design mechanism one of which might be a powerstrap) reduce the skiers ability to push their knee over their toe and depending on other biomechanical issues that might make it difficult for them to stay centred over their feet as they sink down/ stand up (absorb and extend)
2. that said - for me personally I do like a bit of "give" so that I can avoid my fairly chunky thighs and backside moving backwards too much as I absorb/compress (helps keep my CoM over my feet without me having to bend too much at the waist)
3. I recently fitted booster straps (essentially particularly powerful powerstraps) to my touring boots because I found that with fairly big skis (R108 186cms) my touring boots were too low and didn't provide enough support to forward pressure. They have worked well by acting as a true extra / higher buckle that straps my liner to the (more) rigid rear spine. This is the effect he talks about but the starting point was a boot that was inadequately supportive so delivering something which is more optimal for me

So in essence powerstraps are not inherently bad - they can provide additional support/height/stiffness to the boot and that can be a good or bad thing depending on how well suited the boot is to your biomechanics and technique.

No?

But BTW, I don't really understand why it makes sense for someone like @under a new name, (relatively light and short, technical skier) to ski in very stiff boots. What is it exactly that they do for you? And how do you flex them at anything but full on race speeds? (not picking - obviously they DO work, just curious why they are a good choice).
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Yes. IMV.

@jedster, Perhaps it's just habituation?

Although I find (on a performance ski anyway, and noticeably more so on the Bonafides vs. the Mantras) that although I start out the day with only the top buckle done on its loosest setting, and strap adjusted for that, if I want to ski with any performance, without feeling a little "loose", I have to start tightening 1 and buckling up 2. Buckles 3 and 4 (working down that is) never actually do anything.

I have limits though. The nominal stiff=150 Nordicas were probably too much for everyday skiing, notably so at the end of the day esp. on a cold day...
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...I bought some Salomon 1080s from Nigel Shepherd (Modern Rope Techniques) - remember the green translucent ones with orange buckles - rather cool? - which he rejected as being too soft, but I needed them to flap around on with my kids when they were really weeny. For some reason I kept using them for years (slippers) and only last year decided to go from their nominal 80 flex to some Atomic Hawk 110s and Lange RX110s. Which was good, since Christmas was ice, ice and more ice, and no powder. One day I put my 80 flex back on and SH+++++++++T I had NOOOO CONTROOOOOL.....

Out came some stiff old Falcons which lurked in the back of the boot cupboard (which CEM had nicely adjusted and blown for me) and benefited from the stiffness in these, too.

So this week I bought some FT B&E from Absolute Snow and will probably change the flex 6 tongue to a flex 8, but with the benefit of being able to tune the flex rather than muck around with loads of pairs of boots. I will do a quick review post comparing the Hawks and Lange etc if I have 10 mins to spare tonight....

Like Jedster, I think the power strap discussion is an irrelevance. My (intuitive) view is that it's about optimally matching flex, ski and person. I'm looking forward to the FTs as they are tuneable....
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@valais2,

I posted about it before but I recently bought some secondhand FT Classics (they are not quite the same as the current classic as they have the intuition wrap liners, more like the Drop Kick) really as a low cost experiment because I have never had a pair of boots that fitted me as well as my first ones - Raichle Flexons. I've skied about 10 days on them now and really like them. I've got a 6 flex tongue in them and have been thinking about trying a stiffer one, again mainly just as an experiment because I've not found that I've overpowered them yet.
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Quote:

although I start out the day with only the top buckle done on its loosest setting, and strap adjusted for that, if I want to ski with any performance, without feeling a little "loose", I have to start tightening 1 and buckling up 2. Buckles 3 and 4 (working down that is) never actually do anything.



Interesting - with an overlap boot you are effectively skiing a softer boot until you crank the buckles (top two - I agree lower ones are largely decorative!).
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@jedster, for sure I am.

It's more to do with easing my feet in gently, if I crank up too early they cramp. They always have... best boot fitters in the world, as you know, etc.

I have been known, on easy runs for commuting, not to bother with buckles at all...
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 You know it makes sense.
You know it makes sense.
I don't have that problem but I always do my first couple of runs with buckles loose - just find that nicely sets my heel into the heel pocket before I fix it by snugging the buckles
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Otherwise you'll just go on seeing the one name:
"When used appropriately, power straps can be very effective in decelerating forward movement of the shank when transient perturbations in snow reaction force exceed the limits of the balance system"

You know when you read something and think....this is complete bollox?

transient perturbations....
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 Poster: A snowHead
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Thornyhill wrote:
You know when you read something and think....this is complete bollox?


I dunno - usually pretty good at readin' all these big complicated long wordy things an' all, but even I gave up about half way through!

Sides, seems to be predicated on some assumption that the whole foot, ankle and lower leg are held utterly rigidly in the boot without there being appropriate soft tissue and boot lining absorption allowing some movement, never mind some ability to insert the odd finger (or several for us narrower creatures) between leg front/rear and boot inner.
Personally, if I had the power strap that cranked up, I'd have compressed nerves and no blood supply to my feet.
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@Thornyhill, @Grizzler, indeed, I too work in a discipline which needs precise terminology to describe very specific concepts ... but really,...

Actually I feel a transient perturbation coming on ...

Phew

All better now .......
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Thornyhill wrote:
... You know when you read something and think....this is complete bollox?

Yes, when it becomes obvious that the author is relying on mystifying the reader with language which sounds technical but isn't. They assume we're all more stupid than they are.

I've no idea what their point was, but it's probably as you suggest bollocks as otherwise they'd have been able to explain it clearly.

--
Boots? I don't think there's much consistency amongst experts even - they all wear different boots in different states of repair and with different settings. What works for one clearly doesn't work for another. Everyone finds their place..
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@Thornyhill, transcient perturbations happen. You know, when you ski down those green runs and there are bumpy bits, or bits of icy stuff? Deal with it and move on.
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@Steilhang, should I be worried about them for long?
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Maybe he means mathematical perturbation function.... like Fenchel?

https://en.wikipedia.org/wiki/Fenchel%27s_duality_theorem
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Quote:

Yes, when it becomes obvious that the author is relying on mystifying the reader with language which sounds technical but isn't. They assume we're all more stupid than they are.


Almost all academic papers are written like that. It's even worse in social sciences than proper science. My sister (in her 40s) recently completed a phd and was militantly opposed to writing in academic language. She stuck it out and wrote in plain English. All her assessors were amazed but ended up praising it. Some people have suggested that the excessively complex language is designed to be hard to understand so that you can wriggle out if what you've have written is later shown to be garbage.
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@jedster +1
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can someone summarise this please? No more than 3 bullet point if possible.
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@Dr John,

- Get well fitted boots

- Go skiing in them
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@under a new name, got it. Ta. I already have and do, so I'll stop worrying.
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Quote:

Actually I feel a transient perturbation coming on ...

Having now scan-read most of the article I'm having one of those too. As we all know there are stock power straps and there are retrofit Booster straps which have elasticity. They make for a nice fit and work brilliantly in my experience. I've recently gone for a softer boot and added the appropriate Booster and I won't be going back. I do agree about lack of ankle flex being a major issue - see too many people out there in too stiff boots.
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@Dr John, I think I can, with an additional caveat about the paper I posted:

- boots too stiff? You'll get thrown around all over the place.
- boots too soft? You'll be faced with collapsing boots and poor control of edges.
- boots just right? Good control of mass, and good control of skis.

The paper? All this has to do with the ski-boot-body as a system - which the paper, to its credit does mention, but it's not about the power strap being the only element of this system - which the paper is wrong about, IMHO.
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@Pruman, I don't think I've noticed very many people on over stiff boots, I see many on over soft boots, with poor technique and over wide skis however...
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I see many poor skiers but I seldom think the problems are down to boot choice
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@under a new name that's me!
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@valais2, first thing to realize is the owner of that particular blog... David MacPhail has been around for a long time go and research him then come back and tell me what you think.... WWIW he was involved heavily in Canada in the mid/late 80s and the Canadian federation banned him from touching their athletes boots, (not sure if this was led by the manufacturers or the federation themselves, but there was a massive bust up) he also was the creator of the bird cage experiments, a series of experiments to show how forces were transmitted to the ski, some of it is relevant some of it is just heavy reading, he is a theorist and works at the extreme edges of the sport trying to prove that the mainstream is wrong.... much of what he is now publishing is a rehash of his work from the 80's, it appears he has found a keyboard and wants to get his views from back then out to the world
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@CEM, thanks - very interesting background. The blog link was given to me by a colleague, whose offspring is doing a degree in engineering and focussing on mechanics of ski boots. One of the problems of academic research is that free movement of knowledge on the internet has opened up routes to people who have legitimately been rejected by peer review. Peer review is not infallible of course, since it can be an intellectual cartel, blocking new and well-evidenced research which is too challenging to established interests, but on balance peer review is an important process. Students use a lot of stuff of dubious provenance and need to be able to distinguish innovative thinking from hocus pocus. Of course, Snowheads also is an important context for peer review - some of it off-topic and using interesting language....

Back to MacPhail - a different way of seeing the terrain-ski-boot-bodymass system is a set of actively damped cantilevers. Still a rough model only, this has the advantage of being able to be understood in terms such as resonance, feedback etc. The stiffness of the boot is therefore very important, and this model begins to explain the problem of over-soft boots, where the energy input from hitting something like a mogul (I am NOT going to call this a transient perturbation - damn I just did) can cause the body to collapse over the ski. Too much stiffness or lack of reaction in the system will cause the mass to go into the backseat. Goldilocks boots (just right) and appropriate reaction (the active bit, based on skill - automatically-learned responses of the person in balancing) means that the sudden energy input can be countered without the system becoming unbalanced.

Quick Vic (Elford) was very interesting on all this regarding 1960-70s sports car driving - he tamed the lethal 917 Langheck - taking it flat at 240mph through the kink on the Mulsanne Straight - he saw BALANCE as the key to control - he had a strong mental model of balance in the dynamics of the cars, even if they were slipping all over the place under dynamic forces.

Thanks CEM - a very useful useful bit of background on MacPhail....
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@valais2, 240mph!

You raise an interesting point. For a very long time I have believed that one element of skiing well is to consider that your CoM is the important thing and the legs and skis are subordinate. I am not going to explain this well...

So when one sees a good skier skiing well on sheet ice, IMV they are usually spoofing it. Legs and skis are keeping them upright but to an extent, they are just going with the flow and sliding.

To the inexperienced it looks like they are in full control, and to the extent that if they needed to Hard Stop they could, they are, but it's all smoke and mirrors.

I don't know if that makes any sense...
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@under a new name, ....you indeed make sense with that comment - CoM vital and a good way to conceptualise things but I think there's more .. and indeed more on that in a moment ... but first Quick Vic ...

Vic's book 'Porsche Performance Driving' remains a definitive classic - and his driving is legendary - see for example

https://www.hemmings.com/blog/2014/04/18/vic-elford-on-driving-the-917-in-1970-and-today/

And

http://www.mulsannescorner.com/bio.html - '...The aerodynamic specificity that was needed to tackle the Mulsanne Straight was different than any other track during the racing season. The Mulsanne straight was the fastest piece of racing real estate on the planet! In 1970, Vic Elford in the Porsche 917 LH ran over 240 mph down Mulsanne at night, in the rain, through the "kink" flat out. It took Indy Cars nearly 25 years to reach straight line performance levels that the sports cars were achieving back in the early 70s!..'

Although Richard Atwood never forgave Vic for running flat out and stressing the transmission when he could have run at a reduced pace and won, in '69. Theirs was like the the white thing leading in McQueen's Le Mans - the car in the McQueen film is the 1970 917 LH of Elford and Kurt Ahrens.

Now...on ice...only up to a point Lord Copper. I was managing very well on blue water-ice by using your 'balance but hurtle' method, as was the ESS instructor going sideways next to me. Then my son (then 10) showed us how it should be done by running tight turns with edges in on the same surface. He was skiing. We were balancing in the way you describe. He was doing closed turns all the way down, putting in 10 where we were doing 3. That's when I decided to get some coaching. Sasha from Swiss Mountain Sports did a morning with me on ice, and I moved from controlled sliding to genuinely being in control and actually skiing the stuff. A revelation, actually.


Last edited by Anyway, snowHeads is much more fun if you do. on Sun 23-04-17 23:19; edited 1 time in total
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@under a new name, look at 3.45.... elford simply runs past the short-

tail....


http://youtube.com/v/PT59amOra78

....and true flat 12 sound, thanks McQueen, no bull about the soundtrack.

And this is fun - just wind up the volume .... unfortunately the high quality MP3 from the a2z racer site has gone.. this is just a pale reflection ... but shows mcqueen used the real sound


http://youtube.com/v/LWyZImr1qRo


Last edited by You'll need to Register first of course. on Sun 23-04-17 23:21; edited 2 times in total
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@CEM, I read back through the blog the last time a link was posted. I don't see the problems that he describes in his boots in my own current ones, he may be able to claim a fair bit of credit for this but the blog just seemed out of date.
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@valais2, i'm now in conference mode and on limited wifi but will revert appropriately Thursday Happy
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valais2 wrote:
.. the energy input from hitting something like a mogul (I am NOT going to call this a transient perturbation - damn I just did) can cause the body to collapse over the ski....


Is this a transient perturbation?



https://www.facebook.com/brian.bell.98478/posts/1403013096472302?comment_id=1408109112629367&notif_t=feed_comment&notif_id=1492812503913964
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@Thornyhill, ...definitely

Though perhaps it stayed with her rather than being transient.

Vonnbott gets peturbed.....


http://youtube.com/v/Gwb88vsdimA
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