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Relationships between damping & stiffness in skis and back injuries?

MadMacDuff

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Hi everyone, a long time lurker here but thought I might get around to asking for some help trying to understand some equipment issues I have the last few years as they relate to a specific injury. Its a long read so fell free to ignore this post but I being a scientist I can't help but provide a lot information when I have it ogsmile

A few years ago I was competitive fencer but developed a muscle imbalance with my right shoulder being considerably stronger than my left. One day at practice I over extended my arm and ended up torquing one of my vertebrata between the shoulder blades. Now it popped back in to position quickly the muscles in my upper back keep thinking that it was out alignment and were constantly locked up for 3 months trying to "hold" the vertebrate in position. While locked up the the muscles become so tight that they crush the central nerve in between the shoulder blades, leading to crazy muscle spasms, migraines and numbness in the right hand.

This happened when I was 21 and after 5 years of one and off physiotherapy the issue has largely gone away, except the muscle memory comes back anytime my body has to tense up too much and it takes about a week for things to settle down again. Now where it relates to skiing is that I have found certain combinations of skis, boots and bindings tend to aggravate this injury but not others and I was wondering if others might be able to help me identify the pattern?

A bit about me, I am 26 years old ,5'11", ~160 lbs, and definitely qualify as directional skier that likes the odd combination of speed and finesse. I grew up skiing cross country only from age 2 -12 and quickly switched to alpine afterwards, skiing rossignol sl racing skis everyday from ages 14-18 with zero issues (aside from expected sinking on the pow days). My preferences are either to either be making big gs turns over the rollers or to spend my time in the trees and techy steeps when the snow is soft.

My current quiver of skis, i.e. most recent experiments are :
2018 Dynastar Speedzone FIS SL 165cm with Look SPX 12 Rockerflex and racing plate
2018 Nordica Enforcer 93 177cm with Look Pivot 12s
2019 Salomon QST 106 181cm with Look SPX 12s
2019 Atomic Bent Chetler 100 180cm w/ Warden 11s (Just purchased so I don't know yet)

Skis that have caused serious issues include:
2017 Salomon QST 99 181 cm w/SPX 12s
2017 Salmon QST 118 185 w/SPX 12s
2017 Blizzard Brahma 180cm w/Pivot 12s
2018 Volkl 100eight 181cm w/demo attack 13s (By far the most painful, and that was during a slushy day in march)
2014 Dynastar Omeglass FIS SL 165cm
2016 Skevik Lokens 106 180cm w/demo griffins
2017 Blizzard Bonafide 180cm w/demo griffins
2018 Blizzard Rustler 11 188cm w/mo griffins

Other skis that I've tried with no injury related issues:
2012 Salomon BBR 8.9 176cm w/demo STH 13s
2015 Rossignol Sin7s w/axiums
2016 Atomic Automatic 109s 189cm w/ Tracker 13s
2017 Rossignol Soul 7 188cm w/SPX 12s
2016 Rossignol Experience 88s 180cm w/demo STH 13s
2018 Rossignol Black Ops 118cm w/pivot 14s

My current theory is that when there is either a hinge point in the flex pattern or profile (e.g QST 118), the ski has little damping (100eights) and/or is too stiff for my weight (Brahma 180cm), too much of the vibrations and occasional bangs is transferred up my legs and instinctively my body is tensing up to take the load. Does this sound like a reasonable theory? Has anyone else encountered similar stories?

I have also noticed a general increase in the occurrence of these issues after switching my boots from Tecnica Inferno 110s to Lange RX 120 LV and I am attributing this to combination of boot stiffness and the more upright stance.

Thanks for reading this far.
 
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MadMacDuff

MadMacDuff

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I haven't had too much opportunity to play with delta or mount point as much, expect when demo bindings were an option. I currently don't have the space for a work station large enough to mount skis and have that done at the shops which gets expensive quick.

That said I have been looking into both of the delta and MP. I think mounting point was part of the issue with QST 99s and 118s because the recommended mount wasn't centered over spot where the camber peaked, like it does on my QST 106s but the soft tips/stiff tails on the 99s and abrupt rocker/camber transitions on the 118s didn't help either.

Delta was something I've JUST started to play with but typically I have just gone with Rossignol axials/look SPX bindings flat because I like how they feel so secure when I click into them and I have usually been able to get a good sale price on them. I also liked that the look advertised more elastic travel in the heel. However, I was taking a keen liking to the wardens yesterday afternoon so that maybe be part of the issue.
 

James

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I have also noticed a general increase in the occurrence of these issues after switching my boots from Tecnica Inferno 110s to Lange RX 120 LV and I am attributing this to combination of boot stiffness and the more upright stance.
Yeah it's probably not the stiffness but the setup. May be more than just the forward lean.
Try this as an experiment. Install a Booster strap if you don't have one. Then go ski with the top buckle un buckled but clicked. Or make it the absolute loosest so it doesn't flop out and break if it hits snow. After that try that with both top and second buckle loose.

It may be you've bypassed the Stretch Reflex with your boots. According to David McPhail, this leads to issues all the way up to the back. Perhaps some skis exaggerate this more than others. Stiffer front end would be a guess as what's worse. But you have 2 Fis sl skis on there one affects, one doesn't . Odd.
See hear about the stretch reflex. He's a tough one to get a handle on. He really needs an editor.
https://skimoves.me/2018/11/13/learn-the-sr-stance-in-3-easy-steps/
 

cantunamunch

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Hi everyone, a long time lurker here but thought I might get around to asking for some help trying to understand some equipment issues I have the last few years as they relate to a specific injury. Its a long read so fell free to ignore this post but I being a scientist I can't help but provide a lot information when I have it ogsmile

My current theory is that when there is either a hinge point in the flex pattern or profile (e.g QST 118), the ski has little damping (100eights) and/or is too stiff for my weight (Brahma 180cm), too much of the vibrations and occasional bangs is transferred up my legs and instinctively my body is tensing up to take the load. Does this sound like a reasonable theory? Has anyone else encountered similar stories?
..

The boot is very likely ...

That said, you can get better data than just feel - Slam Stick type data loggers are cheap* and robust: https://www.digikey.com/catalog/en/partgroup/slam-stick-x/50315?utm_adgroup=Test & Measurement

* in the sense of 5x the sensor speed of a flagship cell phone for about the same price.
 
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Pdub

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I once spent a few weeks skiing on bindings that had little or no delta, i.e. the heel basically level with the toes. They may have been AT bindings, can't recall. I had several episodes of severe back spasm which ruined me for a week at a time. Switched to "regular" bindings and never had another issue.

Your history does not support this explanation but I figured, you're a scientist, any data could be potentially useful.
 
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MadMacDuff

MadMacDuff

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Thanks guys for the input. @Pdub @James and @cantunamunch I got a few more days in on the FIS SLs, BC 100s and the Enforcer 93s and definitely think the combination of boots and bindings are the principal culprits.

In particular, I got in a long day yesterday, skiing firm steeps on the Silver Star backside in the morning and trees and bumps with kids in the afternoon. Spent the whole day with the Enforcer 93s (177cm), with pivot 12s and the Lange RXs, and had too put an ice pack on both my Achilles tendons and a heating pack on back when I got home. The BC 100s (180cm) w/ wardens were dead easy to ski all day in a mix of soft chop over firm a week ago but the achilles, hamstring were still sore at the end of the day. So I am still having issues with my other skis, they are just less produced, probably because my current skis are little more full flexing than some of the others I have owned.

I also noticed that on true hard pack I was having trouble getting pressure on the front of the skis when I took out my Dynstar Speedzone SLs the other day. Likely boot related but compared to older combination of Omeglass SLs, which were much snappier than the speed zones, and either my Tecnica Inferno 110 or Head S11 boots, I had a hell of time getting tips of the ski to engaged and felt like I was skiing entirely off the back half of the skis.

Playing around with boots at home right now, the Lange's seem to be gently crushing Achilles tendon and forefoot, causing my foot to lock up and the shocks from bumps and ruts to transfer up the leg and back. This seemed to be in line with McPhail's comments, so thanks again @James for forwarding the link on stretch reflex. Combined trying with ski's that have too stiff a tail for my weight range and amount of time I spend in bumps, its not as hard to see in retrospect why I might be having these issues.

I've got some Salomon XMax 120s on order to replace the Lange's, after looking around our local shops the past week. Hopefully, after a bit of tweaking I can start to figure out the pattern and stop beating my self up.

I'll update when after I get a few days on the new boots.
 

François Pugh

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One thing I noticed about your skis that cause problems versus the ones that don't is that many of the problem skis are capable of transmitting much higher forces than some of the ones (the ones I'm familiar with) in your no-problem skis.

It could be you need to strengthen those muscles with targeted exercise before putting sudden high demands on them while skiing.
 

LuliTheYounger

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Not a fitter by any means, but I've spent too much time studying the Achilles for school, and I'm kind of curious about the soreness there? I wouldn't be surprised if you were in super soft boots & pulling the calf tight to compensate for a lack of support on the shin, but the way you describe the boots & the feeling, I kind of wonder if the boot set up isn't letting your ankle flex enough & you're accidentally lifting the heel slightly to get that feeling of forefoot/tongue pressure? Tension in the AT would limit your shock absorption, and I can see how it might feel like more of an issue on stiffer skis, when you want more leverage but aren't quite getting it.
 
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MadMacDuff

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So I got in two days with the new boots, Salomon S/Max 120s. Aside from swapping out the footbed for my own and playing around with the buckles, its setup as out-of-box for now. There are still several tweaks to be made before I am totally comfortable with them but immediately it was major improvement over the Lange RXs. My AT isn't pinched or strained at the end of a long ski day, and I have more power & control while skiing, since I can make use of the forefoot in driving the skis.

Going by the results of the different trials I think I could assign some of my past issues to the the following:
1. Skis too stiff for my weight range. Demoed the QST 99 again and the stiff tail was still a problem skiing steep runs off the face in soft chop with firm snow underneath.
2. Poor fitting boots.
3. Lack of upper body strength (@François Pugh)
4. A tendency to ski too fast through chop and chunder, given said strength and repeating for the majority of my runs over 4-5 hours per ski day.

So far what does seem be working out better are:
1. Proper fitting boots with bit more forward lean and a very even flex .
2. A medium stiff ski, with an even flex pattern between the tips and tail. I found that if the ski is too soft then I end up working too hard to maintain edge hold and stability at speeds when I am in the more open terrain; However, if the ski was too stiff for my weight, then rather than absorbing the bang from bumps and ruts, too much of the energy is transmitted directly to my legs and back (e.g. Brahma 180cm). Hinge points in the flex pattern also seem to cause similar issues (e.g. Skevik Loken 106 180cm)
3. Bindings with a neutral ramp angle (e.g Look SPX 12 or Pivots)
4. Skiing lighter on my edges and making more use of "drifted" turns at speed.
5. Going with a more centered mount point the more powder oriented the ski is. Helps me stay more upright and supple in the choppy snow.

So far my favorite combo has definitely been the QST 106 (181cm) mounted with SPXs and the new S/Max boots. Its too wide for long days on hardpack and isn't quite as much fun in the soft snow as the QST 118s but there are no injury issues, it still has a nice pop at the end of the turn and is comfortable in mixed snow conditions. Now to find a skinnier combo that has most of those characteristics :)

In the mean time, I am finally breaking down and going to get back to more nordic skiing to re-build my muscle strength. Probably, going to keep the Langes too just as for use an experimental pair for making my own boot modifications.
 
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MadMacDuff

MadMacDuff

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Now that (1) is working may I suggest

(1.5) ski with softer ankles and softer knees

as a focus in addition to (4)?

That certainly has been on the list of things to work towards. However, I haven't had too much of an issue in that department, because of my former training as a fencer.

One thing I noticed about your skis that cause problems versus the ones that don't is that many of the problem skis are capable of transmitting much higher forces than some of the ones (the ones I'm familiar with) in your no-problem skis.

It could be you need to strengthen those muscles with targeted exercise before putting sudden high demands on them while skiing.

Out of curiosity @François Pugh, what which of those skis have you tried? I ran another experiment the other day demoing the new Atomic Vantage 90ti, Rustler 9, Head V -10 and the Brahma again but in a 173cm length this time. I was curious if my previous issues with the Brahma were purely because of boots and being too long but still had the same issues, though less produced this time. However, I had zero issues skiing the Vantage 90ti, and making big GS turns through the roughed up groomers? The head was the nice a easy, and the Rustler as well, expect at speed would I noticed more tip flap, which bugged me.

I would think based on the shape and stiffness the Vantage 90ti in 176cm would be comparable to a Brahma in 173cm length, no? On the snow I noticed that the Atomic was tracking and absorbing the terrain better for me, whereas I could fell a distinct "tink" feeling from the Brahma's every time they went over a rut or chop. Might this be related to the elasticy of the Ash core on the Atomics versus the Poplar/Beech core in the Brahma's? I tend to notice that "tink" or a "bang" on skis with maple or beech cores, which would make sense given how rigid the woods are?
 

cantunamunch

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I would think based on the shape and stiffness the Vantage 90ti in 176cm would be comparable to a Brahma in 173cm length, no? On the snow I noticed that the Atomic was tracking and absorbing the terrain better for me, whereas I could fell a distinct "tink" feeling from the Brahma's every time they went over a rut or chop. Might this be related to the elasticy of the Ash core on the Atomics versus the Poplar/Beech core in the Brahma's? I tend to notice that "tink" or a "bang" on skis with maple or beech cores, which would make sense given how rigid the woods are?

Not very likely in skis. If someone had given you identical axe handles of those woods you would probably have felt the difference. Within a couple of strokes.

In skis the woods are so composited that what you're primarily feeling is the shape of the core (how it was thinned and flexed) and the relationship of the core to the surrounding resins, reinforcing mats, sidewalls, and tip spacers. Maple is one of the dampest commonly available hardwoods, but a single extra layer of fiberglass and a change in core thickness and you'd never be able to tell what the specification was. Heck, just using a different adhesive in the core lamination changes ski feel - phenolic or urethane, and if urethane, which type?

Guessing the type of wood from production ski feel is about as likely as guessing the breed of chicken by smelling a pot pie. Unless you have absolutely identically prepared pies from various (but identically grown!) breeds, it isn't going to happen.
 
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