Jump to content

The effect of the ski width on knees


Recommended Posts

Now, don't throw anything at me, I just ran into this by accident, and I'm not a researcher in Montana University either. The title of the article is in contradiction with what's said in it, but for what it's worth, here ya go:

http://www.montanakaimin.com/news/your-fat-skis-are-killing-your-knees/article_b73f0f3a-b0ba-11e4-9f66-fb3b2e4b192c.html

http://www.spokesman.com/stories/2016/feb/10/jennings-thin-is-in-once-again-for-skis/

  • Thanks 1
Link to post
Share on other sites

this is a great topic, especially if you want to ski well into your golden years. but also keep in mind that skiing technique also has an influence on the forces and stresses put on the knees. for me, I've taken the approach of limiting my widest ski to about 88 mm. for firmer days, I'd prefer to be on something sub-70mm...but at the moment my narrowest ski is 81 mm. full disclosure, I plan on acquiring cheater SL skis (approx. 67 to 70 mm waist) to use for firm days.

Link to post
Share on other sites

This research has been known and is very interesting. I read about this a few years ago, I'm not sure if this is the same research, but I've noticed it in my knees the wider that the skis get. I think that is why it is important to rotate through different skis as opposed to being on one set. Similar to having multiple pairs of running shoes so that your muscles,  tendons, ligaments, etc. do not mold to just one repetitive comfort. That being said, I don't think that 'fat skis' should be shunned because of this. Thanks for sharing this again.

  • Like 1
Link to post
Share on other sites

I'm in my golden years. (67 tomorrow). Here's my experience with old knees.

I have two pair of Fischer skis that I'll swap out depending on conditions. 

My "fat" skis are Motive 95-- 134-95-122, 17 radius and 174 length.  I bought these skis as all mountain skis to use out West and the occasional powder day at Elk mainly, and they cut through soft snow, and end of day crud with ease (if you ski fast and don't make a lot of turns =). )  They also handle groomers well, but prefer to be skied aggressively.

My "skinny" skis are Progressor 800-- 122-74-103, 12/15 radius (two sweet spots) and 170 ! length. These skis are very responsive for the average PA skiing conditions. Hardpack and icy at times. They do not have to be "ridden hard" and cruise easily.

The "old knees" part.  Last week a bunch of old farts went on our annual trip to NH. I skied hard for three days in a row in excellent conditions, on my "fat" skis exclusively. Soft packed powder on groomers for the most part, although the Bretton Woods glades were sampled and spectacular. I woke up the fourth day to pack the car and head home and my old right knee said, "hold on old fart, you need a couple of Aleve this morning."  At no time did I twist or injure it during the past days.  I attribute the pain to the extra effort needed to turn the wider skis three days in a row. (And a previous injury.)

Earlier this season I skied my "skinny" skis at Elk just to see how they felt compared to the "fat" skis I'd been skiing the last two seasons, and I really had a fun day. Much easier to turn with a lot less effort.

So, I agree with the article, and find using a "fat" ski or a "skinny" ski has merit depending on conditions, and can also keep "old knees" feeling less abused as well..

  • Like 4
Link to post
Share on other sites

I've never had knee issues but in hardpack snow I Blue I prefer my mantras which are 96 underfoot and in choppy snow I prefer the shiros at 117 I believe. I feel like fat skis preserve me a little more in chop because it's so much less effort..now for Bumps fat skis are a handicap at least the tight seeds at Blue..on natural western Bumps fat skis are fine cause they are more widely spaced and more rounded as opposed to troughs. 

 

The one dude in Jackson who's a friend of a friend had like 16 pairs of skis at his place none narrower than about 115s

  • Like 1
Link to post
Share on other sites

At some level it's just simple physics, the ski is a lever so if you make it bigger its generally going to be a more powerful lever and very slight changes in angle will result in a much different application of force, in this case the load over the various body parts.

That said I would take a bet that it's a factor of which it's not the main factor. For one thing for different types of skiers this would seem to matter less as it relates to both how you ski but probably more importantly the muscles/genetic factors in your legs. For example the quadriceps dampen shock to the knee joint thus depending on the strength of the persons quads load is applied differently, then lets add in all the other factors, I'd bet in reality 90% of skiers require some level of boot fix for lateral alignment and the degree to which they can flex their ankles, plus we aren't even sure whats actually applying the force.

This is sort of unrelated but it's cool. So we all kinda get to carve the ski you roll your foot but there is a bunch of disagreement over what muscles are actually doing the heavy lifting. This is important in WC racing which at some level comes down to how strong are you in the right places so there is actually a decent amount of study and one camp is that's it's mostly muscles of the foot and a smaller camp that says it comes from the glutes and soleus and that among many other things what really really really fast skiers due is build up and apply a rotational force out of their pelvis, think of a spring.  Which if someone told you what separates really good WC skiers from those that just dominate is muscles of the pelvis you'd call out and out bullshit. The biomechanics of skiing are only sort of known and the whole whos doing what in boot ankle dealio is at best confusing.

So I mean does it matter ? Sure but it's probably in reality a very nominal factor if you added up everything that goes into the turn but it's also the easiest to fix. To fix muscle or technique you gotta spend alot of time actively engaged in changing your body or you could say screw all that and just pay 600$ for narrower skis......so once again the answer is to buy more skis.

  • Like 3
Link to post
Share on other sites
55 minutes ago, Johnny Law said:

At some level it's just simple physics, the ski is a lever so if you make it bigger its generally going to be a more powerful lever and very slight changes in angle will result in a much different application of force, in this case the load over the various body parts.

At what point does a persons height take into effect as the other end of the lever?  I.e.... a taller person has slightly more leverage over a fat ski than a really short person. 

Link to post
Share on other sites

jlaw and root have solid points, and i don't think there is necessarily a "right" and a "wrong" side of the narrow v wide ski debate. don't forget that side cut radius also is a factor here. so, each type of ski out there is a tool intended to facilitate different types of skiing. that said, any ski and be skied however you want. also, no matter what ski we ski, our bodies are affected by the forces and stresses developed. 

@RootDKJ i think your question re: skier height is speed dependent. for a skier to really get their entire body inclinated such that your center of mass (COM) is substantially laterally out and away from the skis, one needs to be skiing at a fairly decent clip. to get a ski on edge at slower speeds, it's really the rolling of the ankles that control the movement. for that instance, overall skier height means nothing.

i think another component to the debate is to how ppl tip their skis to set the edge. if ppl are severely laterally tipping their knees to initiate the edge set (i.e. think slalom skiers and bumpers), then i can see how a wide ski would automatically induce more stress upon the knee joint that a narrow ski.

 

 

Link to post
Share on other sites
15 hours ago, guitar73 said:

i think another component to the debate is to how ppl tip their skis to set the edge. if ppl are severely laterally tipping their knees to initiate the edge set (i.e. think slalom skiers and bumpers), then i can see how a wide ski would automatically induce more stress upon the knee joint that a narrow ski.

 

 

This is what's really interesting, to some extent we don't know how humans actually get the ski up on edge.

Conceptually it's easier to think of skiing as standing on a platform that is moving and is perturbed in two directions, we can ski because the COM does not move with the full force of the perturbations because we have momentum and the rest we use movement of the body to balance out the forces. Static tests suck because they can't impart inertia and thus alot of the way we think about skiing is useful but incorrect, in an energy sense it's more accurate I think to think of skiing as a flow of energy.

In the simplest sense we must use the muscles of the feet to flick the ski up on edge but while doing that we must maintain balance, so beyond just the muscles in the feet all kinds of other shit is going on with all the other muscle groups as we impart a flow of energy into the ski, as we progress through the turn that flow transfers into the body and into the finish of the turn. Think about how it feels to crank out a big sweeper, the force builds and flows, it's a constant experience but not at all and it's just as dependent on other muscle groups like in the quads and back as it is on the ankle/foot.  At the extreme end you can see this is in WC. Shiffrin is so much better because her turns are as symmetrical as humanly possible, her next best contender is probably Wendy Holdener who is probably a better athlete but because she cannot get the same hip angulation on left foot down turns she's considerably slower and that has jack to due with muscles of the foot/leg. This dude says it even better because he's actually really smart.

"Hirscher progressively engages his edges, especially on his outside ski then hooks a tight arc close to the gate to establish his line. Once he has established his line, he no longer needs his outside ski. He gets off it in milliseconds and uses the rebound energy to project forward with only enough pressure on his uphill (new outside) ski to influence his trajectory of inertia so his COM enters the rise line at a low angle of intersection. He gets rebound energy from the loading  of his outside ski and from what amounts to a plyometric release of muscle tension from the biokinetic chain of muscles extending from the balls of his outside foot to his pelvis. The energy is created by the vertical drop from above the gate to below the gate similar to jumping off a box, landing and then making a plyometric rebound"

So although the question appears simple it's actually pretty hard to determine what is doing what when your skiing at least to me it seems carving is a concert in which at various points various parts of the body are carrying the tune.

What's cool to me about skiing in some sense is how human it is. It's kind of stupid right, I mean it doesn't actually do anything in a utilitarian kind of way, no other animal would spend the kind of energy humans due to go skiing and we can do it instinctively because its a thing we can feel. Think of the number of humans who can arc a turn and yet while we have some idea if we are honest the knowledge side in which X does Y  which = Z of skiing is still a mystery, I can know nothing of the balancing physics of skiing and be a very good skier. Nobody who can ski thinks skiing, you don't go down the hill going impart force at angle X, angulate skis at position x in the turn. It's why at some level you can't teach another person by saying you need to do X because that's very useful but they still have to learn how it feels to do X. That's what being a human is all about, we are this thinking, tricky box in our heads while at the same time defined by something as vague as feeling.

  • Like 4
Link to post
Share on other sites
11 minutes ago, Johnny Law said:

This is what's really interesting, to some extent we don't know how humans actually get the ski up on edge.

 

true. also, maintaining/manipulating that edge set throughout the turn as you pointed out.....how our bodies react to changes in terrain, surface irregularities, velocity, etc....all those also are factors and contribute to the wear and tear we put on our bodies as we ski. but at the end of the day, one can't argue with how a specific ski makes their bodies feel, and not just for one day, but over the course of many seasons as well.

Link to post
Share on other sites
9 hours ago, Johnny Law said:

So although the question appears simple it's actually pretty hard to determine what is doing what when your skiing at least to me it seems carving is a concert in which at various points various parts of the body are carrying the tune.

So well said. As with any sport, it's relatively easy to reach a level of basic competence, but also easy to stagnate there. Progress thereafter seems to be a matter of numerous and very subtle adjustments to form.  After a lifetime of playing basketball I  can diagnose my jump shot the moment the ball leaves my hand. But skiing is a foreign physical language to me and so far all I can do is ask for directions to the train station. 

 

  • Like 1
Link to post
Share on other sites



This is what's really interesting, to some extent we don't know how humans actually get the ski up on edge.
Conceptually it's easier to think of skiing as standing on a platform that is moving and is perturbed in two directions, we can ski because the COM does not move with the full force of the perturbations because we have momentum and the rest we use movement of the body to balance out the forces. Static tests suck because they can't impart inertia and thus alot of the way we think about skiing is useful but incorrect, in an energy sense it's more accurate I think to think of skiing as a flow of energy.
In the simplest sense we must use the muscles of the feet to flick the ski up on edge but while doing that we must maintain balance, so beyond just the muscles in the feet all kinds of other shit is going on with all the other muscle groups as we impart a flow of energy into the ski, as we progress through the turn that flow transfers into the body and into the finish of the turn. Think about how it feels to crank out a big sweeper, the force builds and flows, it's a constant experience but not at all and it's just as dependent on other muscle groups like in the quads and back as it is on the ankle/foot.  At the extreme end you can see this is in WC. Shiffrin is so much better because her turns are as symmetrical as humanly possible, her next best contender is probably Wendy Holdener who is probably a better athlete but because she cannot get the same hip angulation on left foot down turns she's considerably slower and that has jack to due with muscles of the foot/leg. This dude says it even better because he's actually really smart.
"Hirscher progressively engages his edges, especially on his outside ski then hooks a tight arc close to the gate to establish his line. Once he has established his line, he no longer needs his outside ski. He gets off it in milliseconds and uses the rebound energy to project forward with only enough pressure on his uphill (new outside) ski to influence his trajectory of inertia so his COM enters the rise line at a low angle of intersection. He gets rebound energy from the loading  of his outside ski and from what amounts to a plyometric release of muscle tension from the biokinetic chain of muscles extending from the balls of his outside foot to his pelvis. The energy is created by the vertical drop from above the gate to below the gate similar to jumping off a box, landing and then making a plyometric rebound"
So although the question appears simple it's actually pretty hard to determine what is doing what when your skiing at least to me it seems carving is a concert in which at various points various parts of the body are carrying the tune.
What's cool to me about skiing in some sense is how human it is. It's kind of stupid right, I mean it doesn't actually do anything in a utilitarian kind of way, no other animal would spend the kind of energy humans due to go skiing and we can do it instinctively because its a thing we can feel. Think of the number of humans who can arc a turn and yet while we have some idea if we are honest the knowledge side in which X does Y  which = Z of skiing is still a mystery, I can know nothing of the balancing physics of skiing and be a very good skier. Nobody who can ski thinks skiing, you don't go down the hill going impart force at angle X, angulate skis at position x in the turn. It's why at some level you can't teach another person by saying you need to do X because that's very useful but they still have to learn how it feels to do X. That's what being a human is all about, we are this thinking, tricky box in our heads while at the same time defined by something as vague as feeling.


"Carving is a concert"....Brilliant!!
A perfect description.

Sent from my SM-G930V using Tapatalk

  • Like 2
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...