tracking your CoM and your BoS

[Dakine]

A lot of people are more familiar with the term center of gravity than center of mass.

 

[Scruffy]

... At the center of it all of course, is Balance. This is a word that is much maligned because many instructors think of it in terms of their skill level and not the students. Many think explaining a simple term like Base of Support is too complicated. Well the truth is that beginners come to their first lesson with everything but knowledge and experience in the BOS required for proper skiing. Most instructors will keep shouting "Hands in front" until something finally clicks instead of teaching what our skiing BOS is comprised of and how we use our flex complex (ankles, knees and hips) plus upper body management in a way that supports BOS consistency.

Winner winner chicken dinner. Not just instructors; anyone who has already ingrained those balance skills to the point of performing them automatically. How many of us can really recreate in our minds what our infant selves went through to learn to walk? We can't, that memory has been lost, but the skill has been ingrained. We walk, run, skip and jump without having to think about it everyday.

 

[Scruffy]

Nothing like windsurfing to teach you about COM and BOS.....

Didn't I say that on page one? or was it two

 

[LiquidFeet]

....But how much do you need to see a few more YES’s to your OP?

If different wording generates more yes's, then the original post's words were getting in the way of accurate communication. Word choice matters since we are typing instead of skiing together.

 

[Corgski]

You get mostly a yes from me, which may not be good omen for your thesis. I think at the more advanced levels one's brain works off subconscious cues but I am working on advancing from an intermediate so it is still pretty explicit for me.

For me, thinking explicitly in terms of COM and BOS helps develop beyond classic external cues like athletic stance, hands forward and pressuring cuffs. All good but if you are totally dependent on that, what happens when you try hands on hips, ski with boots barely buckled, increase forward lean by adding spoiler, try to maintain speed through a flat spot by trying a tuck or weighting the back of the skis more? Even if one is not thinking COM, one does need to be able to control fore/aft balance without being dependent on these externally provided cues.

One of the challenges with developing angulation is understanding what it does with respect to COM. Very slow carving, starting from a standstill, is a great way to start becoming aware of managing COM in order to get the required edge angles and to keep weight on the outside ski. A little time on this and topics like passive vs active angulation and angulation vs inclination can become more relatable for the advancing intermediate.

At some point one needs a working mental model of ones skiing - COM/BOS or balance is fundamental. Sometimes one hears the idea that a good instructor is someone who has built up a portfolio of cues relating to a myriad of disciplines (basically teaching to imitate certain movements of a basketball player, a cyclist or whatever). I'd suggest that someone who thinks that is a requirement of a good instructor does not have a functional working model of their skiing and is always hunting for more external cues to fix their skiing.

At the center of it all of course, is Balance. This is a word that is much maligned because many instructors think of it in terms of their skill level and not the students. Many think explaining a simple term like Base of Support is too complicated. Well the truth is that beginners come to their first lesson with everything but knowledge and experience in the BOS required for proper skiing. Most instructors will keep shouting "Hands in front" until something finally clicks instead of teaching what our skiing BOS is comprised of and how we use our flex complex (ankles, knees and hips) plus upper body management in a way that supports BOS consistency.

I think this covers what I am trying to say.

 

[Rich McP]

If different wording get yes's, then the original post's words were getting in the way of accurate communication.
Word choice matters since we are typing instead of skiing together.

I think you got qualified yeses in the early responses. Several people answerd that they don't think of COM. I'm in that camp. I can honestly say that I have never thought about where is my COM except when I'm in an indoor clinic leaning on a chair making angles. I think of BOS in the contect of "Did my skis go where I wanted them to?" I know clearly if they missed that rock, went around that bump or tree or gate, it they took my intended path down that luge line. That's the extent of my thoughts about BOS.
I think about balance. Am I in balance? Can my balance be better? If I want a tighter turn, what do I need to do differently to get more edge angle...and not fall on my butt, or face, or whatever.
BEWARE: Minor heresy follows.
I believe that COM is not a useful fundamental concept when discussing performance skiing.
The basic reason I say this is because of what we say all the time when discussing COM; it moves around. COM is a concept used in engineering to approximate an object to simplify analysis. It really only applies well for a rigid object, one whose behavior can be well modeled over time, or one where that motion is irrelevant. Skiers are none of those things. For basic understanding of skiing, or describing what a rank beginner is doing it has value. The fact that the first thing we say about it is that it is NOT a point but is something that moves around is why I find it of limited real value. Balance, as a consequence of our combined movements, and the timing thereof is what matters. Are we moving our "COM"? Absolutely! does saying "Move your COM in during the apex of your turn." solve your turn challenges? No. Why? Because HOW you accomplish that move of your COM toward the inside is what will make a difference in your turn.
"But Rich, what about Barnes and LeMaster and everyone else who talks about COM? Doesn't that prove you are full of it?" Nope. They are using it in the context where it is appropriate. Teaching about the basic first order physics of skiing. Perfect. High level skiing? I don't agree that it is useful.
@LiquidFeet, if I missed it, I appologize, but I didn't see you answer why you feel that it is something we should look at. I think I know, but I'd rather not assume that I'm right.

 

[LiquidFeet]

...@LiquidFeet, if I missed it, I appologize, but I didn't see you answer why you feel that it is something we should look at. I think I know, but I'd rather not assume that I'm right.

There are different reasons for asking questions. Questions can be asked in order to make a point - by leading others into saying something as they answer that the questioner chooses not to say up front. I've done that many times when conducting discussions in my college classes. It's so much more effective if I can get my students to put into words the major points instead of me spelling it all out for them while they take notes (or not). That's not why I started this thread.

Another reason for asking questions is that one doesn't know the answers and wants to get them. That's why I asked. I am curious about what others do. I know what I do. I am not trying to convince others to do what I do. I want to know if others already think as I do, or if they don't. And how that works for them.

Thread participation so far indicates that many people don't like working with the term CoM. I'm not yet convinced they don't think about it or feel it or pay attention to its relationship to the feet. It may be that the words they use to describe that thinking don't include "CoM." Maybe "my body" or "me" gets closer to what they pay attention to as they move the feet around underneath that something. Not sure yet. Still wondering.

 

[David Chaus]

A lot of the CoM/BoS awareness is what we do after we’ve skied, i.e. movement analysis. This to me is a process of thinking about what we intended to do, then experiencing what we feel when we do it, then analyzing the results to check on whether we did what we set out to do.

This thread seems to be focused on the middle section, what we’re aware of when we’re doing it. This discussions may change my awareness of what I’m doing when I’m doing it. Or it may not, maybe I’ll just focus on if it “feels right” or even “feels about right” and then do the MA afterwards, with the observations of other skilled observers or just with my own analysis, to review if the relationship between my CoM and my BoS was effective.

 

[Dakine]

If we are talking about the physics of the situation, COM is a necessary concept even if it moves around.
But this stuff is for advanced skiers wanting to know how things work and wanting to get better.
Lower level skiers are baffled by all this technique stuff and just want to see how it is done
Drills and repetition under guidance is what they need to get good habits.
My wife's eyes roll up if I mention COM but if I point out someone who is skiing well she sees it.
Monkey see, monkey do...

 

[HDSkiing]

I’ve been following the post and now trying to formulate how I think about CoM & BoS. I would say I am in the “3” group in that I started skiing at a young age (1960’s) and much of what I do is intuitive, or it feels that way (even my bad habits). When I was a youth racer at 5–nothing and maybe 90 pounds it was all about standing on the outside ski which was stiff, narrow and 190 CM or there about. The only conscious things in my memory then was trying to make sure it bent enough to stay in the ruts...the idea of BoS was the outside ski only and I never thought of CoM. I remember the Mahre’s introducing the White Pass turn and was enthralled, the Idea of using the I/S like that was, well nothing less than Black Magic.

Fast forward to the modern era and its sort of the opposite. I don’t actively track my BoS but I do think, (track seems like too much) about my CoM, or more precisely where I want it to go and most consciously I how I get there.

A late convert to shaped skis When I started teaching a few years back I was still stuck in the past. RR Tracks? Tipping? What, you mean the inside ski is not just along for the ride AND I can move latterly over it without catching an edge? Who knew!!

So I will consciously think about tipping the inside ski, shortening the inside leg and not extend the outside leg (so I don't push) as I direct pressure to the outside ski, in a stacked position, with the goal of moving my CoM into the turn.

Which just begs the question (maybe for another thread): Does the CoM travel OVER the BoS or does the BoS travel under the CoM? I am working toward my Level 3 and I find the discussion fascinating even if it makes my brain hurt.

 

[geepers]

Which just begs the question (maybe for another thread): Does the CoM travel OVER the BoS or does the BoS travel under the CoM?

There's an interesting question/reply in the comments on the Paul Lorenz "How to Carve| Tips to get your hips on the snow" vid posted recently by @markojp and it's likely relevant to this thread.

Here's the vid again.


Some-one asks: "Do you get your weight forward are pull your feet back at any point in the turn? If so when and how?"

Lorenz replies:

"I do want to pressure the tip of the skis during the initiation of the turn (after the skis find the new edges and before the fall line). I focus more on the angle that I cross my skis. If I cross too directly down the hill I fall inside and lose outside ski pressure. If I cross too much forward along the length of the ski it forces me to rise into a taller position due to an opening in the knee joint to move forward. As such my goal is to cross the skis (change edges) in a compact position so that I have greater mobility with the lower parts of my leg, and then as the legs extend out to the side and I move in at the top of the turn, I try to extend with movement on to the tip before the fall line. As the pressure builds I try to move my feet forward to find the centre of the ski and balance against the pressure that pushes back from the snow."​

 

[Dakine]

Some-one asks: "Do you get your weight forward are pull your feet back at any point in the turn? If so when and how?"

Lorenz replies:

"I do want to pressure the tip of the skis during the initiation of the turn (after the skis find the new edges and before the fall line). I focus more on the angle that I cross my skis. If I cross too directly down the hill I fall inside and lose outside ski pressure. If I cross too much forward along the length of the ski it forces me to rise into a taller position due to an opening in the knee joint to move forward. As such my goal is to cross the skis (change edges) in a compact position so that I have greater mobility with the lower parts of my leg, and then as the legs extend out to the side and I move in at the top of the turn, I try to extend with movement on to the tip before the fall line. As the pressure builds I try to move my feet forward to find the centre of the ski and balance against the pressure that pushes back from the snow."​

[/QUOTE]

An endorsement for the importance of tip or forebody pressure during turn initiation.
This reads on my comment regarding boot tongue pressure as a metric of technique when carving.

 

[cantunamunch]

. How many of us can really recreate in our minds what our infant selves went through to learn to walk? We can't, that memory has been lost, but the skill has been ingrained..

Tangent: you can re-create that process by learning to use jumping stilts. https://en.wikipedia.org/wiki/Jumping_stilts There is literally no way to analytically think your way into using these - and the best technique to learning is to not think about what you are doing at all.

 

[Henry]

regarding boot tongue pressure as a metric of technique

Pressure on the boot tongue achieved by squatting down and closing the ankle joint is only effective at tiring the skier.
Pressure on the boot tongue achieved by moving the (dare I say) CoM forward over the skis' sweet spot is effective at improving the ski's interaction with the snow. Whether one makes a small CoM-forward movement with the (weak) ankle flexors or a large movement with the (strong) hamstrings to pull the skis back under the CoM depends on the amount the skis and body relative position needs to be adjusted.

I had good success telling first or second day skiers to hinge forward at the ankle so their jacket zipper tab was over the ski name on the outside ski. Of course that's too far, but most of us don't move as far as we think we do (check your video). This got the new skiers aligning themselves with a simple way that they could see how they were doing. And they really liked how their skiing was developing.

Does the CoM travel OVER the BoS or does the BoS travel under the CoM?

Either as noted above. However, find out what the examiner wants to hear and that becomes gospel.

 

[Noodler]

Pressure on the boot tongue achieved by squatting down and closing the ankle joint is only effective at tiring the skier.
Pressure on the boot tongue achieved by moving the (dare I say) CoM forward over the skis' sweet spot is effective at improving the ski's interaction with the snow. Whether one makes a small CoM-forward movement with the (weak) ankle flexors or a large movement with the (strong) hamstrings to pull the skis back under the CoM depends on the amount the skis and body relative position needs to be adjusted.

I had good success telling first or second day skiers to hinge forward at the ankle so their jacket zipper tab was over the ski name on the outside ski. Of course that's too far, but most of us don't move as far as we think we do (check your video). This got the new skiers aligning themselves with a simple way that they could see how they were doing. And they really liked how their skiing was developing.


Either as noted above. However, find out what the examiner wants to hear and that becomes gospel.

The problem with most of the discussions had on ski forums about ski technique is that much of the discussion focus' on "concepts" coupled with "feelings" (or intentions) without providing the detail on what body movements are actually being used to accomplish the task. In this specific case, we're talking about how to properly achieve pressure on the forebody of the ski. Stating intentions about moving CoM around without any discussion of how that's actually accomplished misses the mark IMHO. So it's nice too see a post that gets into the actual body movements and muscles involved. Paul Lorenz's own response to the question posed earlier shows me that he either doesn't fully understand his own skiing or he doesn't have the skills to effectively communicate how he skis. I love his skiing, I think it has really improved over the past couple years, but that response was not helpful to me. I couldn't take what he tells you to do and actually duplicate what he is trying to convey.

 

[Ski&ride]

It's the overwriting of the old patterns by the new that's difficult for me.
Color me jealous.

Perhaps my old movement pattern are so bad/inefficient, new efficient movements makes such a huge difference?

 

[geepers]

An endorsement for the importance of tip or forebody pressure during turn initiation.
This reads on my comment regarding boot tongue pressure as a metric of technique when carving.

Looking at that vid (and some of his others) I didn't take it as such a huge endorsement of loading the tongue of the boot. He moves into each turn from a deep flex to the point where the tail of the new inside ski will typically lift and occasionally both skis will leave the snow. His feet are well in front of CoM through the float - it's in no way backseat as there's no GRF at that point. But as the new outside leg extends into the new turn, both the tip and tail of the outside ski are well engaged way before the fall line. He's built great angles before building GRF. If he's pressing forward it must be for the briefest of times to ensure the tips are on the snow before he's centered on that outside ski.

Watch the 2 turns after 0:24 in this vid:

 

[Scruffy]

Tangent: you can re-create that process by learning to use jumping stilts. https://en.wikipedia.org/wiki/Jumping_stilts There is literally no way to analytically think your way into using these - and the best technique to learning is to not think about what you are doing at all.

Wow... looks like fun. Looked at a few youtube vids... amazing stuff they're doing.

 

[Chris V.]

An issue with forums (on any subject) is that sometimes we fail to provide proper context and more importantly, fail to identify the audience we are trying to communicate with. I suspect our interactions are a result of this phenomenon.

Most of the time, when I read a post, I ask the question: " What impact will this have on a self-taught intermediate or advanced, back seat (survivor) skier?" Many here promote advanced techniques with the assumption their audience has the proper knowledge and skill base to implement what they profess.

Some thread drift here--but this message will address LiquidFeet's request for more of a focus on instruction methods.

The discussion in this thread has been on the technical side--which has been appropriate for responding to LiquidFeet's OP. These forums serve more than one purpose, more than one audience. One function has been as a place for discussion among instructors and theorists, some of whom have very sophisticated knowledge (much more so than I have). I agree with you that in writing, we should have our audience in mind. If responding to a new skier's question or observation, it would likely be appropriate to come at an issue from a little bit different direction, or use different terminology. Suggested exercises could be on a less advanced level.

In my "twilight" years as teacher, I have turned my focus on the teaching of beginners. Key to this focus is finding common, fundamental threads that span the spectrum from beginner to expert. At the center of it all of course, is Balance. This is a word that is much maligned because many instructors think of it in terms of their skill level and not the students. Many think explaining a simple term like Base of Support is too complicated. Well the truth is that beginners come to their first lesson with everything but knowledge and experience in the BOS required for proper skiing. Most instructors will keep shouting "Hands in front" until something finally clicks instead of teaching what our skiing BOS is comprised of and how we use our flex complex (ankles, knees and hips) plus upper body management in a way that supports BOS consistency.

To my mind, there's no nobler pursuit for an instructor than to teach beginners and novices, help them develop a love and appreciation of the sport, and send them on a path of self-discovery and development of excellent movement patterns. So a tip of the hat to ya! Yes, it's all about balance! This is a guiding theme in every good lesson at every level, in my opinion. But beginners obviously have more gross challenges with balance than more advanced skiers. Balancing on a sliding, turning platform isn't something with which we get much experience in everyday activities. So I consider getting new skiers comfortable with that to be THE first goal of beginning lessons. When I was last teaching, a couple of seasons back, my first aim as soon as students started going downhill on skis was to build good stance and balance. I didn't even want to start thinking about turns at that point. There were times that I would see a student in another instructor's class, going downhill in a wedge, bracing against the backs of the boot cuffs, making heroic efforts at precarious turns while badly out of balance and creating only very poor engagement of the skis in the snow. I would think that the student needed to be taken back a step, and simply taught how to be comfortable moving in a straight line while over the arches of the feet.

Your observation that just shouting, "Hands in front," doesn't usually do the trick raises a point that I've been mulling over. We always speak of skiing from the feet up, but what does that really mean? Someone recently put up a link that I can't find right now, but that I thought was really excellent. It was a video lesson by a Squaw Valley race coach, advocating keeping constant, functional TENSION in the muscles around the ankle joints. That really clicked for me, and it struck me as something that I'd want to teach first time beginners. Something that's missing from how most people start skiing, and something that's very different from how we use our ankle joints while walking. What if instead of trying valiantly, but often failing, to keep hands in front, that first time skier thought about maintaining muscular tension at all times, sufficient to hold dorsiflexion while being bounced around by all of the undulations in the snow surface? Do you think that might lead to improved stance--involving ALL joints--and balance?

Another point. The sport of skiing involves the active intentional creation, building and management of Centripetal force. Unfortunately for most newbies and many intermediates, the creation of Centripetal force is unintentional and it happens when a sliding ski is placed on edge. Dealing with the unintentional introduction of Centripetal force can be problematic.

To many of your points, what you profess is perfectly acceptable provided the skier is in control and intentionally trying to create the centripetal state aka carving. This level of skier is free to implement multiple cross ski variations because they know where they are going and what they are doing.

Carving is a form of redirection but not all redirection is in the form of carving.

Well, actually, turning creates centripetal force. Period. Intentionally or otherwise. Sometimes more centripetal force, sometimes less. But it doesn't matter if one is skiing with carved turns, skidded turns, or something in between. So just like with gravity--deal with it, embrace it, kiddies, this is what skiing is all about, and if you don't like it you might want to take up checkers. The amount of centripetal force created is a function of turn radius, speed, and body mass. I think that's about all. A higher angle slope creates more speed, of course, at least in some part of the turn cycle, hence more centripetal force. So--if a beginning skier wants to damp down the magnitude of centripetal force, he can keep the speed down, ski gentler slopes, or avoid very short radius turns. (Or lose weight.) Beginners instinctively do all of these things, except the losing weight part, LOL.

The real question is, what does one do with that centripetal force? The main choices are, redirect it by shaping a turn, or scrub off energy with friction. Most turns employ some mix of these two. Beginners tend to want to use a lot of friction, accomplished with highly skidded turns. As instructors, an important part of our job is to change that bias more in favor of turn shaping. We know this has the capacity to slow a skier as much as desired, or bring a skier to a complete stop by turning uphill, as long as the slope is wide enough.

So to my main point and perspective. IMO, what you see in the "Get over it" vid is ground zero for how the outside ski needs to function end to end. In this scenario, the softening, shortening and tipping (to match) of the inside leg has one main purpose and that is to GET OUT OF THE WAY while promoting the building of edge angles on the outside ski. At Advanced skill levels you can implement all kinds of "Adders" to ski more effectively and adapt to various situations, but that is because you have the established balance skills to do so.

Agreed! It's all a question of how we get that outside ski to perform as stated. And I don't consider a focus on inside ski tipping to be any more taxing than a focus on outside ski tipping.

Again I believe strongly in teaching fundamentals that span all levels of skiing. And in that context, to teach (first move) inside ski tipping to beginners (who are operating primarily under the force of gravity) only serves to instill habits that the current skill level does not support and takes focus off building a ski based BOS, balancing on the inside edge of the outside ski which again is the key to utilizing the design of today's modern ski.

"Teaching fundamentals that span all levels of skiing." That's it, without a doubt. However, I disagree with the proposition that teaching ski tipping to beginners is a mistake. I always like to do a couple of things with beginners and novices. (This assumes that I was constrained to use primarily a wedge teaching pathway.) First, I would work hard on teaching foot tipping (knee angulation, whatever you care to call it) to enable sidestepping uphill, perhaps controlling a little sideslipping, and just creating a secure stance for standing sideways on a slope on skis. As soon as skiers were able to negotiate a full beginner run, I would then have them start a shallow descending traverse with fully parallel skis, and then tip the feet into the hill to discover how this would lead to a turn, coming to a stop, with no additional effort whatsoever. Second, as soon as skiers were good enough to go a little higher on the mountain, to suitable VERY gentle terrain that went on for long enough, I would teach railroad track turns. Just one turn at a time, at first. Then start linking if they were up to it. You might be surprised how capable novices can be at doing this, if it's introduced correctly. Something else I discovered in clinics was that MANY lower level instructors weren't capable of doing railroad tracks! This suggests real deficiencies in the ways skiing skills are often developed. If you can't do slow railroad tracks, you ain't gonna be able to carve under more challenging conditions.

If skiers don't balance strongly on the outside skis while doing these maneuvers, they won't be successful. Leaning into the hill is quite obvious to the eye, and should be corrected immediately.

I believe that introducing parallel tipping moves to beginners very early on will bring them great benefits as they progress.

 

[markojp]