tracking your CoM and your BoS

[geepers]

Interlude.

@geepers, I've stopped riding a mountain bike on our narrow hilly New England singletrack trails. They are filled with rocks and roots. I run those trails instead. The downhills are the big challenge. Let me know if the following answers your question.

I have taught myself, especially on the downhills, to plant my feet beneath/behind my CoM (should I call it the body/hips/core/torso?) rather than out in front of it, and to extend the support leg waaay baaack afterwards. Doing this on the downhills while dodging granite boulders and rocks requires me to consciously monitor (rather intensely) that spatial relationship between my support foot and my CoM. If I don't monitor it, I can't control it, I revert to autopilot and plant the foot out in front. When I do monitor it continuously, I plant the foot back up under me (my CoM). As a result of my conscious tracking, my downhill running is smooth and flowing and I've deleted most of the impact on my knees.

The alternative (my autopilot gremlin) is overstriding: planting the foot out in front of the CoM, thus creating a small braking impact at the start of each stride. On the downhills this is an especially strong temptation.

Perhaps with another few seasons of trail running I will have this monitoring focus so deeply embedded that I won't have to do it consciously. It's hard to embed new motor patterns at my age (probably easier for young folks). Working with conscious competence hopefully will eventually translate to unconscious competence. I'm not there yet, but moving in the right direction.

Now back to the skiing discussion.

The bike item wasn't intended as offtrack. Just an activity where most folk would already be on auto-pilot. Personally in riding (as in skiing) I have no conscious thought of where my core is located. I have some conscious focus on the track intended for the tires/skis, I'm aware of the placement of the inside foot (skiing) and I know where my head is located because of the view. But the body? That's somewhere between the feet and the head. Any conscious thought on the body is on separation and angulation.

Then again I've never run gates except on rare occasions.

Your running reads as a brave activity! If I understand correctly you are in full throttle down the hill with zero braking without even the benefit of lateral translation back and forth across the slope. How steep are these boulder strewn hills? (To bring it back to skiing this does seem useful trained feeling for short turns on the steeps. With some reservation about feet being far behind.)

 

[Mike King]

Boot tongue pressure.
If I have it, things are good.
If I don't I have to figure out why and fix it.

I’m more like if I can’t feel the front or back of the boot, I’m good.

 

[geepers]

I’m more like if I can’t feel the front or back of the boot, I’m good.

That's interesting.

A Canadian demo team member told us he uses light contact with the front of the boot all the time as a reference point. Do my level best to copy that.

Guess it depends on how big the movement is between contact at the front and contact at the back. If it is a narrow then no contact is a good reference point. If it is large then maybe not so good.

 

[Mike King]

That's interesting.

A Canadian demo team member told us he uses light contact with the front of the boot all the time as a reference point. Do my level best to copy that.

Guess it depends on how big the movement is between contact at the front and contact at the back. If it is a narrow then no contact is a good reference point. If it is large then maybe not so good.

Try to keep the BoS under the CoM. My cue is being in the middle of the boot.

Mike

 

[Doug Briggs]

Simple answer: no.
I think the CM is important for understanding what is going on, but of limited real-time use.

You can feel the relationship between the BOS and CM in the pressure distribution on your BOS. And then you can react to the pressure distribution directly, without reasoning about your CM.

Or if you get your CM on the wrong side, you feel toppling in the wrong direction start. Again, CM is an abstract construction, not something you feel.

I guess the closest I come is when I'm struggling to ski on one ski on the "wrong" edge I am acutely aware of where my CM needs to be. But even then, I'm not sure I feel it.

I'll be interested to see if there are other points of view on this.

You nailed it in the first reply.

I understand the relationship between CM and BOS but when I'm leaning in I don't think 'Oh, move my CM.' I think 'Idiot, you're leaning in.' One solution get more upper/lower body separation. This will move the CM to the outside, but that isn't a conscious thought. I just know what I need to do to get back in balance.

 

[Chris V.]

The way Mikaela does this drill, you can really see the effect of tipping the new inside foot--once she does it, which is a bit delayed.

 

[Steve]

The skier in the video is Bridget Currier, not Mikaela. It says that at the beginning.

 

[oldschoolskier]

@LiquidFeet, I’ll give you a YES but only occasionally.

When I do 360 type drills to find the muscle memory of that feeling. The purpose is that it becomes instinctive the rest of the time in the other skiing actions.

 

[LiquidFeet]

...If I understand correctly you are in full throttle down the hill with zero braking without even the benefit of lateral translation back and forth across the slope. How steep are these boulder strewn hills? (To bring it back to skiing this does seem useful trained feeling for short turns on the steeps. With some reservation about feet being far behind.)

No breaking, right. But not seeking speed, just seeking to keep my feet working in concert with the speed my torso/CoM wants to go on the downhills. So not race-fast, as racers propel themselves faster than gravity speed on the downhills. I'm slow by trail-runner standards. I just try to keep my feet caught up with the falling body. The feet/legs are the supports that keep the body the same distance above the ground as it falls downhill. And yes, it's definitely bump skiing training. I think about bumps all the time when I run. I give myself grades on the downhills according to how well I keep my feet back under the CoM to avoid the braking: D, C, B, B+. Occasionally I get an A.

not that steep:

steep for me:

 

[Dakine]

I’m more like if I can’t feel the front or back of the boot, I’m good.

On GS skis, if you can't feel the tongue of your boot you aren't loading the tips.
Other skis, not so much.

 

[Mike King]

On GS skis, if you can't feel the tongue of your boot you aren't loading the tips.
Other skis, not so much.

I don't want to load the tips. I want the entire ski bent and redirecting my mass across the hill. If I load the tips, the tails will be displaced. If I'm really skiing GS, that is slow.

Mike

 

[pchewn]

I definitely track where my feet are going, around obstacles such as trees, gates, moguls, ice chunks, etc. I adjust the rest of my body so my COM makes these feet positions in balance ... by feel of the turn. So I only "track" one item and "adjust" the other to suit.

Unless or until I get off balance or out of whack. Then I sense my COM being in wrong position relative to my feet and move the feet or the COM to get back in balance. (e.g. Spread feet apart when slipping)....

 

[Ski&ride]

It's hard to embed new motor patterns at my age (probably easier for young folks).

I didn’t find embedding new motor skills particularly harder at my advanced age.

Fitness, yes. Reaction time slow down, yes. But learning hasn’t slowed down noticeably.

My body is still craving for movement that feels good. So any new movement that makes the body ache less or joints move smoother, is adopted almost immediately and rarely revert back.

Sometimes, my head would interfere in that pattern due to fear. But that fear came from history of injuries, not age.

 

[Kneale Brownson]

That's interesting.

A Canadian demo team member told us he uses light contact with the front of the boot all the time as a reference point. Do my level best to copy that.

Guess it depends on how big the movement is between contact at the front and contact at the back. If it is a narrow then no contact is a good reference point. If it is large then maybe not so good.

I want my boots to contact the leg all the way around when I stand upright. I want to feel the shin/tongue contact specifically while skiing, which may mean there's a tiny gap at the calf.

 

[Seldomski]

COM = Center of Mass, a point, but not a fixed point since our bodies bend and twist ... it's usually somewhere in the middle of the torso
BoS = Base of Support, fancy way of saying the feet, or the foot, or somewhere between the two, depending....

COM is an abstract mathematical concept. The COM is not fixed in the torso - it depends on the configuration of your joints and your unique physiology. In other words, your body position or stance determines where the COM 'point' is located for your own unique body type. You can also have your COM in the right place fore/aft, but get there by contorting in various ways that are not correct (i.e. butt back and hands forward). You may feel the calf on the back of the boot if you are contorting in that way.

I don't think about my COM. I think about stance. I sense this through proprioception of my joints. And as others mentioned, by whether I feel the tongue of the boot (basically this sets the shin angle relative to the skis). I think proper stance is very dependent on good instruction/coaching - unless you are a 'natural' and know how to stand. A coach is essential in helping a student understand what proper stance feels and looks like, since the student cannot see his/her own body position in real time while skiing. I think it is more useful to think of stance rather than COM while skiing. I'm not saying the concept of COM is useless - just that it is not really helpful for me to think about vs. maintaining 'good stance.' There is not just one static 'good' stance. But there is a normal ready position I am trying to get back to at the finish of each turn that is the easiest launching point from with to adapt to forces during the next turn.

Base of Support I think is something you can describe in words and relatively simple diagrams. It is often mentioned in this forum. Basically the sensation of pressure on the foot, and where that pressure should be at various parts of the turn - ie toward the ball or the arch. Also, the balance of pressure between feet. I do use the sensation of the feet and make adjustments while skiing. Proper stance is something I have difficulty maintaining - it is harder for me to be mindful of it.

 

[LiquidFeet]

I didn’t find embedding new motor skills particularly harder at my advanced age...

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

 

[JESinstr]

The way Mikaela does this drill, you can really see the effect of tipping the new inside foot--once she does it, which is a bit delayed.

The reason you see the tipping as being delayed is because first and foremost, the inside leg needs to soften then shorten. THEN matching the building edge angles of the outside ski. Obviously in this drill the inside ski is intentionally lifted to assure complete focus on getting the COM over the outside ski BOS (see, I am in keeping with the theme of this thread!) and then a smooth and patient creation of angles beginning with the rolling of the outside ski. Don't get me wrong, the inside leg plays a key role in directional guidance but it plays a more important role in promoting angulation aka higher edge angles by the outside ski.

 

[Rod9301]

The reason you see the tipping as being delayed is because first and foremost, the inside leg needs to soften then shorten. THEN matching the building edge angles of the outside ski. Obviously in this drill the inside ski is intentionally lifted to assure complete focus on getting the COM over the outside ski BOS (see, I am in keeping with the theme of this thread!) and then a smooth and patient creation of angles beginning with the rolling of the outside ski. Don't get me wrong, the inside leg plays a key role in directional guidance but it plays a more important role in promoting angulation aka higher edge angles by the outside ski.

You don't begin by rolling the outside ski, but by tipping the inside.

That's a very big thing.

 

[JESinstr]

You don't begin by rolling the outside ski, but by tipping the inside.

That's a very big thing.

So let me get this straight....you focus first on the ski that will not be the doing the heavy lifting? Are you advocating hooking the inside ski? Any movement of the COM to the inside be it via pelvis, upper Mass or legs needs to be in support of the Centripetal force being generated by the outside ski.

I know many get initiation confidence by rolling their inside ankle into the new turn but it has the potential of inhibiting the proper loading of the outside ski. It is only post fall line/Apex when the inside ski engages in a meaningful way and helps complete the turn while at the same time provides a BOS for moving into the next turn. Ref the get over it drill.

 

[ToddW]

So let me get this straight....you focus first on the ski that will not be the doing the heavy lifting? Are you advocating hooking the inside ski?

<snip> ... It is only post fall line/Apex when the inside ski engages in a meaningful way and helps complete the turn <snip>

He means exactly what he said -- "You don't begin by rolling the outside ski, but by tipping the inside. That's a very big thing."

One can tip the inside ski when it's in contact with the snow or when it is lifted off of the snow. Both are effective, so "hooking the inside ski" isn't the focus. This is the first I've heard that the inside ski can't engage in a meaningful way until after the fall line ... maybe ignorance is bliss in the case.