Balance and Weight Commitment
Ken’s Story
I have to admit that this committed balance idea is not a "secret". I have seen it in several books and videos, as well as every coaching situation I've been exposed to. But it is tricky -- easy to overlook and not so easy to learn -- and it's so fundamental to good classic striding that I felt I had to include it in this list of "secrets. I already had pretty good general balance from years of backcountry and downhill skiing. So when I found out that balance was important for classic striding, I was eager to learn and practice another variety of it. Actually I thought there would be nothing to learn. But this turned out to be incorrect. Most of my other one-ski balance experience was on either the inside edge or the outside edge of the ski. But for the classic glide phase I had to learn to balance on a flat ski. This harder to me, because that there are two things that can go wrong: (1) falling over on or "catching" the inside edge; and (2) falling over on or "catching" the outside edge. So it turned out that I did have to spend a lot of time practicing this specific balance, which I did on rollerskis during the summer and fall. When I got to the on-snow camp at Silver Star and they videotaped my classic striding, the instructors said I had good weight transfer and no obvious balance problems. They also gave me some helpful on-snow exercises, and those helped me get the balance even more solid. And I think getting that foundation made it easy for me to learn and experiment with other things.
Why this is critical
Here are some at-home experiments to help learn the basic physics of grip and weight transfer.
Weight commitment and grip friction
Experiment 1: grip and body weight
1) Set a dinner plate on the top surface a flat table or kitchen counter. Slide it with your hand, and feel how much force it takes.
2) Take a medium-size cooking pot with a long handle sticking out from its side and fill it mostly with water. Place this pot centered upon the plate. Slide the plate with your hand, and feel how much force it takes.
4) Remove the pot from the plate. Slide the plate with your hand, and feel how much force it takes now.
I expect you'll notice that it is much easier to slide the plate without the weight of the pot on it.
Conclusion: The degree of grip or "friction" of a thing sliding on a surface is strongly related to how much downward force or weight is bearing down through the thing. That's why transferring my whole body weight over to my current leg-push ski gives me the most grip against the snow.
Experiment 2: complete weight transfer
1) Put the pot with water back upon the dinner plate. Slide the plate with your hand, and feel how much force it takes.
2) Find a drinking cup tall enough to lift the long handle of the pot just a little.
3) Rest the long handle of the pot on top of the cup, so the handle is lifted a little, but the body of the pot is still resting upon the dinner plate. Slide the plate with your hand, and feel how much force it takes now.
I expect you'll notice that is a little easier to slide the plate with the handle of the pot resting on the cup -- even though the weight of the pot and its water really are upon the dinner plate. It still takes more force to slide the plate than with no pot resting on it at all, but not as much as with no cup under the handle.
Conclusion: Even if I really transfer my body weight over to my leg-push ski, if I am also resting a little on something else -- like my pole or my other ski -- then it's a little easier for my ski to slip back when I do my leg-push "kick" on it. So if I can eliminate that little "rest on something else", I will get better grip.
Implication: That's why it's important to practice really solid balance on a single ski -- so I'm not tempted to "rest" a little on my other ski or a vertical pole for support -- like the handle of the pot on the cup.
Dynamic Down-force
Experiment 3: basic dynamic down-force
This next experiment requires a bathroom scale to numerically measure body weight -- and it may help to have a second person to observer the readings of the scale as they rapidly change.
1) Stand on the scale with both feet. Notice what the weight number on the scale is.
2) Jump straight up a little with both feet -- so your upper body goes up too. Which way does the weight number go in the first instant you do that -- up or down? I expect you (or your observer helper) will observe the weight number go initially up.
3) Suddenly push both feet down hard (while trying to hold your upper body stable). Which way does the weight number go in the first instant you do that -- up or down? I expect you will observe the weight number go initially up.
4) Suddenly pull both feet up under you quickly (while trying to hold your upper body stable). Which way does the weight number go in the first instant you do that -- up or down? I expect you will observe the weight number go initially down.
Conclusion: I can increase my "effective weight" or down-force bearing through the ski to the snow either by suddenly pressing my foot down, or by hopping my whole body up a little. If I do this at the same time as my leg-push, it will improve my grip.
Experiment 4: side effects of dynamic down-force
This is the experiment where it could be really valuable to have a second person to observe the weight number on the bathroom scale.
1) Stand on the scale with both feet. Notice what the weight number on the scale is.
2) Jump straight up a little with both feet -- so your upper body goes up too. What is the sequence of changes in the weight number? I hope your observer partner can observe this sequence of the weight number readings from the scale: (1) initially up, (2) then down, (3) again up.
3) Suddenly push both feet down hard (while trying to hold your upper body stable). What is the sequence of changes in the weight number? I hope your observer partner can observe (again) this sequence of the weight number readings: (1) initially up, (2) then down, (3) again up.
4) Stand on one leg (on the floor instead of the scale) and use your leg to do repeated little up-and-down movements to move your upper body up and down. How long can you keep doing this before you notice fatigue?
Conclusion: The use of dynamic down-force is more complicated than it at first seemed. Notice that:
If I tried to do my next leg-push quickly, right after the current leg-push, it might overlap with the phase in which my "effective weight" or down-force has decreased, which could make my ski slip back.
If step (3) of the sequence of changes in "effective weight" falls in my glide phase, then it increases my gliding friction, which hinders my speed and efficiency.
There is a muscular cost to repeatedly applying dynamic down-force for an hour or two of skiing.
Compare: Weight transfer Versus Dynamic down-force
Here are some advantages of making side-to-side weight transfer my main normal technique for getting grip for my leg-push:
I have to carry my body weight around anyway, so I should be glad to use it for some beneficial purpose.
Side-to-side weight transfer has lower muscular cost than dynamic down-force. Side-to-side still has some energy cost, but generally less. And dynamic down-force uses muscles in ways similar to their other work in Classic striding -- so it concentrates the muscle stress in a single "mode".
Dynamic down-force introduces the complexity of additional side effects. It could reduce the speed and efficiency of my glide phase.
Implication: That's why it makes sense to learn side-to-side weight transfer as the main base technique, and reserve dynamic down-force for special situations where it's really needed.