Tim McMichael wrote: I reasoned it out this way. I know that if you hang a 45 pound plate from a foot long rope attached to the top of a 16' pole and then raise the pole to vertical with the end anchored in the box, it will take a lot of force to do this. If you take that same weight and hang it from a four foot rope, it will take much less force. If we look at the chord of the pole as simply a stiff pole that must be rotated to vertical, then the COM can be looked at as the weight hanging from the rope. The lower the COM in relation to the chord of the pole, the less energy is needed to rotate the pole to vertical. This means a higher grip and faster pole speed.
Very true.
Tim McMichael wrote: I guess it would be more accurate to say that the low COM doesn't add energy like a fast swing does, it transfers the energy from the run more efficiently into the system.
That's what I was getting at. It doesn't ADD energy; it only CONSERVES energy.
But does it conserve more energy than a Petrov vaulter that has a higher takeoff angle; doesn't drop his lead knee; and meets the criteria for the Theory of Continuous Motion?
There are two areas of potential delay in the Drive Model: (1) the "
hang time" - instead of continuosly raising the COM; and (2) the pause in the flatback position whilst tucking/rocking back to a full inversion.
Tim McMichael wrote: I think this is why every great vaulter of the stiff pole era dropped their lead knee at takeoff.
Agreed. But it would also have been counter-productive to leave their lead knee up, because their poles didn't sink/bend to give them the time and space to invert with a shorter chord. Agree?
Tim McMichael wrote: There have been plenty of fantastic vaulters in our time who do exactly the same thing. Hooker and Lobinger come to mind. Lavillenie is the first vaulter in the history of the sport to have a free takeoff and a low lead knee while also aggressively swinging the trail leg.
Yes. The differences that I've noticed between Petrov Model and non-Petrov are (1) the speed of the swing; (2) the ability to invert sooner; and (3) the amount of pause while waiting for the pole to roll to vertical. And I think we should completely ignore those vaulters (like Okert Brits) that forced the bend to start prior to takeoff SIGNIFICANTLY, and INTENTIONALLY.
Tim McMichael wrote: KirkB wrote: Let's take the simplest case, where the vaulter's body is locked (frozen) for a few moments without any motion in his arms or legs.
I didn't mean to imply that RL intentionally locked his bottom arm. You've already clarified that. I was merely trying to take a hypothetical situation (just as GV did with his stickmen) to make my point that once you leave the ground, staying low doesn't ADD energy to the vault; it merely PRESERVES energy. I've now made that point, and you've clarified what you meant about this.
Tim McMichael wrote: Locking the body in place isn't what keeps the COM low. Lowering the lead knee and keeping the hips as far behind the chord as possible
while swinging is what does the trick. Your example is still relevant though. The vast majority of vaulters penetrate further when they don't swing than when they do. The tiny fraction of vaulters who penetrate more when they finish the vault either have a free takeoff and an aggressive swing. (Petrov) Or they have found a way to keep their COM low and behind the pole while they swing. (Drive and Tuck) Or they do both and set the world record. (Lavillenie)
And this gets us to the "
gotcha" that I've always considered to be the flaw in a double-leg swing ...
Most Drive Model vaulters (yourself included) stay so low that they must tuck in order to let the pole catch up (in its rotation to vertical). I'm not against swinging low. In fact, I wish the vaulter could swing low (to gain the obvious advantage that you yourself discovered, and that's clearly shown in the Old School vid from Art of the Vault), but then somehow quickly invert without stalling out. That seemed to me to be impossible for a couple reasons: (1) the strength and coordination needed to do it; and (2) the inevitable stall that occurs after hanging low. I agree that RL has now done the impossible, so it's now back to being possible!
But isn't it ironic that the theory (that you've explained, and that's also explained on the vid) of why staying low is a GOOD THING (for Drive Model vaulters and Old School stiff pole vaulters alike) actually has THE FLAW OF THE PAUSE in it?
I mean, you (a Drive vaulter) want to stay low (presumably because if you keep your lead knee up you won't penetrate as much); yet when you stay low, you've lost the time needed to invert without tucking, forcing a pause so the pole can catch up.
Or to say it another way, if you swung long (without tucking) as Bubka did, then you would stall out (the pole wouldn't roll all the way to vertical).
If you understand this quandry, please explain. My current position on this quandry is that I like the lower COM that a double-leg swing gives you, but not at the expense of pausing in the tuck.
Thanks for the vid, and thanks to Coach Eric and Dave Butler (Art of the Vault) for publishing it. Very cool.
Starting at 4:34, the instructor states: "
The highest grip that the vaulter can utilize is one that just permits the pole to reach the vertical. In any vault, the energy of the run and takeoff can be used to raise the body to a particular height. At maximum grip, that height should be reached when the pole approaches the vertical. The maximum grip of the vaulter will depend on the efficiency of his form, running speed, and his height. In this case, the line of dots represents the height to which the body weight can be swung. So far, the string has been hanging freely. This time we will shorten the string to see what happens. Now with the string shortened, and weight closer to the pole, we continue to raise the pole. With the amount of energy at his disposal, the forwards energy of the pole must stop when the weight has reached the height of the dots. The answer is clear that the vaulter must hang. In this way, he keeps his CoG low during the swing, and permits the pole to approach the vertical. The takeoff is the most important part of his vault. "
Sidebar: Notice that at 5:40, you can see that this steel pole actually bends slightly. This type of bend was even more pronounced with bamboo poles, and was a well-known phenomenon in the 1950s and 1960s. Bamboo poles preceded steel poles, and were actually more desirable due to this property. However, steel poles became more popular because they could be built more consistently, without fear of breakage, and to more stringent and more consistent flexes than having to find a series of bamboo poles with similar flexes.
Back to keeping the COM low by dropping the lead knee ...
Relevant to the Old School (stiff pole) Model shown in the vid, they had less choice than us fiber pole vaulters, because their poles didn't bend (nearly as much). So their COM traveled a much straighter line than ours (which is one good reason why they didn't vault as high as us). Whether the Petrov Model; Drive Model; RL Model; or Barber Model (yes, that's what Shawn's dad George has named his model), we could (and we did) control the path of our COM with greater precision than them. And (ignoring all the other reasons for now) some of us chose to keep the lead knee up (to swing faster; to add energy to the vaulter-pole system; and to invert quicker); and some of us chose an even lower (and more curved) path for our COM (to gain the advantage explained in the Old School vid; which was later re-discovered by yourself and others).
I've already asked this question 100 times (but still no good answer): Please help me to understand how RL can (1) have a free take-off; (2) get a good, low swing; and (3) invert quickly enough without much - if any - pause.
Kirk