Powerplant42, Linthorne's paper might help you shed some light on this. I know his scientific papers have been discussed on several PVP threads in the past, but all prior to my involvement, and all with a slightly different focus, so pardon any repetition ...
Here's a THIRD excellent source of some expertise on this "optimum take-off point" discussion. I think it BEGINS TO explain what Vaulterboy is saying
"your hands have moved your takeoff 6 inches back".http://people.brunel.ac.uk/~spstnpl/Publications/PoleVault(Linthorne).pdf (This URL wasn't highlighted properly, until I wrapped it with the
URL button (directly above your edit window - when you're editing a post.)
The title of this paper is
"Energy loss in the pole vault take-off and the advantage of the flexible pole" - Nicholas P. Linthorne (c) 2000.
He also publishes his entire algorithm here :
J9. Linthorne N.P. "Mathematical model of the takeoff phase in the pole vault" Journal of Applied Biomechanics 10 (4) 323–334 (1994). (Abstract) (Publisher) As an aside, I wish I had good references like this when I was vaulting. All I had was
"Mechanics of the Pole Vault" - Dr. Richard Ganslen, and unfortunately, some of his stuff was just wrong - such as pressing with the bottom arm. That misinformation continues to haunt many modern-day vaulters - from the high-school level right thru to the elite vaulters.
So today, you guys HAVE these scientific resources, so USE THEM!
One thing interesting (and surprising) that I found in this paper was that Linthorne concluded that the optimal takeoff angle for a world-class fiberglass vaulter is 18° (compared to 30° for a steel vaulter).
This conclusion is supported by scientific evidence. He developed a software algorithm to compare various combinations of vault height, grip, push height, take-off angle, take-off velocity, and pole stiffness. He then plotted this output graphically, and compared it to the parameters of known world-class vaults. He references all of his sources in typical scientific paper style. In other words, it's scientifically sound - no conjecture; no opinions; no biases. Just sound scientific evidence. I like that!
The present paper proposes a mathematical model of pole vaulting that includes the
relation between the take-off angle and the takeoff velocity, and accounts for the energy losses in the pole plant and take-off phases of the vault. The aim was to produce a model that accurately predicts the optimum combination of take-off velocity, take-off angle, pole stiffness, and grip height for a typical world-class pole vaulter.
I underlined the part that relates to "what the hands are doing".
He asserts that there's 2 aspects of the advantage of fiberglass over steel. 1. higher grip. 2.
lower takeoff angle. We all know the first one. The second one surprised me, as I'd never ever read a scientific study on this before last weekend. Read on ...
The most credible explanation for the higher grips when using a flexible pole is that the pole reduces the shock experienced by the vaulter, and so less energy is dissipated in the vaulter's body during the take-off ... The vaulter therefore has a higher take-off velocity, and is able to rotate a longer pole to vertical.
... and ...
Linthorne (1994) noted that the take-off angles for vaulters using fibreglass poles are lower than for vaulters using bamboo or steel poles ... He suggested that part of the contribution to the advantage of a flexible pole may be that the optimum take-off angle is lower, and so the vaulter does not lose as much kinetic energy when jumping up at take-off.
That makes perfect sense to me!
There is a reduction in velocity when the vaulter plants the take-off leg and jumps up off the ground, and a further reduction when the vaulter plants the pole into the take-off box. In this model, the energy loss associated with the vaulter's jump is separated from that of the pole plant, even though in practice these two events usually occur simultaneously. Here, take-off velocity refers to the velocity as the vaulter jumps up off the ground, just before planting the pole into the take-off box.
Note the sequence: Jump; then Impact. (i.e. if you define the final point of the plant as the point in time when the pole impacts the box, then Linthorne's assuming "Jump off the ground first; then Impact the back of the box" - the same as Baggett and Launder.
... the description of the pole plant phase of the vault was revised to include a mechanism for dissipation of energy in the vaulter's body.
Now we're getting to "what the hands are doing" ...
As the pole is planted into the take-off box, the vaulter attempts to maintain the orientation of the arms and torso through muscular activation, but the force exerted by the pole is too great, and so the vaulter's arms are deflected backward relative to the shoulders, and the vaulter's torso is deflected backward relative to the hips. Work is done by the pole in reorienting the vaulter's body against its muscular forces. Some of the vaulter's kinetic energy is therefore dissipated as heat in the vaulter's muscles. Energy may also be dissipated by inelastic stretching of the tendons and ligaments as the body is hyperextended.
This "heat" and "inelastic stretching" is what I shorten to "leakage". And then ...
During the take-off, the relative deflection of the pole is usually less than a few percent, and so the force exerted by the pole on the vaulter is approximately equal to the Euler buckling load ...
... so he includes "leakage" in his algorithm, using the "Euler buckling load" formula ...
When vaulting with a pole of high stiffness, the force exerted by the pole on the vaulter is larger, resulting in a more extreme deflection of the vaulter's body, and hence a greater dissipation of energy.
... and he also includes "pole stiffness" in his algorithm ...
The parameter k in Equation 3 characterizes the 'stiffness' of the vaulter's body in the pole plant phase of the vault. The value of k reflects the level of resistance of the vaulter's arms and torso to being deflected backward relative to the hips by the pole.
... and he also includes "additional leakage due to the rigidity of the vaulter's body on impact" into his algorithm. This point is also stressed by Launder in BTB2, and by Agapit. i.e. Minimize leakage by eliminating passive phases and by not "dropping the lead knee" and by not "crumbling on impact" (my words - not theirs).
So there you have it! Clear as mud?
I've purposely just quoted snippets to give you the gist of this paper. I hope this is sufficiently interesting to inspire you to read the full paper. Only then can you begin to digest and understand this "Jump." (i.e. takeoff) part of the vault more fully.
I still don't think
"what the hands are doing" is fully explained by Linthorne. He only alludes to it a bit. But his paper is a good starting point to our discussion about this. He puts it into the framework of understanding (and minimizing) energy losses when the pole hits the box - and why that's important (CRITICAL!) to the efficiency of the Petrov model.
Do you resist the top hand going back or not? If so, how much, and when?
But I think this is a good start to zeroing in on that unanswered question.
"What the top hand (and shoulder ... and chest ...) is doing" just after takeoff is just as important as what the trail leg foot is doing. It all happens within a split second after takeoff! And as Vaulterboy suggests, it does affect your target takeoff point!
Kirk
