Physics Based Critique of the Petrov Method

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tsorenson
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Re: Physics Based Critique of the Petrov Method

Unread postby tsorenson » Thu Apr 10, 2014 7:47 pm

I have greatly enjoyed this thread. Thanks for rejuvinating my desire to participate in this website!

I am very impressed with the physics-based analysis by PVstudent, which nicely explains the Petrov method, in the way I understand it as a vaulter/coach/scientist. I also have enjoyed willrieffer's posts, which present a viewpoint shared by many PV coaches and athletes, and which ask a lot of good questions.

I feel that there is a simple reason to support coaching a free takeoff, which actually ties together both sides of the argument, while explaining Bubka's quotes, as well as the empirical evidence cited by willr and others showing that many good vaults did not employ a free takeoff:

You don't always hit what you are shooting for. This is a reality in all sports...e.g. every hitter would love to hit the ball every at-bat. But they don't. .400 batting average is a hall-of-famer!

The fact is, every vaulter would love to get their average take-off point farther from the box, so that they can grip higher (assuming they have the posture, technique, and energy to support this). Petrov et al have described a specific run/carry/plant/takeoff that helps achieve this goal. Altius, et al, and others have explained drills that assist in teaching this method. You shoot for a free takeoff, which helps you get your step out and grip up. Sometimes it happens, sometimes it doesn't. If you take off under all the time, good luck raising your grip!

Perhaps we should be looking for common traits between Lavillenie and Bubka: Lavillenie just broke the WR, and everyone is trying to dissect his double-leg swing/tuck/etc, and assuming it must be better than the petrov method. What they should be noticing is that he is now consistently taking off outside 14', just like Bubka did! Most elite vaulters are lucky to take off at 13'6, and so become increasingly under as they try to raise grip height. Good luck gripping 17' taking off at 12'6!!
Other common traits can be found between Renaud and Sergei, and are worth focusing on.

Thanks for the great discussion,

Tom

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Re: Physics Based Critique of the Petrov Method

Unread postby ADTF Academy » Fri Apr 11, 2014 9:31 am

PVstudent wrote:Thank you ADTF Academy for the pictures.

On the basis of this evidence in regard to the take-off in question I remain skeptical that the fail was due to an “out” take-off.

To be fair, the public domain evidence is perhaps lacking sufficient quality and hence unable to unequivocally resolve the issue.




The fact the pole bounced out of the box and is stick in the pits is what probably caused the crash to occur. The pole ended up outside the box stuck in the mats..... I'll get an exact quote from Renaud at Drake if he was under or out on the crash. Will that work for you?

Everything doesn't have to be scientifically explain its pretty easy. Pole not in box = bad....

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Fri Apr 11, 2014 12:33 pm

tsorenson wrote:
I feel that there is a simple reason to support coaching a free takeoff, which actually ties together both sides of the argument, while explaining Bubka's quotes, as well as the empirical evidence cited by willr and others showing that many good vaults did not employ a free takeoff:

You don't always hit what you are shooting for. This is a reality in all sports...e.g. every hitter would love to hit the ball every at-bat. But they don't. .400 batting average is a hall-of-famer!

The fact is, every vaulter would love to get their average take-off point farther from the box, so that they can grip higher (assuming they have the posture, technique, and energy to support this). Petrov et al have described a specific run/carry/plant/takeoff that helps achieve this goal. Altius, et al, and others have explained drills that assist in teaching this method. You shoot for a free takeoff, which helps you get your step out and grip up. Sometimes it happens, sometimes it doesn't. If you take off under all the time, good luck raising your grip!

Perhaps we should be looking for common traits between Lavillenie and Bubka: Lavillenie just broke the WR, and everyone is trying to dissect his double-leg swing/tuck/etc, and assuming it must be better than the petrov method. What they should be noticing is that he is now consistently taking off outside 14', just like Bubka did! Most elite vaulters are lucky to take off at 13'6, and so become increasingly under as they try to raise grip height. Good luck gripping 17' taking off at 12'6!!
Other common traits can be found between Renaud and Sergei, and are worth focusing on.

Thanks for the great discussion,

Tom


I have from the start advocated that at least the Petrovian take off model has merits based on what you comment on here. In fact this is from my last post...

I find the idea of it precludes me ever thinking at this point the the Petrovian method and model are ideally superior. In a competition environment more actually reliable? Almost certainly so...


I work with HS vaulters and I use this method for these same reasons. What does this say again? From a purely physics standpoint I cannot advocate that it offers the most system energy at take off, a very important consideration, but again that I value the trade off in consistency for a competition environment and especially safety for beginning vaulters.

To be honest take off approach may be the only place I can find any co-incidence between the two world record holders. Lavillenie is a straight left arm lockout, double leg swing, "tuck" vaulter after that. His left use causes better hip placement affording a point to hold them even further back and pressed down. The double by lowering the CoM retards the swing for a better placement of the CoM to the gravity vector through the compression phase. By this method and by gravity he puts more energy in the pole. To get out he has to radically alter his swing rotation with the "tuck". That he stays back further longer makes his "tuck" appear earlier in the swing progression than many who use the method. It's not a part of his getting ready to extend after the hips have passed the pole, its necessary to get there in the first place! In some sense he tries to approach the late Petrov in that he doesn't effect to "reach back" with the "tuck" but simply needs it get to the angle of extension and begins working his CoM up as soon as he can. This again is how, despite being shorter and slower than Bubka he can generate similar heights. He puts more energy in the pole for longer and is able to reclaim it later. Physics says something like this must be happening. Since he has less velocity and less initial pole angle he has to be making up for it somehow either by getting more energy into the system i.e. pole, and/or by directing it better.

Yet I want to mention something here again. I've come to many of my conclusions by watching a lot of beginning vaulters challenged by the vault. And the thing which sticks out most is that hip/CoM placement is what kills almost every vault. They pull up. They tilt the torso forward either by shooting them up into the vault or by something so much as throwing the head back. They fail to reach back with the take off leg and "kick" it causing a radial moment that pulls the hips back and down. Logically then, if these actions are made "bad" by a physics you can't cheat, then we should explore their opposite as possibly being good. You want the hips back and down as much as possible towards the limit of getting them back forward in time. It presses the length of the swing rotation, not from the top hand so much as from the forward hand to the take off foot allowing it to be pressed to even greater length sooner in creating the take off foot swing moment*. IF I see progressed hips/swing progression killing vaults by presenting a bad relation to gravity and allowing it to pull energy out of the swing and add less to pole compression, then again, its opposite should be beneficial. Bubka, the Petrovians, were actually aware of such things and in fact they were very very good at placing the hips by the "free" take off, yet now I feel they missed an opportunity to press the hips back and down to their fullest extent in the manner Lavillenie employs. Or, now it seems some are just better...

*So far as I know I'm the only one who has interest in the front hand, hip, take off foot axis as a means to press the swing back and down and as a means to maximize the effect of the take off foot kick. This, I find has a two fold effect. It again works the hips back and also works to maximize the kick impetus at its greatest radial length. If there are others and anyone can point such out I would be grateful.

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Re: Physics Based Critique of the Petrov Method

Unread postby tsorenson » Fri Apr 11, 2014 3:52 pm

To be honest take off approach may be the only place I can find any co-incidence between the two world record holders.


My point exactly! That is why Petrov and his supporters (including me) talk much more about the minutiae of the approach/takeoff than anything else. Lavillenie has improved his approach, posture, and takeoff a lot in the last few years, I seem to remember reading that his new coach has only focused on that element and let the rest take care of itself. The only other change I have seen is that he does not get stuck at the bottom like he used to; he allows the (double-leg, then tucked) swing to progress more naturally and gets off the pole as soon as possible (like Bubka). This creates a more "sinusoidal" curve to the path his COM travels through the vault. He used to have a more "exponential" curve, which gave him great height but little penetration...I seem to remember him landing on the bar a lot after being way over it; now he lands deep every time, with the obvious exception of his 6.20 attempt. On that note, I have found that vaulters who break a big record followed by celebration rarely have good jumps if they continue vaulting...the adrenaline is spent! Renaud is an exception to the rule in many cases, but I used this as an example to the kids I coach that sometimes it is OK to call it a day!

If you have a free takeoff (by default I mean this in ADTF's context...the whole package) it is good to let your swing progress naturally, since the position of the hips is already back, whereas if you are under your hips are forward, and you must resist more to keep them back at the expense of forward/upward momentum. Having said that, the most important petrov drill I use is the 3 step-stiff pole-stay behind drill, with an emphasis on maximizing grip height and never allowing jumpers to be under. This self-correcting drill teaches the aspects of hip placement, plant mechanics, takeoff, and posture without having to explain it. Cheers to Baggett for teaching me that one!

Thanks again for the good dialogue.

Tom

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Re: Physics Based Critique of the Petrov Method

Unread postby grandevaulter » Fri Apr 11, 2014 7:56 pm

My physics based analysis:
Example 1. An underdeveloped 8th grader takes off under, pole hits the back of the box and she jumps. Pole bends and swing is inhibited.

2. An underdeveloped 8th grader takes off out and jumps before pole/box impact. Swing is dynamic, pole bends early and unbends early. (I'm not sure if the plant was synchronized, so I'll call it a pre jump and not a free takeoff)

This I believe to be true to my best recollection. It happened this morning, but I may have forgotten it already.

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Sat Apr 12, 2014 12:48 pm

Just as a point of reference. This is the 8th grade boy I am working with...and this plant makes me giddy! Really, I've only had about 4 sessions with him (he had to sit out the beginning of the season with a foot injury). I also have a 9th grader who has gone from 8' last year to 10' 6" already this year and who is just beginning to have a swing. By next year I'm hoping to have 3 boys and at least 2 girls, 4 of which will be either 9th or 10th graders at the 2A MO state meet...
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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Mon Apr 14, 2014 12:57 am

Image

PVstudent wrote:What occurs post take-off must meet the continuous on going challenge imposed by non conservative forces acting on the pole plus vaulter total system (see attachment below).

The Bubka performances in meeting these challenges has been recorded and studied using scientifically valid and reliable methods. An example from competition shows that Bubka was superior to other competitors on this occasion at doing work during the pole suport bending and recoil phases.

The graph of the energy exchanges shows indisputably that Bubka added energy to the total system and was able to use the total kinetic energy gain to enhance his flight height, rotation and flight trajectory following pole release (attachment below).

In this graph observing the changing course of the vaulter’s potential energy curve the greatest rate of increase in potential energy, due to height above the ground, occurs when the pole is straight and just prior to the total kinetic energy peak.

Note also that the the pole suport phase kinetic energy minimum occurs a very short interval of time after the vaulter’s total energy is at its minimum.

Throughout the pole support phases (pre maximimum pole bend to pole release) the potential energy of the vaulter is smoothly increasing. This is happening despite the vaulter losing total energy with peak loss occuring coincident with maximum pole bend! Of course this energy loss is that which produces the bend in the pole to overcoming the resisting “stiffness” of the pole deflection. Yet the the vaulter’s centre of mass inexorably continues to gain height! Why?

I assert, without proof, that Bubka most probably worked on the pole to direct the swing created energy (a vaulter is not a rigid body!) to move the total system COM continuously upwards and forward.

If Bubka’s COM is continuously rising upwards (as shown on the graph) he MUST have been actively doing work whilst suspended from and supported on the pole. If he was not doing so the potential energy would peak and decrease due to the continuously acting downward acceleration effect of gravity.


willrieffer wrote:The Graph

My intuitive physics sense is going bonkers. Or, you are going to have to tell me how these numbers were derived. Kinetic Energy is easy enough, measure his velocity and mass. I take it potential energy is his CoM over ground height. Total Energy then would seem to be the difference in the loss in Kinetic energy (measured forward velocity reduction) versus the gain in Potential Energy derived from the change in height. It is of no surprise that CoM goes up throughout the vault. All vaulters go up continuously, and so change of rate in it is of greater importance. IF that IS the case, I must say that this is not enough parameters, notably because energy goes into the pole and so in this case the Total Energy calculation seems to be ignoring this effect. That its quite possible energy is maximized at max pole bend and actually declines by the completion of the vault. Further, my point in total is that the end energy increase comes at least in part, and I might guess in magnitude of importance mostly from the vaulters early relation to gravity being added to pole energy and thus is present in the outcome increase*. Is Bubka's added mechanical energy in there? No doubt it is, but I find it incredulous that he could add something on the order of 2000 to 3000 joules to the vault in the very short time indicated with only his handgrips as a contact point to the pole and system and especially when we consider that his legendary speed at take off only yields a little over 3000j (I calculate a max around 3600j) in KE generated over a much longer time by his powerful legs working over the full length of his run. If I took your outlook on this graph to a literal extreme it might well be telling me not worry when my young vaulters "pull" up early on the pole because they are just adding increased potential energy through their mechanical work! There are many many interesting things here which are in need of illumination. The rabbit hole deepens...

* IF you want to think about gravities presence in the vault in relation to the pole and its energy just think of this. Imagine you take the tip end and somehow affix it so that the pole is held parallel to the ground. Now imagine that the vaulter grabs the pole with his top hand about where he places it when he vaults and hangs down on the parallel pole. It is of course going to deflect and store energy in its elasticity. This effect occurs to some degree throughout the compression phase in a very complex relation between the vaulter, the pole, and gravity, and since the pole ends straight, it must come out redirected into the vaulter in the end. How and to what degree this effect happens in relation to the vaulter, their take off and swing, are of great importance to me. And its my contention that Lavillenie uses the gravity vector in his vault, especially early in his vault ultimately better than even the Petrovian's, which is why he can be smaller and slower than Bubka while also breaking his indoor world record.


And so I reiterate. People with these systems, and indeed when talking about the pole vault in general when it pertains to a successful vaulter or successful system, can and do have a tendency to make claims based on "physics" which are in fact based on gross errors in the understanding of physics, i.e. you cannot have a "Total Energy" curve and leave out pole energy! , and then go on to make claims about what the vaulter is doing, and what advantages the system contains.

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Re: Physics Based Critique of the Petrov Method

Unread postby PVstudent » Mon Apr 14, 2014 9:31 am

And so I reiterate. People with these systems, and indeed when talking about the pole vault in general when it pertains to a successful vaulter or successful system, can and do have a tendency to make claims based on "physics" which are in fact based on gross errors in the understanding of physics, i.e. you cannot have a "Total Energy" curve and leave out pole energy! , and then go on to make claims about what the vaulter is doing, and what advantages the system contains.



Point 1. The graph is a correct representation of the energy exchanges of the VAULTER! It is not a graph of the energy transformations within the total system. It does not purport or claim to be for the total system.
Will, Get real! The situation was a world championship!

How do you collect the data on every vaulter’s pole and the pole changes from jump to jump and then to have access to all these vaulter’s poles before or after the competition and measure their energy storage and recoil capacities. This is required to be able to do what you are criticising, namely the energy exchanges within the total system of pole plus vaulter!

The vaulter on the other hand can be studied by means of high speed cinematography with minimal invasion of, or interference with the competitor or competition. The evidence of the measurable changes in the vaulter’s recorded motion did enable the energy exchanges of the vaulter to be validly obtained and the data properly presented in graphical form.

Point 2. Will, look again at the graph and read it properly from a physics perspective. Your interpretation of what the graph shows is, in my opinion, incorrect.

Point 3. Here is where I think you may be making a mistaken interpretation. Look at the kinetic energy curve of the VAULTER. Does the vaulter’s kinetic energy curve, or does it not, show a low point coincident with MAXIMUM Pole bend?

Thereafter the vaulter’s kinetic energy curve rises until it reaches a peak a short interval before the pole is straight and then declines at a steady rate until pole release.
Surely this rise MUST be due to recoil work done on the vaulter by the recoiling pole and the vaulter doing muscular work against the recoiling pole! (I am an old fashioned Classical Physics Newtonian!).

After pole release the vaulter’s kinetic energy then shows a steady decline, at a lesser rate until the vaulter’s centre of mass reaches peak height!
Note that vaulter’s kinetic energy is still above zero at this point.

This is because the vaulter still possesses constant horizontal translatory energy to which must be added his constant rotational kinetic energy. There is a portion of kinetic energy transformation from vaulter vertical kinetic energy into the vaulter’s potential energy increase following pole release as he loses vertical velocity. Therefore the kinetic energy curve will show a small decline which of course it does.

Now, let’s back track to the rise in the vaulter’s kinetic energy immediately following maximum pole bend. The rise can only be possible due to energy input from two possible sources, the vaulter or the release of the strain energy stored in the pole or both!

Clearly, in this case, it is both energy input sources!

Surely the vaulter must have received some of the stored energy from the pole and this is indirectly revealed in the graph shown.

However there is, in my view, the necessary and sufficient data upon which to draw the appropriate inference that the kinetic energy gain of the vaulter immediately following maximum pole bend is due to vaulter muscular effort in conjunction with some additional energy from the recoiling pole being transferred to the vaulter.

The problem of disentangling how much kinetic energy increase in the vaulter is from the pole and how much from the continuing muscular work of the vaulter on the recoiling pole cannot be fully resolved from this graph.

Will, if this is what you want to know the research effort required is prohibitive and calls for carefully controlled research under laboratory conditions with scientific control and manipulation of the independent variables. The data gathering in 3 dimensions, using motion recorders operating at quite high sampling rates, 3-D force and torque transducers in the pole, a force platform under the vaulter take-off and an instrumented planting box, getting athletes to participate, sample size, funding expertise and time make the whole effort questionable. Particularly when what we want to know as coaches is answerable empirically and is not rocket science!

To do this in a competition (see point one) requires the pole to be instrumented with torque and force transducers, as well as strain gauges and the outputs of these sensors telemetered and synchronised in real time to recorded motion of the vaulter on the pole. Feasibility of doing this in a World Championship, practical and economic challenges aside, is still remote.

The methods used by the researchers who performed the study from which this data is obtained were independent scientists appointed by the IAAF.
Here is the reference to the study:

GROS, H.J./KUNKEL, V. (1988): "Biomechanical Analysis of the Pole Vault", ... World Championships in Athletics Rome 1987,

Point 4. In the graph the Total Energy of the vaulter is the SUM of the Kinetic and Potential Energy of the vaulter as determined from data in frame by frame analysis of the vaulter’s motion obtained by cinematographic recordings from a number of cameras.

Point 5. The kinetic energy was calculated by the researchers by summing the translatory kinetic energy plus the rotational kinetic energies of the individual body segments of the vaulter (body segmental method). This method allowed the full summation of the vaulter’s total energy transformations throughout the vault.

Point 6. The actual total energy gain due to the muscular work of the vaulter is the difference between total vaulter energy at take-off and total vaulter energy at pole release which is about 1450 to 1500 Joules.

This MUST be so because the vaulter acting alone forced the bend in the pole thereby storing some strain energy some of which was recouped in the pole recoil phase. This is an interaction which must have some energy loss that is not doing useful work. Useful work is defined as the energy used to cause a force to displace an object (force x displacement) or a torque causing an object to undergo angular displacement (torque x angular displacement).

Note: if there is no force or torque induced object displacement then in physics by definition no work has been done! The vaulter will be expending some muscle energy in stabilizing some parts of the body which then do not move (isometric active muscle action) and hence no mechanical work has been done. Not all of the vaulter’s muscular effort can be transformed to do mechanical work and thus the vaulter must be also performing “physiological work” for no measurable mechanically observable output. In this regard the energy graph actually underestimates the physiological work demand and input from the vaulter.

Point 7. Despite what you keep insisting I have not really found anything that you have had to say so far invalidating anything I have presented in regard to the vaulter’s energy exchange shown in the graph I put up.

When the issues you have with “Bubka’s semantics” and as yet to be demonstrated physics errors, myths, half-truths, and hyperbole of “Petrovians” are put aside, there is in fact considerable shared ground.

Niggling away though is the issue of your understanding of how the “Petrov-Bubka Model of the “Free Take-off” may or may not optimise the capacity of the vaulter to produce equal to or even greater effective pole bend than that possible by inducing some pole bend before take-off.

You have presented anecdotal evidence by referring to a number of French, Russian vaulters, including Bubka, taking off with obvious pole bend before the take-off foot has left the ground. The question has to be asked was the vaulter in question trying to minimize pole loading resistance or optimizing pole bend before take-off? Ultimately we have to ask the vaulter to ascertain their intention.

Intention is a “psychological” factor and on this there is agreement.

Your critique is of the physics basis of the two techniques and has not as yet become clear to me. I can only speak for myself here.

Your practice as a coach and the general comments you make convince me that after toing and frowing on the “swings and roundabouts” your “intuition” is to lean towards the Petrov-Bubka Technical Model.

But please give us the physics rationale that backs up your intuition and why Petrov’s explanations are inadequate from your physics perspective?

The value I take from your contributions so far is the critical point that coach and vaulter have to understand and sensibly assess the potential gains and losses of these two possible take-offs.

Let’s move the discussion on and examine critically and specifically what your “critique” shows to be the deficiencies in the Petrov-Bubka Physics principles applied in “finishing the take-off” and how and why superior results can be, or not obtained by pre-bending the pole whilst the vaulter is still in the propulsive phase of ground contact!

I make no claims to the specific expertise of a physicist, but if my interpretation of the data shown in the vaulter energy exchange graph is insufficiently exact or wrong I would appreciate having my errors pointed out.

As other contributors point out we all need to be on the same page if we are to get anywhere!

I am hopeful that one of the outcomes might be to settle the push-pull issue.

I optimistically hope that if the discussion continues, the push – pull following the take-off can be explained and illustrate that Petrov and Roman Botcharnikov are not as far apart conceptually as we are led or would like to believe!
Every new opinion at its starting, is precisely a minority of one!

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Mon Apr 14, 2014 12:23 pm

PVstudent wrote:Point 6. The actual total energy gain due to the muscular work of the vaulter is the difference between total vaulter energy at take-off and total vaulter energy at pole release which is about 1450 to 1500 Joules.


I'm sorry, you just cannot make this claim, one which your whole assessment of this graph leans on without knowing the amount of energy in the pole at max bend, especially under the contention I have made that an element of this total pole energy at maximum comes from gravity effecting the compression of the pole and where I have shown how this is possible.

Indeed, why these ideas are still in contention is because of the reasons that you state. It's very hard to know pole energy levels, yet we know they exist. Can you say there is not a component that is gained from gravity and not returned when the pole has completed decompression?

It's not that the graph is wrong, its that its incomplete in such a way that its very limited in the insights that it can reveal and your conclusions take liberties specifically about the relation of the vaulter to the missing information. At best its labeled poorly and even if it were changed to "Total Vaulter Energy" it would still only lead to more difficult and important questions that I have pointed out.

As with many of our exchanges many of the things you say I agree with, some I find inconsequential, and others I find worth mentioning in argument.

PVstudent wrote:But please give us the physics rationale that backs up your intuition and why Petrov’s explanations are inadequate from your physics perspective?


Well, the whole thread is full of things. Let me bullet point them.

1) Positives. Their take off in intent and practice causes a highly beneficial relation to gravity in the early swing. It's also competitively functional as we agree that it should tend to create fewer bad and dangerous take offs and more good vaults

2) The minutia of this take off regarding its pre take off element and pole bend avoidance are at best in contention and on two levels. One is simply cohesion among its practitioners and adherents i.e. Bubka says this, you say Petrov says that. The other is in the actuality of the vaults and their actual span from pre take off to bend take off. Relative to the take off methods, pole bend to pre, there seems to be no actual evidence that they matter within limits. Any vaulter can get too far under, or be too far out, but since the Petrovians were able to enact big vaults along the tolerable spectrum, any "physics" based explanation favoring one type of actual take off over another should be greeted with skepticism. If the pre take off offers a list of possible physics advantages, pole bend might offer another one, added energy, biomech that the vaulter adds by means of adding additional force and energy in pole braking.

3) Box Energy. Box Energy considerations are unnecessary for two reasons. The first is that all vaulters need force in the box to return pole bend. Second, as any motion or velocity of the box (its delta v) in a normal vault situation is going to be at an exponentially fractionally small rate compared to the vaulter and where energy is relative to delta v squared, the amount is going to approach a limit of zero.

4)As far as I can tell you contend that any gain in energy in the vault comes from the vaulter, and to "prove" it you have an incomplete graph. I have a thought experiment based on the idea that gravity can bend poles and be used to store energy in them and that vaulters routinely place themselves by their early swing relation to add from this source of energy and later return it in height. I contend the Petrovians did and do adhere to my ideas it quite well. Other vaulters do it better and worse. This early swing relation limits how much energy a vaulter can biomechanically generate and add to the system during this period. If they happen to "muscle" the pole too much, they will leave the tolerable limit in relation to gravity in the swing arc for the CoM in time and while gaining biomech energy will also lose much more in relation to the gravity component as it will add less to pole compression and/or drain more from swing energy. Or, premature swing progression and its effect leads to two things that either kill a vault or reduce its effectiveness, lesser pole compression and/or greater energy loss from the swing moment. Later, when the vaulters CoM is above the pole master vaulters add their greatest bio-mechanical energy addition to the vault (post take off) while also reclaiming the gravity added component.

5)Lavillenie. I have analyzed his vault in comparison to the Petrovian method and in accord with my ideas. First, his approach to the take off mark may have taken on Petrovian aspects. From a theoretical aspect this is inconsequential to me even as it makes competitive sense. Almost every other aspect of his vault diverges from the Petrovian. He locks the left showing that even his early intent is different and where my contention is its to keep the hips even further back to make better use of gravity in pole compression. He double leg swings. To reach his late vault he has to radically speed up his swing velocity enacted with an early "tuck". He may somewhat return to the Petrovian idea as he wastes no time in his "tuck", he does not pause to "shoot", but when he reaches the proper angle extends as soon as possible to ride the end of decompression. The totality has let a shorter slower man vault to world record heights, and for this there is, and we would like to see a "physics" based explanation. But physics is hard, very hard, and its very easy to make mistakes. I have already made them in this thread. However, since Lavillenie seems to at least possibly use a Petrovian approach to his take off placement and possibly to his extension phase, we must then seriously consider that he must find some gain in the middle in his highly different swing approach.

Lastly...

As this goes on I have the feeling that you keep pressing that I need to provide something on the order of the idea of some physics examples and/or proof that the Petrovian method doesn't or won't work. You exhibit that it has generated a number of 6m plus vaulters and then seem to ask me to disprove the results. I offered from the beginning that it was a valid and valuable system that has displayed impeccable results. But this question again isn't, "Did they really get those results?", but did they get them for the reasons they stated in accord with a physics outlook. And my answer is both yes and no. I did not say its a bad system that should be avoided and indeed advocate quite the opposite. That at its heart it is a straightforward system that is easy to teach and learn and offers elements of both safety and a competitive advantage. But surrounding it I still see and feel that because of its success is has allowed myths, half truths, and hyperbole, and in that I have striven to and probably will continue to separate those elements from its true value.

I know of no one that has specifically considered the early action of gravity in the vault and its effect on pole compression and early swing moment especially in regard to enacting a methodology. In fact almost the opposite is true in that a certain sort of "freedom" in the hips and swing have been advocated over possibly maximizing the vaulters relation to gravity in pole compression while simultaneously minimizing it in swing deceleration. Yet, I cannot guess that these ideas have been completely "missed". The current French approach alone would seem to indicate they are aware of the idea even if its simply intuitive. They straight the left arm to keep the torso, hips, and take off foot pressed back to their limits. They double leg swing to extend the CoM moment in the swing thereby slowing it down. Yet, I do not at this time see that this sort of approach is popular. But then why should it be?! It's difficult to understand, difficult to study, and lacks a defined methodological school, and is a more difficult vaulting style. Perhaps that will change....

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altius
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Re: Physics Based Critique of the Petrov Method

Unread postby altius » Mon Apr 14, 2014 11:25 pm

willrieffer wrote:Just as a point of reference. This is the 8th grade boy I am working with...and this plant makes me giddy! Really, I've only had about 4 sessions with him (he had to sit out the beginning of the season with a foot injury). I also have a 9th grader who has gone from 8' last year to 10' 6" already this year and who is just beginning to have a swing. By next year I'm hoping to have 3 boys and at least 2 girls, 4 of which will be either 9th or 10th graders at the 2A MO state meet...


I would suggest you take a close look at that left hand and arm old son. He is going to load the pole with the bottom hand early and incorrectly if he continues like this.

If you are coaching young athletes you should consider the argument I have been making for years IE that the PB model can provide the basis for introducing the event to beginners and then taking them forward as far as their talent and desire will permit. If you don't agree please post how the technical model you are teaching beginners links to the technical model used by any elite athlete. There needs to a continuous evolution along the same path - if not -as so often in the US system - it becomes three steps forward and two back as athletes move from one coach to another up the chain. That is why we have enjoyed so much success over the years in an environment where the vault does not really exist

As to improvements we can all give examples of those - for example two 15 year old boys improving from 4.05 and 3.80 in december 2012 to 5.05m and 4.85m in March 2014. Both attempting the PB model Or a 12 year old girl from 0 to 3.00m in four months - while continuing to play her main sport of basketball at a high level and with a recognisable PB model for the run and take off.

Yes we know hundreds of better results will be posted after this (Charlie will be first in we suspect!) but we are happy to put up film of our kids so you can see that these are not idle claims. We would then like more coaches to show how what they teach beginners links to a model that will be successful at the top level -

Like Napoleon who said that every soldier has a Field Marshall's baton in his knapsack (implying of course that anyone could rise to that rank from the lowest position in the army) we start with the belief that every athlete we meet has the potential to be the world record holder, we should therefore make sure they start with the world record holders model (IE the PB model) in mind. Idealistic yes, but what is coaching without idealism and passion?
Its what you learn after you know it all that counts. John Wooden

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Tue Apr 15, 2014 9:27 am

altius wrote:
I would suggest you take a close look at that left hand and arm old son. He is going to load the pole with the bottom hand early and incorrectly if he continues like this.



You mean like Lavillenie who vaults with a left arm lock from a claimed evolution to a "Petrovian" take off? Lol.

I have no idea what you mean by "loading" the pole. The pole has to be "loaded" in the vault. It's the physical nature of the system. So you must mean something like "overloaded", no? That's an interesting concept. I'll be interested what you have to say about it.

I have put forth the French (and many other current WC vaulters) use the left lock to keep the hips even further back short post take off. That's what it does. Its influence on pole bend beyond that is generally overstated. SO another thought experiment....

Imagine a pole fixed at an angle slightly above the take off angle so that a vaulter might grip it and hang from it. Now remove the gravity vector. Now imagine the vaulter begins extending and then pulling with the left. What is going to happen? Well, they are going to move their torso along the swing arc of the top hand...and produce almost zero pole bend.

Is there a problem with teaching this method? Oh yes. It's a complicated movement over the free swing and they are more likely to block late.

I was just watching Joe Dial. Vaulted with a bent left for a long time in his evolution, then had to go for the press and power Y when he had to start getting in the really big poles.

Don't worry. It's probably going to go away when I track from plant to swing...

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Re: Physics Based Critique of the Petrov Method

Unread postby PVstudent » Tue Apr 15, 2014 9:51 am

Will many thanks for your considered response to my last post. I have prepared some diagrams to try to clarify, for myself and possibly others, what you are meaning specifically when you discuss the changing role of gravity in relation to the action of the lower arm in particular that you believe is not considered in the PB methodology.

I still do not agree that I have taken liberties with the energy exchange graph. Nor do I accept your argument that there is not a differential increase in the total energy of the vaulter that can be attributed to vaulter's work in the pole bending and recoiling phases.

Also I do not yet understand how an inanimate object such as a vaulting pole can be bent vastly beyond the range of deflection due to that induced by pole weight force and the moment it produces without an external agent producing that deflection increase. The external agent has got to be the vaulter! The other factors influencing the pole bend are trivial in comparison and on this we agree.

Also how do you account for the kinetic energy decrease of the vaulter followed by the increase in kinetic energy? The energy has to have gone somewhere and some of it regained by the vaulter during initial pole recoil. The vaulter has more energy at pole release than at take-off. How do you account for this? How did the pole bend if not from the vaulter exchanging energy with it. The vaulter's weight obviously has a contribution as does his muscular useful work on the pole.
I think we will have to agree to disagree here and move on.

The attachments are sketches/diagrams that attempt to consider the vertical forces action-reactions only and differentiate that the pathway of the vaulter's centre of mass follows a curvilinear pathway. The vaulter actions to achieve this effect are rotational predominantly from take-off til pole release. This should, I hope, prepare the ground so that it is possible to move the discussion on.

The diagrams should clarify pictorially what might be considered push and pull forces in the vertical direction. (We are all fully aware that there are also push and pull horizontal forces. Centripetal /Centrifugal forces are respectively defined as pulling inward towards and outward from the defined axis about which the rotation is taking place). The simplification in the diagrams is deliberate and is done to try to be obvious. I am happy and aware that in this case I am taking liberties in regard to the actual complexity of the situation described.

It is important to be clear as to the difference between vaulter COM linear displacement and the curvilinear pathway the COM actually follows in the course of a vault.

Finally I use the example of Pre-Bend Take-Off of a Petrovian Vaulter, who also is a "tuck and shooter" to set the basic parameters to make a simple statics analysis of the effects of the vaulter's weight and the role of the top and bottom arm in simply hanging in suspension below hand grips.

The statics diagrams will follow in another post without my comments to allow discussants the opportunity to engage answering the simple questions posed as a precursor to the much more interesting dynamics analysis.
Pole vault model of the vertical forces only acting on pole and vaulter.jpg
Pole vault model of the vertical forces only acting on pole and vaulter.jpg (112.16 KiB) Viewed 9794 times
Primary advantages of the flexible composite materials pole in modern pole vault.jpg
Primary advantages of the flexible composite materials pole in modern pole vault.jpg (81.93 KiB) Viewed 9794 times
Statics Conceptual understanding of the instant after take-off A.jpg
Statics Conceptual understanding of the instant after take-off A.jpg (98.97 KiB) Viewed 9794 times
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