Physics Based Critique of the Petrov Method

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willrieffer
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Physics Based Critique of the Petrov Method

Unread postby willrieffer » Sun Mar 23, 2014 12:14 am

First...

I learned to vault with Rick Attig while he was still at Raytown South at camp. I was a MO HS vaulter with a meet PR in HS of 15'. At Attig's camp I went through 13 poles in one day, flew over 15' 6" by a foot before turning my ankle. Rick once told someone that I was the most powerful vaulter he'd ever seen. I then went to Ohio State where I vaulted until injury and also....studied advanced physics, physics engineering specifically. Also, while I there was THE slowest guy on the team. I ran a 5.0 40 and was slower than every guy on the team including all the throwers lol!

For the Petrov Model I will use this article
http://www.carreroart.com.au/polevault/2200f.htm
found commonly on this site and elsewhere.

I contend that the Petrov model is full of hyperbole, half truths, and myths, in part because they got results! First of all is that Petrov and Bubka may have preached the "free take off" but Bubka did not practice it, at least as far as its described, in that if you simply look at the vids in vault after vault his pole starts bending about as soon as his take off foot hits the ground. I contend from a physics standpoint this is actually preferable as it allows the vaulter to add mechanical/muscle energy to the vault/pole in addition to their take off kinetic energy derived from runway speed. Further, Bubka also was a master manipulator of his position and CG along with his rotational axis as the Petrov model claims although the specific claims are somewhat off base in terms of physics. Specifically he was a master at manipulating his rotation speed particularly in the mid vault by altering his body. Watch and he in fact uses his legs by shortening them and speeding his rotation while also using the shoulders. No he did not "tuck", as for almost all vaulters using, working on, or thinking about "the tuck" and its placement, it is so far out of the critical swing zone, that is late, that its just a vestigial motion worth no value. Or, they've already missed the time when they needed to speed their rotation, which Bubka did not.

One of the most important things that Bubka did that many other great vaulters do is that about as soon as they are off the ground and in the C they work to end that position. They retard the hip motion forward, the swing, by use of the arms which is evident in the space created between the vaulter and the pole and the top arm placement to the torso/head, and work to orient the torso as much to the perpendicular as possible as this is by physics optimal. Bubka in fact used the left arm extension to help achieve this, as it is necessary or the swing is or will become progressed with a critical loss of forward momentum in the vault. Bubka (and many other premier vaulters working both in and out of the Petrov system) work very hard to get this position and keep it as long as possible. In slomo you can see how long he actually holds a very still position with the arms (power Y) and torso while the left leg swings. Also, that almost all of his rotation moment as evidenced by the hips has been transferred to energy/speed in the pole(in physics by action/reaction) or carried in the lower take off leg (knee extension) and then take off leg as it swings around what is relatively still hip. It is then when he begins to shorten the swing leg, use the right leg and hips, and abdominal to shorten and speed the swing moment. He also uses the shoulders (lest the "Bubka" training movement would never have to have been invented) to get into position to make the critical transfer of energy from the horizontal and stored to the vertical by swing speed positioning, and I dare say, muscle. Note here that as the vault approaches vertical with both the pole and vaulter the vertical placement of the vaulters CG matters less and less in regards to pole speed. Or, as Bubka practiced, if you have the proper control of the mid swing moment and thus its speed control, you can extend as soon as possible. In fact it is preferable.

Also, taking off under is actually preferable in my model as long as the vaulter can maintain the proper torso attitude and effect swing speed. Many, especially new vaulters cannot. They generally wind up leaning back with the torso and that also effects a progressed swing that kills the vault.

And also...

The article likens the methodology to a rocket. This is a terrible analogy from a physics standpoint as a rocket generally provides constant energy from a conversion of chemical energy to kinetic energy. In the vault, no energy can be added to the system once a vaulter leaves the runway, and the only thing that can happen is that the energy in the system can be controlled by leverage. Certainly and specifically energy in the pole can be manipulated to some degree, in fact that is the essence of the vault, yet once the pole has started to recoil, there is less ability to effect the outcome than prior. As an example, few "bail" on the end pull and turn as the critical elements have already passed! That is did you get speed, plant, and proper swing placement? Still, there is an action/reaction event that can be enacted. That is, the Bubka moment of extension cannot impart energy into the pole, but by action/reaction can regulate its release, but at a point where all of the critical timing elements have passed. Yes, it may certainly effect a higher vault, but if missed, it won't kill the vault.

Bubka may play off his superior speed (which I actually remember being reported in the day as 10.1 100m and a 5th in the Euro juniors 100m) in part because of an ego that wishes to be seen in the intellectual over the physical. His technique? It is evidently not radical. And so any physicist would expect him to have the highest vault. Is it the most efficient? Very hard to say. But I can say this. Looking at the fastest guy who at take off is generating the most kinetic energy and trying to find the most efficient vault(er), is barking up the wrong tree. If you want to find the most efficient vault method what you need to do is look at the slowest guys that have vaulted significant heights.

Lastly. The vault is always going to be looking for athletes. The outcome IS based largely on the kinetic energy available at take off and few coaches at any level are going to want to let a top sprinter go off and work on an event as skill intensive as the pole vault and see points evaporate from the track. Bubka and the Russians may have been special case where they thought the reward was worth it. Bubka wasn't going to make that big of a name as a 100m man when the event was still dominated by the Americans and the likes of Carl Lewis. And I dare think the technical and esoteric nature of the event, dominating it, appealed to their world view. That being said, when I look at what they were saying with their "tech" explanations in fact looks more like a psychological approach. They didn't really "free take off", but to think in that way was beneficial in their true take off placement and in imparting take off angle and effecting the rotational moment of the pole. Like I said elsewhere you could give a young vaulter a PhD thesis on the pole vault, an analysis of the nature of a double pendulum with each pendulum of constantly changing rotational length (an incredibly difficult to analyze problem), but it would not do them any good. Not nearly as much good as standing around yelling, "Swing under that thing!!!".

In 82 I was with Cam Miller at camp at Raytown South and Cam was I think just out of being a HS freshman. Attig put on film of the RS vaulters and I remember at one point I watched in amazement as Cam almost magically flew up the pole while inverted. Rick ran that spot over and over and over. I think he was still trying to figure it out. It was Petrov/Bubka, without the theory. Just some 15 year old kid that would whip under the pole and then fly up it. Or, to end, some vaulters have a combo of natural ability and intuition that will just trump instruction in theory. Think of hitters hitting a baseball. It happens so fast, judgements and adjustments made in hundreths of a second, yet guys hit baseballs. They instruct and they train and yet in the moment they do not think of the theory or instruction. Likewise I contend vaulters routinely make such decisions and adjustments. Sometimes they just bail, and to do so they stop the swing. So I also contend vaulters can adjust their swing moment and swing speed in a way that surpasses an explanation, at least in a way that can easily be condensed into a teaching point or method.

Good Luck. Be Safe. Vault High. And Have Fun!
Will

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Re: Physics Based Critique of the Petrov Method

Unread postby KirkB » Sun Mar 23, 2014 2:22 pm

Thanks for posting this, Will.

Vive la difference! :)

If you want to understand Bubka's intent - right from the horse's mouth - here's a link to what he says about the free takeoff (credit to Phil CarRero - this interview is on his same website as the article that you quoted above):

http://carreroart.com.au/polevault/2200b.htm

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Sun Mar 23, 2014 2:41 pm

Kirk,

Thanks for the assist. In fact I feel I need to post my revision from our other discussion here.

willrieffer wrote: ... Bubka may have preached the "free take off" but he did not practice it, at least as far as its described, in that if you simply look at the vids in vault after vault his pole starts bending about as soon as his take off foot hits the ground. I contend from a physics standpoint this is actually preferable as it allows the vaulter to add mechanical/muscle energy to the vault/pole in addition to their take off kinetic energy.

Kirk wrote:I accept that Bubka often took off under, but I don't think that was his intent. Can you explain how an under takeoff adds energy to the vaulter-pole system? I just don't see it. And I see that you've replied to PVStudent's dissertation on pages 3-5 of this thread: http://www.polevaultpower.com/forum/viewtopic.php?f=38&t=27151&hilit=pvstudent&start=24, so you know that he doesn't see it either. I'll let you two duke this out. :)


I want to change my reply and outlook here just a bit. Lets take this famous video, the 93 Championships, where you have 4 guys, Bubka, Tradenkov, Tarasov, and Yegerov all coming out of the old Soviet system.
https://www.youtube.com/watch?v=KUPBl4xToUM
1st up Tarasov. Foot clearly on ground as pole is bending. He missed it. Good Vault.
2nd Trandenkov. Kinda hard to tell on this vid, but I believe he also has foot on ground and pole bend. So I think he missed as well. We should pay attention to him as he's one of the slowest over 6m. He also deviates from Bubka and the Petrov model in the use of his legs, which can be seen bending in the late mid vault. He almost "tucks"! And another good vault.
3rd Bubka. Hard to tell. Possibly missed it.
4th Yegerov. Hard to tell. Possibly missed it.
5th. Bubka. His winning vault. Well again from this video and angle its hard to tell. But then the next bit is the same vault from overhead and its very evident that his foot is on the ground and the pole is bending. He missed it. Another great sky ride!

So they have Petrov technique and coaching, and a goal, as you mention intent. But its evident that they cannot achieve consistently what they are trying to do, that is be airborn and avoid pole bend. Bubka admits to this same thing! He more or less says, 'well, this is what we are trying to do, but we don't get it very much'*. And the results are less than devastating. By certain elements of the presentation of the Petrov model you would think this would be devastating. It is visibly not. IF its not and they pull off terrific vaults with foot on the ground and visible pole bend, what are we to think? Perhaps possibly the technique is valuable in some way outside of the explanation? Aside from the free take of the Petrov model strives for a certain body position and high take off angle, which is where I think it derives results. And from that we might also derive that teaching the method could in fact be one of the best methods of instruction if not the best one.

And I'll give you one where Bubka gets a free take off. His first 6m clearance. Gads what a wacky vault! Look and you'll see reverse pole bend going on when he takes off! Flippin amazing! That that is such an odd take off and he pulls it out, well, that's speed plus athletic ability that can drive a path under the pole!

willrieffer wrote: They retard the hip motion forward, the swing, by use of the arms which is evident in the space created between the vaulter and the pole and the top arm placement to the torso/head, and work to orient the torso as much to the perpendicular as possible. Bubka in fact used the left arm extension to help achieve this, as it is necessary, for if not the swing is progressed. Bubka works very hard to get this position and keep it as long as possible. In slomo you can see how long he actually holds a very still position with the arms and torso while the left leg swings.


Kirk wrote:This is the classic "Did he push with the bottom arm or not?" paradox. My assertion is that he did not push, and that his posture on the pole (including the space between the pole and his bottom hand) is generated solely on the basis of the pole bending under the pressure exerted on the top hand (pressure which came from the inertia of his speed at takeoff). I realize that you see this differently, and my intent is not to try to win you over in an argument. Rather, I only wish to point out that this is once again a difference of interpretation. It's difficult to prove one way or the other unless you actually interview Bubka. Vive la difference! :)

Kirk


We might quibble about how things are accomplished, but you can watch him, and many great vaulters and they get their top arm back beside their head, and get their torso aligned and down. There is of course action with the swing in this, the body motion coming out of the C, but I'm pretty convinced they are active in the shoulders to reach and hold this position as well. It isn't necessary that the left arm push out and up and is as much an almost radial movement along the pole with both hands. Rowing? I did not say rowing! Rowing might well progress the swing and kill the vault. It's just a very active swinging.

Make no mistake. Swing positioning is essential and to me paramount in such a way that it trumps some small deviations in take off technique. PVStudent explains well the mechanical advantage that the pole gives and the vaulters path through it make. I contend the nature of that path, and maximizing it is the overriding factor in the vault.

Oh, you wacky French with your quasi double leg swing and slow guys vaulting oh so high!


*
Bubka wrote:A. In pole vaulting the crucial factor is how to transfer energy to the pole, through the complete body of the vaulter; the arms, shoulders, hip, back and legs. But, if the pole begins to bend while the vaulter is yet on the ground, it is impossible to transfer the energy, all the energy is lost and goes to the box. The point is how to achieve this? The free take off is a very short period of time, we can say no more than hundreds of a second, going from the end of the take off and the moment in which the tip of the pole reaches the end of the box(ie a Pre-Jump Take-Off). But this very short time makes a big difference that allows the competitor to greatly improve the results. When we begin to bend the pole, while being on the ground, we can see an arched position of the body, on the other hand, if we perform a free take off we can feel the pushing action of the whole body, and we can transfer the speed of the run up and take off.
Additionally, we can increase the angle between the pole and the ground in the moment of taking off. This angle is a very important technical factor, because the bigger this angle the better the result.
But this angle must be achieved with a complete extension of the body, and mainly, keeping that short difference between the full extension of the body and the tip of the pole reaching the end of the box.It is a crucial factor, but at the same time, it is not easy to achieve. During my career, I was able to do it sometimes.


Crucial, but you only got it sometimes? How can something in this event be both crucial and inconsistently achieved?

P.S. To answer another question...
Bubka talks about "putting energy into the box". Well, you can't put energy into the box, it is simply a static counter that provides a force needed to put energy into the pole! IF it has any energy relationship to the vault, it is in bleeding off small amounts of it through rotational friction and heat. I know PVStudent goes through all this, but what for, I don't know. The box is static. It has no way to accept any energy. It does not move, has no mechanical way to deal with energy, and doesn't get burning hot when someone vaults. Whatever the load force, all the energy of the vaulter goes into the vault either in continuing kinetic energy or by converting kinetic energy into stored energy in the elasticity of the pole. However you take off you have this going on. Okay, so the vaulter enters the vault with a take off velocity where Kinetic Energy = 1/2 m (v squared) where with v being squared small amounts of increased velocity yield big end results (Oh physics, do not look at Bubka's speed!). If they free take off that's it, all the energy for the vault is in their flying forward kinetic energy. However, the body can add mechanical energy through use of the foot against the static runway. IF they maintain velocity through this they get more energy in the pole. Or, think about it this way. You can put a vaulter on the runway and through the use of their foot on the ground and muscles can bend the pole and put energy in it. Now think again. If you somehow would hang this vaulter off the runway, they cannot perform the same action. Thus foot on the ground creating force added to velocity can add to pole energy. PVStudent never addresses this potential for added mechanical energy, among other things. Is there a cost? Possibly, but its in whether the energy can be controlled and directed through the vault. Some vaulters pull this off very well. Like Bubka perhaps, foot driving and the ground, pole bending, and then going about 6.2 or more in the air...

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Re: Physics Based Critique of the Petrov Method

Unread postby KirkB » Sun Mar 23, 2014 3:01 pm

You've got a few different posts going on here, Will, with duplicate content. This is YOUR thread, so I suggest for the sake of simplicity that we consolidate the other discussions here, rather than the other two?

The other 2 are here: http://www.polevaultpower.com/forum/viewtopic.php?f=37&t=41915&start=0

... and here: http://www.polevaultpower.com/forum/viewtopic.php?f=38&t=27151&start=48

I can't speak for anyone else, and I certainly can't speak for you, but what I will do is just post to this thread. That's what works for me. :dazed:

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Re: Physics Based Critique of the Petrov Method

Unread postby KirkB » Sun Mar 23, 2014 3:10 pm

Here's the reply that I had on another thread of the same topic ...
willrieffer wrote: ... Bubka in fact used the left arm extension to help achieve this, as it is necessary, for if not the swing is progressed. Bubka works very hard to get this position and keep it as long as possible. In slomo you can see how long he actually holds a very still position with the arms and torso while the left leg swings.

Kirk wrote:This is the classic "Did he push with the bottom arm or not?" paradox. My assertion is that he did not push ...

I think it's better to understand the intent of the vaulter than attempt to reverse-engineer a vid that is easily misinterpreted. Thanks for providing Bubka's intent in your quote here from his interview in Kingston Jamaica ...
willrieffer wrote:
Bubka wrote: A. In pole vaulting the crucial factor is how to transfer energy to the pole, through the complete body of the vaulter; the arms, shoulders, hip, back and legs. But, if the pole begins to bend while the vaulter is yet on the ground, it is impossible to transfer the energy, all the energy is lost and goes to the box. The point is how to achieve this? The free take off is a very short period of time, we can say no more than hundreds of a second, going from the end of the take off and the moment in which the tip of the pole reaches the end of the box(ie a Pre-Jump Take-Off). But this very short time makes a big difference that allows the competitor to greatly improve the results. When we begin to bend the pole, while being on the ground, we can see an arched position of the body, on the other hand, if we perform a free take off we can feel the pushing action of the whole body, and we can transfer the speed of the run up and take off.
Additionally, we can increase the angle between the pole and the ground in the moment of taking off. This angle is a very important technical factor, because the bigger this angle the better the result.
But this angle must be achieved with a complete extension of the body, and mainly, keeping that short difference between the full extension of the body and the tip of the pole reaching the end of the box.It is a crucial factor, but at the same time, it is not easy to achieve. During my career, I was able to do it sometimes.

Crucial, but you only got it sometimes? How can something in this event be both crucial and inconsistently achieved?
Because it's not easy? :dazed:

Yes, you can be under a bit and still pull off a good clearance - especially if the bar is well under your potential PR. I interpret this paradox as to reach your POTENTIAL PR, according to the laws of physics applied in concert with your physical attributes (speed, strength, technique ...) you need to have a free takeoff.

willrieffer wrote: Bubka talks about "putting energy into the box". Well, you can't put energy into the box, it is simply a static counter that provides a force needed to put energy into the pole!

Agreed. This must have been an error in translation. I'm quite sure that he meant "putting energy into the pole".

Will, I'm still looking for your explanation of how being under can put MORE energy into the pole than a free takeoff can. I just don't see it, and I would really like to understand your rationale for this, as it's counter to my understanding of the physics of the PV. This is an important point, and I wouldn't mind PVStudent's analysis of this either - if he would be so kind. May the most solid physics principles prevail! Thanks in advance.

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Re: Physics Based Critique of the Petrov Method

Unread postby KirkB » Sun Mar 23, 2014 3:20 pm

willrieffer wrote: ... If you want to find the most efficient vault method what you need to do is look at the slowest guys that have vaulted significant heights.

This is an excellent point, and one that I have always believed in very strongly! :yes:

This may sound egotistical, but I'm not trying to stroke my ego - I'm only trying to share what I've learned about PV technique, based on scientific evidence, and based on how my best vaults felt ...

I firmly believe that my technique (1971-72) had the potential to break the WR - if only I had better speed down the runway! I was slow as a mule, but got to within 8" of the WR. So there must have been something about my technique that was superior to other elite vaulters. :idea:

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Sun Mar 23, 2014 7:47 pm

Yes, you can be under a bit and still pull off a good clearance - especially if the bar is well under your potential PR. I interpret this paradox as to reach your POTENTIAL PR, according to the laws of physics applied in concert with your physical attributes (speed, strength, technique ...) you need to have a free takeoff.


There were a couple of a reasons that I picked the 93 worlds vid.
1) Bunch of guys vaulting high in the same system. In fact this says at least the intent of the approach and actions yield results.
2) I don't think I see any one of them hit a real free take off and they all vault high.
3) It's considered one of Bubka's highest flights. Not the actual free take off technique AND one of his highest vaults. So...

IF the claims, as they are presented were true, I'd expect somewhere to see actual results. You know, something like a video with a very high vault, or perhaps Bubka or one of them saying something like, "Well, on this vault I actually got the rare free take off and as you can see I was 6.4m in the air." And maybe that stuff does in fact exist, but I'm not aware of it. I think it would have come up early and often. I'm in MO, show me. I also have a bit of a problem in that they expect the feeling of a free take off vault to be different and for it to happen at least somewhat infrequently. If they were like me, they did not like surprises. This is to say that they had to, or were training for basically two different types of vaults. Ones where they got the free take off and ones where they didn't.

Here's something again I'll bring up. Tradenkov was .5m/sec slower on the runway than Bubka.
http://www.polevaultpower.com/6mclub.php
And yet he has a 6.01 clearance. Also, despite coming out of the same system he has some differences in swing as opposed to Bubka. I don't know that I have the resources to try and make a study of them, but that would be a place to look. Once again I'm going to say that I believe that the vaulters swing path and its end efficiency trumps a lot of this, and the Petrov model might well, if not almost probably, creates a highly efficient path.

Here's one.
https://www.youtube.com/watch?v=YMGTiQClVMM
The Bubka comp vid. Look at Tarasov's vault at around 6 minutes in. That's definitely foot on ground and pole bend, and a fantastic vault. The announcer even calls it the best of the day! At least until the next Bubka launch!
Unfortunately I have limited internet and researching vids chews through my allotment. I live in a rural area and have wireless. :( And I'm about to hit my allotment.

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Re: Physics Based Critique of the Petrov Method

Unread postby PVstudent » Mon Mar 24, 2014 5:01 am

To willrieffer

“I contend that the Petrov model is full of hyperbole, half truths, and myths, in part because they got results!”

This is a very provocative opening gambit to your objections to the Petrov Model.

1. If the advocates of the model as exemplified by their actual vaulting results got officially recorded extraordinarily high bar clearance results how then can the results be mythical? Do you mean the method they used was mythical? (A “myth”: a figment, a commonly held belief that is untrue, or without foundation). Some of the underlying principles of the Petrov model have demonstrable physical and biomechanical factual physical laws and biological facts as their basis. (I believe I have demonstrated this in regard to an “idealized correct take-off point!” This is but one of the many Petrov-Bubka Model Principles.)

2. “the Petrov Model is full of hyperbole,”… (hyperbole: a rhetorical (pertaining to rhetoric, the theory and practice of eloquence, whether spoken or written, the whole art of using language to persuade others; false, showy, artificial or declamatory) figure which produces a vivid impression by extravagant and obvious exaggeration) if this refers to my discussion of the take -off point what was false, showy or extravagant in my exposition on the question I specifically addressed? I do not accept your claim that the Petrov Model is full of hyperbole!!!! From my perspective a fair assessment of the model in question is that it has contributed a biomechanically and empirically practicable basis for the technical development of men and women’s pole vault technique during the last three decades. Note I am not claiming it is the only method nor have I claimed it to be so.

“Also, taking off under is actually preferable in my model…”

Since I only have an elementary grasp of the physics of pole vault I am at a loss to understand how “Taking off under” is ideal technique to be strived for according to Newtonian Mechanics and how this enhances the vaulter’s biomechanical attributes in effecting the total system centre of mass translatory and rotary momenta inputs needed throughout the subsequent sequential motions of the pole support “bending /buckling” and “recoil” phases.

Can you explain why taking off under creates more efficiency of energy transmission in the take-off?

“In the vault, no energy can be added to the system once a vaulter leaves the runway and the only thing that can happen is that the energy in the system can be controlled by leverage.”

Is your claim here actually true?

There is repeated, substantiated evidence from pole vault studies of elite pole vaulters in World Class competitions adding energy to the vault after the vaulter has broken toe contact with the runway surface! Your statement here merely perpetuates a long held fallacy!

If this is not a fallacy can you explain the physics of why it is not possible for the vaulter, by means of the chemical energy exchange giving rise to muscular contractions operating on the vaulter’s body and hence to the earth via the tip of the pole in the box, to provide additional energy by means of swing to increases both potential and kinetic energy of the total system?

Your observations on former Soviet vaulters back in the day are indeed reasonable and accurate but the conclusion you draw with respect to the Petrov-Bubka model can be alternatively stated as follows:

Whilst many of the former Soviet System vaulters were attempting to follow the “Free Take-Off Principle” they more often than not did not succeed, yet they achieved remarkably good outcome results because by so doing they actually minimized the deleterious effects of being “excessively under” in comparison with other pole vaulters of that era.
The consistency of performance in competition achieved by Soviet vaulters attempting to apply this principle of take-off may have resulted in them having an associated psychological advantage.


Understanding the physics of the pole vault is one matter. How this knowledge is translated and used to improve coaching is quite another.

If you wish to discuss the physics of the pole vault seriously and with objectivity in this thread then it is important to be accurate in regard to basic physics and biomechanics.

One of the problems in doing this on this forum is that it is coach and elite pole vaulter oriented and in the effort to over simplify, errors of fact and principle are easy to make.

Pole vaulting is indeed very complicated, but it should not be made more complicated by perpetuation of some of the hyperbole, half-truths and myths you and I may inadvertently promulgate.

That said, I remain open to your critique of the specifics of what I have previously had to say on the physics of the free-take off.

Until you can explain the physics rationale in regard to the “under take-off” efficiency of energy input you claim it achieves I stand by my previous contributions on the matter.

Your claims in regard to energy input after the take-off I think are highly questionable and likewise need clearer explanation from a physics perspective.

Another aspect of the take-off to which you referred and I quote:

“Bubka talks about "putting energy into the box". Well, you can't put energy into the box, it is simply a static counter that provides a force needed to put energy into the pole! IF it has any energy relationship to the vault, it is in bleeding off small amounts of it through rotational friction and heat. I know PVStudent goes through all this, but what for, I don't know. “

The nature of the impact of the pole with the planting box, force transmission along the pole, the firmness of the grips on the pole, the relative rigidity and postural vertical alignment of the vaulter’s torso and the vectorial resolution of the total system centre of mass motion at the instant of the take-off critically determine the impact outcomes. Where, how and what the pole tip is doing at the instant of rear wall contact becomes critical to how energy is conserved or dissipated in the pole vaulter and the earth!

What makes the pole bend and how this is exploited by the vaulter during and after the pole tip rear wall impact is a topic for another day. My understanding of the physics of impacts again is limited. But, what the vaulter and the pole are doing at the instant the collision occurs determines the outcome. To deal with those impact circumstances there are some principles in the Petrov-Bubka model that are applied to ensure minimizing of linear kinetic energy losses whilst simultaneously optimizing potential and rotational kinetic energy gain in the system total centre of mass.
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Re: Physics Based Critique of the Petrov Method

Unread postby CoachEric » Mon Mar 24, 2014 11:54 am

Some key things to be considered in this discussion:

1. Willrieffer, the article you supplied as the basis for the Petrov model appears to be an excerpt from BTB, or at least it's written by Alan. All due respect to Alan, because his work has done more to bring some of Petrov's concepts to the rest of the world; however, this is an interpretation of Petrov by Alan and Roman. It's written by coaches, for coaches, for a mass audience. It's not a physics journal. So a physics based critique of metaphoric language (like the rocket analogy) isn't useful. And, in my opinion, the points of emphasis on this interpretation of the model are debatable.

For a primary source, see this article by Petrov himself. http://www.willamettestriders.com/PetrovOnTechnique.pdf Note that the points emphasized in this article are about pole carry, pole drop, run/takeoff mechanics, and plant motion.

2. The takeoff point issue was covered extensively by PVStudent, with a thorough explantation of distinct differences between a pre-jump and a free takeoff. Please clarify which of the two distinctly different takeoff methods you interpret as part of the Petrov model. In my opinion, the Free Takeoff is the correct result of the points emphasized by the model.

3. An issue that this community remains split on, and which introduced this discussion, is the action of the arms post-takeoff. I believe I agree with your position that there is not a row, but an vigorous "realignment" into a hollow-body position, bringing the body in line with the chord of the pole, keeping pressure up on the pole with the bottom arm, accelerating the swing of the hips toward vertical. While I believe this technique to be correct, I don't have much basis to know for sure that this is part of Petrov's model. So, as with this example, please define more clearly what you believe to be part of the model that you are critiqing. For anybody to get smarter on this, we need to agree on what we're talking about.

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Re: Physics Based Critique of the Petrov Method

Unread postby willrieffer » Mon Mar 24, 2014 3:25 pm

IF you get success, you can attribute it to whatever you'd like, which is the problem I see here. The Petrov model got great success. It should be studied and used on that fact alone. It's just that having studied physics and in reading their and their disciples attempts at a physics based explanation, I see either poor efforts at explanation that do not agree with my knowledge of physics, or I'm left with a lot of questions.

PVStudents work misses, at least as far as I can tell, the input or at least possible input of mechanical energy into the pole caused by the vaulter through foot contact in addition to their velocity at plant. Of course as soon as the tip hits the box the vaulter is going to slow down and the box is going to take on force. But this is the case for any type of take off or vault. But for a bend take off vaulter they do have a chance to possibly add more energy. That's just physics. Is it enough to counter some of the problems in vaulting this way? I can't be sure. The free take off and/or its attempt almost in all cases would, I think, provides a higher/better angled force vector at take off but eschews the possibility to add more energy. So the difference as I see it is in more energy versus better vector. Also, how much or how skilled the vaulter is in control of the vault and its energy. In this it may well be that the Petrov method offers easier control of the entire vault. But again, from what I know of physics and the vault, if the free take off is "crucial", as Bubka claimed, then the method is giving up a possible energy source.

Also I do not recall anything being said on the fact that bend take off vaulters are already shorting the rotation length of the pole prior to take off, another advantage or possible advantage. There was extensive work towards angles, and they are indeed very very important. IF I'm wrong about any of this, please forgive me. I read the work once, with a lot of re-reading. I can say I could probably read it many many times and get things out of it. We are talking about a very complex event and physics problem.

So it is that the addition of mechanical energy at plant couple with an immediate shortening of the effective grip height is why I say its possible that bend take off and being under have possible merit. The trade off is the noted one in force vector. It becomes harder to drive a high take off. The vaulter comes in low and hard to the vault and then has to suffer a more radical trajectory change to the vertical. Is it more dangerous? Possibly. Probably. I don't know? LOL. Note however even as I say this you're going to be on a shorter effective grip height longer and make more forward progress to the pit.

As an energy system. Ok. Indeed I must give up that a vaulter can and does add energy to the system throughout the vault. Now note that it all has to be transferred to the pole through the hands. Why? You need to put energy somewhere. Imagine an astronaut floating in space. They can flail their arms and legs all they want, expend energy in the system, and go no where. Why? They have no where to put any force and thus energy. Now, all vaulters do this, but early in the vault the only place they can put such energy is through the hands and into the pole, and, uh, that would be akin to rowing. Late in the vault, when the pole is perpendicular or near perpendicular of course it matters very much as the box is now a perfect counter for the force.

Do you want to bend the pole? As a flexible pole it does not return 100% energy and so if that is your simple intent, to put as much bend or energy into the pole, it is misguided as you are just throwing energy away. The more you put in the more you lose. Again we are talking about another trade off. A high take off angle and thus less pole bend offers a method of efficiency, but at the cost of less grip height manipulation. These sorts of trade offs go on and on and on for this event. It's a two phase double pendulum where neither pendulum is of constant length.

Gotta go for now and get ready for a meet. And look, its been a long time since I've thought about this stuff and I've already made several conceptual mistakes that needed to be corrected and gone over. I moved back to my very rural boyhood home and for years my HS had done away with PV and I didn't think about it much. Then they got a new track and wanted to host districts. For that they had to get PV equipment. Knowing no one else knew about the event, I volunteered to coach. I do not coach any of my vaulters to take off under or do a bend take off. In fact at this stage with these athletes my approach is much more neutral or even closer to the free take off model. It's easier teach, in this case definitely safer, and easier for the vaulter in many ways.

And hey, quasi double leg swing and high swing speed manipulation leads to what??? Lol.

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Re: Physics Based Critique of the Petrov Method

Unread postby Decamouse » Mon Mar 24, 2014 3:39 pm

These types of posts cause one to think- re-evaluate, agree, disagree - but that is what discussion is - not name calling - nice stuff
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Re: Physics Based Critique of the Petrov Method

Unread postby KirkB » Mon Mar 24, 2014 8:18 pm

willrieffer wrote: Knowing no one else knew about the event, I volunteered to coach. I do not coach any of my vaulters to take off under or do a bend take off. In fact at this stage with these athletes my approach is much more neutral or even closer to the free take off model. It's easier teach, in this case definitely safer, and easier for the vaulter in many ways.
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Good job, Will! At least Altius won't be ranting at you for not practicing what you're preaching, and not contributing to the betterment of PV. You're out there helping kids ... with a "good approach" that is "neutral or even closer to the free take off model"! Keep up the good work!

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