Re: Physics Based Critique of the Petrov Method
Posted: Tue Apr 15, 2014 9:58 am
The Pole Vault Community Online
http://www.polevaultpower.com/forum/
http://www.polevaultpower.com/forum/viewtopic.php?f=38&t=45328
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...
PVstudent wrote: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.
PVstudent wrote: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.
PVstudent wrote: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.
PVstudent wrote: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.
PVstudent wrote: 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.
PVstudent wrote:
Firstly great job with this novice.
Secondly from Owen's body posture, depicted in the photo, the orientation and spatial organisation of the limbs and torso is excellent for someone who is just learning to swing.
Given that his take-off is very close to the planting box are you encouraging this young lad to bend the pole at this stage in his development? Have you dismissed the notion that learning to swing following the take-off is easier to teach on a stiff pole? From my experience I have found this to be the better option in terms of long term results. I am very interested to hear what you have to say in this regard.
Bearing in mind the limitations of a single photo, I raise with you the question of how effective you found Owen's penetration towards the landing pads to be? The photo gives the impression that he has "force bent the pole via the stiffened lower arm" and consequently is momentarily stuck in his take-off body shape before he can actively engage swing leg? Is this the case or was Owen swinging relatively freely and penetrating effectively toward the centre of the landing pads.
Great to see what the coach and vaulter actually can do in real world action.
altius wrote:willreifer old son I apologise for questioning you. I bow to your infinitely greater wisdom and experience - and probably your success as a coach. I can see that I have nothing to offer you in any of those areas so I will stop trying. However I would suggest, with great humility of course, that you read my book on the Petrov/Bubka method and appreciate the way the ideas in it can be applied to teaching and coaching young athletes. This will save me a great deal of embarrassment as you publicly rebut anything I post on PVP.
However in my defence I would point out, with great humility of course, that for a period of around thirty years I was as successful as anyone at taking beginners and helping them become technically sound pole vaulters who have achieved satisfactory results. This in the track and field wilderness of Adelaide. You will find an outline of some of those performances in Chapter Eight I believe.
PVstudent is younger and more resilient than I am, so I hope he will continue to try to educate the doubters. I can only wish him good luck.
But just a thought -could you detail how the technical model you are teaching the lad who has jumped 10'8"?? will allow him to progress - say to 16/17/18' - without any major modifications. I have just started coaching individual athletes again after a nine year break and I may be a bit out of date - so I would welcome any advice on how to proceed. Thanks in anticipation.
PVstudent wrote:Just to help readers view the performances and the biomechanics analysis of Bubka's 1987 performances at the IAAF 2nd World Championships in Rome please review this utube video.
http://youtu.be/7j6al8B_ANg
Will, hope you find this informative. I will respond in due course to your and other discussants responses to the Statics analysis and simple model of the vaulter pole vertical force interaction. Similarly I hope their will be some comment on the importance of shape and advantages the curvilinear pathway gives to modern pole vaulters. I understand that ploting this pathway may involve differential and integral calculus.
But by simply ploting the vaulter's COM for every fame/video field and just joining the successive x,y coordinates of the COM gives a pretty good estimate of the curvilinear pathway.
(For this to be accurate the original footage must be from spatially and time calibrated cameras preferably located orthogonal to primary plane of vaulter motion of interest. Panning requires special algorithms to be used in correcting the spatial co-ordinates which were used by the investigators.)
Enjoy the video which has been edited from the original film.
It does highlight some of the post take-off Petrov-Bubka characteristics!
Q. How would you describe the action of bending the pole?
A. Before the fiber glass pole, pole vaulters put their focus on moving the pole, then, when the flexible pole appeared many people put their focus on bending the pole. The pole bends as a result of the speed and mass of the jumper, therefore, it is more important to concentrate more on moving the pole towards the plane of the bar, rather than being aware of bending it. If the vaulter can put all his speed to the pole, the bending of the pole will happen in a very natural way and this, together with a good height of grip will ensure good results.