Re: What is your correct takeoff point?
Posted: Wed Jul 24, 2013 10:08 am
Please review the following videos:
Sergei Bubka
http://youtu.be/y9Q4rL0PC-s
Svetlana Feofanova
http://youtu.be/-TWAbc5TdpM
Annika Becker
http://youtu.be/xpfUUcjMRI4
Dmitri Markov
http://youtu.be/v9Ne--kuMUU
Consider the take-off showing identical body posture orientations at toe tip take-off of a tall and short stature vaulter. Both vaulters take exactly the same grip length measured from the pole tip to the top of the top hand grip. Each vaulter also makes identical grip-width spacing between the upper and lower hand locations on the pole.
With both hands gripped on the pole, the pole tip firmly located in contact with the deepest part of the planting box and the rear wall, the vaulter rises on to toe–tip with their body erect and both arms simultaneously positioned in the finish of the plant position.
Consensus coaching practice is for the vaulter’s upper grip arm to be fully extended in alignment with the ear whilst the head held in the neutral / anatomical position as the toe-tip, with torso held firmly erect, position is reached.
In real life some slight forward lean by the vaulter is required to maintain pressure through the pole-tip against the bottom of the rear wall to sustain a stable balance when fully raised on toe tip.
It is immediately obvious that the taller vaulter has:
(1) Higher reach upwards with the upper grip hand
(2) Greater pole ground angle (Angle B > A)
(3) Take-off toe tip location is closer horizontally along the runway surface in relationship to the pole tip located in the deepest part of the planting box.
The vaulter adjusts the location of their take-off foot toe position until a perpendicular line projected from the toe position on the runway intersects with the top of the upper hand grip on the pole.
The effective pole length is a constant (same length) for both a short and tall vaulter gripping the pole with identically located positions of the upper hand and between grip spacing.
By definition a right triangle will be formed with hypotenuse “C” (the constant effective pole length) for vaulters gripping the pole at the same grip length when the final toe-tip position indicated in the diagram and the pictures below is achieved.
It follows from the Laws of Properties of Similar Triangles and Pythagorian Theory the toe –tip of the taller of two vaulters, who in all other respects is similar to the shorter, must be located closer in the horizontal direction (right triangle side A) to the pole tip contacting the rear wall when it is located in the deepest part of the planting box.
The vertex of the right triangle is side B. The height of side B is measured vertically from the deepest point in the planting box to the highest point of the position of the top grip hand at toe-tip take-off.
If the proposition that the pole ground angle (beta), (the angle between side A and the hypotenuse side C of the triangle) should be maximized to thereby minimize the angular distance the chord of the pole must travel (angle alpha) to pass through the transverse vertical plane from the pole tip in the planting box, is accepted the taller vaulter will have a distinct advantage in making the take-off.
Tall vaulters, because of their height, have higher pole ground angles at touch-down and at take-off and consequently have LESS pole chord angle to travel through to move past the transverse vertical plane from the pole tip located in the planting box. Also a tall vaulter has less horizontal displacement to travel before passing through the transverse vertical plane of the pole chord when the pole is fully straight at the end of its recoil phase (all other factors being the same for both vaulters).
For any individual vaulter, if the proposition holds true in real life, a decrease in effective grip length on the pole should result in the vaulter’s take-off foot toe tip location on the runway being horizontally closer to the rear wall of the planting box. Consequently the pole ground angle should also be greater at the take-off from this closer location (assuming the postural configuration and vertex height from toe tip to highest point on the top hand grip(side B) remains constant for that particular vaulter.
The vertex height can also be considered to be a constant of fixed length because of the:
(1) Unique anthropometric proportions of the individual vaulter
(2) Chosen grip length apart of the upper and lower hand being kept the same for all vaults
(3) Lower grip arm position and orientation with respect to the shoulder joint is also kept the same for all vaults.
***The maximum vertical reach height obtainable by the upper hand, no matter what the length along the pole at which it is located, is primarily determined by the precise 3 Dimensional location of the lower hand grip at the instant the pole tip makes initial contact with the rear wall of the planting box.
This is a fact beyond dispute and confirmable by simple empirical experiment suggested below.
With the pole tip located in the deepest part of the planting box, find the toe-tip location that maximizes the pole ground angle with both hands gripping the pole. Release the top hand grip and extend the lower grip hand vertically upwards maintaining its same grip location on the pole.
When the maximum height holding the pole with the lower grip arm extended upward is achieved, the vaulter with upper grip arm fully extended and aligned to the ear (note does not need to be touching the ear!) will fail to grasp the pole at the same exact grip width along the inclined pole that was possible when it was gripped by both hands.
Note that when the lower grip only is used the vaulter will have to move the take-off foot toe tip horizontally forward because the pole ground angle (beta) will noticeably increase until a right triangle is formed by the pole and the body alignment of the vaulter. The gain in vertex height required of the top hand grip location obtained when holding the pole by the lower arm only, proportionally decreases the horizontal distance back along the runway to the take-off toe tip.
When coaches suggest that the vaulter is “under” or “out” they are, tacitly or explicitly, expressing awareness of the proportional relationships they have observed in the attempt by the vaulter.
Having observed the movement possibly using their “intuition” or the “yardsticks” provided by millennia old geometric and mathematical principles, experienced coaches and vaulters are able to make finely discriminated spatial judgements. This is especially the case with respect to take-off foot placement and the visualized vertical line between the top grip hand placement on the pole and a point where it intersects the surface of the runway.
On this basis the geometric and triangle relationship hypothesis offered, predicts that there is a precise location for the toe tip of the take-off foot in pole vaulting.
This hypothesis (theoretical (conceptual) model) has as its central tenet the proposition that the major objective of the vaulter in effecting a pole vault take-off is, to maximize the pole ground angle at the instant the take-off foot toe tip no longer contacts the ground.
The theoretical model predicts that the precise point of the take-off toe tip location will occur at variable horizontal distances with respect to the rear wall according to the particular grip length along the pole and its associated grip spacing between the hands chosen by a specific vaulter for a particular vault attempt.
My position is that my empirical observations and experiences of real pole vaulting do not falsify this hypothesis!
Therefore I strongly maintain my belief that there is an “ideal correct take-off location” that is precise and specific to each vaulter and is primarily determined by the grip length and hand grip separation width on the pole chosen by them for a particular vault attempt.
The strength of my belief relies on geometrical and mathematical laws that give repeatable, precise and accurate predictions, so far as I am aware, that are corroborated empirically by practicing pole vault coaches worldwide.
In summary, the Laws of Proportions of Similar Triangles and Pythagorian Theory dictate what empirically should be observed to occur in real life pole vaulting at the take-off.
I find there is no convincing evidence to show that the predictions that follow from this theory are not verified in the practical performance of rigid or flexible pole vaulting take-offs.
I leave readers to make their own judgements.
Having established an accurate mathematically predictive basis upon which to describe the pole vault take-off foot location on the runway it remains to be demonstrated what real life pole vaulters actually do when they perform a pole vault take-off.
The take-off I functionally define as:
“The physical method used by a vaulter, whilst attached to the pole by two hands firmly gripping it, to project their body and the attached pole from the ground by a single leg propulsion technique. The propulsion technique adopted to do this should efficiently minimize loss of energy / momentum accrued during the preceding approach run and pole planting actions.
At the culmination of the propulsive projection (projection leg toe-tip breaking ground contact) the vaulter’s body and the pole should be oriented spatially and temporally in such manner the capacity of the vaulter to continue to propel and steer (drive) the total vaulter pole system is optimal in setting up and accomplishing the next sequential component of the vaulting process.”
Currently there are three types of take-off advocated as having efficacy in achieving optimum functionality in the pole vault take-off with a flexible pole.
The oldest and perhaps still the most widely used method of take-off I refer to as,
(1) The Deliberate Pole Pre-Bend Take-Off Technique. In this form of take-off the pole undergoes considerable bend induced deliberately by the vaulter before the take-off leg toe-tip breaks ground contact. Currently this is the method being successfully used by Renaud Lavillenie.
The next most widely adopted method of take-off is the “Free-Take-Off; Petrov-Bubka Model” the take-off technique currently central to the discussion in this thread I refer to as,
(2) The Free- Take-Off. In this form of take-off the pole is deliberately kept straight (recognising there is a natural bend due to the manufacturing method and the location of the centre of mass of the pole) as the vaulter attempts to reduce resistance to the forward progression of the total system during the take-off until the simultaneous pole tip impact with the rear wall of the planting box and the take-off foot toe-tip breaking ground contact. Initial pole deformation, due to impact with the rear wall, occurs whilst the vaulter is suspended from the pole. The vaulter is no longer directly influenced by the foot being attached on the ground and therefore is dependent actively and reactively (Newton’s Laws) upon the pole which is attached to the mass of the earth directly through the planting box contact.
The third and quite rarely seen, even amongst elite male and female vaulters, is what I will refer to as “The Pre-Jump Take-Off.” An extreme example of advocacy of this form of take-off is the “Air Strike System.” I will refer to the pre-jump take-off technique as,
(3) The Pre-Jump Take-Off. The pre-jump take-off has two forms. The first type is a pre-jump technique in which both the vaulter and pole are momentarily airborne before any part of the planting box has been touched by the pole tip (advocated in the Air Strike System).
In the second type of pre-jump technique the pole tip is minimally in contact with the planting box sliding towards the rear wall as the take-off toe tip breaks ground contact. The travel trajectory of the vaulter and pole is uninterrupted (there is a resisting frictional force opposing the motion direction of the pole slide, but it is quite small relative to the inertial force of the vaulter pole system) until the pole tip contacts the rear wall so the vaulter can be considered to be freely suspended from the pole until this time. The vaulter is suspended below the hand grips when the initial deformation of the pole due to rear wall impact occurs.
(Note: the vaulter can never actually be “free” at any stage in pole vaulting because of the mutual gravitational attraction force that exists between the mass of the earth and the mass of the vaulter. The same applies to the pole).
I will delimit the rest of my contribution in the discussion to only consider Free and Pre-Jump Take-Off Techniques before I can comprehensively answer Kirk’s original question.
In my drawings below two of the take-offs depicted are unarguably Free Take-Offs. The other is close to achieving this form of take-off but has to be classified as a Pole Pre Bend Take-off.
Careful examination of the paths of the vaulter centre of mass between touch-down, mid-stance (support), toe-tip take-off and the rate of angular displacement, about the take-off foot toe-tip, during the total ground contact phase is revealing.(The drawings were made from still frames of the videos previously cited and superimposed with respect to the takeoff foot when fully grounded).
The body postures at touch-down, mid-support, and toe-tip take-off are also informative despite the small but practically very significant kinematic differences.
These small differences have quite dramatic consequences on how, where and when the pole subsequently bends under compression forces induced by the take-off resultant linear translation force components and the centripetal force induced pole compression due to initiation of vaulter swing from the wrists joints of the lower and upper arm hand grips on the pole.
What net effective propulsive thrust the vaulter can actually achieve at the instant of toe-tip take-off is critically determined by vaulter actions during both the amortization and propulsive phases of the take-off and is particularly affected by:
(1) Horizontal distance in advance of the position of the vaulter’s centre of mass (COM) of the Take-Off foot at touch-down and the quantum of horizontal inertia generated by the approach run and plant initiation at that instant.
(2) Horizontal displacement forwards of the COM during the amortization phase of the total ground contact time as well as the amount of lowering to be decelerated and redirected during mid stance.
(3) Synchronicity of the timing and coordination of the total combined effort contribution from both arms as they complete the pole plant, the magnitude and direction of momentum transfer from the lead leg action coupled to the take-off limb hip, knee and ankle power delivery to accelerate the COM in an upward and forward direction.
Videos referred to and the drawings above provide some evidence I invite readers to consider against their own empirical experience of pole vault take-offs. Having done this, I trust that you will formulate your own hypotheses as to the effects the take-off has upon pole bending.
In my next posting I shall examine the variability possible in executing any pole vault take-off. Also I will attempt to show why the subtlety of the instruction in the Petrov-Bubka Free-Take-Off to Spring Upwards and Forwards rather than Forward and Upward produces a totally different set of dynamic consequences in the pole compression phase of the vault.
Sergei Bubka
http://youtu.be/y9Q4rL0PC-s
Svetlana Feofanova
http://youtu.be/-TWAbc5TdpM
Annika Becker
http://youtu.be/xpfUUcjMRI4
Dmitri Markov
http://youtu.be/v9Ne--kuMUU
Consider the take-off showing identical body posture orientations at toe tip take-off of a tall and short stature vaulter. Both vaulters take exactly the same grip length measured from the pole tip to the top of the top hand grip. Each vaulter also makes identical grip-width spacing between the upper and lower hand locations on the pole.
With both hands gripped on the pole, the pole tip firmly located in contact with the deepest part of the planting box and the rear wall, the vaulter rises on to toe–tip with their body erect and both arms simultaneously positioned in the finish of the plant position.
Consensus coaching practice is for the vaulter’s upper grip arm to be fully extended in alignment with the ear whilst the head held in the neutral / anatomical position as the toe-tip, with torso held firmly erect, position is reached.
In real life some slight forward lean by the vaulter is required to maintain pressure through the pole-tip against the bottom of the rear wall to sustain a stable balance when fully raised on toe tip.
It is immediately obvious that the taller vaulter has:
(1) Higher reach upwards with the upper grip hand
(2) Greater pole ground angle (Angle B > A)
(3) Take-off toe tip location is closer horizontally along the runway surface in relationship to the pole tip located in the deepest part of the planting box.
The vaulter adjusts the location of their take-off foot toe position until a perpendicular line projected from the toe position on the runway intersects with the top of the upper hand grip on the pole.
The effective pole length is a constant (same length) for both a short and tall vaulter gripping the pole with identically located positions of the upper hand and between grip spacing.
By definition a right triangle will be formed with hypotenuse “C” (the constant effective pole length) for vaulters gripping the pole at the same grip length when the final toe-tip position indicated in the diagram and the pictures below is achieved.
It follows from the Laws of Properties of Similar Triangles and Pythagorian Theory the toe –tip of the taller of two vaulters, who in all other respects is similar to the shorter, must be located closer in the horizontal direction (right triangle side A) to the pole tip contacting the rear wall when it is located in the deepest part of the planting box.
The vertex of the right triangle is side B. The height of side B is measured vertically from the deepest point in the planting box to the highest point of the position of the top grip hand at toe-tip take-off.
If the proposition that the pole ground angle (beta), (the angle between side A and the hypotenuse side C of the triangle) should be maximized to thereby minimize the angular distance the chord of the pole must travel (angle alpha) to pass through the transverse vertical plane from the pole tip in the planting box, is accepted the taller vaulter will have a distinct advantage in making the take-off.
Tall vaulters, because of their height, have higher pole ground angles at touch-down and at take-off and consequently have LESS pole chord angle to travel through to move past the transverse vertical plane from the pole tip located in the planting box. Also a tall vaulter has less horizontal displacement to travel before passing through the transverse vertical plane of the pole chord when the pole is fully straight at the end of its recoil phase (all other factors being the same for both vaulters).
For any individual vaulter, if the proposition holds true in real life, a decrease in effective grip length on the pole should result in the vaulter’s take-off foot toe tip location on the runway being horizontally closer to the rear wall of the planting box. Consequently the pole ground angle should also be greater at the take-off from this closer location (assuming the postural configuration and vertex height from toe tip to highest point on the top hand grip(side B) remains constant for that particular vaulter.
The vertex height can also be considered to be a constant of fixed length because of the:
(1) Unique anthropometric proportions of the individual vaulter
(2) Chosen grip length apart of the upper and lower hand being kept the same for all vaults
(3) Lower grip arm position and orientation with respect to the shoulder joint is also kept the same for all vaults.
***The maximum vertical reach height obtainable by the upper hand, no matter what the length along the pole at which it is located, is primarily determined by the precise 3 Dimensional location of the lower hand grip at the instant the pole tip makes initial contact with the rear wall of the planting box.
This is a fact beyond dispute and confirmable by simple empirical experiment suggested below.
With the pole tip located in the deepest part of the planting box, find the toe-tip location that maximizes the pole ground angle with both hands gripping the pole. Release the top hand grip and extend the lower grip hand vertically upwards maintaining its same grip location on the pole.
When the maximum height holding the pole with the lower grip arm extended upward is achieved, the vaulter with upper grip arm fully extended and aligned to the ear (note does not need to be touching the ear!) will fail to grasp the pole at the same exact grip width along the inclined pole that was possible when it was gripped by both hands.
Note that when the lower grip only is used the vaulter will have to move the take-off foot toe tip horizontally forward because the pole ground angle (beta) will noticeably increase until a right triangle is formed by the pole and the body alignment of the vaulter. The gain in vertex height required of the top hand grip location obtained when holding the pole by the lower arm only, proportionally decreases the horizontal distance back along the runway to the take-off toe tip.
When coaches suggest that the vaulter is “under” or “out” they are, tacitly or explicitly, expressing awareness of the proportional relationships they have observed in the attempt by the vaulter.
Having observed the movement possibly using their “intuition” or the “yardsticks” provided by millennia old geometric and mathematical principles, experienced coaches and vaulters are able to make finely discriminated spatial judgements. This is especially the case with respect to take-off foot placement and the visualized vertical line between the top grip hand placement on the pole and a point where it intersects the surface of the runway.
On this basis the geometric and triangle relationship hypothesis offered, predicts that there is a precise location for the toe tip of the take-off foot in pole vaulting.
This hypothesis (theoretical (conceptual) model) has as its central tenet the proposition that the major objective of the vaulter in effecting a pole vault take-off is, to maximize the pole ground angle at the instant the take-off foot toe tip no longer contacts the ground.
The theoretical model predicts that the precise point of the take-off toe tip location will occur at variable horizontal distances with respect to the rear wall according to the particular grip length along the pole and its associated grip spacing between the hands chosen by a specific vaulter for a particular vault attempt.
My position is that my empirical observations and experiences of real pole vaulting do not falsify this hypothesis!
Therefore I strongly maintain my belief that there is an “ideal correct take-off location” that is precise and specific to each vaulter and is primarily determined by the grip length and hand grip separation width on the pole chosen by them for a particular vault attempt.
The strength of my belief relies on geometrical and mathematical laws that give repeatable, precise and accurate predictions, so far as I am aware, that are corroborated empirically by practicing pole vault coaches worldwide.
In summary, the Laws of Proportions of Similar Triangles and Pythagorian Theory dictate what empirically should be observed to occur in real life pole vaulting at the take-off.
I find there is no convincing evidence to show that the predictions that follow from this theory are not verified in the practical performance of rigid or flexible pole vaulting take-offs.
I leave readers to make their own judgements.
Having established an accurate mathematically predictive basis upon which to describe the pole vault take-off foot location on the runway it remains to be demonstrated what real life pole vaulters actually do when they perform a pole vault take-off.
The take-off I functionally define as:
“The physical method used by a vaulter, whilst attached to the pole by two hands firmly gripping it, to project their body and the attached pole from the ground by a single leg propulsion technique. The propulsion technique adopted to do this should efficiently minimize loss of energy / momentum accrued during the preceding approach run and pole planting actions.
At the culmination of the propulsive projection (projection leg toe-tip breaking ground contact) the vaulter’s body and the pole should be oriented spatially and temporally in such manner the capacity of the vaulter to continue to propel and steer (drive) the total vaulter pole system is optimal in setting up and accomplishing the next sequential component of the vaulting process.”
Currently there are three types of take-off advocated as having efficacy in achieving optimum functionality in the pole vault take-off with a flexible pole.
The oldest and perhaps still the most widely used method of take-off I refer to as,
(1) The Deliberate Pole Pre-Bend Take-Off Technique. In this form of take-off the pole undergoes considerable bend induced deliberately by the vaulter before the take-off leg toe-tip breaks ground contact. Currently this is the method being successfully used by Renaud Lavillenie.
The next most widely adopted method of take-off is the “Free-Take-Off; Petrov-Bubka Model” the take-off technique currently central to the discussion in this thread I refer to as,
(2) The Free- Take-Off. In this form of take-off the pole is deliberately kept straight (recognising there is a natural bend due to the manufacturing method and the location of the centre of mass of the pole) as the vaulter attempts to reduce resistance to the forward progression of the total system during the take-off until the simultaneous pole tip impact with the rear wall of the planting box and the take-off foot toe-tip breaking ground contact. Initial pole deformation, due to impact with the rear wall, occurs whilst the vaulter is suspended from the pole. The vaulter is no longer directly influenced by the foot being attached on the ground and therefore is dependent actively and reactively (Newton’s Laws) upon the pole which is attached to the mass of the earth directly through the planting box contact.
The third and quite rarely seen, even amongst elite male and female vaulters, is what I will refer to as “The Pre-Jump Take-Off.” An extreme example of advocacy of this form of take-off is the “Air Strike System.” I will refer to the pre-jump take-off technique as,
(3) The Pre-Jump Take-Off. The pre-jump take-off has two forms. The first type is a pre-jump technique in which both the vaulter and pole are momentarily airborne before any part of the planting box has been touched by the pole tip (advocated in the Air Strike System).
In the second type of pre-jump technique the pole tip is minimally in contact with the planting box sliding towards the rear wall as the take-off toe tip breaks ground contact. The travel trajectory of the vaulter and pole is uninterrupted (there is a resisting frictional force opposing the motion direction of the pole slide, but it is quite small relative to the inertial force of the vaulter pole system) until the pole tip contacts the rear wall so the vaulter can be considered to be freely suspended from the pole until this time. The vaulter is suspended below the hand grips when the initial deformation of the pole due to rear wall impact occurs.
(Note: the vaulter can never actually be “free” at any stage in pole vaulting because of the mutual gravitational attraction force that exists between the mass of the earth and the mass of the vaulter. The same applies to the pole).
I will delimit the rest of my contribution in the discussion to only consider Free and Pre-Jump Take-Off Techniques before I can comprehensively answer Kirk’s original question.
In my drawings below two of the take-offs depicted are unarguably Free Take-Offs. The other is close to achieving this form of take-off but has to be classified as a Pole Pre Bend Take-off.
Careful examination of the paths of the vaulter centre of mass between touch-down, mid-stance (support), toe-tip take-off and the rate of angular displacement, about the take-off foot toe-tip, during the total ground contact phase is revealing.(The drawings were made from still frames of the videos previously cited and superimposed with respect to the takeoff foot when fully grounded).
The body postures at touch-down, mid-support, and toe-tip take-off are also informative despite the small but practically very significant kinematic differences.
These small differences have quite dramatic consequences on how, where and when the pole subsequently bends under compression forces induced by the take-off resultant linear translation force components and the centripetal force induced pole compression due to initiation of vaulter swing from the wrists joints of the lower and upper arm hand grips on the pole.
What net effective propulsive thrust the vaulter can actually achieve at the instant of toe-tip take-off is critically determined by vaulter actions during both the amortization and propulsive phases of the take-off and is particularly affected by:
(1) Horizontal distance in advance of the position of the vaulter’s centre of mass (COM) of the Take-Off foot at touch-down and the quantum of horizontal inertia generated by the approach run and plant initiation at that instant.
(2) Horizontal displacement forwards of the COM during the amortization phase of the total ground contact time as well as the amount of lowering to be decelerated and redirected during mid stance.
(3) Synchronicity of the timing and coordination of the total combined effort contribution from both arms as they complete the pole plant, the magnitude and direction of momentum transfer from the lead leg action coupled to the take-off limb hip, knee and ankle power delivery to accelerate the COM in an upward and forward direction.
Videos referred to and the drawings above provide some evidence I invite readers to consider against their own empirical experience of pole vault take-offs. Having done this, I trust that you will formulate your own hypotheses as to the effects the take-off has upon pole bending.
In my next posting I shall examine the variability possible in executing any pole vault take-off. Also I will attempt to show why the subtlety of the instruction in the Petrov-Bubka Free-Take-Off to Spring Upwards and Forwards rather than Forward and Upward produces a totally different set of dynamic consequences in the pole compression phase of the vault.