GRV: Lavillenie - From Stall Swing to World Record

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dougb
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby dougb » Fri Sep 05, 2014 8:22 pm

PVstudent

I have been reading your posts for some time and am an admirer of your approach to building a mathematical model of the modern pole vault. However, your attempt to fit the double pendulum to the real world leads to errors.

Why?

The modern vault is not a double pendulum as you are describing. Specifically the axis point A in your diagrams does not exist. Look at film from the leading vaulters in the world from Bubka on, and you will find:

1. The angle of the right arm with ground does not change appreciably throughout the vault until the vaulter is capulted by the release of energy stored in the pole. There is no rotation.
2. The left arm of all these vaulters is used to transfer point A in your diagram to the shoulders.
So the rotation of the COM IS about the shoulder and NOT the right hand.
Again look at film and you will find that when the left leg is pointing at the box the left arm is (almost) universally locked straight. Especially Bubka.

When trying to find commonality or differences between the Petrov/ Bubka style and Levellenie’s style I believe that any model must incorporate the second pendulum pivot point at the shoulders and not the top hand.

Respectfully

Douglas balcomb
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby KirkB » Fri Sep 05, 2014 10:22 pm

dougb wrote: The modern vault is not a double pendulum as you are describing. Specifically the axis point A in your diagrams does not exist.

1. The angle of the right arm with ground does not change appreciably throughout the vault ... There is no rotation.

So the rotation of the COM IS about the shoulder and NOT the right hand.
... I believe that any model must incorporate the second pendulum pivot point at the shoulders and not the top hand.

I see your point, Doug, but let's not refer to the shoulder as if it's a better pivot point to model than the top hand.

It was easier to visualize in the straight pole days, but there is in fact a double pendulum (less so now, with a bending pole, but it's still there).

Rather than focussing on the pivot points of the double pendulum, if you visualize the ANGLE of the chord of the pole and the ANGLE of the "chord" of the vaulter's body as it rotates towards the chord of the pole, then you will get my point.

It's unconventional to speak of the "chord" of the vaulter's body, but what I mean is the imaginary line from the vaulter's top hand to his COM. As long as the relative ANGLES of the 2 chords decrease (converge), then I would call that a double pendulum. Not as visually evident as with a straight pole, but a double pendulum nevertheless.

The reason you must look at the "chord" of the vaulter (rather than any pivot point) is because as he's swinging, he's changing his C position into a reverse-C position, so the relative positions of his elbow, shoulder, and hip are continually changing. These body parts (top hand, elbow, shoulder, hip, knee, and foot) are not fixed points (well, the top hand is), but the vaulter's chord and the pole's chord are always there (even if hard to pinpoint on a frame).

This "vaulter's COM" that I'm referring to is slightly different than (and not to be confused with) PVstudent's "Total System COM". The vaulter's chord (or whatever you want to call it) would be behind the vaulter's hips on takeoff, and then ahead of the vaulter's hips once the C transitions to a reverse-C (coincidentally, the 2 chords would converge as the vaulter whips his trail leg past the pole's chord - when his body is straight, his COM is in his hips). My reference to a "vaulter's COM" is just an additional visualization to take into account - in addition to PVstudent's "Total System COM" and all his articulations.

To be fair to PVstudent's qualifications re his model, he did say ...
PVstudent wrote:I believe the approach I am presenting will ultimately provide a way of observing and understanding the pole support phases that reduces the complexity that occurs if the actions of the vaulter and the pole are viewed as separate pendulum motions.

i.e. Double pendulum or not, it's just a model (with a specific purpose in mind) - not the real thing.

Just my 2 cents worth.

Kirk
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Fri Sep 05, 2014 11:12 pm

dougb wrote:PVstudent

I have been reading your posts for some time and am an admirer of your approach to building a mathematical model of the modern pole vault. However, your attempt to fit the double pendulum to the real world leads to errors.

Why?

The modern vault is not a double pendulum as you are describing. Specifically the axis point A in your diagrams does not exist. Look at film from the leading vaulters in the world from Bubka on, and you will find:

1. The angle of the right arm with ground does not change appreciably throughout the vault until the vaulter is capulted by the release of energy stored in the pole. There is no rotation.
2. The left arm of all these vaulters is used to transfer point A in your diagram to the shoulders.
So the rotation of the COM IS about the shoulder and NOT the right hand.
Again look at film and you will find that when the left leg is pointing at the box the left arm is (almost) universally locked straight. Especially Bubka.

When trying to find commonality or differences between the Petrov/ Bubka style and Levellenie’s style I believe that any model must incorporate the second pendulum pivot point at the shoulders and not the top hand.

Respectfully

Douglas balcomb


Thank you for your response to my most recent post.

To your first point, I am not trying to create a mathematical model. Rather I am trying to simplify my conceptual understanding of the process of the pole support phase of the vault.

Your comment is timely and much appreciated. It points up the need always to make others aware of limitations of any simplifying pole vault analysis.

In so doing I am sensitively aware of the issue you address namely the shifting of the primary axis of rotation especially in the first phase of the vault.

By making the focus of the observer's and the analysis attention the Total System Centre of mass (COM) ,the point that represents a single point at which the distributed masses of the vaulter's body and of the pole, as a total combined multi-body system can be represented, facilitates its motion with being tracked through the 3-D space with respect to time from visual recording records of performance.

I have already previously put the diagram below on PVP which shows the key point you make and with which I think we both agree.

Bubka swing roll up from instant of maximum moment of inertia about the top hand til max pole bend.jpg
Bubka swing roll up from instant of maximum moment of inertia about the top hand til max pole bend.jpg (91.92 KiB) Viewed 7714 times


How the Axis A shifts in phase 1 of the pole support phase has bedevilled biomechanical analyses and coaches alike because hitherto no one has found a scientifically valid way of instrumenting the pole to directly measure the forces at each grip on a continuous time base. In those few attempts reported in the scientific literature that have even addressed this problem the investigators have had to make a choice about how and where to place the vector to represent the 3-D forces acting at each hand. Using inverse dynamics also does not resolve the issue.

The choices are top hand, bottom hand, at both hands or somewhere between the hands when trying to find the vaulter to pole interface during the time the vaulter's COM is supported in suspension below the hand grips.

(I personally will be opting for the vaulter pole interface axes at both hands and will present an analysis that I hope will offer a mechanism explanation that explains how the vaulter moves the primary rotation axis to the mid shoulder region in phase 1 of pole support)

Approaching the pole support challenge from the double pendulum perspective of the total system COM has limitations some of which you have correctly identified.

These limitations in my view do not invalidate the concept that underlies the key to my point that it is the pole chord length change that governs the respective changes in the length of pendulum A to the COM and Pendulum B to the COM because the vaulter is attached at one end of the pole and the pole tip is fixed (relatively) in the planting box.

For a detailed fine grained analysis of the vaulter's use of the actions of the multiplicity of their own limbs and body segment masses the vaulter action is, I would agree, better described using " Multiple local axes for the vaulter acting on the pole" in propelling the total system about a single Remote or Global Axis.

When this approach is used there is a tendency for the detail to obscure the essential goal with respect to what the primary mechanical challenge the vaulter must overcome to achieve success actually is.

Thank you for making readers aware of the limitation to my conceptual model (That is all it is!) which, when used in my practical coaching ,I have found helpful.

I will try to address, the limitations you rightly point out as I develop further the concept of the double pendulum acting on the total system COM in the framework I have been building and will be using in making the comparisons of Bubka v Lavillenie Technique.

Thanks Doug your comment is well taken stick with me for a while longer and continue to comment, it is very helpful!
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Wed Oct 01, 2014 12:54 pm

Once the vaulter has broken take-off foot ground contact and the pole tip is contacting the rear wall of the planting box (start of phase 1 of pole support) the inertia of the total system centre of mass (COM total system) is applied to the pole via each hand gripping the pole.

Sliding Vector concept in explanation of momentum transfer from the take-off into suspension below grips on the pole.jpg
Sliding Vector concept in explanation of momentum transfer from the take-off into suspension below grips on the pole.jpg (72.93 KiB) Viewed 7510 times


The total inertia immediately before take-off becomes a force acting fully on the pole when transferred in some proportion at each of the upper and lower hand grips when the pole tip makes initial contact with the box rear wall and take-off occurs.

(Note the inertia transfer proportion at each hand is functionally dependent on the vaulter’s musculo-skeletal actions, the geometric locations of their distributed segmental centre of mass arrangement once the vaulter is in suspension below the hand grips).

What the proportion of the total force applied at each hand actually is when the pole impacts with the box is difficult to determine with certainty? The relative proportions of force applied through each hand grip is also dependent on considerations such as:

1. The free body diagram representation (FBD) of the forces acting indicates that the resultant force being exerted by the vaulter on the pole is directed forward and slightly below the horizontal (Resultant shown in Green). The reaction force at the pole tip (point B) must be directed horizontally back towards the vaulter and slightly upward (ie., parallel in the same plane and oppositely directed with the same magnitude as the resultant force being applied at a point located between the hands).

2. Resolving the Inertial force resultant into its components applied to the pole via the hand grips can be achieved by treating the total system COM resultant momentum immediately prior to pole tip impact with the rear wall of the box as a “Sliding Vector”. This is shown in the diagram above by sliding the total system COM point of application of the take-off momentum resultant vector to where it intersects the pole to show that when rear wall contact by the pole tip occurs there is an effective inertial force being exerted on the pole via the hand grips.

3. Distance in front of the top hand at which the vertical line projected upwards from the total system COM intersects with the chord of the pole at the top grip axis affects the moment of force about the top grip hand and the ratio of penetration to lift due to the horizontal and vertical components of the inertial forces applied through each hand to the pole.

(Note: in practice this intersection point must be physically located on the real portion of the pole somewhere between the centre of the top and bottom hand grips).

Vector resultant force diagram of take-off momentum transfer to the hand grips at take-off.jpg
Vector resultant force diagram of take-off momentum transfer to the hand grips at take-off.jpg (79.79 KiB) Viewed 7510 times



4. The direction and speed the total system centre of mass is moving at when the pole impacts the rear wall of the box when considered in conjunction with points 1 – 3 determine whether the total system weight force (gravity) will reduce, increase or makes no difference to the magnitude of the tangential force that rotates the centre of mass of the total system (COM system) about the pole tip in the planting box ((Net Torque acting COM system = T net about axis B = (-F mg x length r B . cosine angle theta) + (F tangential x length r B)).

5. The net torque will vary in magnitude, but not direction, when the Total System, combined COM of the vaulter plus the pole, turns clockwise about Axis B throughout phase 1 and most of phase 2 of pole support.

6. The net torque produced by the vaulter about Axis A does change direction shortly preceding the instant the pole chord becomes coincident with the line of the longitudinal neutral axis of the pole and the pole can therefore be considered straight in the 2nd phase of pole support (assuming the pole has not already become straight before completion of the half turn and top hand grip release = “flagging”).

From the diagram below it should be clear that the Total System COM will have an anticlockwise gravitational torque acting throughout the pole support phase of the vault until the COM can be positioned directly above the pole tip location in the deepest point of the pole planting box.

Run to rise ratio in 1st phase of pole support of the total system COM..jpg
Run to rise ratio in 1st phase of pole support of the total system COM..jpg (128.5 KiB) Viewed 7510 times


For the Total System COM to attain the vertical equilibrium point above the pole tip (Axis B) the vaulter has to deliver sufficient net impulse via the pole to the earth at take-off and throughout the total pole support phase to overcome the anticlockwise total system weight force torque about the pole tip (Axis B).

... continues next post
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Wed Oct 01, 2014 2:26 pm

The picture sequence and diagram below of Sergei Bubka in the 1st phase of pole support shows the action pattern he adopted for this particular vault (1st ever 6.00m Clearance).

Total system pendulum and the vaulter pendulum on the connecting pole to Axis B.jpg
Total system pendulum and the vaulter pendulum on the connecting pole to Axis B.jpg (119.75 KiB) Viewed 7506 times


The inset in the diagram represents the vaulter (Pendulum 1) component of the double pendulum Total System COM as a variable length, damped spring loaded pendulum.

The vaulter uses muscle joint systems as torque and force generators to continue to power the vault throughout both phases of pole support without the power flow (Force or Torque x Velocity) being interrupted or misdirected!

Whilst the pole is a “Hookean” type of spring mechanism a vaulter’s muscles, tendons and ligaments are Non – Hookean with the muscle compliance controlled by a viscous dashpot like mechanism.

The vaulter’s skeletal framework depending on how it is fixed or activated by muscle and tendon attachment to bones exhibits “spring like” mechanism characteristics to fixate or move the bone “struts” in the arm-torso coupled with the pelvic girdle lower limbs framework linkages.

Because muscle and joint actions of the vaulter’s body are subject to Viscous Damping human muscles can be stimulated (voluntarily switched on by the vaulter) to behave as non-linear activators of body segmental motion and / or to “absorb shock impulses”.

The diagram above indicates this by placing variable length springs and dashpots to indicate muscles connected in series that symbolically represent damped muscle action torques and forces generated by the vaulter and used to operate a long, slender, thin walled hollow cylindrical pole as a variable length spring leverage tool to accomplish the pole support phases of a vault.

(Muscle; the mechanical driver or controller of the skeleton “strut structure mechanism” fixation or movement of individual body segments in the vaulter’s body).

The following diagram shows a vaulting action sequence used by Sergei Bubka (6.11m clearance) which I have drawn from individual frames of the film recording to show schematically how he transferred his take–off momentum to produce pole bending and consequently turn the total (vaulter plus pole) system about the pole tip pivoting in the vaulting box.

Bubka transfer of momentum in phase 1 of pole support.jpg
Bubka transfer of momentum in phase 1 of pole support.jpg (76.86 KiB) Viewed 7506 times


Images 8 and 9 captures the approximate time interval and 2-D spatial displacements of the vaulter’s body segments occurring in the take-off with this initial vaulter momentum being transfered to the mass of the earth via the two hand grip attachments on the pole.

From image 8 onwards the vaulter is in the pole support phase of the vaulting with his COM still suspended below the top grip hand until the final image 21.

Image 21 marks the start of the turn and push-off part of the pole recoil phase of support.

To transfer momentum to the pole efficiently the vaulter must produce physical actions such that the “Impulse delivered by the vaulter to the pole “causes the Total System COM Inverted Pendulum to acquire sufficient angular momentum about the pole tip (Axis B) to rotate successfully to its equilibrium position with the COM “Bob” vertically above the pole tip.

Vaulter upper limbs body segmental truss structure mechanism 2.jpg
Vaulter upper limbs body segmental truss structure mechanism 2.jpg (79.11 KiB) Viewed 7506 times


Centripetal force generated by the vaulter’s swing action in phase one of pole support can be decomposed into radial and tangential components acting on the total system COM to produce a net Torque (F tangential Vector x Pendulum Length Vector rB) in the clockwise direction sufficient in magnitude to turn the total system COM about the Inverted Pendulum Axis B at the pole tip.

The radial component of the resultant force acts to compress and bend the pole whilst at the same time the tangential force acting at perpendicular distance rB to axis B turns the pole forwards in the XY plane during the initial part of the 1st pole support phase of the vaulting motion.

The horizontal component of the vaulter applied resultant force contributes primarily to propelling the pole bend horizontally forwards to produce total system COM penetration as well as clockwise rotation about the pole tip axis B in phase 1 of pole support.

The vertical component of the vaulter applied resultant force is responsible for the lift and rise of the total system COM and reduces the gravitational (system weight) torque retarding effect on pole rotation during phase 1 of pole support.

During pole bending and recoil of the pole the vaulter swing and upper limb effort is directed to maintain pole chord rotation forwards in the XY plane until the time the vaulter’s whole body COM is supported above the height level attained by the top grip hand and pole release occurs.

How the vaulter transmits translatory and angular momentum to and from the pole, particularly about the transverse axes at shoulder and pelvic regions of the body, requires a basic understanding of the pendular linkage structures and mechanism being employed in the 1st and 2nd phases of pole support.

... continued next post
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Thu Oct 02, 2014 10:21 am

The Centripetal Force generated by the vaulter’s swing action in phase 1 and 2 of pole support can be decomposed into a radial and tangential component acting on the total system COM to produce a Torque (F tangential Vector x Pendulum Length Vector rB) in the clockwise direction sufficient in magnitude to turn the total system COM about the Inverted Pendulum Axis B at the pole tip.

The 1st phase is dominated by the vaulter pendulum swing effort to rotate and compress the pole. On the other hand, the second phase of pole support is primarily concerned with vaulter inversion accompanied by a turn to redirect the vaulter’s body so that its frontal aspect faces directly towards the plane of the cross-bar whilst the pole completes it's recoil.

The following two diagrams portray the key mechanical effect that the vaulter has on the pole and the counter effects the pole has on the vaulter in the two phases of pole support.

1st phase pole support forces 3D 3.jpg
1st phase pole support forces 3D 3.jpg (112.23 KiB) Viewed 7465 times


Diagram shows the vaulter at the start of the “Whip Swing” by the take-off leg in the 1st phase of pole support.

The take-off momentum has been transferred to the resisting pole. Pole bend with horizontal and vertical translation of the total system COM has already been initiated prior to the retarding of the vaulters shoulders due to the maximum elongation of the top grip arm combined with shoulder girdle elevation brought about by the vaulter's reaction to the impact against the pole's flexural stiffness.

The stopping of the forward upward motion of the shoulder advance (relative to the top grip hand position on the pole) in the + x direction in the sagittal plane sets up a top – down (proximal to distal) kinetic chain of momenta transfers through the vaulter’s suspended body which combined with vaulter muscle energy input generates the centripetal forces of vaulter swing about the shoulder and hip horizontal transverse axes.

The time taken to retard the forward advancement of the vaulter's shoulders at the end of the range of the joint motion has to be quick so that muscle stretch mechanisms can be more effective in the creation of a propulsive impulse due to momentum change and transfer interactions between the vaulter and the pole.

A second propulsive impulse to the total system COM can be induced by the force, velocity and length of the whip swing leg kicking action and follow through if the swing is started coincident with the stopping of the advance of the shoulders.

The time interval over which the momentum transfer occurs in relation to the magnitude and direction of the change in velocity of the COM is a critical determinant of the particular differences in techniques adopted by Sergei Bubka and Renaud Lavillenie in propelling the total system COM whilst at the same time storing elastic strain potential energy in the compression phase of pole support.

2nd phase pole support pole recoil forces 3D 1.jpg
2nd phase pole support pole recoil forces 3D 1.jpg (106.2 KiB) Viewed 7465 times

Diagram above shows the vaulter at the start of the pole recoil in the 2nd phase of pole support.

It is important to note that the pole is now restoring energy to the total system COM via the hand grips of the vaulter and that the length of the pole increases as the pole spring restoring force decreases throughout phase 2 of pole support.

The radius (vector r axis B) from Axis B at the pole tip to the total system COM continually increases in length whilst the COM point location in space revolves around the + Y axis perpendicular to XZ Horizontal Plane at the pole tip.

During approximately the first 2/3 of the recoil the vaulter inverts their body to bring it closer to the initially unbending pole shaft which also begins to reflect (reverse of deflection) to maintain the pole chord direction of rotation about the pole tip primarily forward in the + X direction in the Sagittal plane.

The ratio of rise to penetration becomes inverse to that found in phase 1. (see previous posts).

The vaulter actions are coordinated to optimize the rate of vertical lift and yet maintain sufficient total system COM translation and rotation, with respect to the pole tip axis point B and the Frontal (YZ) plane location setting of the crossbar, so that the vaulter’s COM achieves an optimal projection trajectory at final pole release.

The diagram below illustrates the situation at the commencement of the “Inversion” by a technically poor vaulter who at this instant in phase 2 is shown to have already failed to synchronize the inversion action to the rate of pole recoil.

Pole support phase front and side view and 3D motion of pole rotation about transverse and longitudinal axis through the pole tip.jpg
Pole support phase front and side view and 3D motion of pole rotation about transverse and longitudinal axis through the pole tip.jpg (85.34 KiB) Viewed 7465 times


Renaud Lavillenie’s optimization technique used to gain inversion, vertical lift and projection from the pole is common and in widespread use compared to the mechanism espoused and used in the Petrov – Bubka Technical Model in the 2nd phase of pole support.

... continued next post.
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Fri Oct 03, 2014 1:17 pm

In this post I conclude the development of a conceptual framework based on considering the propulsion of the total system COM as the focal point of the technical challenge to be met by the vaulter in the pole support phase of the vaulting sequential process.

In a previous post I indicated a three bar linkage framework to help the viewer consider the mechanism of momentum transfers (exchanges) to the pole and back from the pole in the sequential order through the vaulter’s arms to shoulder joints and girdle, torso, hip joints with pelvic girdle and finally to the lead and swing legs.

The linkages enable the vaulter to produce “Bi –Filar Ballistic Pendulum Type Swing” into inversion leading to vaulter projection off the pole at final pole release.

The slightly flexed elbow combined with shoulder abduction (upper arm moved outward and upward laterally in the YZ (Frontal) plane) of the lower grip limb reduces twisting (Torsion) of the shoulder – torso body segmental unit about its longitudinal vertical axis. This central axis is taken to be located in the vertical line though a mid-point between right and left shoulder joints (approximately at the level of the sterno-clavicular manubrial joints).

Hence Pendulum 1 acting about Axis A will behave in the manner of a Bi-Filar Pendulum when the pole tip collides with the rear wall of the planting box at take-off.

The wrist and shoulder joint linkages allow the structure to undergo rotation and torsion whilst the difference in flexion angle of the separate elbow joints is a significant determinant of control for “Yaw”, “Roll” and “Pitch” of the vaulter’s remaining body mass configuration whilst in suspension below the level of the transverse axis between the right and left shoulder joints. (See diagrams below).

Vaulter upper limbs body segmental truss structure mechanism 3.jpg
Vaulter upper limbs body segmental truss structure mechanism 3.jpg (86.77 KiB) Viewed 7429 times


Just prior to maximum pole bend the pole buckle deflection to the vaulter’s left clearly shows the pole segment between the two hand grips 1, and the Lower and Upper grip limb segments numbered 2, 3 and 5, 6 respectively.

Both arms form the “filar structure struts” that will act as the suspension connectors to the shoulder joints for the pendulum swing by the vaulter through wrist and shoulder axes about the two hand grip attachment points on the pole.

Also the trunk abdominal core and pelvis (linked by the centrally located spine) provide a complex frame structure to support a transverse axis through the hips.

The lower limbs may be swung independently of each other, swung in synchrony with the entire lower limbs legs held apart or together in the same plane or in different planes of motion about the hip axes (hip joints are multi-axial joints).

Also each entire lower limb can be moved about the transverse hip axis simultaneously in conjunction with assisting or resisting pelvic girdle movements powered by the abdominal and spinal musculature acting between pelvis and trunk.

The pelvic girdle role in inversion technique has hitherto received scant attention and will be specifically addressed in differentiating Lavillenie’s from Bubka’s inversion technique.

Just after take-off, because the grips are located at different heights in the XY (Sagittal) plane and the pole lever is inclined with respect to the ground.
The leading lower arm grip radial length to the shoulder is shorter than the upper arm radial grip to shoulder length and this enables the shoulders to be kept level in the XY (Frontal / Lateral) plane.

The asymmetrical right to left side body segment arrangement, immediately upon take-off, requires dynamic stabilization by judicious muscle engagement through both arms being coordinated with the strong dynamic fixation of the shoulder girdle and joints to the thoracic cage of the vaulter’s trunk segment.

This is necessary to provide the upper body rigid base for the shoulder joints transverse axis upon which a powerful, fast and accurately directed torso and lower limbs combined swing can be established to continue pole penetration as it bends and to maintain pole chord rotation thereby ensuring an almost constant velocity rise (pole lift) of the total system COM.

Vaulter upper limbs body segmental truss structure mechanism 1.jpg
Vaulter upper limbs body segmental truss structure mechanism 1.jpg (80.15 KiB) Viewed 7429 times


As depicted in the diagram above this framework orientation focuses the penetration and lift directly forward and upward from the vaulter to the pole. With the vaulter aligned in the same vertical plane but on the runway and concave aspect relative to the bending pole, the vaulter plus pole combined COM rotate about the global inertial reference point origin axis at the pole tip in the sagittal plane.

Whether the lower arm flexes at the elbow or is pulled into extension relative to the vaulter’s shoulder joint and hand grip on the pole the vaulter’s COM will still remain suspended at a much lower height than the attachment point of the lower hand grip on the pole. Some portion of the vaulter’s weight must therefore act to pull downwards against the lower grip point on the pole.

The pole must react to this pull via the tensile force that exists between the grip points on the pole and the shoulder joints which produces pull downwards on the pole and an equal and opposite pull on the vaulter even if the lower grip arm elbow flexes or extends.

Remember the old adage … “You can’t push a load with a rope”!

Structure segment 4, the transverse axis formed by the shoulder joints and girdle complex, forms the vaulter bi – filar pendulum 1 axis attached by tensile forces exerted through the arms to the pole section between, and including both grips. Firm tight hand grips provide the bi-filar pendulum attachment points on the physical pole compression and tensile spring lever as it pivots about the pole tip in the box.

Vaulter upper limbs body segmental truss structure mechanism 4.jpg
Vaulter upper limbs body segmental truss structure mechanism 4.jpg (97.42 KiB) Viewed 7429 times


The total system COM is thereby constrained to follow a curvilinear path as the pole “spring” operated lever shortens, lengthens and turns about the pole tip Axis B which is the origin point (X o, Y o, Z o) of a 3-D coordinate reference frame within which the displacement, first and second derivatives of the Total System COM motion can be described.

Dropping the lead leg slightly and blocking the lower arm shoulder by extending the elbow against the momentum of the vaulter’s shoulders in the initial “run” direction of the total system COM continues to be widely misinterpreted.

The lower arm controversy arises largely because the “kinaesthetic feel” is interpreted on the part of the vaulter as “pushing out against the pole” (the vaulter is correct on the feel analysis) and this interpretation is reinforced by what the coach observes (also observation by the coach is correct).

The explanations from each as to how the vault is affected advantageously or disadvantageously due to this action are, more often than not, at odds with the mechanical facts of the situation.

Considering the vaulter as a bi-filar pendulum rotating about the axis of the top hand in the initial part (prior to maximum moment of inertia about the top hand axis) of the 1st phase of pole support Newton’s action – reaction principle must be applied to the “push out” (elbow extension plus some shoulder adduction and flexion of the lower grip limb) action.

(Note the “push out” is often observed to be accompanied by a lead leg hip extension occurring at about the same time the end of the range of joint motion of the top grip arm and shoulder girdle elevation is reached. This lead leg hip extension, after a short delay, is then counteracted by a return to hip flexion).

The inertia of the vaulter’s shoulders will be acting in approximately the same plane and direction of the “push –out” actions of the lower grip limb and thus the pole must produce an equal in magnitude and opposite direction reaction to the “push out”.

Because the total system COM is located some distance vertically below the level of the shoulders the pole reaction force to “push out” can be directed either horizontally or at some angle to the horizontal or vertically downward, depending on total system COM 3D spatial location with respect to the action line vector of the pole reaction force on the vaulter.

In the case where the reaction force is directed downward it will be in the same direction as the vaulter’s weight and thus produce an increase in the retarding torque acting on the total system COM rotation about the pole tip axis!

In the case where the pole reaction is directed either horizontally or at an angle below horizontal the force from the pole will create an acceleration of the total system COM about the vaulter’s top hand grip axis on the pole.


This total system COM acceleration is simultaneously accompanied by some shifting of the physical pivot axis within the vaulter from the shoulders towards the transverse axis through the hips.

The consequent increase in vaulter moment of inertia about the top hand shifts the pole grip vaulter rotation axis towards the lower grip on the pole as the pole itself continues to increase its “flex” which until the "push out" occurs is primarily along its whole length about the pole tip transverse axis in the box.

The pole chord (line between the pole tip and the vaulter’s top grip) continues to rotate about the transverse axis through the pole tip but at a slightly lower rate if "push out" occurs early in the 1st phase of pole support.

The local “couple” created by “lower arm push out” against the inertia of the vaulter’s shoulders produces an increased local bending of the pole about the lower grip pivot point.

The pole radius of curvature in the upper portion of the pole is decreased with the pole shaft in that region undergoing an associated increase in local bending deflection strain energy storage.

Despite considerations above the vaulter’s own centre of mass is in suspension below both the hand grips on the pole and therefore vaulter weight force must exert some amount of pull on the pole vertically downward for the duration of the 1st phase of pole support. The weight amount being supported at each hand grip is difficult to determine as it varies throughout the entire pole support phase.

Bearing in mind foregoing considerations I make the conclusion that the vaulter pulls on the pole with both hands from the instant of take-off and continues to do so until the first hand release occurs in the 2nd phase of pole support.

As I explore the similarities and differences in the Renaud Lavillenie and Sergei Bubka techniques the issue will be exposed to further scrutiny.

The framework has now been set for the comparisons that follow. Renaud Lavillenie’s technique will be examined first.

… to be continued
Last edited by PVstudent on Sat Oct 04, 2014 3:39 am, edited 1 time in total.
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KirkB
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby KirkB » Fri Oct 03, 2014 2:10 pm

Good stuff!
PVstudent wrote: Bearing in mind foregoing considerations I make the conclusion that the vaulter pulls on the pole with both hands from the instant of take-off and continues to do so until the first hand release occurs in the 2nd phase of pole support.

The underlining is mine.

I agree with this, and I think this is the same "pull" that Agapit must have been referring to a few years back.

It is also the same as the "full body pull" that PVDaddy and I bantered about last year.

PVStudent, you just explained it better! :)

But I caution vaulters and coaches that might think that this is a "sudden" pull - a pull that requires some sudden action to initiate. I even think that I got that wrong when I tried to understand what Agapit was talking about re his "pull".

PVStudent is referring to a "continuous" pull, from take-off to lift-off. Thus, there's no instantaneous action needed by the lats (or any other muscles) to achieve this - it's a continuum.

Kirk
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Fri Oct 03, 2014 9:40 pm

Thank you Kirk for reinforcing that the pull I describe is continuously applied.

Once it is established that the pole pulls continuously on the vaulter and the vaulter pulls continuously on the pole from the "Get Go " after take-off the importance of emphasizing the "Hochsprung " in Stab Hochsprung (upspring) during take-off ground contact becomes quite easily understood as a vital coaching cue and performance objective for the vaulter.

I may add that for me as a coach it de-emphasises any need for the vaulter to be thinking at all of "deliberately trying to bend the pole" whilst still in ground contact.

I am addressing, at this time, the essential mechanics of pole vault. As such I am leaving the translation of the analysis into key coaching points until I have completed the Lavillenie comparison with Bubka.

I appreciate the encouragement your comments provide. Thank you.
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Sat Oct 04, 2014 9:26 am

So that discussants and readers can refer to the same evidentiary sources, the Renaud Lavillenie technique analysis that follows in this and subsequent posts will use the still frame sequence of Renaud Lavillenie’s 6.01m performance obtained from the reference video as an exemplar typical of his state of technical development achieved in February 2014.
The exemplar video is located at:

http://youtu.be/ehtzp3OL0kg

The recording used for this purpose is of the successful clearance of 6.01m (3rd attempt) immediately preceding Renaud Lavillenie’s 6.16m Indoor Pole Vault World Record.

The Renaud Lavillenie Technique in Take-off, Pole Support Phases, 2nd Take-off at Pole Release, Flight Trajectory and Bar Clearance for a 6.01m Official Height Performance are shown as a sequence of still video images in the illustrations below.

Renaud Lavillenie sequence for 6.01m vault 2014 1.jpg
Renaud Lavillenie sequence for 6.01m vault 2014 1.jpg (100.98 KiB) Viewed 7399 times



Renaud Lavillenie sequence for 6.01m vault 2014 2.jpg
Renaud Lavillenie sequence for 6.01m vault 2014 2.jpg (106.95 KiB) Viewed 7399 times



Renaud Lavillenie sequence for 6.01m vault 2014 3.jpg
Renaud Lavillenie sequence for 6.01m vault 2014 3.jpg (86.39 KiB) Viewed 7399 times


The remaining portion of the vault sequence illustration will follow in my next post.
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby PVstudent » Sat Oct 04, 2014 10:45 am

Renaud Lavillenie Sequence continued …
Renaud Lavillenie sequence for 6.01m vault 2014 4.jpg
Renaud Lavillenie sequence for 6.01m vault 2014 4.jpg (93.66 KiB) Viewed 7397 times


Renaud Lavillenie sequence for 6.01m vault 2014 5.jpg
Renaud Lavillenie sequence for 6.01m vault 2014 5.jpg (102.99 KiB) Viewed 7397 times


In the diagram below I have drawn the Renaud Lavillenie vault sequence from the take-off foot toes breaking ground contact to the instant of estimated peak height of the vaulter COM.

Using background landmarks in the selected video images from which the drawings were made I have adjustment for spatial errors introduced in the images caused by camera panning and tilt in obtaining the original video.

The drawn images as presented also suffer from some perspective changes in image size due to the subject moving past and at an oblique angle away from the camera position.

The concordance of my drawn images to their photographic originals is left to judgment by readers.

Renaud Lavillenie pole support action sequence for 6.01m vault 2014 1.jpg
Renaud Lavillenie pole support action sequence for 6.01m vault 2014 1.jpg (74.78 KiB) Viewed 7397 times


The diagram identifies the instants in time used to define the critical events demarcating the start and end point of the 1st and 2nd pole support phases, the 2nd take-off at final pole release and highest point in the vaulter’s COM flight trajectory.

The comparative analysis is delimited to the pole support phases of the vault only.

The scope is limited as being merely qualitative due to lack of scientifically obtained source material and insufficient objective and reliable quantitative measures being available for Renaud Lavillenie in particular.

In viewing the diagram above readers please take particular note that the pole clearly recoils for a considerable time after maximum pole bend before Lavillenie is sufficiently inverted and close enough to the curve of the pole to commence his “toe shoot action”. A fore-aft leg split with flexed hips and knees position is adopted through the start of pole recoil that initiates the 2nd phase of pole support!

(The very slow motion section in the reference video is very instructive on this aspect of the technique execution adopted by Renaud Lavillenie).

… continued next post.
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Re: GRV: Lavillenie - From Stall Swing to World Record

Unread postby KirkB » Sat Oct 04, 2014 4:43 pm

I love frames #5 and #6 (shown in PVStudent's posts above) of Lavillenie's 6.01m vault! :yes:

This "C" position is why he's the WR now!

Say what you will about his technique after the C (with distinct differences from SB), but if you can't get to the C (as he has), then if you want to vault high, it doesn't matter what you do in subsequent parts of the vault. He makes it or breaks it by his speed down the runway, to the point of the C. His bottom arm is so high above his head at this point that any perceived or real "push" on the pole is quite immaterial.

It's all about getting to this C, then whipping out of it! And the "whipping out of it" is the continuous pull (from take-off to lift-off) that PVStudent mentioned (and I commented on) yesterday.

And say what you will about RL's technique vs. SB's, this "C" (and all the good body posture that goes along with it) is what they both have in common! :idea:

Kirk
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