Vaulting heel drive...

[blantonnick]

Ask any gymnast or coach 'when does heel drive start on vault?' and the majority would say from the springboard to the vault table. In other words, once the feet contact the springboard the heels are driven upwards over the center of mass to facilitate rotation. I would challenge this answer in that I believe heel drive should start before the feet contact the springboard, during the hurdle phase. This process is very quick, allows for explosive compression of the springboard, which in turn will facilitate a stronger heel drive in the end. Any thoughts or disagreements?

[Geoffrey Taucer]

I think in the case of vault, the term "heel drive" is not as accurate as it could be.

If we take "heel drive" to mean a tight arch (which is how I would normally interperet the phrase), it does not start until after the feet leave the springboard. If you snap to a tight arch when your feet are still on the springboard, it rotates you in entirely the wrong direction, the opposite of what a heel drive is intended to accomplish. What you have to do (and I don't actually tell kids to do this, because they tend exaggerate it if they try to do in intentionally) is a snap to hollow with the feet on the board, and then a snap to a tight arch right after they come off.

So the process of generating rotation starts as soon as the feet contact the board, but the snap to a tight arch occurs just after the feet leave the board.

[blantonnick]

Just recently had a National Coach come back from a FIG conference where a lecture was performed by one of the Canadian National Coaches Edouard Iarov. A new trend is emerging and being recognized in advanced level vaulting to emphasize the hips being raised off the springboard then initiating a heel drive...quite an interesting concept, and one that is very evident when you look at Alicia Sacromone's Front Handspring Front 3/2.
However, aside from that, I think your comments are very valid in the context that you put them. Very good points.
It would seem that the heels being thrustfully driven into the board was the idea that I was referring to when driving the heels before they contact on the board.

[Valentin]

I would have to say, i am definitely with the majority on this haha..

Biomechanicaly speaking, you can't generate any torque (rotation)without and eccentric force (one that doesn't pass through the center of mass).That being said it means that for the body to be rotating on take-off from the board the center of mass (so roughly the belly button). So regardless of when you start heel driving, without this there is 0 rotation.

No why do i think you have to heel drive as you push of the board.
1- Heel drive is really a leg drive, which is done mainly by the hip extensors, that is the butt muscles, hamstrings, and knee extensors (quads)
2- When you impact the board the knees bend and the hips flex a little

thus it means that as you impact the board you have to use the hip and knee extensors and quads to push on the board and extend the knees and hips to take off. If on the take off you are floopy, this strong fast/explosive push/rebound is not very effective. The tighter the better. THis can be demonstrated by the stick test.. If you throw a stick at a stick on a anglebut you throw it so that only one tip hits, given that its throw hard enough it will flip over its end..like in a vault take off-layout.

Thus saying that you heel drive before impact it means that you are hitting the board with straight legs, and open hips. which is just not efficient way to generate any kind of roation or explosive push of the board.

The heel drive in my opinio based on these facts occurs from the take-off.


Valentin

The Gym Press
http://hosted.filefront.com/TheGymPress

[blantonnick]

Let me take a second to clarify what the concept is because possibly the idea of heel drive is being confused...
Using the stick test as you did Valentin is a great way to illustrate what I was referring to. By throwing the stick forward, you the thrower, are in essence creating a heel drive by throwing the stick so that rotation begins from the second the stick leaves your hand. This rotation allows the stick to rotate such that once its impact occurs on the floor (feet contact the springboard) the transfer of energy from the stress on the floor to the stick generates maximal rotational forces forward from where the stick contacts the floor. This happens because as the stick contacts the floor the top (the other side of the stick, up in the air) of the stick is thrusted forward by a transfer of energy (the upper body rotates forward and the hands are reach towards the table).
That being stated (as confusing as it may be) the transfer of energy forward from the feet on the board, to the vault table, I believe happens just prior to the feet contacting the springboard. The idea is for the gymnast to produce 'that throwing of the stick towards the floor' as stated above.
The idea was not to imply that an arch is performed onto the springboard as pointed out ( that would actually be dangerous if performed at full speed). Heel drive in the case that I am referring to is actually the idea of thrusting the feet downwards into the board in such a direction that the upper extremeties of the body are thrusted forward (just as the stick was thrusted forward on the floor) allowing for less time from the feet leaving the board to the hands contacting the table.
Please keep up the reply as this seems to be a nice topic to chat about...

[Valentin]

Hello

I have to be honest i think that i am really confused now about what you refer to heel drive.
Lets first clarify some of the biomechanics here, because it seems to me that you are confusing it, or applying it incorrectly.

First.. Throwing the stick actually does not generate rotation (well it should not if we could throw the in a way such as hurdle).

" By throwing the stick forward, you the thrower, are in essence creating a heel drive by throwing the stick so that rotation begins from the second the stick leaves your hand'

This is not true. When the thrower, throws the stick, they are imparting linear momentum to the stick in a specified direction which should be at something like 60deg for the stick test to work well. There is NO rotation, otherwise the stick will be rotating in the air before it hits the floor which it does not. It just flys ina straight line at a 60 angle downward towards the floor. Of course this is the resultant momentum vector, which is the result of a horizontal and vertical (downward) momentum. Meaning that the stick is moving forward and downward.

"rotation allows the stick to rotate such that once its impact occurs on the floor (feet contact the springboard) the transfer of energy from the stress on the floor to the stick generates maximal rotational forces forward from where the stick contacts the floor. This happens because as the stick contacts the floor the top (the other side of the stick, up in the air) of the stick is thrusted forward by a transfer of energy (the upper body rotates forward and the hands are reach towards the table)"

This is not entirely correct. When the stick impacts the floor, yes there is a action reaction pushing the stick back at a 60deg angle back towards where it came from, but because there is also a horizontal momentum, and the rebound of the floor is not instanenous (even though it may appear that way, because the eyes cant see at 2500 frames per second..haha... I WISH!!!).. and what we dont see is that as the stick ins going down and compressing the foam top of the floor (the stick test dont work on concrete very well haha)..it is also moving at a constant forward velocity (due to that horizontal momentum). By the time the ground vertical donward force (momentum) of the stick is attenuated, stoped, and then the ground reaction force pushes the stick back, ideal the stick should have rotated over the point of impact to about a 30deg-45deg (approximately). This is know as the centrifugal force. When the ground reaction force eventually pushes back on the stick the force doesnt pass through the center of mass of the stick, and thus produces a torgue.

One thing that you are not taking into account when you compare the stick example and the body is that the body is far! from rigid like a stick and thus the actual forces that take place are more complicated and always changing due to muscular effort and point of force application of the feet. The stick example only roughly illustrates the point that for the gymnast to get a good first flight they need to hit the board with the center of mass behind the feet...so that while the board springs are compressing the body rotates over the feet. When this happens the center of mass should ideal be as high as possible, and thus only about 30deg infront of the feet.

"transfer of energy forward from the feet on the board, to the vault table, I believe happens just prior to the feet contacting the springboard."

This is impossible... I am sorry but how can you tranfer energy without even being in contact with the object?? Think about what you are saying.. you are in the air flying towards the board and you are tranfering energy somehow to the table..it makes no sense. You need to rethink this..


For a bette explanation of how the vaulting works and why i say what i say please read the article i wrote on vaulting for The Gym Press newsletter from
- July Issue of the Gym Press

Valentin
The Gym Press Blog

[blantonnick]

Very educational, thanks...

Let me clarify, are you throwing the stick like a javelin at the floor? if this is the case then yes i agree with you. However, I am interpreting you are thrusting the stick at the floor by holding the very bottom and allowing it to flip end over end to contact the floor...if that is the case then i must disagree with you...please clarify..

The other issue I would like to raise is regarding this comment...
'for the gymnast to get a good first flight they need to hit the board with the center of mass behind the feet'
I must agree maybe with younger gymnasts this may be the case. However, at advanced levels I believe you are greatly encouraging a loss of power by instructing a gymnast to place his center of mass behind his or her feet. By instructing this you are encouraging the gymnast to lean backwards on the springboard. This I believe is very detrimental to an effective hit on the board. The board is sloped so that the center of mass does not have to lean backwards to get an effective strike/compression of the springs on contact. If the springboard were flat as the floor is, then yes lean backwards. However, the shape of the board allows for the center of mass to be directly positioned over the feet for a dynamic and effective strike....please elaborate on the reasoning behind COM behind the feet...
Thanks
Nick

[Valentin]

Hi Nick

"Let me clarify, are you throwing the stick like a javelin at the floor"
Yeah totaly. I would not throw the stick by holding the very bottom and allowing it to flip end over end to contact the floor, because this would imply that as the gymnast is jumping toward the spring board he/she is flipping and has a certain degree of rotational velocity. This however is obviosuly not true, because the gymnast is not rotation in the air, but rather following a parabolic flight curve from the floor to the board.

"please elaborate on the reasoning behind COM behind the feet..."
The reasoning behind it is, in order to allow the gymnast compression time of the board, and a take-off that optimises a vertical take off. The slopped is to maximise this. Here is a good photo of illustating what i am saying.

As you can see there is virtually no slope... Also the design on the board requires it to be sloped because
1- it reduces the risk of gymnast cliping feet as they hurdle
2- It allow the gymnast to enter the spring board long and low.
3- Stability

From studies on the worlds best vaulters, its actually been clearly be reported that they have a lean of about 30deg backward on impact of the baord. This being 1 key variable separating the great vaulters from the others.
But dont take my word for it here are 2 references to this.

1. Cuk I., Karacsony I. (2004). Vault : Methods,Ideas, Curiosities, History. Tiskarna Ljubljana: Slovenia. STD Sangvincki
2. Smith. T (1984).Gymnastics: A mechanical understanding. Holmes & Meier Publishers, Inc. New York.
3. Prassas, S. (2001).Vaulting Mechanics. [url]http://www.coachesinfo.com/category/gymnastics/315/

[blantonnick]

I tried to find both the abstracts you referred to however, were not able to locate them on the internet. However, I must ask you, do you advocate then instructing gymnasts to lean backwards on the springboard? I think sometime biomechanics and actual coaching can conflict greatly. For instance, keeping the head tucked in on a dismount off the high bar is something we all advocate for safety reasons when first learning, however, biomechanically speaking it actually will decrease angular momentum about the longitudinal axis...

[blantonnick]

sorry that should read about the transverse axis...