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Tue Mar 09, 2010 11:50 am

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A very important question that is asked only infrequently is "How much horizontal rotation do you need?


Horizontal rotation is sometimes referred to as rotation about the bar. It is the rotation that causes the jumper to rotate from a vertical orientation at takeoff, through a horizontal position above the bar, and then up-side-down into the pit.


This rotation is originates during the takeoff drive as the sum of two separate rotations:


1. Lateral rotation, which is rotation in the plane formed by the hips and shoulders (at their orientation at takeoff). Lateral rotation supplies the bulk of the rotation about the bar. Lateral rotation is sometimes called cartwheeling rotation. The axis of this rotation is front to back.


2. Somersaulting rotation, which is rotation in the plane formed by the spine and sternum (breastbone, also as they are oriented at takeoff). Somersaulting rotation, when used, provides only a small fraction of the rotation about the bar. Indeed, I consider using any somersaulting rotation at all to be an advanced technique, thus somersaulting rotation will not be discussed in this post. I would, in fact, avoid somersaulting rotation unless analysis of your bar clearance clearly shows that it is necessary. The axis of this rotation is side to side.


So, what is the proper amount of rotation about the bar? The correct amount is: just enough to rotate your body to a horizontal orientation at the moment the center of mass reaches it's apex (highest point). If everything else is done correctly, the apex of the flight will be directly above the center of the bar.


Executed in this way, your body can be held in a gently arched position throughout the flight and all parts of your body will clear the bar by approximately the same amount (lumps, bumps, and other projections from the underside of your body not withstanding).


Some will claim that you should lift your feet at the last moment, but in my opinion raising your feet is unnecessary at best, and counterproductive at worst. This is because raising your feet will drop your butt, and when the jump is really close you can't time this well enough to avoid catching something on the bar. Better to get your rotation about the bar exactly right and avoid the need to lift the feet.


Clearly, if you bend your knee too much you will have to straighten your knees so they are in better alignment with the arch in the remainder of your body. I think it is better to travel over the bar with your body in one flowing arch throughout the flight and avoid "drooping calves" altogether.


This isn't the whole story, but I'll start there and invite discussion. I'm sure I'll get some disagreement, because some people still think that a very arched body, and the resulting increase in rotation rate that it causes, is necessary. It is not; but more on that later.

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Tue Mar 16, 2010 6:59 am

 
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Hi Glen, you here, you miss the high jump forum?!
The high jump can be seen as a combination of a somersault forwards and a somersault sideways, but for a high jumper it doesn't feel like that. But it is nice to see the whole movement as a combination of two movements, and that is more or less the same...
Rotation around a vertical axis: at the moment of planting the take off foot the upper body points to the far away stand approximately, at the apex the shoulders are parallel to the bar and you look to the side of the run-up. So the line of your shoulders has rotated about 120 degrees, which is considerable.
Rotation around a horizontal axis: at take-off the body is upright, above the bar the body is laying flat. That means it has rotated about 90 degrees. But a complication is that 'horizontal' in the air is a meaningless word. It is better to take a certain line and see how that rotates. The line from a point in between both shoulders to a point in between both hips is a good one. At take-off this line is nearly vertical, at the apex it is horizontal in weak technicians like me or the hips are much higher than the shoulders in a jumper as Stefan Holm. So rotation of that line goes from 90-120 degrees.

What is the proper amount of rotation? Just enough to pass the bar at record height...
For us masters there is a complication. The older we are, the lower we jump, the shorter we are in the air. But we like to pass the bar in the same position as Holm, so we have to rotate much faster! I am puzzling about that all the time...

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Wed Mar 17, 2010 6:52 pm

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Joined: Tue Mar 09, 2010 11:47 am
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Yes, the lower you jump the less time you spend in the air between takeoff and the peak of your flight. This means that you must spin faster to get horizontal at the peak of your flight. If you use an approach designed by the High Jump Coach 2010 approach calculator, then it is easy to adjust your approach to account for this. All you do is estimate how much short you are of getting horizontal at the peak of your flight and reduce your curve radius by 1 percent for each degree you are short of horizontal. Simple. You can read about it in the pages on approaches and approach adjustment at:

http://sites.google.com/site/hjcoach

Glen

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Fri Mar 19, 2010 6:07 am

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Location: Utrecht (Netherlands)

HighJumpCoach wrote:
you must spin faster to get horizontal at the peak of your flight.

There is no 'horizontal' in the air, it depends on the reference system you are using. We jumpers loosely use at least three reference systems at the same time. Often we don't have problems in understanding each other, fortunately! What you mean is that the reference system fixed to the jumpers trunk becomes more or less horizontal compared to a reference system bound to the ground or the bar. There is no way to calculate the horizontalness of a body in the air! Only the horizontalness of a certain line, like the line from shoulder to hip, can be the reference for judging horizontalness.

Only changing the radius of the run up would be an easy way to spin faster, but that will inevitably lead to a too sharp bend at a certain high age. (I am not yet at that age.) Futhermore the spin speed is not only produced by the curve. The action of the swing leg is very important too, the (over)stretching of the hip also. Plus some minor things.

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Fri Mar 19, 2010 3:05 pm

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Hi Weia,

By horizontal I mean that, if straightened out, the body would be horizontal. You have to estimate "horizontal" when you are watching or looking at photos. I agree with your descriptions of horizontal as well. Any of these descriptions seem to me to describe "getting horizontal" well.

With regard to the curve, assuming that you:

- run a constant radius curve
- stay in your curve until you plant your takeoff foot
- leave the ground with your body oriented vertically
- keep the same style of takeoff drive with the same time on your takeoff foot

then changing the curve radius directly controls the spin rate.

You are absolutely correct that at a certain age jumpers would have to run a very tight curve. I think the answer for coaches is that they should stop tightening the curve at some point and accept that rotation about the bar is inadequate - there is nothing further you can do for a young jumper's rotation rate. I think the limiting factor is stress on the ankle due to high angles of bank in the curve, so that is what coaches of young jumpers should be watching out for.

I don't think that leg swing (meaning lead leg drive) has anything to do with rotation about the bar - or at least it doesn't for the method of approach and takeoff I teach. However, I do think it should be the primary method of inducing rotation about the vertical axis during takeoff. I think the knee should be driven up to the level of the hip (level upper leg) and slightly across the body so the thigh ends up roughly parallel to the bar. That way everything else about the takeoff drive is exactly like a the takeoff drive you would have if jumping straight ahead. That seems most efficient to me.

Glen

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Sat Mar 27, 2010 10:44 am

 
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It would be nice if it was that simple, but I don't think so. Good rotation for masters means fast rotation and therefore everything has to be optimal. I do not think that 'too few rotation means sharper bend' is enough. There are three major things that result in rotation: leaning into the curve, proper swing leg action, (over)stretching of the hip. Try it, run a good curve but forget the swing leg.

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Sun Mar 28, 2010 9:30 am

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Hi Weia,

My method is aimed at jumpers who are:

- just starting out and need to develop techniques that will serve them now and, more importantly, in the future as they mature,
- other jumpers who wish improve the efficiency of their technique to use the impulse they produce off the ground to best advantage in the air.

For these two classes of jumper, I believe the problem of rotation about the bar is just that simple. However, I think you may have a point with regard to some masters jumpers. So I guess I will have to add a third class of jumpers which is those who are:

- masters jumpers with relatively little impulse off the ground, raise their centers of mass relatively little during the jump, and are not looking forward to vast improvements in either impulse or how much they raise their centers of mass.

I can see why one would want to try to modify the technique a bit under those conditions. I must admit that I have not given much thought to the possibility of improvements to technique in masters jumpers where their impulse is sufficiently small off the ground that the lean at plant can not induce enough rotation about the bar. With that in mind, I would like to understand your other two methods of producing rotation:

-proper swing leg action,
-(over)stretching of the hip.

Can you explain what you want the jumper to do in some detail so I might understand what you are proposing.

Thanks,
Glen

The curve and the resulting

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Sun Mar 28, 2010 10:04 am

 
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Leaning into the curve and coming upright during the last stride results in rotation (partly sideways), the same for the swing leg: the movement both upward and away from the bar continues as rotation. The stretching of the hip does not add rotation in itself, but it relocates the cg and so the axis of the rotations. In such a way that especially the rotation (angular momentum) produced by the swing leg has more effect. The swing leg is farther away from the axis of rotation.
My cg is at 1.30m at the moment of last contact, the apex of my cg wil be somewhere between 1.55m and 1.60m. That is not much higher than 1.30! Maybe sometime I'll have to think about technical improvements that are only of use for older masters... For my pupils I do not think about those things. I learn them the standard technique and when they become older and stronger they will leave imperfections behind. They'll have an air phase ever longer.

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Sun Mar 28, 2010 5:34 pm

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Assuming that by "swing leg" you mean the right leg of a jumper who takes off from the left leg. That being the case, I view the action of the swing leg as driving through to an ending position with the thigh parallel to the ground and approximately parallel to the bar, and the lower leg perpendicular to the ground. I think this is just a different way of describing the same thing you are describing. Is that correct?

Assuming for a moment that we agree about the description of the swing leg movement, I view the net effect of this movement as:

- adding upward momentum in support of the takeoff drive, and
- imparting a spin about the vertical axis

As a part of the upward and forward swing of the swing leg components, one possible side effect could be some component of somersaulting spin, but this spin normally does not show up during the flight. I think it is compensated for by the jumper during the takeoff drive.

As a part of the leftward swing of the swing leg components (for vertical axis spin) one possible side effect could be a bit of lateral spin (about the bar). I suspect that you are right about this effect existing. I don't know it's magnitude, though I suspect that it is small.

One could imagine making it bigger by increasing the leftward swing of the swing leg. The problem with this strategy would seem to be it's effect on vertical rotation - I think it would cause the jumper to cross the bar with the left side of the body lower than the right side. The evidence for this is to look at what would happen if the jumper did not give the swing leg any leftward swing , and therefore no vertical axis spin at all. That would result in the jumper crossing the bar with the right hip down and the left hip up - the opposite direction of using more leftward swing. Not a good side effect to have.

In addition to changing the hip orientation while crossing the bar, changing the vertical axis rotation rate via changes in leftward swing leg swing would also cause some other interesting changes in body orientation over the bar. These effects should be obvious. So, although increasing leftward swing may add some lateral rotation, I don't think it can do so without compromising vertical axis rotation and it's various desirable effects. Feel free to shoot holes in this analysis and let's see where it takes us.

Glen

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Sun Apr 04, 2010 4:50 am

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HighJumpCoach wrote:
Assuming that by "swing leg" you mean the right leg of a jumper who takes off from the left leg. That being the case, I view the action of the swing leg as driving through to an ending position with the thigh parallel to the ground and approximately parallel to the bar, and the lower leg perpendicular to the ground. I think this is just a different way of describing the same thing you are describing. Is that correct?

Correct. But I should add that it is better to swing the leg more away from the bar, not parallel but say 20-50 degrees away at last contact.

A colleague of mine says that the swing leg is the most important cause of rotation... I don't believe that, but on the other hand: there are jumpers with a straight run up and nevertheless with a rather good amount of rotation! Where does that come from? I do not advocate a run up like that, because getting rotation from the lean into the curve is rotation for free. The lean does not cost height, in the contrary.

Quote:
I view the net effect of this movement as:
- adding upward momentum in support of the takeoff drive, and
- imparting a spin about the vertical axis

Spin, yes. Adding momentum, difficult story. All upward momentum is produced by the takeoff leg. In the past I thought that a fast upward swing of the swing leg and/or the arms added upward velocity, but in newtonian terms that is not correct. What happens is that the upward movement of a leg or arm is countered by a downward movement of the rest of the body. This means that the pressure to the ground becomes bigger, that leads to a bigger ground reaction force and so more upward momentum. But only if the takeoff leg is strong enough to withstand the pressure, so it still is that leg that produces the upward momentum.

Quote:
As a part of the leftward swing of the swing leg components (for vertical axis spin) one possible side effect could be a bit of lateral spin (about the bar). I suspect that you are right about this effect existing. I don't know it's magnitude, though I suspect that it is small.

One could imagine making it bigger by increasing the leftward swing of the swing leg. The problem with this strategy would seem to be it's effect on vertical rotation - I think it would cause the jumper to cross the bar with the left side of the body lower than the right side.

Interesting point! You often see jumpers with one hip higher above the bar than the other hip. This will cost them some millimeters, up to 15 maybe. That can be the difference between gold or silver, so it is to be avoided. I see this rotation as a result of a mismatch between forward somersault and somersault sideways. Trying to find the correct match is time consuming...

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Sun Apr 04, 2010 10:31 am

 
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I color coded these in groups by question - new original question (or statement) and the responses to that question in one color, then a new color for the next question. Your background changes were good for your last post - made it easy to follow the flow, but I couldn't figure out how to continue that pattern. Hope this works...

Glen (original post):

Assuming that by "swing leg" you mean the right leg of a jumper who takes off from the left leg. That being the case, I view the action of the swing leg as driving through to an ending position with the thigh parallel to the ground and approximately parallel to the bar, and the lower leg perpendicular to the ground. I think this is just a different way of describing the same thing you are describing. Is that correct?

Weia (reply 1):

Correct. But I should add that it is better to swing the leg more away from the bar, not parallel but say 20-50 degrees away at last contact.

Glen (reply 2)

Also correct. When giving a breif description I teach parallel (as a target); but the final position of the thigh in the horizontal plane could be more or less cross-body. How much cross-body depends on the angular momentum due to leg mass and speed, and how much time you are in the air. Given a particular jumper's individual impulse producing style, the adjustment the jumper makes for the actual final angle between the thigh and the bar should be enough to turn his/her back to the bar and get the hips properly oriented on top of the bar - no more, no less. If the jumper targets parallel on the first jump, he/she will "feel" how much to adjust the angle on subsequent jumps.

The higher you lift your center of mass, the less cross-body movement of
the swing leg is required because the required vertical axis spin rate is relatively low. If you don't lift your center of mass much you will need a lot of cross-body movement of the swing leg because the vertical axis spin rate needs to be relatively high.


Weia (reply 1):

A colleague of mine says that the swing leg is the most important cause of rotation... I don't believe that, but on the other hand: there are jumpers with a straight run up and nevertheless with a rather good amount of rotation! Where does that come from? I do not advocate a run up like that, because getting rotation from the lean into the curve is rotation for free. The lean does not cost height, in the contrary.

Glen (reply 2):

I too disagree with your colleague's assessment of the importance of leg swing. I don't seriously doubt that swing leg contributes, but the amount of that contribution is not immediately apparent to me. I would like to hear what Jesus Dapena (Prof. Kinesiology, Indiana University) has to say about it. I think the effect is small because the movement is low on the body. During the takeoff drive the takeoff foot is restrained on the ground and the angular momentum produced about the roll axis of the body would be relatively small relative to the angular momentum about the roll axis of the rest of the body.

I believe that the roll (lateral) rotation produced by someone running a straight approach, or an approach where the jumper comes out of the curve early, comes from planting the takeoff foot a bit to the left (for a left footed takeoff) of where the foot would fall if jumping straight ahead. This is the same method employed for producing rotation if you stay in the curve until the takeoff foot is on the ground. The disadvantages of the straight (or straightened curve) approach are the loss of height due to a laterally angled takeoff and the increase in likelyhood of upper-body contact with the bar on the way up (also due to
a laterally angled takeoff.

Regardless of the amount of lateral rotation produced by cross-body swing leg motion, it can not be used to adjust the lateral rotation for the reason we previously agreed on.


Glen (original post):

I view the net effect of this movement as:
- adding upward momentum in support of the takeoff drive, and
- imparting a spin about the vertical axis

Weia (reply 1):

Spin, yes. Adding momentum, difficult story. All upward momentum is produced by the takeoff leg. In the past I thought that a fast upward swing of the swing leg and/or the arms added upward velocity, but in newtonian terms that is not correct. What happens is that the upward movement of a leg or arm is countered by a downward movement of the rest of the body. This means that the pressure to the ground becomes bigger, that leads to a bigger ground reaction force and so more upward momentum. But only if the takeoff leg is strong enough to withstand the pressure, so it still is that leg that produces the upward momentum.

Glen (reply 2):

I asked Jesus Dapena about this many years ago and he agreed with the following assessment:

The muscles of the takeoff leg have a maximum contraction rate that is not influenced by the load they are moving as long as the load is modest. Obviously, if you are trying to do squats with 300 pounds, the contraction rate is SLOW. The additional load on the takeoff leg muscles that is imposed by the reaction force due to driving the swing leg and both arms is indeed modest, and has no effect on the speed of leg muscle contraction. Thus, there is a substantial benefit in driving all three upward in concert with the takeoff leg thrust.


Glen (original post):

As a part of the leftward swing of the swing leg components (for vertical axis spin) one possible side effect could be a bit of lateral spin (about the bar). I suspect that you are right about this effect existing. I don't know it's magnitude, though I suspect that it is small.

One could imagine making it bigger by increasing the leftward swing of the swing leg. The problem with this strategy would seem to be it's effect on vertical rotation - I think it would cause the jumper to cross the bar with the left side of the body lower than the right side.

Weia (reply 1):

Interesting point! You often see jumpers with one hip higher above the bar than the other hip. This will cost them some millimeters, up to 15 maybe. That can be the difference between gold or silver, so it is to be avoided. I see this rotation as a result of a mismatch between forward somersault and somersault sideways. Trying to find the correct match is time consuming...

Glen (reply 2):

Oddly enough, most jumpers seem to get their hips level and their backs to the bar without much effort; I have only seen a few jumpers who can't seem to get that right.

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Sun Apr 04, 2010 1:00 pm

 
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When you press 'quote' the quoted text gets the word quote (between square brackets) in front and /quote at the end. You can cut the quoted text in two blocks of text by adding /quote and quote at the point of the cut. Again between square brackets. Etcetera!

Most of my knowledge of the mechanics of the high jump comes form Jesus Dapena... So when we disagree it are two interpretations of Jesus Dapena that clash!

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Sun Apr 04, 2010 5:20 pm

 
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Shall we invite Dr. Dapena into the conversation to set us straight?

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Mon Apr 05, 2010 8:29 am

 
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That's a very good idea! I'll ask him.

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Thu Apr 08, 2010 10:37 am

 
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Looking in your website High Jump Coach:

" Plant your takeoff foot slightly inside the point that would allow you to continue running in your curve. "

All makes sense, but what do you mean "inside"?.

Toward the pit or toward the center of the curve you are running?



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