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Front-hip, back-hip, and clear-hip circles

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Geoffrey Taucer

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I've never fully understood the physics of front and back hip circles. I've just been teaching the techniques I've been taught without fully understanding why they work. It seems to me that the skill should require massive shoulder and ab strength to get around the bottom part of the circle, but obviously it doesn't require very much.

The same goes for a clear hip circle; I know the technique I've been taught well enough to teach it, but I don't understand why it works. A free hip passes briefly through a front lever under the bar (actually, not quite a front lever, but something close to it), and with the added centrifugal force, it seems like it should require as much strength as a front lever, and then some. But obviously it doesn't, since I've taught the skill to a lot of kids who were not nearly strong enough to hold a front lever.
 
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infinitegymcoach

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That is a good question, my thoughts would be, that with the proper cast and proper hollow body "scoop" on the uderneath, enough momentum is already there. All of gymnastics requires strength, but high bar is a swinging event. So with the right timing, all tricks should be easily completed as a swing with out much effort. Does that make any sense at all?
 

Geoffrey Taucer

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That is a good question, my thoughts would be, that with the proper cast and proper hollow body "scoop" on the uderneath, enough momentum is already there. All of gymnastics requires strength, but high bar is a swinging event. So with the right timing, all tricks should be easily completed as a swing with out much effort. Does that make any sense at all?
I understand that the momentum is there, but it seems to me that at the point where the body is under the bar, the gymnasts momentum is downward, which should pull them right off the bar.
 

ACoach78

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I'll give you a very brief idea of what's going on here mechanically. Let's start with the front hip circle...

The skill starts from a stretched position with the bar pushed down around the gymnast's mid-thighs. (or that's at least the starting position that I see for the better ones) The gymnast's axis of rotation is the bar. By positioning the bar as such, the gymnast has moved the center of gravity further away from the bar and this will allow for a torque (rotational force) to be created as the gymnast begins to fall forward. The force is obviously gravity in this instance.

Just prior to half of a revolution, the gymnast will bend at the hips (pike) in order to complete the skill. This simply shortens the radius of the body and allows for the rotation to speed up. In biomechanics lingo, the moment of inertia (resistance to rotation...i.e. a long body) has decreased, so the angular velocity (speed of rotation) has increased. These two quantities share an inverse relationship. And, both make up the body's total angular momentum. Angular momentum = Moment of Inertia x Angular Velocity.

The total angular momentum never changes due to the law of the conservation of angular momentum. Only the parameters (MOI & AV) change and they change inversely. In layman's terms...if the body gets longer, then it's harder to rotate. So, the rotation is slower. Thus, a tuck rotates faster than a layout.

As far as strength goes, the gymnast would need adequate abdominal strength and in a dynamic manner in order to be able to successfully flex at the hips quickly and complete the skill.

I'll tackle the clear hip and back hip circle in a few days...
 

Geoffrey Taucer

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But how does that rotation take them up to support at the end of the skill? What prevents them from comming off the bar as they go around the bottom of the circle?
 

ACoach78

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Basically, by keeping the center of gravity so close to the axis of rotation (the bar), they are able to overcome the resistive force of gravity because of the increased angular velocity. In essence, they are speeding up just enough to prevent the force of gravity from pulling them off of the bar.

The gymnast must also learn not to grip the bar too firm so as to be able to overcome the frictional forces that occur at the hands.

The other force that we must consider would be air resistance. However, most researchers disregard this even during aerial skills as they feel that the gymnast is not really airborne long enough for air resistance to play a real significant factor.
 

JBS

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This is a great conversation.

Would you agree that a front hip circle could be done without hanging onto the bar if the gymnast could get into the correct starting position.:confused:
 
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infinitegymcoach

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If the momentum was pulling you downward, then falling or getting pulled off the bar would hold true for almost every skill. A giant would never get around either.

Very true about the center of gravity.

About that front hip circle with no arms......I believe it can be done. I think the girls used to do a dismount similar to that off the low bar, but it may have been a back hip circle. But it was done without holding on.
 

Geoffrey Taucer

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If the momentum was pulling you downward, then falling or getting pulled off the bar would hold true for almost every skill. A giant would never get around either.
In a giant, the body is already extended outward from the bar. In a front hip or back hip, the body is compressed towards the axis of rotation in such a way that the outward force, it seems to me, should decompress it -- in other words, pull your hips from the bar. This isn't an issue with giants, as the hips are already extended away from the bar, and the only way to get further from the bar is to let go.
 
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infinitegymcoach

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You have a great point there. Makes me laugh in the last sentence.... "only way to get the hips farther away is to let go" That is a humerous comment. I love it.

I think we just have to go with what we know for sure... The skill works.
 

JBS

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About that front hip circle with no arms......I believe it can be done. I think the girls used to do a dismount similar to that off the low bar, but it may have been a back hip circle. But it was done without holding on.
I never though about those old bar wrap tricks. Olga Korbut does one in this video.

[YOUTUBE]YsiLsguqXBU[/YOUTUBE]​
 
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