conservation of angular momentum, whip physics, and a serve question

watching your video again. u are pretty good.

do u ever play intercounty for churchill?

 

Don't be offended but you're quite naive and don't know what you're talking about!!!!!

WTA pros all have very technically sound groundstrokes, FH, BH, volley, ect. They don't have the level of ATP men's power but they're still superior to almost all recreational players!

A year ago, like you I thought girls hit like...a girl LOL, until I saw some girl juniors, 15, 16 yrs old, playing a doubles. Their shots were freaking fast and furious, man. Faster than any games I ever played in at the parks. And, they were only juniors.

And there's another girl I occasionally saw practicing with a guy. Her bh shots consistently landed close to the baseline and then hit the back fence at waist height. If you could hit with that much pace and spin, 8 out 10 shots, I'd consider you better.

 

u dont think i have considered that?

 

Thanks. It's my first year there, so I decided not to join the leagues. Played in the ladder and tournaments though.

Might try out for C league next year though, and maybe even B if I'm feeling ambitious. Thing is, I much prefer singles to doubles...

Send me an email btw about the coaches - have something to discuss.

 

LOL this thread is EPIC, LOVE IT!

As for Whip theory it sounds like it describes the serve exactly. I dunno why people say it doesn't. I actually am unfamiliar with instruction about shoulder "squaring." and if i were to guess I would say they square BEFORE.

Dug up this video. Mechanics of throwing football is very similar to serve:
http://www.youtube.com/watch?v=asIfwF68xqE&feature=related

It's more obvious their shoulders square to target BEFORE extension.
Difference? Being airborne. You don't have a grounding to pivot against. So how does the transfer occur? You are working with gravity. the energy of the kinetic chain goes against the weight of the body, simulating the BRAKE of the shoulders rotation more than a physical pivot.

That being said. I don't pay attention to this thing, I would say naturally the shoulder leads and would "square" before

 

Wrist muscles must be active!

I think that the wrist muscles are active. Our brain should not rely on passive channeled action. I'll try to proof this statement without speculation.
There are a lot of different serve routines. In case of the spin serve, during pronation phase we usually keep the wrist in neutral position (racquet string bed constantly in vertical position) and we use only wrist ulnar deviation to produce spin, and pronation to create flat component of the racquet speed. There is no wrist flexion at all.
In case of the flat serve, during pronation phase we keep the wrist bended back, the face of the racquet in the semi open position until the last moment before impact. Then we use the wrist flexion to create flat components of the racquet speed. We also should stop ulnar deviation from active action. All these different complicated routines cannot just rely on unconscious whip effect. They must be controlled by our brain, because they are very different. Hence, the wrist must be active and controlled by brain until we write all this information in our muscle’s memory.

 

Since I was mentioned in the OP, I believe the example I put up was that the poster was flying open with his chest too soon, and cutting off his power, and I was advising to stay closed/square longer.

J

 

That makes sense, that would mean a more pronounce brake like the OP suggested.
This is why you want to prolong the tossing arm extension at ball toss. It would add some mechanical brake along with gravity.

 

How interesting, but you should know the debate between conscious wrist snap vs a natural wrist snap makes regular appearances in this forum. I will try to find them.

 

Ya, it has to build naturally from the ground up.

On serve and forehand so many people throw their hips/chest open and leave their arm behind completely cut off from the power.

J

 

http://tt.tennis-warehouse.com/showthread.php?t=251543
Okay here it is. OP arguing for a "conscious wrist snap." Many views for the natural pronation of the wrist as part of a chain.

Look at Rafa: http://www.youtube.com/watch?v=n76f2KJ36yA
Following how he finishes, it's just so clear to me that his wrist is moving from a whipping mechanism vs. a conscious snap.

That being said. Yes the brain is controls small muscles that directs fine motor movement, however the power is lent by the whipping mechanism. It is a vertical kinetic force vs gravity. Explaining it as brain controlling small muscles are not enough to explain transfer of power. You cannot sit down and produce this power. You have to explain how energy transfers with physics otherwise it's a very incomplete explanation.

 

I believe that my previous post proves that Whip Effect Theory cannot be used to describe any tennis serve.

 

Nope you describe fine motor movement. That's actually a related, however separate topic than OP which describes transfer for energy. This doesn't have to occur without energy transfer. Otherwise are you going against the idea of a kinetic chain?

 

Your font tags aren't working properly. Makes your posts difficult to read.

I get your point. And perhaps ulnar deviation is consciously controlled to an extent.

But to address your main argument, I think that pronation (either through elbow joint or internal rotation of the shoulder) can set the conditions for this passive transfer.

If you don't pronate at all, then the momentum is not going to be channeled in a manner that facilitates passive wrist flexion.

But if you do pronate, then the extension of the elbow joint will naturally facilitate wrist flexion. This is simple geometry and physics.

 

I see... thanks for clarification!

 

[FONT='Calibri','sans-serif']I have different definition of the kinetic chain. Suppose we have four straight pieces of steal. First imitates the torso, 2 – upper arm, 3 – forearm, 4 – wrist. We connect them in special chain together. Between each of them we install joint with powerful electrical motor which imitates active angular movement. The last connection should have complicated joint and corresponding motors to imitate ulnar and flexion of the wrist. This kinetic chain is active and much more powerful then passive one. Obviously, the passive model cannot describe properly behavior of the active one. Hence, passive Whip Effect Theory is not very good for description of the any tennis stroke. [/font]

 

Not necessarily. If the motor at each joint can't provide enough force to match and exceed the passive force, it can end up slowing down the system.

 

[FONT='Verdana','sans-serif']Passive model also should have one motor between torso and upper arm. Suppose both models have the same first motor. About font, I do not know what I can do. Sorry.[/FONT]

 

Not sure what you're getting at.

I'm not saying that the whole thing is passive. In fact, Brian Gordon's research shows that there's a lot of active torque generated at the shoulder.

It's the later links in the chain that are questionable, especially the flexion of the wrist. There's no research out there that answers the question fully, but there's good reason to suppose it's passive.

Did you read the thread that addresses this very question? It was discussed in a huge amount of detail.

As for your font tags, just type the message normally. Not sure why you're trying to include the weird verdana tags... when you look at your posts after you've made them do you see the problem?

 

But passive transfer means uncontrollable action. To produce different proper serve routine we have to produce different arm action. It means we must control or change them somehow. Question is – how are you going to control something without control?

 

I answered this question earlier. By changing things earlier in the chain (for example pronating by internal shoulder rotation), you set up different conditions. It's like adjusting a railway track at an early point so that the train follows a different path.

In the case of changing from a slice serve to a flat serve, internally rotating the shoulder will achieve this.

 

Lol of course when we apply physics to the human body we do not imply it's completely void of muscular control. Most of what we talk about on this forum is a very watered down simplification. Angular forces and rotational forces are very superficial visualizations over broad networks of muscles.

"kinetic chain" is how force generated by one muscle is transferred to another muscle.
Your diagram is incorrect. If you've taken Application of Physics or Physics in Biology/Medicine, the muscles actually acts in various angles on the segments. Like how muscles are connected in reality to the bones. It is not a motor between them. Transfer occurs when a activated muscle works against a reactionary muscle.
A motor implies an acceleration. The force is not amplified after every joint. Reactionary forces are equal, not greater than the initial action. The force from your body does not completely transfer to your racquet.

Leg muscles generate force against the ground, which work against reactionary muscles of the hips, to the core, to the shoulders and the arms.
The force generated by the rest of your body > forces generated by arm which are reactionary.
Push lightly against your desk. It requires a reactionary force from your chest and shoulders. The more you want to push, the more your chest and shoulders have to react.

That being said whip physics is obviously a simplification, but that doesn't make it's mechanics absent because the brain asserts control.

 

awesome video.

By gravity, I think you meant to say inertia, right? (provided by the (airborne) mass of the body)

 

That's a much better word thank you lol.

 

What part of the body is the handle of the whip and how this handle is able to make the wrist to move in so complicated way (slice or flat serve)? Are you magician?
If we use Continental grip, pronation can produce just flat component of the racket velocity. For slice serve we have to use wrist ulnar deviation. And pronation is not passive action. Right now you started to use active model of the Kinetic Chain.

 

Active model of kinetic chain? are you serious? That's the most redundant thing I ever heard. Don't make stuff up and give it bad names.
The Handle would probably be the shoulder because that's where rotation begins.
Of course the serve happens with various voluntary muscle activations, we decide everything! timing, keeping arm stable, to jump up! We also control the swing pattern. The whip physics simply describes the transfer of force. These things can co-exist. this is not exclusive, get it??
Kinetic chain assumes all of this, you don't have to create a new one.

Now with Pronation/Ulnar deviation. The difference in slice and flat serves actually start before the wrist and in the swing path. The slice being more sideways.

However let's follow a passive pronation.
Take a racquet and relax your risk, take it at takeback.
slowly simulate your jump and inward rotation of shoulder, your elbow is pointing to ceiling. The wrist naturally supinates because of the weight of the racquet and the position of the elbow.
Now speed it up, extend the arm and with the force moving to the racquet the wrist has no where to go but pronate!! Unless you are really stubborn.
Make the swing sideways and ulnar deviation!

Go ahead and make a forced wrist snap, however this would disrupt your kinetic chain. Kinetic chain doesn't mean no muscle activation!! The muscles work against each other to transfer force! The brain is always present to stabilize these movements.

I went over this for the benefit of practical application. However control over the swing path doesn't disprove anything. They're both subject to energy transfer no matter what type of serve it is. Transfer of force can be applied to either.

Man I really have nothing to do.

 

Man I think I'm becoming a troll and that last post was unnecessarily belligerent. I'm going to just stop now. I'm going to slowly back away from these forums lol. bye LOL

 

I personally, don't consciously use ulnar deviation in my slice serves. The swingpath I imagine sets the racquet path, and if the throwing motion leads out, when my arm straightens then the racquet will continue on the path leading to natural ulnar deviation.

Conversely on a flatter serve the racquet will continue forwards resulting in harder pronation.

I can't tell you exactly what is going on, but I can tell you what it feels like to me.

Here is me hitting some slice serves, in regular speed, and 210fps high speed.

http://vimeo.com/13793486

And here is a guy who is a little better than me hitting similar serve.

http://www.youtube.com/watch?v=J3pZ-mAgQQg

J

 

And when I pull some pics out of the slow motion video...









J

 

J

 

No, you said it exactly correctly.

I think that toly is big on looking at video and doing math, and not so much on actually hitting tennis balls himself.

J

 

In this instance, the active portion of the chain would be the shoulder rotation. I've explained this over and over to you... I get the impression you don't understand what internal shoulder rotation is, how it contributes to pronation, and how that changes the passive dynamics at the wrist.

 

If I have time later today, I'll render some images that should illustrate exactly what I mean.

 

toly's article

To clarify the matter, let me send to you my article about this stuff. I did no finish it, but I belive it can clarify something.

 

toly, I'm not sure you sending me an article will help at this point. You've articulated your argument, and I responded directly to your point. But you haven't countered my response yet, so I'm not sure you even understand my argument.

Later on tonight I'll try to get those renders and post them here so you have a better idea of the role of internal rotation.

For now, answer this question:

Do you understand that internal rotation of the shoulder pronates the racquet? Yes or no?

 

In medical terminology - pronation means counterclockwise rotation of the forearm. In tennis jargon - pronation also can be counterclockwise rotation of the arm. The answer is yes.

 

So do you recognize that activating a muscle group only at the shoulder joint can cause pronation?

 

The shoulder is the part of the body between the neck and the upper arm. In anatomy, internal rotation is rotation toward the center of the body. But, what is internal rotation of the shoulder? If the right shoulder can somehow rotate toward the center of the body (I think it practically impossible), it produces clockwise rotation of the arm. Pronation means counterclockwise rotation of the arm. I'm completely lost with your explanation.

 

http://www.exrx.net/Articulations/Shoulder.html

Look at internal rotation in the above link (second from the bottom), and imagine what would happen if you performed that rotation when your arm is above your head and fully extended.

Here is another image that may help - I created this for another thread, so just pay attention to the first two poses:

The shoulder is internally rotating between the first and second pose. If you like, I'll spend some time creating an image that shows that same rotation when arm is fully extended above the head, but you should be able to figure it out from the info so far.

 

it's a bit confusing, because the internal rotators don't always rotate the limb inwards. According to a friend I just asked, the movements and muscles are named with reference to the baseline anatomical position (lying down, arms by side, palms face up).

At that position, the movement will indeed rotate the arm inwards.

But change the configuration of the body, and that same movement will achieve very different things.

with arms straight by side, internal rotation (achieved by activating the internal rotators of the shoulder) will bring the forearm towards the body.

That very same movement, in the configuration of the first two poses in the above rendered image, will rotate the forearm downards.

And when the arm is facing upwards towards the sky, with elbow fully extended, it will achieve the same movement of the racquet head as would pronating the forearm.

 

OK, I got it. It means conunterclockwise rotation of the upper arm.

 

Yep, and this movement of the shoulder is the primary force behind racquet pronation.

I never actually thought of it as counterclockwise rotation of the upper arm, but you're right - no matter what position the body is in, internal rotation of the shoulder does rotate the upper arm counterclockwise. Thanks for the insight

 

Forearm also can pronate by using much faster elbow joint. But, it doesn't matter.
Can you be more specific and explain how we can use Whip Effect in case of the kick serve.

 

Toly,
spacediver's use of "pronation" coming from the shoulder on serves is well accepted in tennis. Anatomically speaking it is really, "internal rotation of the shoulder". But among tennis players, "pronation on the serve" is such an ingrained concept that there is absolutely no chance that "internal rotation of the shoulder" will replace the term of "pronation" on the tennis serve.

 

This is right, because the term "internal rotation of the shoulder" is one of the most confusing I ever met. But, I do not care about terms if I am able to comprehend them.

 

Brian Gordon's research shows that just before contact, internal shoulder rotation contributes a lot more towards the racquet head speed than does forearm pronation.

As for whip effect and kick serve, I'm not as clear as to the biomechanics of the kick serve compared to the flat serve (and even the flat serve I'm still trying to understand).

What I can tell you is that in both cases, the legs and the trunk provide the bulk of the power, which is then channeled up through the arm (with the aid of shoulder abduction and shoulder transverse adduction (see that exrx link i posted earlier for descriptions).

The trunk ends up cartwheeling forward into the court, so there is a huge amount of forward angular momentum in the system. Brian Gordon calls the trunk the "momentum superhighway". This forward momentum can be channeled into the elbow joint to enable elbow extension, so long as the arm is positioned correctly. In other words, if the circle along which the trunk is carthwheeling forward is parallel to the circle that would be traced out in space by elbow extension, then the momentum will be able to channel into that joint rotation.

Similarly for the circle that elbow extension traces compared to the circle that the wrist traces through space. If the forearm pronates while the elbow joint is extending, the wrist will be able to flex passively. If the forearm doesn't pronate during elbow extension, the wrist will experience passive ulnar deviation.

I may have actually mispoke earlier when I said that shoulder rotation modulates the direction of passive movement of the wrist. I definitely know that forearm pronation does. But keep in mind that when I say this, I don't mean that the momentum used to flex or deviate the wrist will be channeled from forearm pronation. That momentum comes through the trunk rotation and elbow extension. The forearm pronation here will simply modulate the direction, sort of like a traffic cop (although it also contributes a bit to racquet head speed).

 

Kick serve and wrist

There are a lot of speculations about the wrist movement (the wrist snap, the wrist whip effect) during the last second before impact. Some of the tennis specialists (Vic Braden etc) say no such thing occurs. But, others (Brian Gordon and so on) insist the wrist motion is very important. But what does the wrist really do? When I’m serving I feel like my wrist is doing something very essential, however maybe my feelings mislead me. But, the pictures never lie. This time I’m going to analyze the pictures (Figure. 2.9 and Figure 2.10). They show the set of the video’s frames (last second before impact) taken during the Florent Serra and Lleyton Hewitt kick serves. Let’s pay attention to the wrist motion. These players employ the Continental grip. From above pictures we can see the racquet string pane has the practically constant vertical orientation. The hand is absolutely out straight and there is no extension or flexion of the wrist before and for the duration of the impact. At the same time the wrist ulnar deviation directs the racquet upward very fast. The pictures on Figure 2.9-2.10 show this movement takes place in the plane which coincides with the racquet string plane. Hence, it can produce the brushing boll motion only. But, the brushing motion mostly responsible for the ball rotation, not for the ball speed. The wrist ulnar deviation might be used to create different types of the spin serves and this is a very good option. Unfortunately, it also can destroy pronation effectiveness (it reduces the angle β, see step 2.1), the most important part of the tennis kick serve. The tennis players must exploit the wrist ulnar deviation very cautiously, because it can completely destroy the pronation component |VLH| of the racquet speed! OK, so far I don’t see any wrist snap in the kick serve which could add any real speed to the tennis ball, except the spin!

 

I'll read your post soon toly, but in the mean time, what is going on in your posts? Why do you try to put these weird font tags? Are you doing it intentionally? Are you using a regular computer?

 

i just read your post, and it looks like you just copied and pasted from something you had written and saved.

It would be helpful if instead, you responded directly to my comments.

You asked a question, I did my best to think about it and answer it carefully, and you paste this out of context stuff.

 

I'm Russian old man. English is my third language and it does not like me. That's why, I have to use Word Processor for spelling check. For example, when I copy text from your post and paste it to Word. It automatically changes the font. I tried to change font myself, but I always choose the wrong one.