physics/science behind pronation

[SuperDuy]

Originally Posted by sennoc

For you, this:

http://www.vimeo.com/20613921

is a forehand of 3.0 NTRP. Almost every tennis player I meet laughs loud after your rating (yes, you are a quite famous person here in Poland).

I think you should just shut up. You are wasting our time and making idiot from yourself.

Saw your others videos, what city you in?

[sennoc]

Originally Posted by LeeD

Sennoc, ONE forehand doesn't make you a good player.

Yeah. Are you able to understand that this video is not the best one, it's just a technical video of a single stroke? It's so short because I use it for many replays. That's the nature of this movie.

And what do you expect? 30 hits? With a 3.0 player like you?

Originally Posted by LeeD

You know your serve has several problems, which I pointed out, so Mr Pollack, go suck your big toe.

Rude old idiot. An uneducated tennis idiot:

- no archer's bow

Do I need it? Who the hell am I? Davydenko? Have you read my previous post about my problems with my back? Do you know that archer's bow is not essential for good stroke? No? Oh. I understand. All you can do is to copy mindless rules from your youth.

- tossing hand not too high (that's OK, neither is mine)

Stupid comment. What's important is the point of ball release (it is on a good height, typical for pro players) and the line of shoulders (which is in a good shape during this serve).

- no forwards movement

Have you ever seen Federer's serves during trainings?

- level shoulders not the best

Empty words. Shoulders work well. There are other things to improve. Unfortunately for you, you do not see them.

Originally Posted by LeeD

Even YOU admitted your game is still progressing, and as such, you are not close to having a good serve....at least not at the 4.5 level.

Quite interesting argument. Typical for low skilled players.

Yes, I admit, my game is still progressing. For your information, tennis world agrees that Nadal's serve is also progressing. That's quite nice that you place me and Nadal in the same league. BTW is he 3.0 too?

Originally Posted by LeeD

True, I have not posted a vid of myself, but I can tell you what YOU are doing wrong, and I've already listed the stuff I"M doing wrong.

No, you can't tell me what I'm doing wrong. You can write empty words which look like real arguments in the eyes of uneducated players.

Originally Posted by LeeD

Nobody is perfect, unless you are already playing on the ATP, which YOU ARE NOT!

I understand your point of view. ATP - this is the only guarantee of good technique.

I have to copy Nadal's slices.
Would be interesting to copy Roddick's topspin backhands.
Oh, wait, I'll copy Davydenko's volleys.

Man, do you read your own words?

Also, you are a liar. My comments were about your stupid arguments, not about your game.

Originally Posted by LeeD

I never accused you of being a 3.0, but maybe you have the intelligence of a 3 year old.

You are a clown.

[sennoc]

Originally Posted by SuperDuy

Saw your others videos, what city you in?

Warsaw. Wanna play? Tickets are not cheap.

[Djokovicfan4life]

Originally Posted by LeeD

Sennoc, ONE forehand doesn't make you a good player. You know your serve has several problems, which I pointed out, so Mr Pollack, go suck your big toe.
Even YOU admitted your game is still progressing, and as such, you are not close to having a good serve....at least not at the 4.5 level.
True, I have not posted a vid of myself, but I can tell you what YOU are doing wrong, and I've already listed the stuff I"M doing wrong.
Nobody is perfect, unless you are already playing on the ATP, which YOU ARE NOT!
I never accused you of being a 3.0, but maybe you have the intelligence of a 3 year old.

And yet you don't have the intelligence to realize that sennoc didn't ask for any advice here? In this kind of thread you just say "nice serve, thanks for posting," and then maybe casually point out a few issues. He didn't post a thread titled "Urgent help needed on my serve!"

[Chenx15]

Talk about LeeD getting pawned on my thread. anyway to those helpful ones.Thank you very much.

[sennoc]

Sorry for that. Unfortunately, we all here play tennis. There is an action, there is a reaction, you know.

[Djokovicfan4life]

Originally Posted by Chenx15

Talk about LeeD getting pawned on my thread. anyway to those helpful ones.Thank you very much.

We don't even have to, he pawns himself.

[charliefedererer]

Originally Posted by sennoc

Toly, you are right, I didn't read everything, have a lot of work. But without reading, I think you must be wrong somewhere. First at all, mathematics behind physics of human body is very complicated and you use very simple methods. They may be good alone, but the result - that pronation generates power at serves - doesn't agree with my experience and knowledge. I'll try to find the weakness of your analysis in a few days, k?

Bhupaes, yes, I know, knowledge hurts

I play tennis since late 70., with a 10 years break in 90. (those women...). All my life, I was a very good server. 2-3 aces per game? Where is a problem? 10+ aces per set? Quite normal. 200 kph? Rare, but doable.

Unfortunately, my serves were unstable. There were days when I made one mistake after another. Also, I had big problems with my back and elbow. I'm not too young (44 now), so I decided to change my sequence. The goal was to make it more stable and more friendly for my body.

Three or four years ago I began to think about new sequence. I knew that the days of powerful serves were finished, I had too many things to change - I made some movies and my serves were technically horrible. So I read many scientific papers, spent many hours thinking about physics of the stroke, played a lot at the wall, watched many pros. I decided to introduce one element after another. Now, my new sequence is almost finished. It's not perfect, I know, but it's technically quite solid. So, it took me three years to do this:

http://www.vimeo.com/20614075

There are minor things to improve, but fundamentals are quite solid now and I can think about increasing power. I hope I'll do this in a few months.

What's important here is that what you see on the movie is a result of my UNDERSTANDING of tennis physics and biomechanics. No trainers. No mindless copies of pros' movements. Yes, I spent many hours watching Federer, but I am like a cat, I have to find my own way. It was really funny to find an amazing biomechanical part of sequence and... discover it in Federer's sequence. So, if my serves or forehands look a bit similar to Federer's - it's because we both use the same physics. He was not a source of technique for me, he was a method of verification.

I'm really proud of my sequence now. Not because it is so good, but because it shows the real power of understanding. My sequence is a product of logical thinking, not a result of mindless rules like "do that", "don't do that", "pronation generates", "jump at serves" etc.



Do not think about elbow. "High elbow" is a mindless rule. Trainers use it because they do not understand physics and biomechanics. Now you know that the forearm rotates along axis made by upper arm and shoulders. Just remember that this axis should be straight - and tilt it (high elbow is a result of this action - just a result!). This is a very simple thing to do. One hour at the wall and it will be quite natural (but it will take you months or years to remove "quite"... ). You will also see that your elbow moves forward - exactly as in another popular mindless rule. Everything seems to be more simple - and more easy to do.

What's important, tilting gives you better point of view on the ball. That's a small bonus for our visual perception system.

Yes, you are right about the role of pronation and supination at modern topspin forehands and backhands. I have some scientific papers and they say that it generates 30-40% of kinetic energy of the stroke. It is quite easy to demonstrate (maybe one day I'll make a movie). Of course you have to remember that power of modern forehand topspin or backhand is also a result of energy transfer along kinetic chain (this is what people usually don't see and don't understand in Federer's strokes).

Now you can see the real power of understanding in tennis - in practice. We were talking about serves, but now you know what to do at topspin forehands and backhands. That's a kind of magic for me, that tennis is so intellectually beautiful. Its beauty is very similar to the internal beauty of special theory of relativity. I was so inspired by this coincidence that I created my own "special theory of tennis" (scientifically correct of course). I will present it one day, it's too good to be hidden.

I am a few days late to this party, but Sennoc, have you seen this video?
http://www.youtube.com/watch?v=pLf_M...sGyu258h97u1DQ

While there are some oversimplifications and shortcomings, I think it helps bridge the gulf between you and Toly.

The analogy is made between the kinetic chain of a tennis player, and that of a five stage rocket.

There is a separation in the sequence in which the legs, then hips, then shoulders, then arm and finally the wrist all "fire".

Energy is applied at each of the steps, and they really flow into one another, as a wave rippling through the body.

In the above video, there is an emphasis in the role of hip rotation being so very important to the rotational energy. There is the graphic representation of the "force multiplier" that multiplies the speed at the racquet being 16 times the speed of the hip rotation because of the outward length that the arm and racquet extends beyond the central axis of rotation.

Well, they are trying to sell a hip rotation product, so their analysis stops there.

But certainly, hip rotation is a significant contributor the force of the serve, as is pronation.

If one wants to attempt up all the linear and rotational energy components, one would still fall short of the individual components, because each component influences the subsequent.

Merely measuring the last component, pronation, ignores that energy was transferred from the leg pushoff, through the hips, shoulders, arm and wrist.

Pat Dougherty (among many others), the Bolletieri "Serve Doctor" had long been a proponent of recognizing each of the components of different types of rotational and linear energy components in the serve. Hence the following videos:

Pat Dogherty's Simple Spring Loaded Technique emphasizing hip rotational energy:http://www.youtube.com/watch?v=Ixx-M...eature=related
Pat Dougherty - The See Saw [or Cartwheel shoulder-over-shoulder] Motion emphasizing the rotational motion about an axis perpendicular to the central body axis http://www.youtube.com/watch?v=cU2bF...ABE64&index=26
Pat Dougherty: The Pole Vaulter's Pole emphasizing the whole body bow to unbow motion) http://www.youtube.com/watch?v=SZqhH...=24&playnext=1
Hammer that Serve emphasizing the power of pronation http://www.youtube.com/watch?v=xjXJGsRtm08&NR=1

Put it all together smoothly in a kinetic chain, add in a good tossing motion and plenty of practice and youv'e got a decent chance of developing a good serve. And from seeing your serve video, it looks like that's exactly what you did.

[sennoc]

charliefedererer,

First video is quite interesting and... almost good. Almost, because tennis players do not work as 5 stage rocket. There are many more stages and the process of energy generation is more complicated.

There is also bad physics and biomechanics in this movie. I'm talking about this 16x multipier. Totally not true. I'm sure I can serve without moving my hips and the speed of the ball will be over 120-130 kph. So, does it mean that if I add 20 kph to my hips (quite easy to do, do the math), my serves will be 120 + 16*20 = 440 kph?

Also, all those angles look very magical, but in reality, what we are talking about? We are talking about place for motion. The larger angle means that there is more way and more time to accelerate, that's all. This is obvious at every joint in our body, at every stroke. Fundamental tennis rule: make place for the motion (btw the next rule is: if you don't want to be injured, remember about place where you can dissipate your energy...).

Hips are important, that's true. Why? Because you can use them to rotate the axis of upper arm rotation (the main source of energy at serves) around the main vertical axis of the body. This adds energy. But not too much.

At serves, there are many other sources of energy too. As example, you can decrease distance between shoulders. Or you can bend your whole body just before contact (that's typical for Federer).

"But certainly, hip rotation is a significant contributor the force of the serve, as is pronation" - please, not "pronation"

Have no time to watch other videos, maybe later.

There is also one very important thing in your post. You are not quite precise when you talk about adding energies and 5 stage racquet.

It's time for magic.

[sennoc]

This is the most important theoretical analysis of tennis serves you have ever seen. Its depth is huge. At first, I couldn't believe that I see a diagram so perfectly representing my way of thinking about tennis technique. After so many years, I had a scientifical proof that I was right. It was an amazing moment for me. I spent many hours talking about this image with my friend, who is coaching tennis 30 years. He was amazed, too.

Please save this image in case of hosting problems.

The image above shows kinetic energy (in joules, vertical axis) as function of time (frames, 125 Hz). It was published in 2009 in one of scientific magazines. This paper was first (ever!!!) scientific analysis of kinetic energy during serves (what, btw, shows the real level of modern tennis science...).

Two really good tennis players, 15 serves per player, 3D photogrammetry, 28 points body model, statistical analysis. You know, all that stuff...

So, what do we see? We see evolution of kinetic energy during serve from platform stance.

Ke LL - kinetic energy of lower limbs (both thighs, tibias, feet and pel).
Ke Tr - ...of trunk
Keuarm - ...of upper arm
Ke Larm - ...of lower arm
Ke H-R - ...of hand and racquet.

MER - Maximum External Rotation

I could write many words here, but I think it will be better if you try to interpret the image. I'll help you a bit.

So, guys, what do YOU see on the image above?

[toly]

What is the time elapsed between two successive frames? What is MER - Maximum External Rotation? What type of the serve is it?

[AJB]

LeeD, the OP was specifically about the physics of pronation. From the content of your posts, it appears that - whatever your tennis skill level and on-court experience may be - you do not have any specialized knowledge of the physics of tennis. Why then did you weigh in at all - and why did you start in with childish personal insults of other posters who actually addressed the OP's question about physics?

Your remarks trying to correlate number of posts with their worth make no sense. As the saying goes, "It is better to remain silent and be thought a fool, than to open your mouth and remove all doubt."

Seriously, it's behavior like yours that degrades this forum and makes it less worthwhile for everyone.

[bhupaes]

At MER, it seems that all the moving parts are slowing down except H-R. The boost of energy in the H-R component suggests that potential energy stored by the other components (which have now slowed down) is released into H-R. In addition, we know that there is an active component adding energy to H-R at this point (muscles, mainly shoulder, I am guessing). At impact, of course, the abrupt transfer of energy to the ball causes H-R to slow down drastically. It's probably not a coincidence that the graph showing the drop in energy looks like the path of the racquet head after impact!

What is surprising is the differential in the maximum energy levels - 140,000 for H-R vs 40,000 for Tr! Surely, the shoulder/arm does not produce that much, does it? The work done by the other components must have stored the excess energy as potential energy in the internal rotator muscles of the shoulder, I suppose. I won't even try to guess what the efficiency must be, it is already too complicated!

Fascinating, Sennoc! I eagerly await your explanation!

[Kevo]

Originally Posted by AJB

LeeD, the OP was specifically about the physics of pronation. From the content of your posts, it appears that - whatever your tennis skill level and on-court experience may be - you do not have any specialized knowledge of the physics of tennis.

I think the thread has traveled far from what the OP was getting at. I did notice that one poster did come to understand that you do actually hit down on the first serve, so I think someone has gotten something from the pics posted.

[gzhpcu]

Here is the article Sennoc is referring to:

http://oa.upm.es/5310/1/INVE_MEM_2009_69379.pdf

[sennoc]

Bhupaes, your way of thinking is impressive. You didn't find solution, but you said almost everything.

To make physics of modern serve/forehand/1h backhand really clear, let's think in steps.

First, if you look at this forum, at other tennis forums, if you listen to coaches - everybody talks about "loading" energy, more precisely - about adding energies generated in different parts of kinetic chain. This is "your" 5 stage rocket OK. Do we see this process on the image? Where?

[sennoc]

Toly,

MER is explained here:



Maximal rotation in + direction on the last image.

This is not important, what kind of serve we are talking about. The physical phenomena discussed here are so fundamental that they work at forehands and backhands too. I'm sure that a diagram of kinetic energies at modern forehands would be very similar.

[gzhpcu]

Racket speed is essential on the serve. An important factor is the use of elastic energy in the stretch-shorten cycle. During the stretch phase energy is stored and released in the shorten phase. This must occur very quickly after the stretch phase, otherwise energy is rapidly lost.

An example is the bottom of the backswing, where maximum external rotation of the upper arm occurs. Leg drive, trunk rotation serve to further accentuate the MER, allowing an explosive internal shoulder rotation towards impact (stretch-shorten cycle). Pre-stretched muscles apply force better. Aiming high causes the arm to straighten and "stop", whipping the racket forward. The high elbow position after impact shows that one aimed high and not forward.

Correct timing pre-stretches the arm muscles for a fast serve.

[sennoc]

Yes. On the image above, loading mechanism is clearly visible.

There are 4 curves (except H+R): Ke LL, Ke Tr, Ke Uarm and Ke Larm. Their order in time is obvious: we start with legs, then there is torso, then upper arm, then forearm. Every curve has its own maximum. Ke LL has maximum at frame 24 - ca. 20 J, Ke Tr max is ca. 38 J, Ke Uarm - 22 J and Ke Larm - 30 J.

We can see good time synchronization here. If a curve has maximum, the next curve (in time) is perfectly at the half of its increasing slope. This is how "loading" works in tennis. This is what every tennis coach is talking about.

OK, guys. If you agree, then please add all those energies and check their sum.

You will be amazed.

[bhupaes]

Originally Posted by sennoc

To make physics of modern serve/forehand/1h backhand really clear, let's think in steps.

First, if you look at this forum, at other tennis forums, if you listen to coaches - everybody talks about "loading" energy, more precisely - about adding energies generated in different parts of kinetic chain. This is "your" 5 stage rocket OK. Do we see this process on the image? Where?

I think I see what you mean. The energies peak in the following sequence before following: LL, Tr, uarm, LArm, then finally H-R. Each causes a transfer to the next component, it seems. That would be the 5 stage rocket, right?