physics/science behind pronation

[sureshs]

Originally Posted by sennoc

Toly,



The image above is totally wrong. As far as I remember, it was published in a popular tennis magazine, am I right? Do not believe in words and numbers you see in popular magazines and newspapers. Believe me - in my country I work as a science journalist, I spent my last 20+ years as an author and an editor and I know the quality of journalists' work. Perfectly know. And it's low.



This image is EXCELLENT. It perfectly shows one of the most important sources of energy in modern tennis strokes: energy transfer along the kinetic chain.

What do we see?

We see that in a sufficiently short time, kinetic chain does not move! Something wrong is here, don't you think? We have generated so much energy at many parts of kinetic chain, but at the contact everything seems steady. Where is kinetic energy of our legs? Shoulders? Elbow? It cannot disappear. It moves into the only moving part of kinetic chain: into the racquet. This energy transfer produces ca. 30% of stroke energy. Amazing, don't you think? Your image shows a fundamental physical phenomenon which was never discussed here. Until now you were talking about the rest (which is 70% only).

So, if you want to add "power" to your stroke, you need to hold your kinetic chain. "Hold" relatively, of course. How can we do that? By extending kinetic chain into as straight line as possible. Try to serve by moving your palm along a huge circular path, you will see it produces significantly less power. You can use your legs, shoulders, arm, hand, everything you want - and this kind of stroke will never produce powerful hits. Why? You can't transfer energy this way, so you do not have access to 30% of kinetic energy.

Another important part of the energy transfer along kinetic chain is time. Power is not only a function of energy, but also a function of time. If you can transfer energy of your kinetic chain in a very short time, you produce powerful strokes. The longer interaction, the less powerful stroke.

So, there are two important physical phenomena here: effective energy transfer along kinetic chain and short time of interaction - as short as possible. In practice, if you know how to use the first phenomenon, you do the second one.

In your picture, we can also see the work of ulnar deviation and the pronation of forearm. Ulnar deviation moves racquet head significantly, so it is obvious that it is an important source of energy. Pronation starts at frame 5, when the arm, forearm and racquet are almost straight. At this position it cannot produce significant amount of energy. Sorry, that's physically impossible.



Next excellent picture - but you do not describe the most important things here.

Ask yourself: why the main, usually vertical axis of human body is tilted here? Federer is tilted ca 45 degrees. Why? Maybe he doesn't know how to serve?

The answer is simple: internal rotation of upper arm. If you want to use it as a source of energy, you have to find a solution: should I hit with straight hand, as high as possible, or should I hit lower, but tilt my body to extend time when upper arm can increase energy of forearm?

Let's look at Sampras.



Do you see the energy transfer here? The path of racquet's head is not circular here, it's narrow! This is the result of extension of kinetic chain at contact into one direction. Of course, the line is not straight, but it is as straight as it is biomechanically possible.

Interesting. The Roddick and Federer photos also show that the ball is hit down on the first serve.

[sennoc]

Originally Posted by spacediver

sennoc, have you checked out my recent thread that talks about pronation and internal shoulder rotation?

http://tt.tennis-warehouse.com/showthread.php?p=5461174

You did almost good job OK, I'm joking, your thread is quite good, but there are some mistakes. First at all, you have to write that you are talking about biomechanics of serves. As example, pronation of forearm is one of the most important sources of energy at topspin forehands and (supination) at topspin backhands (30-40%!).

Also, this image is wrong:



Upper arm and shoulders should be colinear. The straight line along upper arm and shoulders is an axis of rotation of forearm. This axis should be tilted at ca 45 degrees at serves. Due to educational reasons, you should make corrections in the picture above and add an image with tilted axis.

[sureshs]

^^^ How is he playing without strings?

[sennoc]

Originally Posted by sureshs

^^^ How is he playing without strings?

If you do not pronate you do not need strings

[gzhpcu]

I think some of the misunderstanding is perhaps due to misidentification of biomechanical definitions:

Pronation alludes solely to rotation of the radioulnar joint at the elbow around a superoinferior axis, and is confused with internal shouder rotation which occurs at the shoulder.

Seems to me that the active internal shoulder rotation results in the passive pronation if the arm is kept loose...



To be clear: we are talking about multilevel movements around two separate joints - shoulder and elbow

[Chenx15]

Originally Posted by gzhpcu

I think some of the misunderstanding is perhaps due to misidentification of biomechanical definitions:

Pronation alludes solely to rotation of the radioulnar joint at the elbow around a superoinferior axis, and is confused with internal shouder rotation which occurs at the shoulder.

Seems to me that the active internal shoulder rotation results in the passive pronation if the arm is kept loose...



To be clear: we are talking about multilevel movements around two separate joints - shoulder and elbow

This guy got it absolutely right. Pronation/supination is only applicable to the forearm. while the actual movement of the serve is the internal rotation of the shoulder which in a way is also pronating the forearm.

[spacediver]

Originally Posted by sennoc

Also, this image is wrong:



Upper arm and shoulders should be colinear. The straight line along upper arm and shoulders is an axis of rotation of forearm. This axis should be tilted at ca 45 degrees at serves. Due to educational reasons, you should make corrections in the picture above and add an image with tilted axis.

read my post carefully - those images are not meant to depict what happens on the serve, but rather to illustrate abstract components of the rotations. They're for biomechanical illustration of the consequences of rotating certain joints while in different anatomical positions.

[spacediver]

Originally Posted by Chenx15

This guy got it absolutely right. Pronation/supination is only applicable to the forearm. while the actual movement of the serve is the internal rotation of the shoulder which in a way is also pronating the forearm.

yep, as I wrote in my other thread:

Forearm pronation actually contributes relatively little to racquet head speed - rather, it is internal shoulder roation that achieves this (this is counterclockwise rotation of the upper arm). Because the forearm is colinear with the upper arm, and because the forearm tends to adopt the same motions that the upper arm generates, internal rotation of the shoulder achieves a very similar effect upon the racquet as pronating the forearm does.

This is true only if the forearm and upper arm are colinear, as in the below images. In both these pairs of images, the forearm is NOT pronating - the only rotation is the shoulder internally rotating.

[sennoc]

Originally Posted by spacediver

read my post carefully

I did. In my opinion your image will be easier to read if the upper arm and shoulders are in line.

[spacediver]

Yea I guess I can re-render all the pics with the upper arm being colinear with the clavicle - good suggestion, thanks.

[toly]

Originally Posted by sennoc

So, here you have the real physics of tennis serve. Should I publish my account number now?

Thank you very much for comments about the article. But I think you missed the main data from the article. The diagram below illustrates the racket speed which produced by the pronation and internal shoulder rotation |VLH|. If the beta angle = 45 degrees, |VLH|= 105 mph. And this speed is created practically exclusively by pronation and internal shoulder rotation. Tiw these motions are the most important.

[bhupaes]

Originally Posted by sennoc

As example, pronation of forearm is one of the most important sources of energy at topspin forehands and (supination) at topspin backhands (30-40%!).

Sennoc, your posts have literally been a treasure trove of information - thanks! The mistake I made today was to think about all of these things while playing doubles, and I couldn't get a first serve in to save my life... luckily, my second serve was working well!

The other thing is the significance of the high elbow. I found that I could not get my elbow high unless my body was tilted. One significance of it therefore is that a high elbow means a good cartwheeling motion. Of course, as you point out, it also enables better utilization of upper arm rotation.

I have a question regarding the portion of your post that I have quoted above. Isn't there a lot of biceps action and also upper arm rotation in the topspin forehand, that contribute both to spin and power? Here also, isn't the wrist by itself too weak to do anything other than to orient the racquet head correctly? Try to isolate the pronation movement by holding your upper arm with your non-dominant hand to prevent it from rotating in a topspin forehand motion, to see what I mean. After reading tricky's posts regarding transverse adduction of the shoulder, I now believe that is also a major power source.

A similar argument applies to the one-handed backhand as well, except the shoulder rotation is external.

[sureshs]

Originally Posted by toly

Thank you very much for comments about the article. But I think you missed the main data from the article. The diagram below illustrates the racket speed which produced by the pronation and internal shoulder rotation |VLH|. If the beta angle = 45 degrees, |VLH|= 105 mph. And this speed is created practically exclusively by pronation and internal shoulder rotation. Tiw these motions are the most important.

Is 160 then the maximum achievable serve speed by a human?

[toly]

Originally Posted by sureshs

Is 160 then the maximum achievable serve speed by a human?

I think it can be more than 160, but reliability would be next to the 0%. I read somewhere that registered maximum was around 170.

[ramseszerg]

It's very simple.. with zero pronation, your wrist would break. It can only flex so much. Pronation is what allows you to swing freely all the way through.

[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.

Originally Posted by bhupaes

The other thing is the significance of the high elbow. I found that I could not get my elbow high unless my body was tilted.

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.

[LeeD]

I'll give you a nice, solid 4.0 serve. No archer's bow, tossing hand not too high (that's OK, neither is mine), no forwards movement, good strong swing, level shoulders not the best, but good balance overall.

[bhupaes]

Sennoc, your strokes are excellent - I peeked into the other videos also. You are one of the few people who is able to subject your body to the dictates of logic... normally, either the logic is missing, or the body is uncooperative! I agree with you, there is a beauty and symmetry about tennis that fascinates me, and to the extent that my middle-aged body will allow, my goal is also to make it as perfect a player as I can!

Upon reflection, I believe your statement regarding the elbow is correct, and its position and movement are a side effect of doing other things correctly. Great post, thanks!

Edit: Forgot to say, I look forward to reading your "Special Theory of Tennis"!

[sennoc]

Originally Posted by LeeD

I'll give you a nice, solid 4.0 serve. No archer's bow, tossing hand not too high (that's OK, neither is mine), no forwards movement, good strong swing, level shoulders not the best, but good balance overall.

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.

[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.