physics/science behind pronation

[sennoc]

Originally Posted by bhupaes

Sennoc, when you say the upper arm contributes, you mean upper arm rotation as in internal shoulder rotation, right? This would move the racquet in the same way (almost) as forearm pronation, and because of this, a lot of people probably consider upper arm rotation to also be pronation.

I agree.

The problem is that both kind of rotations work at different parts of kinetic chain. Internal shoulder rotation is a source of energy at serves when there is L between upper arm and forearm. Pronation (of forearm) as a source of energy works when we have L between forearm and racquet. As a result, there are totally different forces acting at elbow/wrist. If you think that pronation of forearm is a source of energy, you will force your wrist to do impossible things. This is not a source of energy, this is source of injuries.

LeeD, find another thread.

[LeeD]

You are a techno weenie on the techniques of hitting a serve.
A good server pronates, period. If he's not allowed to pronate, his serves are slow, period.
Pronation good, not pronating BAD!
How can you debate whether a server holds the racket off line? Of course they do, every server who can serve! You MUST know that, or shut the frick up!

[sennoc]

Originally Posted by salsainglesa

I fpound this one... wich explains better the position.
http://www.youtube.com/watch?v=1t6bLABbebc&NR=1

This is a good advice if you want to hit serves at full speed. But the explanation is wrong.

Racquet not in line with forearm has nothing to do with additional energy. It is a kind of buffer - wrist is not fully extended, its position is more natural at impact, more stable and the risk of injuries is lower.

Watch best servers, frame by frame. They pronate as late as possible, just before contact. Why? Because pronation is not important. They have to pronate because they do not want to hit the ball by the edge of the racquet. They do that as soon as possible, because they want to use as long as possible the main source of energy at serves: arm rotation.

So, why to pronate? Can't we start with the racquet's head in hitting position? Try to do that (carefully!).

We can't. Our wrists are too weak to deal with so huge forces. This is the real source of forearm pronation at serves: weakness of wrists.

LeeD, could you help me, just once? Could you tell me, where can I find "Ignore" button here?

[salsainglesa]

Sennoc no disrispect here, but if serve was only done by the hand then that would be true, but there are more axis and levers than that.
you know the drill, legs, hips, torso, shoulder elbow, bones of the forearm... this kinetic chan not only produces the necesary power but also the necesary alignment.

The most effective spin serve is done accelerating the raquet through the edge, the alignment can be done with the torso... the raquet moves through the edge in reference to the body, but the torso is moving and aligns the string bed in reference to the ball... its two separate things... pronation depending on hand position and grip can add spin or pace.

[LeeD]

I get it now.
You see things from a different perspective, but the same thing!
You see the glass as half full. Other's see it as half empty.
You say we are weaklings and pronate to achieve rackethead speed. We say we pronate to get rackethead speed thru pronation, but don't dwell on our weakness.
We both agree we cannot swing fast with an open face, so a closed face is necessary to get up to speed, then the opening to contact the ball square for a flat serve. That supports my argument that we should swing faster on spin second serves than we do for flat first serves because WE CAN!
So we are different (our theories), but the same (in actual practice)!

[Fugazi]

Originally Posted by LeeD

Yes, you of the 85 mph first serve telling someone not to pronate because it's of minor importance.
If pronation wasn't important to adding speed, everyone would serve with and eastern forehand grip.

You got that right. Sampras had tremendous pronation...

[spacediver]

I'm composing a post that will explain the relationship between pronation and racquet head speed. Give me a bit of time. Am including custom rendered graphics of the biomechanics.

[spacediver]

Here we go:

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

[toly]

Originally Posted by sennoc

Pronation as a source of racquet's head speed at serves is NOT IMPORTANT. Dot.

I posted the article (see please thread http://tt.tennis-warehouse.com/showthread.php?t=361610 ) where I tried to proof importance of the pronation. Can you give any particular negative comments about that?

[sennoc]

Originally Posted by salsainglesa

Sennoc no disrispect here, but if serve was only done by the hand then that would be true, but there are more axis and levers than that.

There is more, I agree. Much more, in reality. But this is a scientific fact: iternal rotation of upper arm generates 40% of energy, horizontal flexion 15-25% depending on the type of serve. Contribution of palm ulnar flexion is ca. 30% at power serves and negligible at kick serves, while ulnar flexion generates ca. 20% at kick serves and almost nothing at power serves.

People believe in the magical role of other parts of kinetic chain because they usually watch the best servers. They (best pros) really use many many other elements, so many that they sum to important values. But what about players like Wawrinka? His kinetic chain is very short but he serves quite well. Does he use magical powers of the other universes?

You also have to remember that kinetic energy of racquet's head is not a simple sum of energies generated at every part of kinetic chain. This energies contribute to ca. 70% of kinetic energy of the stroke. Just 70%. The rest - ca. 30% of the sum!!! - is generated by energy transfer along kinetic chain. I have a beautiful picture here from one of the scientific papers, but I can't attach the file and I'm too lazy to find a host. But I promise I'll post it here - in hours after LeeD's first video from the court

And here is the most funny part. If you want to have an access to this "additional" 30%, you have to use your kinetic chain in a way similar to a whip. The problem with amateur tennis players is that they do not use this method. But if you start working on proper serve technique, you unintentionally learn how to use better energy transfer! So, when a player starts to think about "upper arm rotation", about "pronation", he begins to move energy along kinetic chain! "Wow!" - he thinks - "that pronation is a really huge source of energy!".

Funny, don't you think?

Toly, give me please some time.

[dominikk1985]

Originally Posted by LeeD

You are a techno weenie on the techniques of hitting a serve.
A good server pronates, period. If he's not allowed to pronate, his serves are slow, period.
Pronation good, not pronating BAD!
How can you debate whether a server holds the racket off line? Of course they do, every server who can serve! You MUST know that, or shut the frick up!

That's a little rude, but basically you are right. some people over analyze things.

People just need to actually grab a tennis racket and try it out to realize what's going on.

anyone who says that pronation doesn't add to racket head speed has not experienced, period.

look at this badmintion video by some asian nerd:
http://www.youtube.com/watch?v=HNVC5PVJyPQ

go to 1:20

[sennoc]

Originally Posted by dominikk1985

anyone who says that pronation doesn't add to racket head speed has not experienced, period.

So you are sufficiently experienced to negate results in scientific papers written by most famous experts in the world.

You know, I begin to hate empty words. May I ask you for a video with your serve sequence? If you are not an active player but a scientist, may I ask you for your publications in biomechanics?

[sennoc]

Originally Posted by sennoc

This is a good advice if you want to hit serves at full speed. But the explanation is wrong.

Racquet not in line with forearm has nothing to do with additional energy. It is a kind of buffer - wrist is not fully extended, its position is more natural at impact, more stable and the risk of injuries is lower.

Watch best servers, frame by frame. They pronate as late as possible, just before contact. Why? Because pronation is not important. They have to pronate because they do not want to hit the ball by the edge of the racquet. They do that as soon as possible, because they want to use as long as possible the main source of energy at serves: arm rotation.

So, why to pronate? Can't we start with the racquet's head in hitting position? Try to do that (carefully!).

We can't. Our wrists are too weak to deal with so huge forces. This is the real source of forearm pronation at serves: weakness of wrists.

LeeD, could you help me, just once? Could you tell me, where can I find "Ignore" button here?

It was a bit late yesterday and I forgot about the most important thing, of course. At impact, racquet not in line with forearm is also a result of ulnar deviation - this is the last phase of its motion.

[Chenx15]

So far, these two gave me the best answers. anyway. regarding the Sennoc vs the LeeD debate. i will side with Sennoc on this one.

Here is why, pure pronation has no impact on the ball. Try it, just keep hitting the ball with pure pronation. Mind you pronation is simply applicable to the forearm so you can't move your elbow or your shoulder because then you are applying internal rotation into the action.

so why is continental or EBH is the optimal grip for serve is because it has the less wind resistance. you are basically hammering the ball but to avoid the frame you pronate at the point of impact because that's what you want to hit it with. but by using continental or EBH, there is less wind resistance and less and it's better biomechanically because you can coil and explode with it. unlike EFH the coiling is almost impossible because the way the racket is held is already internally rotated.

so from what i learned, pronation doesn't put spins on the ball it's actually the internal rotation of the shoulder. Pronation is basically the way of contacting the ball, either you want flat, kick, or slice. and if you actually review every shots the follow through is different but they all have pronation. so the shots are affected by elbow and shoulder movement but not by pronation

in continental grip, you can go from external rotation of the shoulder to internal rotation. while efh the arm is already internally rotated therefore losing that part of the energy.

[Kevo]

Originally Posted by Chenx15

I would like to understand the physics behind pronation. i am not sure how it makes the ball stay up and makes it spin to go down.

Not sure if anyone's already said this, but pronation doesn't make the ball stay up and it doesn't make the ball spin to go down. It simply allows you to use some leverage to get faster racquet speed.

You can hit the ball up or down and with or without spin using pronation.

[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.

[sennoc]

Next amazing picture. 4th, 5th, 6th frame - why the elbow is so high? Why it doesn't move? Because Sampras uses INTERNAL ROTATION OF UPPER ARM as a fundamental source of energy and on these frames we see the artifacts of this method.

Generally, if you think about tennis strokes, do not think about angles, velocities etc. Think in terms of energy and its transfer - it is much easier to understand tennis physics this way.

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

[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

[Chas Tennis]

Energy from the rotational component around the axis of the racket on the serve.

FYB has a very clear introductory description of pronation. Just after 3 minutes he describes rotational energy and its transfer into the ball.

http://www.youtube.com/watch?v=Y1C6V_3s4nA

For this question the body's source of the rotational energy is not relevant.

This issue involves the rotational component of racket head speed, it's axis and where the ball is contacted in relation to this axis. Let's say that the racket is rotating around an axis running through the center of the handle to the top of the frame. The racket strings have a large translational velocity component and a rotational velocity component that varies to each side of the rotational axis. This depends on which side and how far off the the axis the ball is contacted as the racket strings have a velocity either greater than or less than the larger translational component. That is, to one side of the axis the racket strings have a greater velocity and might produce a considerably different serve velocity.

Complicating things while being struck the ball may translate across the strings toward or away from the axis. Probably there is no significant translation on the flat serve but on the spin serves the ball might move closer or farther away from the axis while the racket is rotating.

If I could somehow get a good service motion do I want to hit a little to the right or left of the racket axis?

High Speed Video Set Up.To study this issue close up high speed video of the racket face when the ball is struck would be useful. An optimal camera location would probably be behind the server with the camera high and viewing the racket face. Viewing also to the corner of the opposite service box would allow seeing the resulting serve trajectory. The camera has to be 12' high or so for my serve or 14' if mounted above the fence - a little inconvenient. Maybe looking through the net would also be OK but the ball trajectory is not that observable. Any video experience, other set ups? Or, some links to very close up, high speed video strikes would be useful.

Chas Tennis

[sennoc]

Originally Posted by Chas Tennis

FYB has a very clear introductory description of pronation. Just after 3 minutes he describes rotational energy and its transfer into the ball.

http://www.youtube.com/watch?v=Y1C6V_3s4nA

I appreciate Will work. His site is one of the best, no, in my opinion it is the most useful tennis site ever made. But Will is not a pro player, didn't learn how to play with the best coaches in the world. Also, Will is not a scientist. His videos are very useful, but there are things which are not perfect there.

The kind of serve motion shown by Will in this video is not biomechanically optimal. I mean, people can use this kind of motion and it will work for many amateur players. But this is not a technique of a professional tennis players.

His explanation of the role of pronation is wrong, unfortunately. He needs time to read some papers, make some experiments on the court and to think about casual sequence of things during serves. I hope this thread will help him to make better videos.

Slo-mo sequence at the end of movie presents good technique.