physics/science behind pronation

Discussion in 'Tennis Tips/Instruction' started by Chenx15, Mar 2, 2011.

  1. dominikk1985

    dominikk1985 Legend

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    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
     
    #51
  2. sennoc

    sennoc Guest

    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?
     
    #52
  3. sennoc

    sennoc Guest

    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.
     
    #53
  4. Chenx15

    Chenx15 Banned

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    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.
     
    #54
  5. Kevo

    Kevo Hall of Fame

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    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.
     
    #55
  6. sennoc

    sennoc Guest

    Toly,

    [​IMG]

    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.

    [​IMG]

    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.

    [​IMG]

    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.

    [​IMG]

    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.
     
    Last edited by a moderator: Mar 3, 2011
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  7. sennoc

    sennoc Guest

    [​IMG]

    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? ;)
     
    Last edited by a moderator: Mar 3, 2011
    #57
  8. spacediver

    spacediver Hall of Fame

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    #58
  9. Chas Tennis

    Chas Tennis Hall of Fame

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

    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
     
    #59
  10. sennoc

    sennoc Guest

    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.
     
    #60
  11. sureshs

    sureshs Bionic Poster

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    Interesting. The Roddick and Federer photos also show that the ball is hit down on the first serve.
     
    #61
  12. sennoc

    sennoc Guest

    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:

    [​IMG]

    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.
     
    Last edited by a moderator: Mar 3, 2011
    #62
  13. sureshs

    sureshs Bionic Poster

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    ^^^ How is he playing without strings?
     
    #63
  14. sennoc

    sennoc Guest

    If you do not pronate you do not need strings ;)
     
    #64
  15. gzhpcu

    gzhpcu Professional

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    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...

    [​IMG]

    To be clear: we are talking about multilevel movements around two separate joints - shoulder and elbow
     
    Last edited: Mar 3, 2011
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  16. Chenx15

    Chenx15 Banned

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    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.
     
    #66
  17. spacediver

    spacediver Hall of Fame

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    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.
     
    #67
  18. spacediver

    spacediver Hall of Fame

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    yep, as I wrote in my other thread:

     
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  19. sennoc

    sennoc Guest

    I did. In my opinion your image will be easier to read if the upper arm and shoulders are in line.
     
    #69
  20. spacediver

    spacediver Hall of Fame

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    Yea I guess I can re-render all the pics with the upper arm being colinear with the clavicle - good suggestion, thanks.
     
    #70
  21. toly

    toly Hall of Fame

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    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.
    [​IMG]
     
    #71
  22. bhupaes

    bhupaes Professional

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    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.
     
    Last edited: Mar 3, 2011
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  23. sureshs

    sureshs Bionic Poster

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    Is 160 then the maximum achievable serve speed by a human?
     
    #73
  24. toly

    toly Hall of Fame

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    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.
     
    #74
  25. ramseszerg

    ramseszerg Professional

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    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.
     
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  26. sennoc

    sennoc Guest

    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.
     
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  27. LeeD

    LeeD Bionic Poster

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    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.
     
    #77
  28. bhupaes

    bhupaes Professional

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    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"!
     
    Last edited: Mar 3, 2011
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  29. sennoc

    sennoc Guest

    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.
     
    #79
  30. LeeD

    LeeD Bionic Poster

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    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.
     
    #80
  31. SuperDuy

    SuperDuy Hall of Fame

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    Saw your others videos, what city you in?
     
    #81
  32. sennoc

    sennoc Guest

    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?

    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.

    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?

    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.

    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.

    You are a clown.
     
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  33. sennoc

    sennoc Guest

    Warsaw. Wanna play? Tickets are not cheap.
     
    #83
  34. Djokovicfan4life

    Djokovicfan4life Legend

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    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!"
     
    #84
  35. Chenx15

    Chenx15 Banned

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

    sennoc Guest

    Sorry for that. Unfortunately, we all here play tennis. There is an action, there is a reaction, you know.
     
    #86
  37. Djokovicfan4life

    Djokovicfan4life Legend

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    We don't even have to, he pawns himself.
     
    #87
  38. charliefedererer

    charliefedererer Legend

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    I am a few days late to this party, but Sennoc, have you seen this video?
    http://www.youtube.com/watch?v=pLf_...EJM6eSD0i-YBYKp-0bo6tWfTQrQKoCusGyu258h97u1DQ

    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-MCC7D88&feature=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=cU2bFqdEnlQ&feature=BF&list=PLD4C2A7ED17FABE64&index=26
    Pat Dougherty: The Pole Vaulter's Pole emphasizing the whole body bow to unbow motion) http://www.youtube.com/watch?v=SZqh...y&list=PLD4C2A7ED17FABE64&index=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.
     
    Last edited: Mar 4, 2011
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  39. sennoc

    sennoc Guest

    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.
     
    #89
  40. sennoc

    sennoc Guest

    [​IMG]

    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?
     
    #90
  41. toly

    toly Hall of Fame

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    What is the time elapsed between two successive frames? What is MER - Maximum External Rotation? What type of the serve is it?
     
    Last edited: Mar 4, 2011
    #91
  42. AJB

    AJB New User

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    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.
     
    #92
  43. bhupaes

    bhupaes Professional

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    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!
     
    #93
  44. Kevo

    Kevo Hall of Fame

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    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.
     
    #94
  45. gzhpcu

    gzhpcu Professional

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    Last edited: Mar 5, 2011
    #95
  46. sennoc

    sennoc Guest

    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?
     
    #96
  47. sennoc

    sennoc Guest

    Toly,

    MER is explained here:

    [​IMG]

    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.
     
    #97
  48. gzhpcu

    gzhpcu Professional

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    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.
     
    Last edited: Mar 5, 2011
    #98
  49. sennoc

    sennoc Guest

    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.
     
    #99
  50. bhupaes

    bhupaes Professional

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    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?
     

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