physics/science behind pronation

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

  1. sennoc

    sennoc Guest

    Look at Fujifilm HS10 too, very good camera for tennis purposes (my choice).
     
  2. toly

    toly Hall of Fame

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    I even do not understand the term – ‘energy transfer’ in relation to the human body. I spent a lot of years in the fields where we designed special devices (antennas, cables, wave guides etc.) to transfer electromagnetic energy. Right now it is very big problem to transfer properly electrical energy inside of the very fast computer processors. I think human body doesn’t have special mechanisms, for example, to transfer left ankle energy directly to the right wrist.:)
     
    Last edited: Mar 7, 2011
  3. toly

    toly Hall of Fame

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    Thank you very much for information about camera.
     
  4. gzhpcu

    gzhpcu Professional

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    To quote Brian Gordon:
     
  5. toly

    toly Hall of Fame

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    OK. Right now we know that we don’t know anything!?
     
  6. gzhpcu

    gzhpcu Professional

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    Did you ever hear of the saying "the more you know, the less you know...?"....:)

    or to quote a Chinese philospher:

    "Without stirring abroad, one can know the whole world,
    Without looking out the window one can see the way of heaven.
    The further one goes, the less one knows". Lao Tzu
     
  7. nabrug

    nabrug Rookie

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    Excactly. It gives you the why's not the how. In my words it gives you the caracteristics (the outside). Not the inner system. Not the technique.

    There for I repeat my earlier remark. I think it is very interesting to compare graphics from pro players to the graphics you would get from the girl in the video or from sennoc.

    Sennoc, what would your graphic be like based upon your video?
     
  8. sennoc

    sennoc Guest

    I'll make a video of me and Federer on the same screen. Thought about that, time to do that... I'll allow for downloading so you will be able to compare strokes frame by frame.

    Roger, beware! ;)
     
  9. toly

    toly Hall of Fame

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    Russian proverb: Less knowledge = more healthiness. :)
     
    Last edited: Mar 8, 2011
  10. charliefedererer

    charliefedererer Legend

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    For better or worse, in tennis circles the term "pronation" has taken on a meaning other than it's strict anatomic meaning.

    This often happens, where the "common usage" of of a term may not be truly the "correct one", but it becomes so widely adopted that there seems there is no turning back the tide.

    So in most instructional videos, coach-speak, and tennis circles in general, I think when "pronation" is used, it is really a short-cut for "internal rotation fo the shoulder and pronation of the forearm." I even often hear it as a shortcut expression to even include the prolonged "laying back of the wrist" that proceeds the pronation on ground strokes and the serve.

    We can object to it, but I am not sure this will impact its "common" [mis-] usage.
     
  11. bhupaes

    bhupaes Professional

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    Or, to put it simply: Ignorance is bliss!

    I am still grappling with the world of possibilities and new insight that sennoc has opened up. Maybe they were always there, and maybe some coaches who have given wonderful tips/cues instinctively knew how it all worked - but man, I am looking at the whole thing differently now!

    Basically, there seem to be (at least) two ways of hitting the ball. In one way, there is more emphasis on actively powering the racquet towards the ball, as most of us tend to do. In the other, the emphasis is to release as efficiently as possible the built up energy. Forget the math and any quantitative analysis, and look at it qualitatively - these are totally different ways of thinking about the same problem, and will impact coaching techniques, IMO. Or maybe this is all well known and I am just waking up... but I have started looking at every stroke in a new light since yesterday!
     
  12. charliefedererer

    charliefedererer Legend

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    I would be interested in your comments as real student of the game on what you think is the most we can break down a stroke, and still have it usefull to help us learn.

    For instance in the serve, I am impressed that Pat Dougherty breaks the serve down into several big separate motions .

    It seems that these "motions" involve the co-ordination of mutliple body parts and allow a server to work on one of these motions if it is not being optimally incorporated in his serve.

    Pat breaks the serve down into:
    leg push-off
    coiling/uncoiling
    cartwheel
    bow/reverse bow
    swing motion of racquet drop though pronation to contact

    Another big co-ordinated "motion" to work on is the "toss while coiling/forming bow shape going into trophy pose".

    A potential advantage to using these big motion subdividions would seem to be that adjustments within them would be seen to advance a bigger goal, rather than just giving advice on moving one body part, which so often affects multiple others.
     
  13. gzhpcu

    gzhpcu Professional

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    That's a tough question Charliefederer.

    I agree that obsession with a single aspect of the serve (for example "pronation") is a seeing the tree but not the forest situation.

    Good, perhaps, for an pro player when his coach sees a glaring weakness, but maybe not so good for a weekend warrior trying to improve his serve.


    Pat Dougherty has a number of good tips, I have his Serve instruction video.

    When in a technical "trees" mood, I like studying Brian Gordon's articles on the serve.

    I find also find a visual approach as suggested by John Yandell not bad: picking a particular pro player, say Federer, with a clean serve motion, and just watching his motion in slow motion video. Just watching the clips over and over help I find. You watch the clip and imagine doing the same motion...
     
  14. charliefedererer

    charliefedererer Legend

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    ^^^Thanks for your thoughts and hints.
     
  15. sennoc

    sennoc Guest

    Charliefederer, breaking strokes into separate motions is fundamental if you want to learn good technique.

    If you understand what kind of motions are available during the stroke, you can work on separate motions and introduce them to your sequence step by step. But first, you have to know what kind of motion are available. Then, you should find the connection between them.

    Personally, I think about serve sequence as a set of motions fired one by another. A specific position in one motion is a signal form me to start with second motion. This is very important part of the process. Set of motions has no meaning if you don't know when to fire next motion.

    This is not natural, of course, but this is the fastest way to learn good technique. If you know what to do, you can reproduce the proper serve sequence - as I do on my video. Think about this as a kind of program in your mind. You execute it. You can learn how to do it, very fast.

    In reality, this is how human biomechanics works. There is no such thing like "natural moves" for humans. Every kind of mootion we do as mature people was artificial at the beginning. It took you a few years to learn how to move on two legs, guys, so remember that your bipedal motions are totally artificial. Are they artificial for you now? No. You moved "bipedal program" into your subconsciousness.

    The same is at tennis strokes - they are artificial at the beginning. Nothing new, but there is one important thing here: if they are artificial, you can consciously optimize them - and then repeat them and repeat to transform into "natural" motions.
     
  16. toly

    toly Hall of Fame

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    I envy you. I cannot comprehend your or sennoc idea, "release as efficiently as possible the built up energy”. Behind every kinetic energy is always force. The force produces work and work is energy. When racquet meets the ball, the energy releases automatically. We just have to take care about racquet face orientation and direction of the racquet speed. Tiw we should “actively powering the racquet towards the ball” Unfortunately I’m engineer and my brain doesn’t allow me to forget about quantitative analysis. I’m cursed man. It’s really very sad.
     
  17. sennoc

    sennoc Guest

    Here we go...

    http://www.vimeo.com/20768407

    (I hope Will won't kill me)

    The movie is waiting in a queue, please wait an hour or so (I'm to tired, it's really late here).

    Please download the movie and compare both strokes frame by frame.
     
  18. bhupaes

    bhupaes Professional

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    Hi toly, don't be too sad - a 14 year old kid who practices 4 hours a day and doesn't give a fig for the theory of tennis will probably kick my butt to the next county. :)

    Just as an analogy, consider a whip (a not too long one). There are two ways to use it. You can either pull it all the way by the handle until the tip hits the target, or you can accelerate the handle and pull back, causing a wave to flow on the whip so the tip actually cracks on the target. The second method is similar to what we call releasing energy. The first method is similar to what I referred to as "actively powering".

    Although whip theory does not apply to tennis directly, there are similarities. The final act of releasing is a kind of momentum/energy transfer to the racquet during the phase just before contact. I think this gives you an idea, but if not, no problem - hopefully somebody will be able to suggest an actual experiment you can try on the court.
     
  19. bhupaes

    bhupaes Professional

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    There is a very close similarity. What I see is that in Federer's stroke, he bends his elbow earlier than you do, and a little more than you do.
     
  20. sennoc

    sennoc Guest

    He will not. In 14 years...
     
  21. Chas Tennis

    Chas Tennis Hall of Fame

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    Video Pronation Test, Non-Serving, Elbow 90 d.

    Here is the video for measuring pronation magnitude. Casio EX FH100, 240 fps, 1/800 sec exposure time, ISO 3200. Quicktime has convenient frame-by-frame control by using the arrow keys.

    107 MB long so you may want to watch it there. I just got the VIMEO account. I did not see how to do stop action, frame-by-frame on Vimeo.

    http://vimeo.com/20779304

    Video could be improved with more lighting, maybe white tape on the racket frame, etc.

    Chas Tennis
     
  22. nabrug

    nabrug Rookie

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    I thought we were mainly talking about the service?
     
  23. sennoc

    sennoc Guest

    There are huge similiarities between both strokes, if you know where to look at.

    As you can see on my movie, Federer is using his left hand at forehands in less technical way than me (yuppi, I'm better than GOAT! ;) ). At the beginning of swing, his hand is straight and high. My left hand is bend and closer to me, what helps to rotate shoulders around hips (due to angular momentum conservation law). Also, my hand moves in horizontal plane. As a result, I do not see my left hand during stroke and my visual system is not disturbed. I can concetrate on the ball only.

    You can also see that Federer does not use energy transfer along his left hand. My left hand extends - it "stores" kinetic energy of the body - and then rapidly bends, what means that energy is transfered back to the body (once again, due to angular momentum conservation law). So, my left hand works as another source of energy at shoulders rotation, while Federer's left hand just does not disturb motion of his shoulders (this is a small but important difference). I'm much older, but I can hit quite similar forehand in terms of dynamics, as you can see on the movie. I think that's quite amazing. I'm an amateur. This year I spent 30 hours on the court, while he is playing a few hours per day, he has the best coaches, free access to courts and infrastructure etc.

    So, my swing begins with left hand which works as a source of energy. Now you check the role of left hand during serves, and you will be surprised. It's exactly the same. On sufficiently deep level of understanding, both strokes are identical at this point. That's very, very important, because if you understand the role of left hand at forehands (what seems to be easier), you "magically" improve your serves.
     
    Last edited by a moderator: Mar 8, 2011
  24. chico9166

    chico9166 Guest

    Sennoc,

    I've enjoyed your posts(really have), but why do you think this is anything new? As a coach, I can tell you that the use of the left arm is talked about on a regular basis. It is an external force acting on the system. Right, isn't this your point?

    As such, the manipulation of the arm is used to regulate (to the positive or negative) the body's rotational speed. (moment of inertia,)

    Anyway, again, I really enjoy the scientific angle you bring to the forum.
     
    Last edited by a moderator: Mar 8, 2011
  25. nabrug

    nabrug Rookie

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    And there are huge differences in technique between both strokes, if you know where to look at.
     
  26. sennoc

    sennoc Guest

    Of course they are. But that's obvious for everyone. And it's not obvious for everyone that there are strong similarities. This is the power of knowledge: to discover the same things between different phenomena. This is how science evolves.

    Chico9166, left hand as important part of every stroke is nothing unusual. But look at Federer's left hand. He bends it, so he reduces radius of rotation and his shoulders are colinear during stroke. Great, but I do different thing - I'm loading my left hand by energy transfer along it and then, when its energy is higher, I bend it. The result is different, because forces are different. Try to copy my motion and Federer's, without your racquet. You will immediately see the difference.
     
  27. toly

    toly Hall of Fame

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    In the article http://www.facebook.com/notes/tennissmith/2-biomechanics-workshop-notes-by-robert-wojcik/145086245548662 step 12 Robert Wojcik stated, “Swing is 1.7 times faster if you immobilize non-dominant side”. What does it mean?
     
    Last edited: Mar 8, 2011
  28. toly

    toly Hall of Fame

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    Chas Tennis,
    Thank you so much. It is really very nice video. In sennoc video I even cannot see the racquet during impact (maybe wrong exposure time or camera?). With your camera you do not need speed gun. You can easily calculate ball speed.
     
  29. Chas Tennis

    Chas Tennis Hall of Fame

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    For High Speed Video

    Motion Blur = Object Velocity X Shutter Speed

    A camera has to have manual control of shutter speed and the exposure times ("shutter speed") have to be very short to stop motion blur. If auto control is used you will not know the shutter speed and the camera may choose a long time. The camera screen itself has to do stop action frame-by-frame. Not enough light indoors for short shutter speeds..........

    FYB has a discussion of high speed video for tennis.

    Lots on the internet. Golfers have been using HSV much more than tennis players so search golf applications also. Maybe I'll do a separate thread in a week or two.

    Chas Tennis
     
  30. gzhpcu

    gzhpcu Professional

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    In any case, sennoc, modesty is not one of your strong points...:lol:
     
  31. Djokovicfan4life

    Djokovicfan4life Legend

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    Sennoc, maybe I'm just too hard to please, but wouldn't it have been better to compare your forehand with one of Federer's in the same kind of situation? Your forehand is in a fairly stationary setting, while it appears that Federer really got on his bicycle to make that shot a forehand.
     
  32. sennoc

    sennoc Guest

    I'll made some better videos in the future. Unfortunately, now I have limited angles where I can record my game. It's also hard to find steady shots with Federer at full speed (in most cases replays are slower). So, I have to check my huge base of Federer's matches (over 100 DVDs), choose his shots, then try to replay the situation on the court, what is not quite easy (it's easier to hit a good stroke if you do not think about that). But I'll try to do that, I want to make some conclusions.

    It's important for me to say here that I do not want to copy Federer's movements and also do not want and do not think that I'm better than Federer. My goal is to use biomechanically optimal sequences of strokes and this is why I want to compare myself with Federer. And at my age, so advanced sequences don't mean consistency. For me it's impossible to hit this way all strokes, my athletic performance is much worse. Please remember that I'm not an old idiot who thinks he is better than Roger. I'm just a man "who wants to play real tennis once in his life".
     
  33. Djokovicfan4life

    Djokovicfan4life Legend

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    I meant the other way around. Find a clip of Federer hitting a forehand in a similar situation to your forehand in the video. Just a suggestion. All I'm saying is that there are going to be differences that wouldn't exist otherwise when you compare your shot from the middle of the court to one where Federer ran a long way around his backhand.
     
  34. nabrug

    nabrug Rookie

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    So take a service to compare. It is much easier to find and it was the initial issue.

    But more important it will prove my point that you know a lot about key caracteristics but it will not give you the inner technique.
     
  35. sennoc

    sennoc Guest

    OK, I'll do the movie. Unfortunately, I can't make better videos of my serves (need 2-3 months to compensate 5 months of winter - and more serve practice than one recreational set per week), so I will use that accidental serve from one of my previous videos.

    What's inner technique?
     
  36. nabrug

    nabrug Rookie

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    Make one from the back perspective. Like this one http://www.youtube.com/watch?v=kGWdoNobnCM&NR=1. Try to make it with the same intention. I am only interested in the arm and racket action. That is to say I am already convinced that you don't have the elite player serve technique. I hope that it will convince you.

    Reread my posts.
     
  37. sennoc

    sennoc Guest

    So you have to wait till June. Maybe May at good weather. I promise I'll do the movie, I'm personally interested.

    Also, in my opinion you do not exactly understand the connection between the power of knowledge and good technique in amateur tennis. Usually, amateur technique is horrible. It's so full of errors that if you suddenly discover a law or rule, you can rapidly improve. That's why knowledge works good here.

    The problem is that every change is artificial at the beginning. You have to work many hours (usually a few hundred at least) to learn how to use new element as a "natural" one. This is something you probably understand as inner technique. But this is just a simple process of many, many repeats.

    That's quite obvious and natural that pure knowledge doesn't quarantee really good technique. During repeats, you have to control your results - by recording your strokes as example. By watching your body in the window. By tracking your shadow on the court. You move your new scheme of the stroke into subconsciousness and it becomes more and more "natural".

    My forehand is my only "natural" stroke now, serves are very artificial. But they won't be artificial. In a year, maybe two. The same with other strokes.
     
  38. nabrug

    nabrug Rookie

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    So you admit that you do not have the serve technique now. From all your posts I really got the idea that you had. Than why are you so sure that statements from others are so wrong?

    Pure knowledge of a technique will guarantee really good technique.

    In two years everybody here plays at Wimbledon. So we see you there than.
     
  39. charliefedererer

    charliefedererer Legend

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    First of all, you do have a nice forehand.

    Second, you certainly provide some interesting thoughts for discussion.

    But I have a couple of questions for you.

    If you had to hit your forehand on the run against Rafa and Djoker, stop on a dime after hitting it, and retreat as fast as possible to your backhand corner to hit an inside out forehand...

    ... would you engineer your forehand to be like it is now...

    ... or would you engineer it with your left hand out for balance during your rapid movement like Fed does?


    Second question (even though I think I know the answer):

    Against the players you are playing, do you think your forehand is better engineered for movement and hitting than the type of forehand Fed hits?
     
    Last edited: Mar 8, 2011
  40. sennoc

    sennoc Guest

    Both situations on the movie are not the same, of course. But Federer's forehand wasn't hit in a match. It was recorded by Will Hamilton during one of Federer's training sessions in Indian Wells last year, as far as I remember.

    It's also obvious that I do not hit my every forehand the way you see on the movie. If you have an extreme technique, footwork becomes more and more important. Perception also. But I can't cheat my age, I do not run so fast, have problems with my eyes, wrist etc. So, on average, my forehands are worse than what you see on the movie. Their dynamics is a bit slower, if I have no time the sequence doesn't look so good. But what's important for me, if I really want I can hit forehand on a very professional level. This is a source of huge satisfaction. Take two random people, give them racquets, go with them on the court. One hour later one of them will be a winner, but none of them played real tennis. I do not want wins, have no motivation. My motivation is that I can watch the best players in the world and say: "Yeah, nice shot. I can hit exactly the same, at least sometimes...".

    This is a very good question.

    If you want to improve, you have to find a good partner. My sparing partner is 59(!), has 30 years of experience as a player and 20 years as a coach. He plays a few hours per day, still wins against young pros here. He is a winner of many amateur tennis tournaments in Poland in 90. As far as I remember, he was also a finalist (or semifinalist?) in doubles on national level. But I like to play with my less skilled friends also. They are usually 3.0-3.5, what gives me opportunity to concentrate on details of my technique.

    I do not play in amateur tournaments. They give me no satisfaction and my technique works against me there. Imagine: you have a very good, fast strokes which involve your whole body. Your swing is really fast, you should know perfectly the bounce of the ball. You go to play in a tournament. New surface. New balls, typical for club level. And you hear: "guys, we have no time, please warmup no longer than 5 mins". 5 mins? After 5 mins I'm usually unable to hit my tennis wall ;)

    So, very good technique doesn't mean you will win all tournaments around. You probably will if they are organized in a way similar for pro tournaments: full sets, at least two sets per match, time for warmup, a place for training before the match (court, wall). I do not know such amateur tournaments in Poland. In my city one of them was almost good, but concentration of matches was crazy: three per day. Three sets per match (nine total) and my result: withdraw, wrist injury and two months of recovery. I said: thank you very much, never again. That's why I do not play in tournaments. I prefer to play against really good players privately.
     
  41. Chas Tennis

    Chas Tennis Hall of Fame

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    A very interesting article on biomechanics and tennis, especially the serve. Table of contributors to the final velocity includes: 5% pronation, 40% internal rotation, 30% wrist flexion, etc. Well worth reading and looking up the technical definitions of these body motions.

    Tennis Basics Biomechanics and Tennis

    Br J Sports Med 2006;40:392-396 doi:10.1136/bjsm.2005.023150

    http://bjsportmed.com/content/40/5/392.abstract

    You have to join for a free 30 day subscription to the BJSM to get the article.

    Chas Tennis
     
  42. charliefedererer

    charliefedererer Legend

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    Sennoc,

    Since you have been injured yourself (wrist), do you take into consideration body positioning or stroke mechanic considerations to minimize shoulder, or other overuse injuries, like in the article above by Elliot or these videos from Pat Dougherty, Jim McLennan and Todd Ellenbecker?

    Your serve technique doing more harm than good? http://www.youtube.com/watch?v=GgdX...y&list=PLD4C2A7ED17FABE64&index=31&playnext=8
    Preventing Rotator Cuff Injury http://www.youtube.com/watch?v=lTRvxaBMh8s&feature=related
    http://www.tennisresources.com/index.cfm?Rotator cuff injury ATT=&area=video_detail&basicsearch=1&media_name=&rv=1&vidid=3712

    [By the way, I've got to agree with you that the format of three matches in one day is crazy.]
     
    Last edited: Mar 9, 2011
  43. sennoc

    sennoc Guest

    Thanks for information, but injury was caused by my wrong diagnosis. I thought I have problems due to fatigue and my topspin action and decided to play last match with slices only. This idea was a horrible mistake. At this time I was slicing with quite intense wrist action. Everything was ok in the match. Next day I had to withdraw.

    That's a cost. The better your technique, the larger forces. You have to spend more and more time working on your athletic condition and you should better know limits of your body. I'm very careful now, do not do things I know I'm not ready for. That's why my serve on the movie was relatively weak. I need a few months to use new sequence with full power (I want to introduce one additional element into it, too).
     
  44. Chas Tennis

    Chas Tennis Hall of Fame

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    Issues, Questions & What I thinks happens during some serve motions.

    I have gotten a lot out of this thread adding completely new viewpoints and clearing some of my misunderstandings. Not having read much of the scientific literature I guess that these issues have been well understood for years by the sports researchers such as Dr B. Elliott (my post #191). Unfortunately, this knowledge seems not to have been that widely communicated to the tennis instructors & players, everything is so watered down. I keep expecting & hoping that one of the academic sports researchers will send in a few lightening bolts to illuminate this thread ……

    I am an average tennis player without much background in sports science. Some knowledge and logic can get very useful results………about 70% of the time. The rest of the time there may be serious misconceptions …(help!)……..

    Here are some issues and questions on arm rotation when serving. Using all sources I describe what I think happens and would appreciate other views.

    1) Experts. If we wanted to get an idea of the current thinking, who would be some of the preeminent tennis sports researchers to start with? Specializing in the serve? Open source references?

    2) “Pronation” – As discussed in post #160 by charliefederer we all here seem to agree that what is often called “pronation” in tennis is really upper arm rotation plus pronation. I believe the proper term for the upper arm rotation would be internal rotation at the shoulder or glenohumerol joint.

    The distinction between 1) just pronation and 2) upper arm rotation plus pronation is extremely important! It’s new to me. I have always…many years…tried to practice the serve using mostly true pronation, unaware of the summed upper arm rotation plus pronation. That misunderstanding was for me a very bad consequence of misusing the terminology. It could have have caused an injury risk.
    -----------------------------------------------------------------------------
    Reference (for body motions): Manual of Structural Kinesiology, 15th Ed. 2004, Clem W. Thomson, R.T. Floyd

    Clarification of terms –

    Internal or External Rotation – the motion of the body part
    Internal Rotation Muscle or Internal Rotator – Muscles can only pull (like a rope) so the term identifies the muscle that internally rotates the body part, mostly the upper arm, humerus, in this discussion.
    For example, External Rotation stretches or “loads” an Internal Rotation Muscle.
    ------------------------------------------------------------------------------

    Picking some of the body motions before the ball is struck in the serve, (timing uncertain, all completed in less than one second):

    3) Extenal Rotation to Stretch the Internal Rotator Muscles. When the striking shoulder in down and the elbow is bent (at about 90 degrees for many servers) the arm and racket rotate so as to externally rotate at the shoulder or glenohumerol joint.

    This external rotation is clearly shown in this high speed video. Server not identified, but it looks like Karlovic, who just set a new serve speed record of 156 MPH.

    http://www.fastecimaging.com/video/highSpeed/TennisServeBackViewE.wmv

    This external rotation motion stretches the glenohumerol joint’s internal rotator muscles loading or storing energy in them (spring-like). The reference above lists the shoulder joint’s internal rotator muscles. Among others the two largest muscles are clearly 1) the upper & lower fibers of the Pectoralis major (Pec) and 2) the Latissimus Dorsi (Lat). The lat and pec are both attached to the arm on the front in the same area of the bone and both rotate the arm only internally. The lat for serving is a new concept for me as a tennis player. I guess that the lat is the most significant serve driving muscle since it is the biggest muscle attached to the arm. Does anyone have information on the lat’s contribution especially in comparison to the pec?

    4) Leg Thrust & Trunk Motion – The lower right shoulder is thrust up with leg and complex trunk motions. This probably adds muscle stretching to the lat & pec because the arm and racket are accelerated upward. I believe that is well known. Maybe there are other forces?

    In addition, the above reference makes a statement, page 89, last text - “This stretch may be accentuated further by abducting the shoulder fully while maintaining external rotation and then laterally flexing and rotating the trunk to the opposite side.” Can someone interpret this interesting statement? I uncertainly interpret it to mean that the trunk’s bending farther stretches the internal rotator muscles, and probably mostly the lat. ? That is as the shoulder goes up and the trunk bends & rotates the lat must be farther stretched on that side. Correct? This is why it is important to know which muscles are involved.

    5) Trunk & Shoulder Orientation. The trunk motions that position the shoulder up must be done to allow the shoulder to freely internally rotate while staying clear of impingement. This is discussed in the rotator cuff injury videos below. Probably the trunk also orients so that as the lat & pec muscles are completing the internal rotation along with the lower arm pronation the racket will be oriented properly to strike the ball. That is, when the arm rotation is nearly complete it has a limited orientation to the trunk, more or less. Roughly, does the orientation of the arm after internal rotation determine the necessary trunk motion and orientation for striking the ball?

    I will never again attempt internal upper arm rotation unless my shoulder is properly aligned as indicated in the rotator cuff injury videos.
    ------------------------------------------------------------------------------------------
    The tennissources link - in-depth discussion of the shoulder injury issue by Tod Ellenberger. Type "Rotator" in the Search block.
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    To me this now gets very uncertain because the last part of the serve is a very complex motion and I have not looked at enough high speed videos yet:

    6) Arm Extension. The arm is extended, driven mostly by the triceps.

    7) Now mostly the arm is up but always maintaining a small elbow bend to reduce stress and the racket is at a large angle to the arm. In the first image of Sampras serving the racket appears to be at about 90 degrees to the slightly bent arm.

    8) Internal Rotation (the biggest serve contributor): From the stretched position the lat and pec muscles contract to internally rotate the arm and the racket. The racket speeds up with translational velocity and spin. ? The angle between the slightly bent-straight arm and the racket is changing in a very complex way. I guess that beta is this angle defined when the ball is struck? Pronation is also occurring. Pronation adds racket spin. If the upper arm is rotationally accelerating very strongly it will make it more difficult for the smaller pronation muscles to also rotationally accelerate. In any case, in a non-serving test, post #145, I measured the magnitude of pronation possible from the lower arm muscles as considerable. Therefore, it is not clear to me that pronation is just a small effect.

    7) Racket Spin. On a serve video examined in post #106, the racket spins with enough of a rate so that the strings have a considerably different velocity from the right side to the left side of the strings. Because of the spin the racket could be pictured with varying velocity vectors all over its string face. The vectors would vary in magnitude and direction (non-parallel). The effects of racket spin velocity variation and ball impact location have probably been studied and some references would be interesting. As for me, I’m going to try and rotate the racket rapidly and to hit the ball a bit on the left side.

    8) Wrist Flexion. According to the Elliot reference, my post #191, in his table the wrist flexion adds very significantly (30%) to the racket velocity. Does that “contribution” to velocity mean the wrist flexor muscles are adding power or simply flexing without adding power? For example, the wrist flexor muscles could be contracting or the arm could have slowed down and the wrist just flopped forward. For that reason high speed videos have to be interpreted including acceleration. Is this the “whip” action with a lose wrist?

    INJURY RISK. This is not advice and I’m going to worry about my safety.

    For comments:

    Personal Plan. My personal plan is to study high speed videos. To practice serving using the shoulder orientation discussed in the injury prevention videos. During internal arm rotation be very aware of new stresses on my arm especially at the elbow. Never have a straight elbow but always at least a slight bend. Especially pay attention to a “golfer’s elbow” injury (medial epcondylitis) caused years ago by a very forceful internal rotation with a 90 degree elbow. Spin the racket rapidly with some mix of upper arm internal rotation and pronation, to be determined. Become aware of the effect of hitting to the left or right on the strings on the serve’s velocity. Use feedback from high speed video.

    Last night at a weekly doubles match I tried a few serves with upper arm rotation and they were not difficult. Not sure that I did what I think I did without the high speed video.


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  45. gzhpcu

    gzhpcu Professional

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    Not quite sure what you mean by trying to rotate the racket. With arm pronation, the racket rotates. Hitting on the left side of the ball is correct, since good servers hit up and inside out.
     
  46. Chas Tennis

    Chas Tennis Hall of Fame

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    I should have used the term racket spin to indicate approximately axial spin (axis through the rackets handle) as produced by pronation plus upper arm rotation.

    I'm talking about hitting off the center of the strings. If it spins as fast as in the video of post #106 the strings have a higher velocity to the left for a RH server.

    Can the posts be edited after they are posted somehow? I can't find out how to do that.
     
  47. gzhpcu

    gzhpcu Professional

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    There is an edit button at the end of your posts....

    As far as hitting off center is concerned, I believe most top servers hit the serve at the high point of the racket, since that is moving fastest...
     
  48. Chas Tennis

    Chas Tennis Hall of Fame

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    Seems reasonable that the pros would hit high on the strings. I have not looked at videos to estimate that effect. I don't know the velocity difference between the top and bottom of the frame but with wrist flex it is probably large. Any references or studies of the pro's?

    In the post #106 serve I estimated the right to left velocity difference as 70% to 130% at the very racket edge, as explained.

    If we could do the experiment:

    Andy Roddic is serving in the lab. We look at his racket face with one 5,000 frame per second camera with a very short exposure time. We also have a 5000 fps camera 20 ft directly above him (careful Andy). 3 cameras are probably better....... He serves 200 times or as required and we record racket head speed as indicated by the center of the strings, H rotation rates at impact, location of impact on the strings X, Y, and serve velocity.

    Plot serve velocities vs X,Y. Parameters: racket H spin rate & racket velocity (string center). Has anyone seen this type of measurement?

    Hitting off the center might hurt or cause loss of control and is avoided or maybe the heavy racket spin takes care of that. ??

    We could then see the effect of the location of the impact point on the strings. Maybe top-left is optimal? Interesting issue.
     
  49. gzhpcu

    gzhpcu Professional

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    If these technical issues interest you, "The physics and technology of tennis" by Brody, Cross and Lindsey go into it.
     
  50. sennoc

    sennoc Guest

    Changing sweetspot is a common pratice in advanced tennis. There are two important elements here. As example, the tipspot moves a bit faster and is less elastic than main sweetspot what allows you to "dynamically" change the power of your string. If you use tipspot, you have more control.

    Usually players use tipspot at slices/chops/volleys, also at running forehands, main sweetspot at typical ground strokes and best bounce spot (the closest to the hand) at dropshots.
     

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