Pronation, Internal shoulder rotation, ulnar deviation, leverage & racquet head speed

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

  1. spacediver

    spacediver Hall of Fame

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    Ok there was another thread discussing this but I figure this post deserves its own thread.

    NOTE: this series of images doesn't depict what actually happens during the service motion. It is intended to break down the different rotations into simple components. I have also not yet included images that show what happens when the wrist deviates and flexes, even though these motions do make significant contributions

    note: ignore the fact that the torso angle would result in horrible shoulder impingement, just pay attention to the arm and ignore the torso.

    Part One




    Pronation is a technical term that refers to the counterclockwise rotation of the forearm around its own axis.

    See figure below:

    [​IMG]


    Important thing to note is that this movement contributes nothing to useful racquet head speed, in this particular anatomical configuration. In fact, if the ball is struck in the centre of the racquet, pronation in this position contributes absolutely zero to racquet head speed. This is because the racquet is simply rotating around its own axis. It is twisting, and this twisting is useless for the purpose of increasing racquet head speed.


    Next point:

    Consider the exact same rotation of the forearm, but with the wrist cocked to the side (radially deviated).

    [​IMG]

    Now something important happens. Because the racquet is no longer colinear (i.e. no longer in a straight line) with the forearm, it no longer only twists. It undergoes a rotation about a different axis. This allows something rather magical to happen. Consider the image below:

    [​IMG]

    The image depicts a rotating stick. The start position is black and the end position is red. The angle that the stick traverses is about 45 degrees. Now the key thing to understand here is that the right end of the stick travels at a much faster speed than the portions of the stick closer to the left end. This is a form of leverage, where we can generate high velocities by increasing the length of our lever. It's one of the reasons Del Potro is capable of such devastating forehands - his arms function as a very long lever, and even though he is rotating into the stroke at the same angular velocity as someone shorter than him, the end result is a faster forehand (though perhaps with less torque, but we need not worry about that).

    Now in the previous image that shows forearm pronation with a cocked wrist, you can see how the racquet is moving in a way that exemplifies this form of leverage. Try it at home with your own racquet, and it should become clear.
     
    Last edited: Jan 21, 2015
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  2. spacediver

    spacediver Hall of Fame

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    Part Two

    Now for the final point:

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

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

    [​IMG]

    [​IMG]





    Note, however, what happens when the forearm and upper arm are NOT colinear, such as when the elbow is flexed as shown below:

    [​IMG]

    In the above image, the only rotation involved is internal shoulder rotation, but notice how much racquet head speed is achieved due to the extra long lever provided by the flexed elbow.

    In reality, things are not this simple - the serve is a dynamic motion where joint rotations are evolving over time, changing the relative angles between joints. These images represent abstract components of the motion.


    In sum, pronation, strictly speaking, does contribute to racquet head speed, but internal rotation of the shoulder provides much more. These days, people in the know are starting to dissociate technical pronation from internal rotation. Often in the past, they were lumped together. In this lumped state, "pronation" certainly contributes to a great deal of racquet head speed.
     
    Last edited: Jun 27, 2014
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  3. salsainglesa

    salsainglesa Semi-Pro

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    thats what i said but the naked guys makes it cristal clear ... also, your torso is at an angle, not straight like this, this will hurt your shoulder.

    http://www.youtube.com/watch?v=1t6bLABbebc&NR=1

    since this is a new thread i'll repost the nice video of this guy showing this thing
     
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  4. toly

    toly Hall of Fame

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    It is very good idea about bend elbow!
     
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  5. salsainglesa

    salsainglesa Semi-Pro

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    good luck with that, the force generated by the shoulder will need to be countered by the biceps... i sense danger!

    the idea would be to let this force straighten your elbow, not actively doing so with your triceps...

    but tell me how it went, maybe you find out something
     
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  6. spacediver

    spacediver Hall of Fame

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    Are you referring to my post salsa? If so, I think you've misunderstood my meaning.
     
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  7. toly

    toly Hall of Fame

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    Roddick bends elbow during pronation phase and impact of the flat serve.
     
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  8. spacediver

    spacediver Hall of Fame

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    Salsa, don't look at the images I posted thinking they represent how the service motion actually occurs - I explained in my post that the joint angles evolve over the motion.

    The elbow starts in a flexed position and reaches extension by the end of the motion. This happens while the shoulder is internally rotating.

    Think of the images as abstract components of the motions.
     
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  9. bhupaes

    bhupaes Professional

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    Good post, spacediver. Thanks.
     
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  10. WildVolley

    WildVolley Legend

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    I'm confused. No one holds a racket as you show in the first diagram. The racket is naturally cocked to the side if you grasp the handle with your fingers. In such a motion, the racket acts as a lever and the motion DOES contribute to racket speed.

    Was that your point?
     
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  11. larry10s

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    .........yes
     
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  12. spacediver

    spacediver Hall of Fame

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    yep - I'm trying to break down how pronation affects the motion of the racquet, starting with the simplest case, and then illustrating what happens when you change the anatomical conditions. Also, in the other thread where people werre discussing this, one of the posters claimed that pronation does nothing for racquet head speed, since it only twists the racquet. I thought this series of images would shed light on the discussion.
     
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  13. WildVolley

    WildVolley Legend

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    Then I did read it correctly. Your diagram does a very good job of showing the difference a little twisting of the forearm, arm, shoulder (I really don't know which is most important) does for racket speed.
     
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  14. LeeD

    LeeD Bionic Poster

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    You can say whatever you want, but if you don't pronate on the flat serve, you cannot even hit the ball.
     
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  15. salsainglesa

    salsainglesa Semi-Pro

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    Hey hello you people... well i did understand but i was thinking it was important to note the angle of the torso.
    Its a good analysis nevertheless, i do like it very much.

    about the bent elbow, you should look better at it as not straightening actively the arm articulation, it does seem slightly bent but not at contact, maybe a little bit before and a little bit afte. its more like not not completely straighten, it is loose, its a better image, and a better feeling, since you wont be contracting muscles here and there and hurting yourself.
     
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  16. gzhpcu

    gzhpcu Professional

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    If you are referring to pure rotation of the forearm, yes. Pronation is the biomechanical consequence of a loose arm on the correct service motion.
     
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  17. sennoc

    sennoc Guest

    Not exactly. It's not a biomechanical reaction of your body, it is a conscious but effortless action of muscles.
     
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  18. spacediver

    spacediver Hall of Fame

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    Yea I think I'll re-render them with the bent torso to make it look more realistic.

    As for the bent elbow thing, the elbow is supposed to remain bent in the before and after. Again, this isn't to illustrate what happens on the serve, but to show the biomechanical consequences of certain anatomical configurations.

    The important point was that with a bent elbow, internal shoulder rotation doesn't have the same effect upon racquet movement as it does with a straight elbow. Also, with a bent elbow, there is increased leverage.

    In reality, the elbow extends over time (and reaches just about full extension before contact), but these images are to illustrate the components, not reality.

    Not sure if I understood your point about the elbow though - perhaps you meant something different.
     
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  19. gzhpcu

    gzhpcu Professional

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    It is a natural, low-stress movement, which helps avoid injuries. You do not consciously pronate. Set your movement up correctly and the pronation occurs without your being conscious of it.
     
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  20. sennoc

    sennoc Guest

    I almost agree :)

    Yes, pronation is very natural at serves. But if you use it as a tool, things become more complicated.

    Take your racquet, do some tests. Close your eyes, listen carefully to your body. You will find that natural pronation is much longer and happens later than during good serve sequence.

    If you want to gain all benefits of upper arm internal rotation, you have to pronate as late as possible before the contact - and as fast as possible. And this motion is not natural. It's almost natural, but definitely not natural.
     
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  21. charliefedererer

    charliefedererer Legend

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    "Set your movement up correctly"

    Therein lies the problem.

    The vast majority of tennis players are self-taught, or "took a few lessons".

    They don't set up correctly.

    They don't understand what they even should be doing, never mind learning how to set up so they can be doing it.

    (Indeed, they practice over and over and over, building muscle memory, of how NOT to get set up correctly and how NOT to swing with the proper mechanics.)

    But at least there is this forum to help push concepts that will result in more sound technique that will result not only in a better serve, but a reduced chance for injury. (Serving with a "straight" arm puts much more stress on the shoulder joint, and puts the player at higher risk for rotator cuff injuries and the "impingement" syndrome.

    For those who would like a short video tutorial from the great coach and TennisOne Editor Jim McLennan, check out the following:
    Racquet Angle on Serve: http://www.youtube.com/watch?v=1t6bLABbebc&feature=related

    And if they want the body positioning to prevent shoulder injury:
    Preventing Rotator Cuff Injury: http://www.youtube.com/watch?v=lTRvxaBMh8s&feature=related

    [​IMG]
     
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  22. gzhpcu

    gzhpcu Professional

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    Right.... this photo of Safin also shows that his arm and shoulders are practically lined up, and the racket shaft is angled in respect to his arm.

    [​IMG]
     
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  23. sennoc

    sennoc Guest

    The angle between racquet and forearm (image above) is not important. What you see is an artifact of arm rotation.

    There are two goals at serves:

    1. Hold 90 degrees between upper arm and forearm - as long as possible.

    2. Hit the ball as high as possible.

    You can't do both. But there is a solution. Use first method as long as possible, then transform it into second one - as late and fast as possible.

    If you will think about that angle as something important, you will never find good serve sequence. But think about 1. and 2. goal and everything seems to be simple and easy.

    True magic will begin in my next post in this thread :)
     
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  24. spacediver

    spacediver Hall of Fame

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    If I understand you correctly, I strongly disagree. The angle between racquet and forearm is precisely what allows for the leverage provided by pronation and internal shoulder rotation. With a 0 degree angle, the racquet would merely twist on its axis (see my first two posts in this thread).
     
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  25. mntlblok

    mntlblok Professional

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    Internal rotation of shoulder

    Excellent explanation. Definitely learnt something today.
    Thanks!

    I have an idea that this is related to something that Brian Gordon tried to explain about the "straight arm" forehand, but that I had a hard time "getting". If the upper and lower arm are in "a straight line", then internal shoulder rotation can come into play with less "weirdness" being caused by it (with a double bend) - and apparently, some valuable stuff coming from it.

    Looking forward to Brian's forehand series at some point.

    Kevin
     
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  26. GuyClinch

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    I think the OP is correct. But its of very little use to players because we do not need to determine which muscle groups are contributing what - only how to hit the ball in the most optimal way.

    So yes most of the power of pronation might come from internal shoulder rotation. But a pro might tell you to pronate or snap your wrist.. Even if that is totally incorrect biomechnically it can get your body to do the righ thing..
     
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  27. gzhpcu

    gzhpcu Professional

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    Sure, that is important for leverage. You help to achieve it with the proper serve grip (continental, or even more, eastern backhand) and by tossing a bit to the left of the front foot...
     
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  28. Djokovicfan4life

    Djokovicfan4life Legend

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    I don't see how it would be natural for my racquet to stay in line with my arm, since I toss the ball Sampras style for the most part, around 12 o'clock.
     
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  29. gzhpcu

    gzhpcu Professional

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    I think what is meant is that the shoulders and the arm must be more or less in line (by cartwheeling, tilting the left shoulder down at impact), to avoid stress the rotator cuff, as shown in my photo of Safin, for example, or as explained in the video by Mclennan.
     
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  30. Djokovicfan4life

    Djokovicfan4life Legend

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  31. GuyClinch

    GuyClinch Hall of Fame

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    The serve doctor says the same thing in his video - so its likely true. The angle matters - sennoc is wrong. With the greater angle the internal shoulder rotation causes the racquet to move more - and the force becomes mutiplied.
     
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  32. NLBwell

    NLBwell Legend

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    If you are studying biomechanics this is all very useful. For teaching a tennis serve, not so much.
    Simplicity of thought is key.
     
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  33. gzhpcu

    gzhpcu Professional

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    Sure the angle matters: you see it on every great server from Tilden to Gonzalez to Sampras to Federer.
     
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  34. sennoc

    sennoc Guest

    I do not think so :) There is also another possibility - that you and him are both wrong.

    Once again.

    We all agree that internal rotation of upper arm is the most important source of energy during serves (1).

    As I explained in another topic, the second most important source of energy is "whippy" energy transfer along kinetic chain (2).

    (1) means that the angle between forearm and racquet should be 90 degrees as long as possible.

    This means that you have to pronate as late as possible before the contact, just to turn racquet's head.

    (1) is in contrary to the fact that the server should hit the ball as high as possible.

    So, if you want to hit a powerful serve and land in the court, you have to extend your elbow.

    Unfortunately, if you fully extend your arm, you do not do (2) in a right way. At this position, your muscles are too weak to deal with so huge forces. Your arm moves along the largest possible circular path and you waste your energy.

    If you want to do (2) in a way which works so perfectly at whips, you have to make the path of racquet not circular, but "sharp" - in practice, similar to an elongated ellipse.

    The funny part is that players do this quite unconsciously. Let's think about rotation of upper arm as a long process, where contact with the ball is somewhere in the middle. So, you rotate your forearm around upper arm axis, extend elbow just to hit the ball and then you bend elbow again. And voila - that's what changes circle into elongated ellipse.

    ...but this means that your muscles are working before and after the impact! You need them to bend your elbow. You can't do that sufficiently fast if your arm is fully extended. That's why there is an angle between forearm and racquet. This is not an important source of additional energy. This is a biomechanical ARTIFACT of doing (1) in a way which maximizes (2).

    What does it mean? It means that every good server:
    - has an angle between racquet and forearm just before contact;
    - finishes with elbow high.

    So, if you do not understand the underlying physics, you think: "OMG, Sampras has an angle, Federer has an angle, so angle - this is it!".

    This is totally not true. From my point of view, as a physicist I think that's quite funny how many players - and the best coaches in the world too - do not understand that what they see is a result, not a source. Funny - and sad at the same time. But what can we expect between people who usually say "Science is not important! You do not need to understand what you do! Just do what the rule says! You are a tennis player, not a scientist!".

    So, players work years on "the angle". They gain experience and, at last, they discover how to hit "with the angle". Their serves become powerful. But not due to the angle - they changed their motion in a way which guarantees more effective using of (2). But their coaches think: "Wow, his serve is so powerful, the rule works perfectly!".

    If you know what to do, your results will be the same not in years, but in months. Without injuries. And without 1000$ per hour for my beloved Nick.
     
    Last edited by a moderator: Mar 10, 2011
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  35. nabrug

    nabrug Rookie

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  36. charliefedererer

    charliefedererer Legend

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    I do like your explanation of the mechanical reason for why the elliptical arm motion is the result of fist optimizing rotational energy and then extending for maximal height while pronating at the last instant.


    But what really is the souce of the energy in our serves?


    Certainly it can't be the relatively small internal rotators at the shoulder combined with the even smaller pronators of the foream.


    Don't you mean to say that internal rotation at the shoulder transfers the energy built up in the arm and from the body in the most efficient way for the serve?


    The arm muscles that are accerating the racquet from the point of the deepest racquet drop are the extensors of the shoulder and forearm. While at first glance this looks like only linear motion being directed forward, in fact the shoulder and elbow function as axes around which the upper arm and forarm are accelerating. (This also is largely what is happening at the "wrist snap".)

    But I just don't know any way of separating out the energy produced from the rest of the body as the result of coiling + cartwheel + bow/unbow. So while the muscles involved in all these actions are very much bigger, and the mass much larger than in the arm, because of the ineficciencies in energy transfer, obviously most of this energy is wasted.

    I'm not sure that it is possible to state with any certainty how much "energy" in serving really comes from any part of the kinetic chain, and how much our arms behave as passively as the rope in this strobe photo of a trebuchet catapult:

    [​IMG]

    Trebuchet Catapult at rest (note: no "muscle" [or energy source] in its "arm" or rope):

    [​IMG]



    So it turns out the serve in a human body is such a series of catapult-like actions with energy from our muscles being generated through axes about our hips, waist, shoulders, elbows and wrists. [Interestingly those muscle groups get progressively smaller/less capable of producing as much energy as we go from hips to forearm.]

    Each body part above the hip axis derives at least some of its "energy" from the preceding element in the kinetic chain, as passively as the rope in that catupult.

    Therefore the precise individual sources of "energy" along the kinetic chain in the human serve that actually get transferred into the energy to swing the racquet remains a beautiful mystery:

    [​IMG]

    But opimizing each source of energy, and most efficiently transferring it along the kinetic chain - now that is something to keep working on.
     
    Last edited: Mar 10, 2011
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  37. Djokovicfan4life

    Djokovicfan4life Legend

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    Well, bollocks. After videoing my serve yesterday, it appears that my racquet is roughly in line with the arm at contact. Now I'm just basing this on a cheap video, no slow motion, so maybe this is not the case. But I think I'm right, and I'm not really sure how to go about fixing this. I guess you would swing with the hitting hand more to the right of the ball?
     
    Last edited: Mar 10, 2011
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  38. charliefedererer

    charliefedererer Legend

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    Djok,

    As usual you have a way of asking just the right question and putting things into perspective.

    And having pronounced a lack of deep mechanical therapy, is there hope for you?

    Of course!

    You have a keen insight and huge work ethic.

    You are poised to make improvements from a coach who doesn't force you to learn biomechanics, but can still help you move along by "concrete" suggestions. [I am not trying to put down the mechanical approach of Sennoc, just pointing out the reality of what most players and coaches face.]

    Have you watched these videos from Jim McLellan and Pat Dougherty?:

    Racquet Angle on Serve: http://www.youtube.com/watch?v=1t6bLABbebc
    Serving Leverage: http://www.youtube.com/watch?v=7bsYFra60Q0&feature=related
    Hammer that Serve (skip the first 3:10 meant for beginners) http://www.youtube.com/watch?v=xjXJGsRtm08&feature=related

    Do they make sense to you?

    Do you think you can produce these arm movement modifications?

    Do you think you can make these arm movement modifications and not screw up the rest of the mechanics of your serve? (I would think this change would be a relatively easy one for you.)

    What do you think of the step by step approach of introducing this modification that Pat Dougherty uses to make this change?
     
    Last edited: Mar 10, 2011
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  39. chico9166

    chico9166 Guest

    The angle of the trunk is key, in this discussion. If one believes in the science of optimal positions for maximizing joint contributions. The angle of the trunk, is critical in this regard.
     
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  40. gzhpcu

    gzhpcu Professional

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    Check your serve grip. The more it goes towards eastern backhand the greater the angle. Also make sure you are not tossing the ball to far to the right. Impact should be in front of your left foot. Look at Safin...
     
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  41. Djokovicfan4life

    Djokovicfan4life Legend

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    Well, when I'm not chasing my toss all the way to Tulsa I make contact around the 12 o'clock position, so probably not a toss problem (other than getting it consistent, the biggest problem). Grip is continental.

    Watching my video it seems like my wrist ulnar deviates to bring the racquet in line with my arm, but again, unless there's some way to do it, I don't have slow motion to verify this.
     
    Last edited: Mar 11, 2011
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  42. mntlblok

    mntlblok Professional

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    #42
  43. charliefedererer

    charliefedererer Legend

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    Pat Dougherty, the Bollittieri Academy "Serve Doctor" does a great job of breaking down a serve into several big motions, but does so with the idea of putting it all together into a big serve. He is a great (and enthusiastic) communicator.

    You can download his entire serve video for $18.99 - it's $11 more to get an actual DVD sent to you. For the amount of insight and practical help for your serve, it's a bargain: http://www.servedoctor.com/
     
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  44. Jake Speed

    Jake Speed Banned

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    I started teaching pronation in 1972, it was never heard of then.

    What I don't understand, is why couldn't you put a shirt on that guy?

    JS
     
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  45. hnstabe

    hnstabe New User

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    want the extra pace of this technique

    I realize this is a old discussion but I just read it and want to know if it is realistic. Does it work?

    Here is what I understand has to be accomplished during the motion:
    wrist ****, bent elbow, internal shoulder rotation, fast and late wrist snap and late arm extension, and wrist flexed downward and to the right at end.

    I AM NOT ALL SURE I CAN DO IT BUT I AM GOING TO WORK ON IT TOMORROW.

    Comments please. Thanks
     
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  46. GuyClinch

    GuyClinch Hall of Fame

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    I think its better to work on your throwing motion then overthinking it with all this stuff. For the serve get into the power postion and imagine you are throwing the racquet at the ball.

    The classic drill is to toss one ball into air and throw another ball at it.. Novak can serve big now - and he didn't really understand what was going on in his serve at all..
     
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