"Accelerate evenly through the ball"

Discussion in 'Tennis Tips/Instruction' started by Bergboy123, Apr 27, 2012.

  1. toly

    toly Hall of Fame

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  2. julian

    julian Hall of Fame

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    Wrist speed

    SA,
    A piece of your quote probably for me
    ---->
    When we speak of hand/wrist speed are we talking about an articulation of the wrist, a rotation of the forearm/hand or simply the forward linear motion of the wrist/hand w/o wrist articulation? It is not always clear in the articles and in the posts here what is meant.

    Note that some players will uncock the wrist just before contact on the serve with little or no flexion. Some will incorporate more flexion -- but primarily after contact.

    On the forehand, some players will lay back the wrist and will not release it prior to contact. Others will lay it back and will incorporate moderate flexion prior to contact. I don't believe that a forceful snapping of the wrist is common at all.

    It is also unclear as to what if meant by the relative contribution of the hand/wrist compared to the shoulder or some other part/kinetic link. Are we including forearm rotation when we speak of the contribution of the hand/wrist? Are we only considering the speed of body part/link? Or are we taking about the momentum or the kinetic energy associated with that part? While the shoulder may not be moving as fast as the hand/wrist, it is moving a larger mass. In turn, the torso and previous links are also moving larger masses. Is this taken into consideration when speaking of relative contributions.

    Note also, the the speed/kinetic energy at the hand/wrist is an accumulation and transfer from previous links. I'm not sure that this is always taken into account when speaking of the contribution of the hand/wrist.
    ---->
    1.the basic problem is lack of definitions/dictionary

    2.
    The following quote could be useful-
    "Hand flexion produces approximately
    30 percent of racket speed at impact (for serve)"
    Elliot and saviano in world-class tennis technique page 212

    It is up to u to decide what is the relation between "hand flexion" and
    "wrist contribution"
    3.I am browsing through
    http://www.itfcoaching.com/elastic-energy-in-tennis/player.html
    4.
    Journal of Sports Sciences
    Volume 14, Issue 2, 1996
    Special Issue:
    The role of upper limb segment rotations in the development of racket‐head speed in the squash forehand
    The role of upper limb segment rotations in the development of racket‐head speed in the squash forehand
    Preview
    Buy now

    DOI:
    10.1080/02640419608727697

    Bruce Elliotta, Robert Marshallb & Guillermo Noffala

    pages 159-165
    Available online: 15 May 2007
    Alert me
    Abstract

    In the squash forehand drive, the contribution that each of the upper limb segment's anatomical rotations make to racket‐head velocity towards the front wall (x‐direction) during the forward swing and at impact were calculated. Eight squash players (3 females, 5 males) capable of hitting a high‐performance squash forehand drive were filmed at a nominal rate of 300 Hz by two phase‐locked Photosonics cameras. The three‐dimensional displacement histories of 12 selected landmarks were then calculated using the direct linear transformation approach and three‐dimensional individual segment rotations were calculated using vector equations. Internal rotation of the upper arm at the shoulder joint (46.1%), hand flexion at the wrist joint (18.2%) and forearm pronation at the radio‐ulnar joint (12.0%) were the major contributors to the mean 30.8 m s‐1 x‐direction velocity of the centre of the racket‐head at impact. Pronation of the forearm at the radio‐ulnar joint and extension at the elbow joint both played a significant role in generating racket velocity in the period prior to impact.
    5.http://w4.ub.uni-konstanz.de/cpa/article/view/3484/3277

    6.
    / JAB Volume 11, Issue 4, November
    JAB Contents
    JAB Back Issues JAB Current Issue JAB Extras JAB In Press JAB Supplements & Special Issues


    JAB Volume 11, Issue 4, November
    Original Research

    Contributions of Upper Limb Segment Rotations During the Power Serve in Tennis

    433 – 442

    In the high-velocity tennis serve, the contributions that the upper limb segments' anatomical rotations make to racket head speed at impact depend on both their angular velocity and the instantaneous position of the racket with respect to the segments' axes of rotation. Eleven high-performance tennis players were filmed at a nominal rate of 200 Hz by three Photosonics cameras while hitting a high-velocity serve. The three-dimensional (3-D) displacement histories of 11 selected landmarks were then calculated using the direct linear transformation approach, and 3-D individual segment rotations for the upper limb were calculated using vector equations (Sprigings, Marshall, Elliott, & Jemings, 1994). The major contributors to the mean linear velocity of the center of the racket head of 31.0 m . s-' at impact were internal rotation of the upper arm (54.2%), flexion of the hand (31.0%), horizontal flexion and abduction of the upper arm (12.9%), and racket shoulder linear velocity (9.7%). Forearm extension at the elbow joint played a negative role (-14.4%) and reduced the forward velocity of the center of the racket at impact.

    Authors: Bruce C. Elliott, Robert N. Marshall, Guillermo Noffal
     
    Last edited: May 25, 2012
  3. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    I am not seeing the large hand flexion contribution on the serve that Elliot & company speak of. When the wrist is cocked on the serve (at the racket head drop), it appears to me to be radial deviation with some wrist extension. When this is released prior to impact, I see primarily ulnar deviation in addition to some hand flexion. Some servers may have a bit more hand/wrist flexion prior to contact but I find it difficult to believe that it produces some 30% of the racket speed at impact. Perhaps the 30% that is attributed (by Elliot et al.) to hand flexion is actually a combination of ulnar deviation and some flexion.

    Some elite servers, but not all, will also exhibit some hand/wrist flexion after contact. If this flexion is only present after contact, then it could not very well contribute to racket speed before/at contact.

    Brian Gordon's analysis of the serve talks about wrist deviations. It seem that his numbers differ somewhat from Elliot et al. His analysis and conclusions are not exactly what I would have guessed but it does shed a bit more insight into the mechanics of the serve.

    Serve mechanics (computer graphic)

    Brian Gordon's serve analysis


    [​IMG]

    Roger Federer's upward serve swing (w/ulnar action)


    The Elastic Energy presentation by Bruce Elliot looks very interesting. I'll have to look at it further when I have more time.
    .
     
    Last edited: May 27, 2012
  4. toly

    toly Hall of Fame

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  5. 5263

    5263 G.O.A.T.

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    Good stuff SA.
    I agree that radial and ulnar deviations should be more used for tennis and
    flexion should be held to a min.
     
  6. julian

    julian Hall of Fame

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  7. julian

    julian Hall of Fame

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    are Austrians consistent with predictions of Rod Cross?

    SA,
    are Austrians consistent with predictions of Rod Cross?
     
  8. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    What Austrians would that be? Did you mean Australians (which would include Cross, Elliot and others)?
     
  9. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Not certain. I think that it may be misleading. The 30% figure is an extrapolation. Gordon indicates that his analysis actually stops 10 ms prior to contact because measurements taken at contact are subject to potentially large errors (those data smoothing errors I mentioned in a previous post?). At the "near contact" position, he shows just a wrist flexion contribution just over 20%. However, the previous figure shows the wrist flexion contribution to be 24%. I suspect that this number may possibly be a combination of wrist deviation + wrist flexion.

    I am puzzled as to exactly how these contributions are determined. Dr. Jack Groppel, human performance expert, in High Tech Tennis indicates very different contributions.

    [​IMG]

    Note that John Yandell also emphasizes the role of ulnar deviation and indicates that the wrist does not snap (forward flexion) but is more passive than a "wrist snap" would suggest. (If you have not seen his analysis, I can email this info to you).

    Perhaps the some of the collegiate players that Gordon studied employed more wrist flexion than Federer and other elite players. In analyzing my own serve, I see quite a bit radial deviation and a bit of wrist extension with the racket head lagging (at the start of the upward swing) followed by some wrist deviation and rather mild wrist flexion as the elbow extends and the racket head is accelerated upward to meet the ball. I see the same thing in many elite servers. OTOH some elite servers do seem to employ a bit more wrist extension and flexion in their upward swing to contact.

    For the most part, the wrist is fairly neutral at contact. A combination of forearm pronation, ulnar deviation with some flexion get the wrist to its contact position/orientation. Here are a few of the serve videos that I have scrutinized:

    Djokovic serve motion
    Nalbandian serve mechanics
    Federer serve motion

    http://www.hi-techtennis.com/video_sample.php?player_id=19&stroke=serve
    http://www.hi-techtennis.com/video_sample.php?player_id=40&stroke=serve
    http://www.hi-techtennis.com/video_sample.php?player_id=29&stroke=serve


    To study these sample videos from Hi-TechTennis, pause the video and then use the left & right arrow keys on your keyboard to step thru the motion frame-by-frame. Here is a photo sequence showing the upward swing to contact:

    Upward swing sequence of the serve
     
    Last edited: May 31, 2012
  10. julian

    julian Hall of Fame

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  11. julian

    julian Hall of Fame

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    why the racket head in z direction is negative before -0.145 s

    SA,
    why the racket head speed in z direction is negative before -0.145 s

    (see Fig 3 of

    http://www.jssm.org/vol9/n4/15/v9n4-15pdf.pdf


    Please note that the racket head speed in z direction is NEVER POSITIVE at the very beginning of the time analyzed.

    Does zero of racket speed z direction is around Fig 14 or Fig 15 of post #244 ?


    PS
    -0.145 of second corresponds to 58 frames of the Austrian equipment
    One frame corresponds to 2.5 millisecond
     
    Last edited: May 28, 2012
  12. julian

    julian Hall of Fame

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  13. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^^ it is not clear to me which direction the authors are referring to as Z. I suspect that is not the same convention that I have used in the past. I have not been able to read the document thoroughly. Do they indicate which directions are X Y Z?
     
  14. julian

    julian Hall of Fame

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    z direction

    Perpendicular to the surface of the court,I think
     
  15. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    My initial thought was that the Y would be the vertical direction since that is the convention that we most commonly see. I would have guessed that Z would be in the general direction of the forward swing path. But after looking at the article for a while, this did not make sense. You are probably correct that the authors of that article have Z as the vertical direction.

    Assuming that this is correct, this would suggest that the racket head is still dropping for quite a while during the forward swing as the wrist is laid back (hence the negative speed). Inspection of the Stosur sequence (post #244) shows that her racket head is still dropping for quite a while. To me is looks like the racket head is at its lowest point around image #12 or #13. (It also appears that she might be hitting a rising ball or the ball is close to the peak of the bounce).

    Where did the 145 ms (0.145 s) number come from? From figure 3, it would appear the the racket head does not stop dropping (v = 0) until close to 17 ms before contact. That seems too late for the racket head to start rising. Am I looking at this wrong?
     
  16. julian

    julian Hall of Fame

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    -0.145

    SA,
    The racket goes up (VERY slightly) at -0.145 of second
    (NOT 0.145 of second)
    It maybe the LOWEST point of the racket
    Maybe 17 ms is the lowest point
    Switching gears
    The trajectory of the racket resembles a boot ( probably)
    Pl see Doug Eng
    More later-I. am in a bit of hurry-I have to teach,very sorry
     
    Last edited: May 29, 2012
  17. julian

    julian Hall of Fame

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    The boot

    SA,
    please see
    Developing an ATP Forehand Part 1: The Dynamic Slot
    Post #63 by Doug Eng
     
  18. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Are you referrring to Fig 3 of this page:

    http://www.jssm.org/vol9/n4/15/v9n4-15pdf.pdf

    Still do not see what you are talking about here. The velocity is negative. this say the racket is still moving downward.
     
  19. julian

    julian Hall of Fame

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    You are right

    You are right,I was wrong
     
  20. julian

    julian Hall of Fame

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    For SA

    Could you see my post #267
     
  21. julian

    julian Hall of Fame

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    17 ms is too close to the contact

    17 ms is too close to the contact,I agree
    May data of Brian Gordon will be different
     
  22. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    If the vertical component of the swing starts to move in an upward direction 17ms (or less), I would think that the shot hoes not have much topspin. But I could be wrong about that.

    Will look at the other post later.
     
  23. julian

    julian Hall of Fame

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    Stosur and Nadal

    SA,
    1.it looks like it takes more than 17 mililsecond for Stosur and Nadal
    We can do some simple calculations knowing number of frames multiplied by a time spent
    for one frame
    2.we may try to talk to Austrians via E-mail on this subject
    3.It is possible that the PARTIAL GOAL set for players was to hit FLAT to maximize the HORIZONTAL SPEED
     
    Last edited: May 30, 2012
  24. julian

    julian Hall of Fame

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    Trajectories

    SA,
    trajectories I am interested in are SIDE VIEW TRAJECTORY
    for the position of the racket.
    An example (NOT a good one) would be the U-shape
    (up-down-up) side trajectory
     
    Last edited: May 30, 2012
  25. julian

    julian Hall of Fame

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    Drawings

    SA,
    I have problems with producing drawings here.
    I have tried to use "the x symbol" but the clever EDITOR of TW
    ADJUSTS them (after the SAVE command) to the left boundry/left margin.
    I teach tennis using drawings a LOT and it bothers me
    a lot that I cannot use/post any drawings here.
    I was trying to draw a trajectory/boot.

    I understand that I can "beat the system" using a scanner somehow
    Please describe parts of the process using the scanner
    Thank you
     
  26. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    You can use periods in between the X's to get around the forum editor issue. If you want to use images, you would need to upload them to some server, an image hosting website, I believe. If you don't have suitable image files, you can create them with your scanner software. Here are some of the most popular hosting sites:

    http://www.ebizmba.com/articles/image-hosting-websites
     
  27. julian

    julian Hall of Fame

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    The picture of the backswing

    SA,
    I have sent you the E-mail with the picture of the backswing.
    Any comments?
     
  28. julian

    julian Hall of Fame

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    The picture 4.7 of Knudson

    The picture 4.7 of Knudson compared with
     

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