"Accelerate evenly through the ball"

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

  1. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Actually, the forearm has already slowed down prior to the image #1 in your post #137. As the racquet head moves upward from the scratch position, the server drives upward with the shoulder and then the elbow. As the elbow continues to drive upward, the arm extends at the elbow (with the racquet head still lagging). With this extension the forearm is moving faster but at full arm extension, the forearm is has slowed down quite a but in the upward direction.

    However, the forearm is still pronating after full extension. When the max forearm rotation occurs is dependent upon the type of serve. We also have some ulnar deviation as the wrist uncocks during the sequence that you've shown.

    So, in one sense the forearm and hand have slowed down (in the upward direction), but they continue to rotate.
    .
     
    Last edited: May 9, 2012
  2. toly

    toly Hall of Fame

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    All this matter I explained in thread http://tt.tennis-warehouse.com/showthread.php?t=361610. :)
     
  3. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    It doesn't matter. We have driving forces other than gravity for the double or triple pendulum action of the serve. The drive is generated by the muscles of the body rather than gravity. Perhaps you would be more comfortable with a trebuchet model for the serve.

    Physicists have applied the double pendulum and trebuchet models for both baseball and golf. There are obviously some differences between tennis and these other two sports. Baseball is probably more unlike golf than tennis is to either of these other 2 sports. However, they all have quite a bit in common with regards to the kinetic chain. It's a matter of degree more than anything else. The relative contributions from each link in the chain will differ somewhat from one sport to the next. However, they share most of those common links. Here are some links that discuss the trebuchet and double pendulum in golf:

    http://www.tutelman.com/golf/design/swing1.php

    http://www.tutelman.com/golf/swing/golfSwingPhysics3a.php
    .
     
    Last edited: May 9, 2012
  4. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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  5. AlpineCadet

    AlpineCadet Hall of Fame

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    "An expert is a man who tells you a simple thing in a confused way in such a fashion as to make you think the confusion is your own fault." So true, its not even funny, though I'm sure there aren't any experts here in this thread.
     
  6. toly

    toly Hall of Fame

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    Brilliant!!!:):):)
     
  7. toly

    toly Hall of Fame

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    Trebuchet just transfers the potential energy of the big mass m1 to the kinetic energy of the small mass m2.

    [​IMG]

    IMO, trebuchet model also cannot describe any real tennis serve. :(
     
  8. julian

    julian Hall of Fame

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    I meant the link from the bottom of your post #130

    I meant the link from the bottom of your post #130
    I have tried to cut and paste from your post but I failed.
    It is the second time today
    My wife and 5263 told me:"Julian,you are such a failure".
     
    Last edited: May 9, 2012
  9. julian

    julian Hall of Fame

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    The blue curve(vertical) in the article of Brian Gordon

    The blue curve (called vertical) in the article of Brian Gordon shows
    exactly the same behavior ( I am referring to the post #143)
     
  10. julian

    julian Hall of Fame

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    Have a beer and digest the quote

    You may try to digest the quote
    "The summation of speed principle states that to maximise the speed at the distal end of a linked system, the movement should start with the more proximal and progress to the more distal segments, such that each segment starts its motion at the instant of greatest speed of the preceding segment and reaches a maximum speed greater than that of its predecessor (Bunn, 1972)."
    The quote does NOT say whether the racket is considered to be ONE of segments
     
    Last edited: May 9, 2012
  11. DjokovicForTheWin

    DjokovicForTheWin Banned

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    Why is everyone talking about acceleration through the ball? Acceleration is an active process. Isn't the arm supposed to be loose and simply respond to the kinetic chain begun by the racquet leg push off? How fast it goes through the ball depends on how hard you push off with the leg. Once the arm is in motion it's passive, is it not? i.e. you don't actively control the acceleration once the arm is in motion.
     
    Last edited: May 9, 2012
  12. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Ok, I guess you copy/pasted directly from my post. This copies the link text as it appears in my post but does not get the actual address. You need to click on link to see the full address. The link should be:

    http://www.racquetsportsindustry.com/articles/2004/10/the_worlds_most_efficient_tenn.html
     
  13. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    He may have been referring to you more than anyone else.


    Ok, that later post was very difficult to follow. Difficult to determine what points you are trying to make there. Are you contradicting the statement you made that "just before impact forearm doesn’t slow down"?
     
  14. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Where did those numbers come from? Are those limb/racquet images supposed to indicate equal time intervals? It seems that the interval shown between 74% and 87% is smaller than the interval immediately before and after it.

    You have indicated that the max speed for arm/forearm/wrist is at the green racquet position. However this would not appear to be the contact position. The subsequent racquet position appears to be closer to the contact point. In light of this, doesn't your graphic show that the forearm/wrist velocity actually peaks a little bit before impact?
    .
     
    Last edited: May 9, 2012
  15. 5263

    5263 G.O.A.T.

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    Should be useful, even if not exact.
    I'm not saying that it's not exact.
     
  16. toly

    toly Hall of Fame

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    There are the data.

    [​IMG]

    In Federer APAS picture shown the wrist's speed for frames 4, 7, 10 , , , 25. The speeds are taken from approximation graph.
     
    Last edited: May 10, 2012
  17. 5263

    5263 G.O.A.T.

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    No, the arm is not passive once in motion. I believe the pecs and biceps (along with other groups) pull to bring the hand across in a medial fashion.
     
  18. julian

    julian Hall of Fame

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    Silly questions

    Are data in the post real #148 3D data or 2D data?
    I apologize for asking YOU this question but you seem to be miles in a front of me on this subject.
    Can someone explained to me deeper the phrase "Federer APAS picture"
    Is the Federer APAS picture produced from 3D data?
     
    Last edited: May 10, 2012
  19. netguy

    netguy Semi-Pro

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    Post #148 and 166 from Toly explained it very clearly. The racquet head speed accelaration keeps going up throughout the stroke, but the rate at what it accelarates changes as shown by the black line on post #166. Federer is not a machine, and therefore he can't hit exactly at the maximum racquet head speed (green racquet) every time, but he does it close enough to have one of the best FH ever.
     
    Last edited: May 10, 2012
  20. 5263

    5263 G.O.A.T.

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    type in Federer apas on youtube.
     
  21. dominikk1985

    dominikk1985 Legend

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    yes. the hips rotate first but every link of the kinematic chain fires. they just fire in sequence: first hips, then shoulder, then arm, then wrist. but every link is active or you would waste energy. why would you not use your shoulder, pec and arm muscles? this would be a waste.

    but it is true that they are passive first. if they are active while the hip rotation starts you will disrupt the chain.

    usually when the next link is fired the former chain decelerates. thus the arm starts to decelerate before contact and the energy is transfered to the wrist and racket.
     
  22. dominikk1985

    dominikk1985 Legend

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    what matters is not wrist speed but racket head speed. maximum RHS is after maximum speed of the hand.
     
  23. netguy

    netguy Semi-Pro

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    You are right. I just edited it.
     
    Last edited: May 10, 2012
  24. DjokovicForTheWin

    DjokovicForTheWin Banned

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    But what about the liquid whip effect? Don't you deteriorate that if you actively try to swing and include arm in it?

    edit: What about the Lock and Roll guy and the drum with loose swinging arms????? I thought that was the way it was supposed to be.

    edit2: What about the wrist??? At the very least the wrist must be kept completely passive before contact no? Else how can you get the double bend slot position.
     
    Last edited: May 10, 2012
  25. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Isn't this somewhat similar to what we are accomplishing with the kinetic chain? Gravity and pre-strech of muscles also provide a potential energy in tennis strokes. The trebuchet model is mrealy a convenient device to help us undertand the double catapult actions in the serve (and to some extent, the FH).
     
    Last edited: May 10, 2012
  26. 5263

    5263 G.O.A.T.

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    You make some excellent points, but that is the paradox of tennis strokes. They
    are driven much like you say and need to be relaxed in ways, but need to active aspects in certain segments.

    Like on the serve which requires a loose arm, you can't push enough with the legs to drive the whole stroke.
    It must have the shoulder and other inputs as well.
     
  27. dominikk1985

    dominikk1985 Legend

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    You can do that but in that way you would only swing at your rotation speed (multiplied by the length of the lever- of course a more distal part will move faster in space than the torso).

    this is a "unit turn" or what the golfers call "tilt and turn" (or whatever I don't know golf). there are now baseball guys who teach "rotational hitting" in just holding the bat and rotate into it.

    however this is not how elite athletes do this. elite athletes use a SEQUENCE. basically the arm stays back as the body rotates. that means the rotation does not so much pull the arm around the body but prestreches the arm and shoulder muscles which rip the arm through.

    muscles are no rubber bands. they don't store energy. they work by ACTIVE contraction.
    however if they are stretched dynamically (no pause) they will be able to contract stronger.

    just watch federer. when his arm whips through his body has already stopped. so his rotation does not create that much speed but it does create a lot of stretch to rip his arm through.

    look at this dude:
    [​IMG]

    his rotation is nearly finished but his arm has hardly started to accelerate and far back. after the arm strike the body has only rotated a little bit more.

    good athletes rotate first and then strike (but of course with no pause-the arm strike begins slightly before the body is fully rotated).
     
  28. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    This graphic was derived from film made by tennis scientist, Stanley Plagenhoef, way back in 1970. He was ahead of his tim in many respects. Some of his ideas are still considered valid, some are not. I have not seen the actual data for this graphic.

    We can readily see that the racket head speed increases until contact and then drops off. We can also see that the forward speed of the shoulder and the elbow/upper arm decreases prior to contact. However, it is difficult to tell how much the speed of the hand/wrist varies. The accompaning text states that, while the speed of the racket drops after copntact, the speed of the wrist stays the same (after contact). No real mention of the speed of the hand/wrist just prior to contact.

    http://www.science-animations.com/tennismechanics.html
     
  29. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    I don't really know. The APAS system is supposed to be able to gather 3D data. The data points in #166 seem to jump all over the place. The graphic represnetation in #148 "appears" to be flawed. Myabe toly will provide more insight on this (without confusing us further).
     
  30. toly

    toly Hall of Fame

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    There are data about racquet tip and wrist speed.

    [​IMG]
     
  31. toly

    toly Hall of Fame

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    Last edited: May 12, 2012
  32. toly

    toly Hall of Fame

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    There are the charts from article, BIOMECHANICAL ANALYSIS OF TOP TENNIS PLAYERS, by Gideon Ariel, Ph.D., Vic Braden, Ann Penny, and ctr.

    [​IMG]

    [​IMG]

    Figure 1 - Agassi backhand, Figure 2 - Clijster backhand, Figure 3 – Federer backhand, and Figure 4 – Federer serve.

    Red lines represent measured racquet handle speed, blue lines – racquet tip speed, and green lines – ball speed.

    In all instances, the handle doesn’t slow down before impact. This clearly demonstrates that double/triple pendulum models cannot be used for the tennis stroke analysis.

    There is also good correlation between Federer FH (APAS) calculated data and above charts.

    IMO, the reason that pendulum model doesn’t work completely is that the best pros use their arms muscles very actively. They don’t rely on energy transfer from the body, whip effect, passive wrist, or whatever. All their muscles work very hard during powerful tennis strokes.
     
  33. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^ I've got to take issue with your last paragraph. Transfer thru the kinetic chain is VERY important. You cannot dismiss it that readily.
    .
     
    Last edited: May 11, 2012
  34. julian

    julian Hall of Fame

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    Couples

    I have attached my little post to your post.
    It was done this way to avoid some fire and keep issues going forward.
    It is a bit unorthodox

    A very minor comment-
    a lot of factors are "hidden" in AD HOC couples in the paper of Rod Cross
    Couples are denoted by symbols C1 and C2,I believe
    I believe they are TIME-DEPENDENT

    Switching gears:
    there are seven areas I will expand in future:
    1.kinetic chain
    There is a contribution by Stanley Plagenhoef here
    There is another paper
    APPLICATIONS TO THROWING OF RECENT RESEARCH ON
    PROXIMAL-TO-DISTAL SEQUENCING
    R.N. Marshall
    The University of Auckland, Auckland, New Zealand

    2.long axis rotation

    3.smoothing data "around the contact point"

    There are two possible links here
    http://www.tandfonline.com/doi/abs/10.1080/026404101753113787#preview
    http://w4.ub.uni-konstanz.de/cpa/article/view/1169/1057
    Once more please do NOT bust my chops if links do NOT work

    4.APAS and FOREHAND and 3D data
    Before I forget let me specify important links

    http://www.arielnet.com/start/apas/studies/toptennis.pdf
    http://www.arielnet.com/start/apas/...tem later I have sent you an E-mail as well.
     
    Last edited: May 11, 2012
  35. dominikk1985

    dominikk1985 Legend

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    BTW: If the racket slows down at contact (which it does of course) this doesn't mean a player isn't accelerating through contact.


    I have heard that almost 60 pound of force are created if you hit a hard hit ball back hard. so even if you do accelerate as hard as you can your racket will not continue to become faster if it faces that kind of resistance.

    hitting is an energy transfer from the racket to the ball. anytime you transfer energy to former link will lose energy. this is called the conservation of momentum. if the racket adds momentum to the ball it has to lose momentum.
     
  36. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Very curious tho' that your graph in post #180 shows the wrist speed peaking before that racquet tip speed. Wrist speed has decreased somewhat by the time the racquet tip speed peaks. It appears that we are getting some data that shows a decrease in wrist speed while other data does not. Very curious.
     
  37. toly

    toly Hall of Fame

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    The frame #25 represents point of contact with ball. It shows that racquet and wrist reached their maximal speeds just before impact. The wrist doesn’t slow down before impact, but after impact it does.
     
  38. julian

    julian Hall of Fame

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    Black or red

    SA,
    you are again light years ahead of me.
    Do we discuss red data or black data when analyzing post #166?
    I am very embarased to ask this question
     
  39. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^ I suppose that the approximation data (black) is more meaningful. However it puzzles me why the actual data fluctuates from one frame to the next as much as it does.

    What is the frame-to-frame time interval? Why do we see so much variation from one frame to the next? You say that the contact happens at frame #25, yet we see the speed drop and rise again after that so that we have several racket speed max values that are equal to or greater than frame #25 (in post #180). From the frame #31 to frame #33 we see the greatest jump in racket speed values -- a delta of more than 14 mm/sec in only 2 frames. This is a greater slope, change of speed, than we see prior to frame #25. This is what lead me to believe that impact happened at frame #33 (or possibly frame #28).

    The data/graphs in post #182 are also somewhat puzzling. These graphs show 6 intervals of time for every 100 ms. This would put the data points about 17 ms apart. The most disturbing feature is that the ball speed increases prior to contact (1 or 2 data points prior to contact). Figure 2 shows quite a bit of ball speed increase prior to contact. How do we account for this? Can we trust this data with such an apparent discrepancy?

    Another interesting that these graphs show is the the maximum ball speed happens several data point (time intervals) after contact. The ball is in contact with the strings for some 4 ms. These graphs would seem to indicate that the ball is still accelerating after it has left the strings. Is this possible? Is it a artifact of the compressed ball expanding to recover to its original state after it has already left the strings?
     
  40. toly

    toly Hall of Fame

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    This is great post. Thank you.

    1. About Federer APAS forehand:

    The video is done by Andy Fitzell. According to his description he made high speed videos of Federer FH with 3-6 video cameras. Then he digitized a lot of needed points of the display picture manually for each frame and for all cameras. Then APAS program generates all this skeleton stuff.
    I did reverse process and defined manually coordinates of the shoulder, wrist and racquet tip for each frame of the APAS video. Then I calculated corresponding speeds.

    Obviously, these two manual digitizing processes create a lot of random errors. That’s why my charts have so much “noise”.

    2. About data from article:

    I really didn’t pay attention to the ball behavior. This is nonsense!!!???

    Thank you so much for pointing this out. IMO, it is much better to disregard this “scientific” information. I apologize for posting pictures from this article without proper scrutiny.:cry::shock::mad:
     
    Last edited: May 14, 2012
  41. 5263

    5263 G.O.A.T.

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    Good character shown in this post. You are commended.
     
  42. julian

    julian Hall of Fame

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    Interesting book

    SA,
    Applied Anatomy and Biomechanics in Sport-2nd Edition
     
  43. julian

    julian Hall of Fame

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    Energy expression

    SA,
    I was trying to write down an expression for energy for
    the discussion in this thread
    I did NOT go very far.Let me summarize couple of points
    1.The energy will be the sum of three expressions
    the sum of kinetic energies(linear movement)
    the potential energy
    the sum of rotational energies

    2.The equation (A7) of the Rod Cross's paper should help with formulating the expression for THE SUM of ROTATIONAL ENERGIES
    Let me quote this equation for cpmpleteness

    C1 − C2 + Fx1h1 cos + Fy1h1 sin + Fx2L1 − h1cos
    + Fy2L1 − h1sin = Icm,1
    d1
    dt

    where Icm,1 is the moment of inertia of the forearm about an
    axis through G1.

    3.The potential energy would obviously depend on g.
    g shows up one line above Equation (A2a)

    4.Is it true that the energy is constant here?
    Would it be true if both C1 and C2 are BOTH equal zero.



    If you can push this subject by a bit I really would appreciate it
    regards,
    Julian
     
    Last edited: May 17, 2012
  44. julian

    julian Hall of Fame

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    Is Plagenhoef wrong?

    SA,
    was Plagenhoef wrong?

    A quote from

    http://w4.ub.uni-konstanz.de/cpa/article/view/1169/1057

    "Combined these results do not support the hypothesis (Plagenhoef, 1971) that skilled striking involves reaching peak implement velocity prior to impact. This apparent striking coordination is likely an artifact of inappropriate data smoothing or hitting a ball of large mass relative to the implement."
     
    Last edited: May 15, 2012
  45. 5263

    5263 G.O.A.T.

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    what is this saying?
     
  46. julian

    julian Hall of Fame

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    You have to be patient

    We have to wait for SA
     
  47. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    It's not completely clear to me either exactly what Knudson is saying. I can follow his reasoning that data smoothing can introduce errors in implement (racquet head) velocities at/near impact.

    I'm having problems with my eyes (and brain) today -- trying to read this all stuff is a little bit too much of a challenge. Does Knudson actually say when peak implement velocity occurs?
     
  48. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Last edited: May 16, 2012
  49. julian

    julian Hall of Fame

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    The picture difficukt to read

    I do NOT want to be a pest but the picture is diffiicult to read
    i.e it is very hard to see which solid line represnts what
     
  50. julian

    julian Hall of Fame

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    Interpolated smoothing is good according to Knudson

    Two points by Knudson
    1.Interpolated smoothing is good according to Knudson
    2.With interpolated smoothing the peak of velocity is ON THE CONTACT
     

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