conservation of angular momentum, whip physics, and a serve question

Discussion in 'Tennis Tips/Instruction' started by spacediver, Aug 29, 2010.

  1. 5263

    5263 G.O.A.T.

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    I love this illustration!

    The best servers get to the fourth one, but still have the wrist lower than the elbow, and racket face still down near the belt line. When done like as i describe, it is what I refer to as launch position with a delayed elbow extension. The one you have here looks like a normal server or a big server's second serve.

    Great sequence!
     
  2. toly

    toly Hall of Fame

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    Hewitt's kick serve.
     
  3. toly

    toly Hall of Fame

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    All beginners usually use elbow extension very hard. But, Hewitt completely ignores it, at least, in case of kick serve. He mostly relies on pronation. Because, pronation can provide much more consistent and faster serve then elbow extension. I do not see any correlation between Brian's data and Hewitt’s kick serve. That's why I quit reading his articles. They are mostly misleading.
    Thank you very much for pictures instructions!
     
  4. spacediver

    spacediver Hall of Fame

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    What are you talking about? Are you basing this on that single picture that doesn't even show the proper angle? I'd be willing to bet that every single pro uses elbow extension on every single serve, no matter what kind of serve it is.

    First off, Brian's data is based on elite college level players, not on Hewitt's serve. Secondly, the stuff I've read of his only relates to flat serves.

    Based on the level of knowledge you've displayed in this thread, I can't imagine you actually read (and comprehended) Brian's articles.
     
    Last edited: Oct 3, 2010
  5. spacediver

    spacediver Hall of Fame

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  6. toly

    toly Hall of Fame

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    Hewitt uses elbow extension to bring the racquet up. Then elbow brakes. It means the elbow extension is not moving racquet anymore. What motions are moving the racquet? They are: pronation, arm rotation in vertical plane (by using slow shoulder joint), and wrist ulnar deviation.
     
  7. spacediver

    spacediver Hall of Fame

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    wrong. The elbow reaches full extension as contact is made.

    Show me evidence to the contrary. That photo you posted is terrible for analyzing elbow extension, because of the angle.
     
  8. toly

    toly Hall of Fame

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    I’ll try to find more evidences.
     
  9. toly

    toly Hall of Fame

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    [​IMG]
     
  10. toly

    toly Hall of Fame

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    [​IMG]
     
  11. toly

    toly Hall of Fame

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    Do you want more pictures?
     
  12. spacediver

    spacediver Hall of Fame

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    better angles. I admit that they look fully extended in those photos (clearer view in second).

    Few possiblities:

    1) I'm wrong, and in fact, elbow extension doesnt contribute any racquet head speed before contact. Instead, all the momentum from elbow extension gets channeled into wrist. This contradicts empirical evidence from Brian Gordon's research that shows a 35% contribution to racquet head speed just before contact.

    2) These particular servers are using bad form (in which case I'm wrong about my previous statement when I said all pros reach full extension at point of contact and not before).

    3) The elbow isn't really fully extended. It just appears to be.

    Thanks for posting these pictures. They do appear to challenge the claims I've just made. Perhaps you have a point here. I'll try to get John Yandell and/or Brian Gordon to comment on this particular point.
     
  13. J011yroger

    J011yroger G.O.A.T.

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    OMG dude, why can't you just stop talking to this guy, I already had to unsubscribe to the other thread because of him.

    If nobody talks to him he won't post anymore.

    If he was right, you could hold your arm up over your head completely extended and toss the ball up and serve 135mph.

    Obviously not the case.

    J
     
  14. spacediver

    spacediver Hall of Fame

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    I think he's going more along the lines that elbow extension is important, but that all the momentum experienced at that joint gets passed onto the wrist.

    Doesn't make any biomechanical sense to me, but those pictures he posted do deserve an explanation.
     
  15. 5263

    5263 G.O.A.T.

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    Think of a catapult and how it flies up and stops,
    But the load continues and is whipped over the top.
    The catapult is driven up hard like the forearm, and
    the wrist takes over like a second catapult that uses the Mo of the first cat IMO,
    opposed to just a sling on the normal catapult.

    The forearm extension IMO has two main power sources.
    First there is the drive from the legs and torso,
    then the lesser power of the elbow extension from the triceps.
    All this sets up something similar for the wrist in it's Ulna deviation action.
     
    Last edited: Oct 4, 2010
  16. spacediver

    spacediver Hall of Fame

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    yea I get that 5263... I just find it hard to believe that the wrist would carry that much momentum. I suppose there is ulnar deviation as well as flexion to share the burden. And perhaps forearm pronation can absorb some of the momentum from elbow extension.

    I still think that elbow extension continues until impact. I suspect it's hard to make conclusions based on photos, and even slow motion footage. You really need sensors that can accurately measure joint angles over time and at a very high temporal resolution.

    I'll pass this question along and see what happens.
     
  17. 5263

    5263 G.O.A.T.

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    Not sure what u mean by wrist carring the Momentum. The momentum is mostly in the racket and shifting out to the racket head; moving away from the wrist.

    Side note:
    Flexion as an exertion is to be avoided in tennis IMO and should show up mostly in follow thru from momentum.
     
  18. spacediver

    spacediver Hall of Fame

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    As in, if elbow reaches full extension before contact, and the momentum experienced in that elbow joint is not to be wasted, it will be channeled elsewhere in the kinetic chain. In this case, upwards to the wrist (this theme has been explored in detail throughout this thread).


    I wasn't saying it was passive or active. Many people tend to think it's passive. We had a great discussion of this issue over here:

    http://tt.tennis-warehouse.com/showthread.php?t=343931


    Some of the best data we have on serve mechanics shows that the wrist flexion contributes a significant chunk of racquet head speed before contact. Most likely this is passive movement of the joint (hasn't been properly studied whether it's passive or active or some combination of both, but there are good reasons to suppose its passive, i.e. no exertion).
     
  19. toly

    toly Hall of Fame

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    There is example of the slice serve.
    Chanelle Scheepers has radically different (compare to Hewitt) serve’s course of action (Figure 1). But, she also ignores elbow extension in case of slice serve.
    [​IMG]
    Figure1. The arm at the last second before impact (Chanelle Scheepers’s slice serve)
    Chanelle Scheepers’s fastest serve speed at Roland Garros 2010 was 98 mph, average 1st serve speed 90 mph, and average 2nd serve 78 mph. Her height is 5' 9" (1.74 m). First serve reliability was more than 75%. It looks she possesses very fast and consistent serves.
    During the serve, Chanelle Scheepers bent her wrist backward. That opened the racquet face around 60°, nearly to the water’s tray position (see Figures 1.1 - 1.2). Then she rotates the arm (by using the shoulder joint) in the vertical pane with the angular speed about Ωv =400°/sec and pronates in the horizontal plane. She flexes the wrist in the vertical plane with the angular speed Ωw=2000°/sec. Besides, Scheepers creates extreme ulnar deviation. The last action completely destroyed the pronation’s component of the racquet velocity |VLH|, because the arm and the racquet’s long axis represent the straight line, hence the angle β=0.
     
    Last edited: Nov 15, 2010
  20. spacediver

    spacediver Hall of Fame

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    interesting. How did you arrive at those figures. In particular, how did you measure the angular speed of the the internal rotation of the shoulder joint, based on the information in that camera footage?
     
  21. toly

    toly Hall of Fame

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    I copy these pictures frame by frame from 300 fps video. Time elapsed between two consecutive pictures is 1sec/300=3.3333 msec. By using a protractor, I measure corresponding angles (degrees) between previous and next (pictures) arm positions. Then I calculate angular/ or linear speed /or acceleration. You also can read my very first post on this website. I described this process in detail.
     
  22. spacediver

    spacediver Hall of Fame

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    I haven't read your original post, but how can a protractor help with joint angles that aren't parallel to the camera angle?
     
  23. toly

    toly Hall of Fame

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    In case of pronation, we can use 3d engineering drawing rules or Descriptivegeometry. It is the branch of geometry which allows the representation of three-dimensional objects in two dimensions, by using a specific set of procedures. This technique is not accurate. We really need 3 or 4 cameras to calculate exactly.
    [​IMG]

    Figure 2.3. Set of the pictures around impact (Florent Serra’s kick serve)
     
  24. spacediver

    spacediver Hall of Fame

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    thanks. Yes, I can see how this method requires multiple cameras for higher accuracy.

    btw, it turns out you were partially right about the elbow extension issue. I will summarize the responses I got from John and Brian later today.

    I apologize for my arrogance earlier.
     
  25. toly

    toly Hall of Fame

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    There is no problem my young opponent. Thank you for inserting pictures instructions and so on!
     
  26. toly

    toly Hall of Fame

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    Where are responses? Post them please!
     
  27. spacediver

    spacediver Hall of Fame

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  28. toly

    toly Hall of Fame

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    My next post will be exclusively about flat serve. There are some different ways of the elbow actions. It looks like I was wrong about Brian Gordon’s data. I apologize for my arrogance earlier.
     
  29. toly

    toly Hall of Fame

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    Flat Serve

    2.2.2 The Flat Serve with Effective Pronation, Wrist Flexion, and Moderate Wrist Ulnar Deviation
    Figures below give us an idea about arm actions during typical flat serve.
    [​IMG]
    Figure 2.15. The arm’s actions during Marat Safin's flat serve
    [​IMG]
    Figure 2.16. The arm’s actions during Kevin Anderson’s flat serve
    In case of the typical flat serve the main components of the racquet speed are the arm pronation, the wrist flexion and the vertical arm rotation. The most important is the arm pronation.
    It follows from these photos during the pronation phase of the flat serves both players keep their right elbows in bent position. In all previous analyzed cases (the spin serves), most pros maintain their arms practically straight.

    Question: Why during the pronation phase these players keep elbows in bent position?
    Answer: When we swing the racquet upward our shoulder joint brings the upper arm in vertical and the forearm in horizontal position. After that, by using fast elbow extension motion, the forearm moves upward and the pronation angle β usually equals 90 degrees (Fig. 2.15.1). If the elbow unbends completely, it brakes and inevitably the racquet starts moving upward by using inertia and very fast wrist ulnar deviation. This motion reduces the pronation angle beta (Fig. 2.15.4 β=45°) and can kill pronation component of the racquet speed. To prevent it from occurrence, even during the impact, the elbow joint should be bent.
    Next pictures (Figure 2.17) illustrate Andy Roddick’s arm action during flat serve and confirm last statement. Pay attention on the angle between axis of the upper arm and the forearm. This angle is never less than 30 degrees. Andy constructs the motion which often called as elbow snap. Maybe this is the main secret of his so successful flat serve. For instance, Marat Safin keeps his elbow straight (Fig. 2.15.4), that’s why perhaps his serve is slower than Roddick’s.
    [​IMG]
    Figure 2.17. Andy Roddick's arm actions during flat serve
     
    Last edited: Dec 23, 2011
  30. toly

    toly Hall of Fame

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    Flat Serve

    There is one more way to keep pronation angle β in proper range 30° - 45°.

    We may also use slightly modified Continental grip. Next picture shows what kind of the grip Taylor Dent uses for flat serves.
    [​IMG]
    Figure 1. Taylor Dent uses modified Continental grip


    Taylor keeps his finger knuckles parallel to the long axis of the tennis racquet. With this type of grip it is physically impossible to align long axis of the racket in parallel to axis of the forearm/arm. Practically, the pronation angle beta cannot be less than 30°. I would recommend this grip for any type of the serves, except the slice serves.
     
  31. bhupaes

    bhupaes Professional

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    Hey Toly, when I saw your first post I thought you were making fun of the guys who were getting too technical, but I guess I was mistaken. I agree with your observation regarding this grip. I started using this grip recently - finger knuckles parallel to the long axis - to achieve better pronation. Actually, I use a similar finger orientation for my forehand also, since it seems to allow for more degrees of freedom of movement for the wrist and forearm... helps me to better hit up and across, and pull back the racquet with an elbow break. This works very well for me, but obviously, I still can't hit as well as Dent... :(

    Thanks for the great pictures.
     
  32. toly

    toly Hall of Fame

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    Hey bhupaes, thank you for your post. I really like all your posts on this forum. Tennis is just fun for me. But unfortunately, I’m engineer and my brain always makes me analyze and calculate everything and I cannot resist.
    I also use this type of grip, but for any stroke. My FH is western, 1HB is eastern backhand, slice and serve continental. I’m a little bit upset about it. With this grip my thumb cannot squeeze handle hard enough and practically is doing nothing. It creates some problems. For example, when I try to block very hard serve I often cannot keep the racquet in proper position during impact. What kind of grip do you use for forehand? And what is your opinion about Roddick’s elbow bent? Maybe it is really very important???
     
  33. gzhpcu

    gzhpcu Professional

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    Here's a good video from tennisone...
    http://www.youtube.com/watch?v=7bsYFra60Q0&feature=related

    Leverage is all about angles at the joints when the segments are rotating.
     
    Last edited: Nov 16, 2010
  34. toly

    toly Hall of Fame

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    Leverage

    Yes, this is Jim McLennan from TennisOne.com. He is very famous and knowledgeable coach. I watched this video many times.
    But, I do not understand expression: “Leverage is all about angles at the joints when the segments are rotating.” Can you give a simple example to clarify the matter?
     
  35. bhupaes

    bhupaes Professional

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    Hi Toly, thanks for the compliment - I am a very ardent student of the game, all for fun, and I like to think that I will reach the 5.0 level before my legs fail me. Now to the technical part...

    I did notice (this morning) that my knuckles were not totally parallel to the long axis. Between the index finger and the pinky knuckles, the spread is approximately one bevel. However, I don't spread my fingers - they are close together like in the Dent picture. I use the continental grip for the serve and the semiwestern grip for the forehand, with fingers clasping the racquet in a hammer grip. I make sure that the pinky is still on the racquet, for both serve and forehand. I grip more with the pinky side of the palm, like you seem to be doing.

    I use the 2HBH for my bread and butter topspin backhand, so there I'm different from you.

    For the slice, I use a continental, and here, I spread my fingers a little more. The grip pressure seems to be more towards the thumb side for this stroke, it seems. I tend to supinate the forearm a little as I pull the racquet through the slice, and the thumb does provide some support.

    In reality, I try not to think too much while playing. Whenever I think, I find I'm too slow - my brain can't multitask at all, unfortunately. I try to remember a certain "feel" and go for it... and hope the ball lands in! :)
     
  36. bhupaes

    bhupaes Professional

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    Regarding Roddick's elbow bend... well, I guess you are comparing him with the guys who hit with a straight arm like Federer and Nadal. I am no expert, but I have my opinions. IMO, the two types of forehands recruit slightly different muscles and use the kinetic chain slightly differently.

    The bent elbow guys, IMO, contact the ball slightly closer to the body than the straight arm guys (hence the bend in the arm), and use a little more of the deltoids than the biceps to pull the racquet up and across. I think Roddick falls in this category.

    The straight elbow guys contact the ball literally at arms length (hence the straight arm), and use more biceps than deltoids to pull the racquet up and across.

    To me, all this says is that there are multiple ways to hit the ball effectively. Depending on the distance from the ball, the same player's arm could be bent or completely straight or somewhere in between. I think we have seen Federer do this.
     
  37. bhupaes

    bhupaes Professional

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    Hi Toly, it occurred to me that you might be talking about Roddick's bent elbow in the context of his serve, and not his forehand. If so, yeah, I think your explanation as to why the bend is required is correct. For a given amount of rotation of the upper arm, a greater bend in the elbow will yield a correspondingly greater amount of movement of the racquet head. But keep in mind that there are other contributors to racquet head movement, such as the cartwheeling motion, which benefit from a higher racquet position, so the elbow cannot be at a right angle! Roddick's elbow is probably closer to the optimal bend than others... that's my best guess.
     
  38. toly

    toly Hall of Fame

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    Hey bhupaes, thank you for explanation. I'll try to modify my grips accordingly.
     
  39. toly

    toly Hall of Fame

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    Hi bhupaes, yes, I was talking about Roddick’s flat serve. He keeps elbow bend during all pronation phase of the flat serve including impact. What does cartweeling do so important during his flat serve? I think this motion is too slow (compare to elbow extension, pronation etc) to bring anything significant to the serve.
     
    Last edited: Nov 16, 2010
  40. toly

    toly Hall of Fame

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    About forehand

    Why are you using semiwestern grip for the forehand?
    Most of the pros are using western grip. There must be good reason. I’ll try to explain why the westen grip is more natural and much better than other forehand grips.
    To produce modern forehand we should use the wrist very intensively. In this case, the wrist has just two motions: flexion and ulnar deviation. When we use heavy tools, for example hummer, sword etc, we naturally use ulnar deviation. In case of light tools like pen, surgical scalpel and so on, we use wrist flexion. I believe most pros treat the tennis racket like heavy tools, that’s why they are using western grip. There is one more reason for that. The wrist ulnar deviation has angle range around 90 degrees. The wrist flexion has 180 degrees and it can significantly increase error’s margin. :confused:
     
  41. bhupaes

    bhupaes Professional

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    Toly, I see it very simply as follows. There is a motion of the body which launches the racquet forward like a catapult, using the arm as a lever. I called this motion "cartwheeling", which I believe is the commonly used term. The longer the lever (the arm), the faster is the racquet head motion. Super imposed on these are other motions such as upper arm rotation, forearm pronation, elbow extension, wrist flexion, ulnar deviation, etc. I believe you may be right in that the contribution due to upper arm rotation, amplified by a bent elbow, is the most significant contributor. But due to the other motions which benefit from a straight arm, I believe the amount of elbow bend has an optimal value beyond which it will act negatively with respect to generating racquet head speed. I don't think this contradicts what you are saying.
     
  42. bhupaes

    bhupaes Professional

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    Hmm... not sure I have an answer for you. I guess it's just a personal preference that I use a semi-western grip. Nothing wrong with full western if you prefer that, I sometimes use it from mid-court to get more spin. I like to mix in flat bombs with heavy spin, and the semi-western suits me fine for that. I have to think about your analogy with using heavy tools - I don't see offhand how it applies.
     
  43. gzhpcu

    gzhpcu Professional

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    Extend your arm straight out to the side. Place your hand, say, against a door sill, and try to exert torque.
    Now lower your upper arm and create an angle with your forearm and repeat. In this case you will see you can exert more torque.

    Another aspect is what Jim mentions: if you have an angle between the racket shaft and the forearm, when rotating the arm, the racket head has a greater range of movement (=speed).
     
  44. toly

    toly Hall of Fame

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    Yes, you are absolutely right. At last I got this biomechanical leverage stuff. Thank you very much for clarification.
    When we pronate/supinate screwdriver we always keep elbow in bend position to increase a force applied to screwdriver’s handle. The same takes place with Andy’s flat serve. He uses bend elbow as a force multiplier. I think this force should be very active during impact. This is one more very convincing argument against Whip Effect theory.
     
  45. toly

    toly Hall of Fame

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    I’m not very good with English. I would say, the racket head has a greater radius of the rotation (=speed). Which one is better?
     
  46. toly

    toly Hall of Fame

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    Let’s compare two players.
    [​IMG]
    Federer has eastern grip. To increase the flat component of the racket speed by using the wrist only, he has to flex it. The wrist ulnar deviation will move the racquet downward, which is wrong. Nadal has western grip. He has to use ulnar deviation. The wrist flexion will open racket face, which is also wrong. Nadal is using natural movement for heavy tools, Federer‘s technique is natural for light tools.
    1. I already stated the wrist flexion has angular range 180 degrees. It gives us too much freedom to generate mistakes. The ulnar deviation has just 90 degrees, that’s why it creates more consistent stroke.
    2. It looks like Nadal grips handle very hard. In this case he is still able to produce ulnar deviation, but flexion would be practically impossible.
    3. From safety point of view, I believe the western is the best grip.
    In case of the semiwestern grip we have to use both, flexion and ulnar deviation somehow. I think this combined motion is very complicated and very difficult to control.
     
    Last edited: Nov 18, 2010
  47. bhupaes

    bhupaes Professional

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    I see what you are saying. I agree a full western grip will tend to make shots be more consistent... definitely because of the increased spin, but maybe also because of decreased wrist flexion. It is a good point, definitely something to think about. The caveat, of course, is that it demands more flexibility in the wrist, and it requires more effort to generate pace - something that older folks may find difficult.

    I also see how your comment about heavy vs. light tools applies. Having the palm right under the racquet as in a western grip would support the weight of the racquet better, and is more supportive of an upward motion of the racquet, as we know.

    As with everything, grips are also a compromise. The Eastern grip has its advantages - a little easier on the wrist, a little easier to generate flat out pace, a little easier to deal with low balls - and it has its drawbacks - it's less consistent than the full western. The SW grip would be in between, and gets some of the best of both worlds, some would say. I have seen people with continental grips play pretty good tennis, so a lot depends on the individual for sure.

    But this is definitely a very good observation on your part, and I have gained a little more insight into tennis as a result - thanks! But using Federer as an example of inconsistency is not good for your argument... you know why! :)
     
  48. toly

    toly Hall of Fame

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    When woodcutters chop trees by using heavy tool like axe, they always apply the wrist ulnar deviation. They practically never have wrist injury. In order to maintain a heavy axe, they should grip hard the handle of the axe. The ulnar deviation allows them to do it. The wrist flexion will never move properly if we grip handle very hard.
    However, when a surgeons uses a scalpel (light tool), they prefer to use the wrist flexion. This is very delicate and frail motion, that’s why it is not good for heavy tools.
    We should know first, is a tennis racquet heavy or light tool? Since the eastern grip is dead, but the western grip is the most popular, I think we must treat racquet as heavy tool and apply ulnar deviation (not the wrist flexion).
    The semiwestern grip is not natural. I even cannot describe the wrist motion in this case. We just have to rely on our subconscious motions, which is bad approach to tennis stroke. I wasted around one year trying to use it and never got consistency.
     
    Last edited: Nov 19, 2010

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