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julian
01-30-2012, 01:40 PM
Any comments welcome
Julian


PS The smiley BELOW is NOT mine.I cannot remove it from the post
see as well http://www.actakin.com/PDFS/BR0202/SVEE/04%20CL%2006%20ND.pdf


J Sports Sci. 2000 Aug;18(8):579-92.
Changes in angular momentum during the tennis serve.
Bahamonde RE.
Source of the ABSTRACT only
http://www.ncbi.nlm.nih.gov/pubmed/10972409

Biomechanics Laboratory, Indiana University-Purdue University Indianapolis, 46202, USA. rbahamon@iupui.edu
Abstract

Three-dimensional cinematography and the direct linear transformation method were used to obtain the coordinates of the landmarks of five right-handed collegiate tennis players. A 15-segment model was used to calculate the total body angular momentum about three orthogonal axes (X, parallel to the baseline; Y, normal to baseline and pointing towards the net; and Z, pointing upwards) passing through the centre of mass and to obtain the segmental contribution of the trunk, arms and legs. Most of the clockwise angular momentum about the X-axis was concentrated in the trunk and the racket-arm. Between the events of maximum external rotation and ball impact, the clockwise angular momentum about the X-axis of rotation of most body segments was reduced and the racket-arm gained clockwise angular momentum. The body angular momentum about the Y-axis of rotation had two distinct patterns and was the result of the lateral rotation of the trunk as the racket shoulder was elevated in preparation for impact. This body angular momentum was clockwise from the event of maximum external rotation to impact for the players with the greatest ball speed, whereas it was counterclockwise for the other players. The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern. The largest source of angular momentum in the tennis serve derives from the remote angular momentum about the X- and Y-axes of rotation, which are then transferred from the trunk to the racket-arm and finally to the racket. Near impact, most of the angular momentum (75.1%) was concentrated in the racket-arm. Of the angular momentum of the racket-arm, the largest percentages were concentrated in the racket (35.9%) and the forearm segment (25.7%).

PMID:
10972409
[PubMed - indexed for MEDLINE]

LeeD
01-30-2012, 01:58 PM
Humans cannot redirect their bodies into a direct linear motion into the tennis ball, that's just body mechanics.
Study was only good rightie players. If they included lefties, they'd generalize that lefties tend to add more angular, and much less linear action on all their strokes, especially the serves. That might be a generalization, but one that every tennis player has observed.

sureshs
01-30-2012, 02:15 PM
Humans cannot redirect their bodies into a direct linear motion into the tennis ball, that's just body mechanics.
Study was only good rightie players. If they included lefties, they'd generalize that lefties tend to add more angular, and much less linear action on all their strokes, especially the serves. That might be a generalization, but one that every tennis player has observed.

Why is that? I have observed it in Nadal and Feliciano, and several club players, men and women.

LeeD
01-30-2012, 03:13 PM
I suspect the human body hitting a tennis ball has an AXXIS OF ROTATION, the pivot points from hips and shoulders that don't line up directly behind the ball and go thru the ball.
Lefties take more windup, which usually exxagerateds the offset rotation to the ball on serves and groundstrokes.
An old eastern forehand has the most direct path to the ball.
Who uses eastern forehand anymore? Fed has a new eFh, but with a stronger grip and a modern swing, so it's NOT an old eastern forehand.

sureshs
01-30-2012, 03:15 PM
Lefties take more windup,

Pursuing it further, why?

Because they have been socially conditioned that the out-wide serve is their weapon?

toly
01-30-2012, 03:17 PM
IMO this is very bad article.

It is well known that the main contributor of the translational ball speed is arm pronation (pronation and internal shoulder rotation). This motion rotates the racquet around Z – axis.

The author of the article failed to recognize this simple fact. He stated, “The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern”. That’s why he ignored it completely.:(

LeeD
01-30-2012, 03:21 PM
I suppose, for the players who are celebral, any article is better than nothing, and leaving out important facts just invite replies, which invite interest in the subject.
Why indeed? Don't you find most lefties TEND to take more wild swings at serves? Most are good athletes, but seem undiciplined compared to most righties. Can you envision a lefty version of Monfils? Of course.
Can you ever expect to find a lefty version of DJ or Fed? Never.

toly
01-30-2012, 03:32 PM
There are too much misleading articles about tennis!!! This is one of them!!!!!!:(

LeeD
01-30-2012, 03:39 PM
I find, for every "expert" in the mechanics of tennis, there are thousands of real experts who only see PART of the equation. Knowledgeable as statistitions might be, they don't see the overall picture, which can lead to very askewed findings.

bhupaes
01-30-2012, 03:41 PM
I am interested in knowing whether there are any sudden peaks (like impulses) in the angular acceleration (more like the first derivative of the angular momentum) of the torso. In my experience (limited as it is), what I have found is that near about the point of maximum external rotation of the shoulder, one has to abruptly jerk the body in a way that drags the racquet towards the ball. The core and legs play a big role in this movement for me. On the days when my back is stiff, and I am not able to use the body as much, my serve really sucks - speed is lower, and my topspin serve simply lacks the bite and accuracy (tends to go long). The difference is pretty big when the body is working well, and I am able to launch into the ball.

I figure if the pros are doing something similar, I am on the right track, albeit in the slow lane (relatively speaking). :)

LeeD
01-30-2012, 03:43 PM
I see the OPPOSITE happening.
Instead of trying to increase the hand and arm, you might consider SLOWING down the torso and body!

toly
01-30-2012, 03:52 PM
I am interested in knowing whether there are any sudden peaks (like impulses) in the angular acceleration (more like the first derivative of the angular momentum) of the torso. In my experience (limited as it is), what I have found is that near about the point of maximum external rotation of the shoulder, one has to abruptly jerk the body in a way that drags the racquet towards the ball. The core and legs play a big role in this movement for me. On the days when my back is stiff, and I am not able to use the body as much, my serve really sucks - speed is lower, and my topspin serve simply lacks the bite and accuracy (tends to go long). The difference is pretty big when the body is working well, and I am able to launch into the ball.

I figure if the pros are doing something similar, I am on the right track, albeit in the slow lane (relatively speaking). :)
About second derivative you can read in jumpulse.com, but please be careful. :)

toly
01-30-2012, 04:13 PM
I see the OPPOSITE happening.
Instead of trying to increase the hand and arm, you might consider SLOWING down the torso and body!
According to simple physic, in order to slowing down the body/torso we have to increase arm/hand actions. Everything must be active, no sleeping please during the serve. :)

bhupaes
01-30-2012, 04:16 PM
I see the OPPOSITE happening.
Instead of trying to increase the hand and arm, you might consider SLOWING down the torso and body!

Sure, eventually the body does slow down, and the arm/hand/racquet shoots on ahead. What I mean is that if one only looks at pictures and videos, one can't tell what the server is feeling. I think this is because pictures and videos (especially slow motion videos) don't convey a sense of acceleration, which is what I think creates the feel. But if one is going to measure it, I think it will show where we should concentrate.

bhupaes
01-30-2012, 04:18 PM
About second derivative you can read in jumpulse.com, but please be careful. :)

Ha ha! No jumpulse for me, my friend - my brain is not that advanced!

LeeD
01-30-2012, 04:18 PM
Wow.....
2 of the most technical strokes experts here on TW's forum don't speak or write English. How's about that? Ho and Toly. Limpin does quite well.
I read Toly's last post 3 times. Still don't know if he's agreeing with me or countering my thoughts.
Without regard, I'll press on......
Think of a whip. You cannot create supersonic speed if you hand keeps moving as fast as you can make it go. You CAN create supersonic tip speed if you slow down your hand.
The key is slowing down and knowing when to slow down. In tennis's case, tis slowing down your torso.

toly
01-30-2012, 05:51 PM
Sure, eventually the body does slow down, and the arm/hand/racquet shoots on ahead. What I mean is that if one only looks at pictures and videos, one can't tell what the server is feeling. I think this is because pictures and videos (especially slow motion videos) don't convey a sense of acceleration, which is what I think creates the feel. But if one is going to measure it, I think it will show where we should concentrate.
What exactly do we need to do to slow the body? :confused:

LeeD
01-30-2012, 05:57 PM
You need to reach the end of your rotation/movement into the court.
That's the whip effect, shown by a high hand, high finish after the ball strike, the racket now pointing straight down at the ground, your hand still above your head.

toly
01-30-2012, 08:22 PM
You need to reach the end of your rotation/movement into the court.
That's the whip effect, shown by a high hand, high finish after the ball strike, the racket now pointing straight down at the ground, your hand still above your head.
Our body cannot reach the end of the rotation/movement into the court by itself. You have to do something to stop body rotation. :)

Chas Tennis
01-30-2012, 08:42 PM
Any comments welcome
Julian


Julian, May we ask why you are interested in this article?

Have you seen this often referenced one, also from 2000?


Long-axis rotation: The missing link in proximal-to-distal segmental sequencing

Authors: Marshall R. N.; Elliott B. C.

Source: Journal of Sports Sciences, Volume 18, Number 4, 1 April 2000 , pp. 247-254(8)

Publisher: Taylor and Francis Ltd

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Abstract:
Most assessments of segmental sequencing in throwing, striking or kicking have indicated a proximal-to-distal sequencing of end-point linear speeds, joint angular velocities, segment angular velocities and resultant joint moments. However, the role of long-axis rotations has not been adequately quantified and located in the proximal-to-distal sequence. The timing and importance of pronation-supination in the development of racquet head speed have been examined in the tennis serve and squash forehand drive and considered in relation to conventional concepts of proximal-to-distal sequencing. Both long-axis rotations reached their peak angular speeds late in both strokes, typically after shoulder flexion-extension, shoulder abduction-adduction and elbow extension. These results clarify and confirm the importance of upper limb long-axis rotations in the production of racquet head speed. It appears that traditional proximal-to-distal sequencing concepts are inadequate to describe accurately the complexity of the tennis serve or squash forehand drive. It is essential to consider upper arm and forearm longitudinal axis rotations in explaining the mechanics of these movements and in developing coaching emphases, strength training schedules and injury prevention programmes.

Keywords: KINEMATICS; LONG-AXIS ROTATION; SEGMENT SEQUENCING

Language: English

Document Type: Research article

Publication date: 2000-04-01

bhupaes
01-30-2012, 09:43 PM
What exactly do we need to do to slow the body? :confused:

Nothing, IMO. I don't believe one deliberately slows down any part of the body. Having the right visualization/intention in mind will get the job done, for the most part. There is also, of course, the fact that every movement has a natural range which will limit or stop the movement at some point.

thug the bunny
01-31-2012, 05:08 AM
Paralysis by analysis. Hit the ball.

julian
01-31-2012, 06:14 AM
IMO this is very bad article.

It is well known that the main contributor of the translational ball speed is arm pronation (pronation and internal shoulder rotation). This motion rotates the racquet around Z – axis.

The author of the article failed to recognize this simple fact. He stated, “The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern”. That’s why he ignored it completely.:(
All your statements above are incorrect (the second sentence is partially incorrect).
Please refer to your conversation/posts with Ash_smith on a related subjects
(of papers/data collection by Elliot)

toly
01-31-2012, 07:27 AM
All your statements above are incorrect (the second sentence is partially incorrect).
Please refer to your conversation/posts with Ash_smith on a related subjects
(of papers/data collection by Elliot)
Sorry, but I don’t understand your post. Can you be more specific?:confused:

julian
01-31-2012, 07:39 AM
Sorry, but I don’t understand your post. Can you be more specific?:confused:

Please read ITF Biomechanics of Advanced Tennis Page 62-65

LeeD
01-31-2012, 07:41 AM
For all those who don't understand the "slowing down" part...
Do you have a big serve yourself?

The Bawss
01-31-2012, 07:59 AM
I can't take this seriously, there is no physics.

LeeD
01-31-2012, 08:02 AM
No, where the human body is concerned, physics is much harder to understand.
You can use #'s, studies, and physics for mechanical stuff, but for serving a tennis ball fast and accurately, you gotta look closely at those who can.

toly
01-31-2012, 08:51 AM
Please read ITF Biomechanics of Advanced Tennis Page 62-65
Unfortunately I don’t have this book. But I read Bruce Elliot article about powerful serve in tennisplayer.net. Is it enough? :confused:

julian
01-31-2012, 08:55 AM
Unfortunately I don’t have this book. But I read Bruce Elliot article about powerful serve in tennisplayer.net. Is it enough? :confused:
You have to read the book or the article quoted in OP
No more posts from me before you will do that

spacediver
01-31-2012, 09:52 AM
IMO this is very bad article.

It is well known that the main contributor of the translational ball speed is arm pronation (pronation and internal shoulder rotation). This motion rotates the racquet around Z – axis.

The author of the article failed to recognize this simple fact. He stated, “The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern”. That’s why he ignored it completely.:(

I haven't yet read the article, but Toly, you can't criticize an article by reading an abstract, just because you don't like the results. Read the whole paper and then discuss.

toly
01-31-2012, 09:59 AM
You have to read the book or the article quoted in OP
No more posts from me before you will do that
I read both articles: Bahamonde RE, Changes in angular momentum during the tennis serve and Niksa Durovic, NEW BIOMECHANICAL MODEL FOR TENNIS SERVE.

About first one, I expressed my opinion in post #6.

About second one, Niksa Durovic repeats very popular but wrong idea (IMO), “In the case when a blockade of the trunk rotation is done during the serve (by the arm under the chest) the transition of the force moves to another connection or in other words to shoulder-elbow-wrist. That kind of serve is 1.7 times faster than the serve without the blockade of the trunk rotation”.

julian
01-31-2012, 10:06 AM
I read both articles: Bahamonde RE, Changes in angular momentum during the tennis serve and Niksa Durovic, NEW BIOMECHANICAL MODEL FOR TENNIS SERVE.

About first one, I expressed my opinion in post #6.

About second one, Niksa Durovic repeats very popular but wrong idea (IMO), “In the case when a blockade of the trunk rotation is done during the serve (by the arm under the chest) the transition of the force moves to another connection or in other words to shoulder-elbow-wrist. That kind of serve is 1.7 times faster than the serve without the blockade of the trunk rotation”.
So you are wrong about the article by Bahamonde
How do you argue with experimental data?
The topic is closed

toly
01-31-2012, 10:31 AM
So you are wrong about the article by Bahamonde
How do you argue with experimental data?
The topic is closed
According to you, all experimental data are true. I can assure you there are more than enough wrong experimental data and their interpretations. Every PhD should know this.:)

Kevo
02-01-2012, 06:55 AM
I agree with LeeD about the slowing down part. That advice has helped a lot of people I've worked with on the serve. They don't realize that the arm needs to slow down or momentarily end it's upward and forward path for that energy to transfer into the rotation of the arm. Way too many people swing forward with their arm and give away a lot of the serve's potential in doing so.

LeeD
02-01-2012, 08:20 AM
Problem with the "slowing down" part is that it's counterintuitive.
Why slow it down? I mean the shoulder, to allow the arm to come thru, the hand at the end of your fulcrum, the rackethead the end of the entire lever.
Whip effect. The tip of the whip is supersonic. Your hand cannot possibly swing an 8' long whip into those speeds unless you slow down your hand at the end of your swing.
A javelin thrower, running full speed, then planting and throwing with full arm speed, but the body has slowed down.
A good sign you're serving correctly is the old high hand finish, when just after striking the ball, your hand is still at the top of your head, the racket has come thru to point straight down at the ground. That means the rackeHEAD accelerated past your arm, hand, and the rackethandle.

bhupaes
02-01-2012, 03:32 PM
I fully agree with you both (Kevo, Lee) that the phenomenon you describe (slowing down of body/arm/other link as appropriate) does happen. But IMO, one should not do it consciously, or teach it explicitly.

Take the serve, for example. I believe the proper form which includes full extension into the ball at the top of the swing, with the intention to hit the ball as hard as possible into the opponent's service box, will cause the right things to happen. Thus you have the famous sequence of still images of the Roddick serve (posted many times) where the whole body and forearm is almost at a standstill at full extension, while the hand/wrist moves the racquet into the ball with flexion/pronation (with both passive and active movement). I believe this type of extension, along with intention, creates the right motion.

Ground strokes lend themselves to similar analysis. Sometimes it's the wrist that's released, sometimes the whole forearm may be released, sometimes it's a slowing down of some link that causes this release, and sometimes it's an abrupt change of direction. IMO, it's too complicated to choreograph with explicit instruction, so it's best to teach the right form and provide the right cues, and leave the heavy lifting to the body's innate mechanisms...

Anyway, that's my take and I am sticking with it. :)

LeeD
02-01-2012, 04:02 PM
In the past two years, I"ve seen over 60 vids of guys serving. In less than 5, the player actually adopted the high hand finish (after the ball is hit). That means, in at least 55 cases, the player did NOT adopt the high hand, slow torso, mechanics.
I think most things taken for granted NEED to be taught.
I"m guilty myself. I KNOW how to serve fast. But given senility, I forget quite often to adopt the idea of allowing the rackethead to come thru ahead of the rackethandle.

5263
02-01-2012, 06:06 PM
I"m guilty myself. I KNOW how to serve fast. But given senility, I forget quite often to adopt the idea of allowing the rackethead to come thru ahead of the rackethandle.

I know what you mean here Lee. My data on this leads me to believe the approach we backslide to is an effort to get more control. Leading with the handle to whip the head feels to have less control with that whippy action, but when you do it more often, I'm not sure that is the case. I think we still feel that way though, so we backslide.