# Racket head acceleration through impact

Discussion in 'Tennis Tips/Instruction' started by Povl Carstensen, Jan 20, 2013.

1. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
I find it rather revealing that some people have to make up that others propose that you hit the ball backwards, to have something to critisize and be right about. But it made me think about racket head acceleration. During the debate someone put forward (I can't find it now) that the foreward velocity decreases after impact, while the upwards increases. And ofcourse the sideways speed accelerates as the racket goes across the ball and/or body. And it is only natural that the foreward vektor goes down as the upwards and sideways goes up. If you factor them together, I think it is very likely that the combined sum goes up, meaning that the racket in a lot (most?) of typical modern forehands (and other shots as well) accelerate after and through impact. Maybe this is obvious to some, perhaps others disagree. I wonder if the movement in all three planes have been factored together?

2. ### dominikk1985Legend

Joined:
Feb 11, 2011
Messages:
6,680
I have read a study somewhere that it is a good sign when the racket decelerates a lot at contact because that means you have a good energy Transfer and all the energy is in the ball (just like the shoulders and hips decelerate to Transfer energy to the arm).

however while that might be true from a Point of physics I still think that the old fashioned swing through the ball is a better advice since it ensures that you don't decelerate before Impact although technically the swing is over at contact and the follow through does nothing with the ball. but the Body is not a machine and when you don't accelerate through the ball there will something bad happen before or at Impact.

3. ### sureshsBionic Poster

Joined:
Oct 1, 2005
Messages:
40,493
In that study, sideways numbers were not supplied. I went back and calculated the resultant velocity of the forward and upward components at impact and it was 36 m/s. After impact, the first decreased and the other increased (up to a point) as noted by you above. I calculated the resultant velocity again when the upward component reached its maximum value, and it was 26 m/s. So, at least for the case when the sideways is ignored, there seems to be a net deceleration.

4. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Yes, of course the hit with the ball deccellerates the racket. And the more solid hit, the more decelleration. I suppose with a brush of the ball there is less.
Someone suggested actually shadow swinging should be measured. Allthough perhaps not 110 % scientific, I think a valid suggestion.

Last edited: Jan 20, 2013
5. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Agreed. I would say acceleration into the ball would increase ball contact, maybe even dwell time.

6. ### sureshsBionic Poster

Joined:
Oct 1, 2005
Messages:
40,493
Actually the opposite. While trying to find some info on dwell time last week, I found a paper (by Rod Cross I think) which stated that dwell time decreases with the speed. I don't remember exactly what speed was, but probably the relative speed of the ball wrt racket.

7. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Yes, but disregarding speed, acceleration might increase dwell time, alltough perhaps marginally. The racket plays catchup with the ball during contact.

8. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
Majority of reasearch disagrees with you

Majority of research disagrees with your sentence:
"If you factor them together, I think it is very likely that the combined sum goes up, meaning that the racket in a lot (most?) of typical modern forehands (and other shots as well) accelerate after and through impact. "
Read John Yandell,Andy Fitzell,read some quotes in a paper by Rod Cross

Last edited: Jan 20, 2013
9. ### dominikk1985Legend

Joined:
Feb 11, 2011
Messages:
6,680
can you summarize their results in one sentence for our convenience?

10. ### OHBHSemi-Pro

Joined:
Aug 8, 2009
Messages:
589
This thread reminds me of a similar debate in the golfing world. They actually did a study of the top pros swing and found that all but one of the top golfers reached their maximum swing speed just BEFORE impact. The one guy who continue to accelerate past impact was Johnny Miller, a man who just happened to be the very best ballstriker on tour at the time of the study.

Most amateurs, tennis and golf alike tend to reach their maximum head speed too early in the swing

11. ### luvfortyBanned

Joined:
Dec 17, 2012
Messages:
1,294
not sure about the point of all this....

trial and error... aint rocket science to figure out how you achieve max ball speed.

12. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Yes but of course the hit slows down the racket/club. But if the racket picks up speed afterwards again, I think it is an indication of that the intention is racket head acceleration through impact (or applying of power through impact if you want). I think intent is a perfectly ok word here btw. But interesting result! And yes swinging too early often results in bad contact I guess.

Last edited: Jan 21, 2013
13. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
True, trial and error, experience, intuition, I guess is the way most of us go. And from shadow swinging myself, and watching others, it seems acceleration through strikezone is normal (and I am not just talking about Marion Bartoli here...). Also it seems intuitive that you apply more momentum by swinging, accelerating, dare I say pull through impact, than by just letting the hand passively follow the racket at a pace previously achieved.

Last edited: Jan 21, 2013
14. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
Golf has different constraints

Golf has different "DISTANCE" constraints
Please see a quote from today's Wall Street Journal below
Some similarities were discussed by Rod Cross
---->
Distance, it seems, is the handicap golfer's version of happiness, the one part of the game for which they are prepared to pay an ever higher price.

"Our research shows that golfers love to hit it long; distance is the number one reason golfers buy a new driver," Cindy Davis, the president of Nike Golf, said in a recent interview. "Plus, as more golfers determine their purchases based on launch monitor testing and club fitting, distance is measurable and even further influences the purchasing decision."
----> the end of quote

15. ### luvfortyBanned

Joined:
Dec 17, 2012
Messages:
1,294
I don't buy that Johnny Miller being the 'only' guy... if interested, check EA Tischler's work.. he categorize golfers into 3 release types - covering, diagonal and extending..... referring to the full release point where both arms are fully extended, which would also be the point of maximum club speed if player shadow swings without ball contact..... and the release point varies from about a foot past the ball (covering), to 2 ft past the ball (diagonal, tiger style), to club almost parallel to ground (extending, and Zack Johnson comes to mind).

it is therefore perceivable that player with later release points reach the maximum speed later, and possible after impact.

but to Tischler's point, all 3 categories are technically valid.

16. ### cornersLegend

Joined:
Jul 31, 2008
Messages:
5,447
If a tennis player is sufficiently skilled at spinning the ball he or she also has no distance constraints. Spin takes hitting long out of the equation and allows a player to swing as fast as possible, and presumably to accelerate after contact, although I don't know if this is done.

I remember reading in Steve Tignor's book on the Borg Mac rivalry that Mac was taught by [Palifax I think] to decelerate this racquet into contact, which might account for the peculiar appearance of this strokes.

I also remember reading that Martina N.'s serve stroke reached maximum acceleration just after ball impact, but I don't remember where I read that and don't even know quite what means.

17. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
I disagree with the first part of the post

I disagree with the first part of the post.
To go a little deeper if I may.
For ATP forehand 3 (see the classification of Yandell et al) the vertical component of the racket head speed has to go from 0 to 20 mph in 11 milliseconds.
It is NOT a piece of cake to achieve it.Some shanks are generated.
The banner example is reasonably skilled Fderer who shanks A LOT during some matches.

18. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
Last sentence

Last sentence-it is NOT true for a serve of Federer-see Andy Fitzell.

19. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
Some little problems with a tennis net

Some little problems with a tennis net for TENNIS (NOT GOLF) should be mentioned as well.

20. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
LAST TIME I checked

LAST TIME I checked it was the TENNIS forum

21. ### luvfortyBanned

Joined:
Dec 17, 2012
Messages:
1,294
he started it

22. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
Systemic Anomaly

Systemic Anomaly has a full thread on this subject.
I would advise to find it.
His expertise is much higher than mine.

23. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
For corners

post #17
1.Converting from the atp forehand 2 to the atp forehand 3 is NOT automatic
muscle strength is ONE of issues but NOT the only one
2.Probably John is a good person 2 ask/talk

Last edited: Jan 21, 2013
24. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
But of course tennis players are also interested in applying power, and spin.

On the other hand it need not be extreme. I am talking about acceleration, not maximum possible acceleration at all costs.

I think that the impact of the ball slowing the racket needs to be taken into consideration. I would guess it is more or less impossible to not have the ball deccelerate the racket at impact. The question is more, does the player also do it.

Which is why spin is important. It is both about applying spin and speed in the right combination. If you were talking about the subject at hand, I am not sure.

Well I do not mind a few golf analogies in the thread. I guess everbody knows there are differences, but it is all good with me.

Last edited: Jan 22, 2013
25. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
I have looked through all his thread titles. There does not seem to be such a thread. But thank you for the advice though.

26. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
I think it is true that it is the ratio between spin and speed that defines the control of the length. (Of course also how high you hit the ball, but that is not the subject here). So I would say Julian is wrong about this.
And yes Mac looks like a good example of someone who does not accelerate a whole lot through the strike zone. Somewhat pushy, but a genius none the less.

Last edited: Jan 22, 2013
27. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Of course you may go a little deeper. But that does not change that the spin/speed ratio is the key to control in topspin shots, whether or not Federer shanks some balls. That is probably just as much due to taking them early. And we less reasonably skilled than Federer people can opt for less acceleration (or just less speed), it does not change the principal at all. So I will have to disagree.

Last edited: Jan 22, 2013

Joined:
Sep 2, 2010
Messages:
1,993
29. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Very interesting, and I think it could be very analogue to a tennis stroke, exept for volleys I reckon.

30. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Thank you, looking foreward to reading!

31. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Fascinating read. It seems that the overall consensus is that there is (and in most cases should be) racket head acceleration right up to contact, and, had it not been for the impact of the ball, through contact.
Concerning whether the hand slows down a little before impact or not, there seems to be a bit conflicting evidence. But a slowing down in foreward speed could be explained by the change in direction of the hand (up and across), and acceleration in these directions, which lessens the foreward component of the hand speed, while overall speed does not go down, as was the hypothesis in my first post.

Last edited: Jan 22, 2013
32. ### dominikk1985Legend

Joined:
Feb 11, 2011
Messages:
6,680

Of course the racket head is decelerating at contact. but I still think you should try to accelerate through contact.

many beginners accelerate too jerky and then slow down by contact. that is bad, a gradual acceleration all the way is better.

however it is also bad to accelerate too late. if you approach to contact slowly and then jerk across violently you will not be effective either since that leads to a "pushing" through the ball. you want to hit, not push it.

this is especially pronounced in the baseball swing. elite hitters in baseball generate their batspeed deep in the swing behind the body so that they can be late and still hit a ball hard while mediocre hitters often reach their max. batspeed more than 30 degrees behind contact. that is wasted either as you are not doing anything after the ball leaves the racket.

so you should make sure to reach top speed at contact but not much before.

I would recommend to swing as hard as you can to a point 5-10 inches in front of the ball and then relax and just let the racket fly (no active deceleration).

33. ### tolyHall of Fame

Joined:
Sep 2, 2010
Messages:
1,993
The speed maybe doesn't go down but acceleration usually does, see http://tt.tennis-warehouse.com/showthread.php?p=6835828#post6835828

34. ### dominikk1985Legend

Joined:
Feb 11, 2011
Messages:
6,680
I think the hand slows down because energy is transferred from the hand into the racket.
in the kinematic chain energy is alway transferred by decelerating the prior body part.

think cracking a whip: the handle is accelerated and then suddenly stopped which causes the whip to crack

Last edited: Jan 22, 2013
35. ### TennisCJCLegend

Joined:
Apr 20, 2010
Messages:
6,073
is anyone really advocating that a players should train to decelerate their stroke at or near contact?

I don't think this is correct if they are advocating decel.

I think take the racket to the ball and accel thru the contact and let it wrap to finish by the opposite shoulder or over the dominant shoulder for extreme top, late hits, or lobs.

But, I find decel on topspin strokes or serves to pretty much result in an error or a poor shot. I think start slow smooth, pull faster thru contact and continue to complete follow thru.

I have never practiced, been taught or observed good players decelerating at or immediately after contact.

So, maybe the racket heat slows due to ball impact. I can believe that due to impact and recoil of the stringbed. But, so what - start smooth and finish strong.

36. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
It is incorrect

It is incorrect
1.The head racket speed decreases AFTER the contact
(when speed means the length of a three dimensional vector)
2.The acceleration is changing the sign at the contact
i.e it is POSITIVE before the contact and NEGATIVE after the contact

37. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
Observation of ATP pros

Observations of APT pros (for example Federer) show that they do NOT accelerate AFTER the contact i.e the racket head speed decreases
See references in the link by toly
It is my last post on this subject in this thread.

Last edited: Jan 22, 2013
38. ### DellonNew User

Joined:
May 24, 2010
Messages:
65
Hi guys,

don't want to hijack the thread, I couldn't create a new one for some reason, I thought this is was a very good read .

The importance of the three ‘L's’ in a world-class forehand

by Raul Saad, USPTA Master Professional

December 2009 -- The modern forehand has become the weapon of choice for most high-performance players.

The majority of world-class players has shifted the traditional baseline "home base" 3 to 5 feet to the backhand side, strategically imposing the power of the forehand over two-thirds of the court. The biomechanical swing on the forehand side has kinetically evolved from a traditional, mild-elliptical swinging pattern to a more extreme and elongated arching motion. This wider arch enables the velocity of the racquet head to continuously increase throughout the swing and makes the energy transfer to the ball more fluid and powerful. However, the biomechanics of a world-class forehand are complex. In this article we focus specifically on key technical components that are a common denominator among top players: the three "L's."

The first and second "L"
One of the commonalities of the world-class forehand originates as the unit rotation begins. As the shoulders and hips turn, top players **** the wrist up, placing the racquet straight up, perpendicular to the court (aided by the nondominant hand). The forearm of the hitting arm and the racquet shaft resemble an "L," with the tip of the racquet head usually higher than the player's own head. The elbow of the hitting arm is typically bent nearly 90 degrees, thus forming the second "L."

The "L" positioning of the elbow and wrist is critical to the ability to generate speed and explosiveness in the forehand. It places the racquet head high above and allows it to begin dropping from this high location in a circular pattern, accumulating velocity at a continually increasing rate throughout the motion. At the bottom of the circular pattern, the racquet will be below the level of the ball and will immediately move forcefully but fluidly forward and up, continuing to accelerate through the point of contact. The player's dominant arm is naturally relaxed throughout the entire elongated motion. In the following photos, the "L" formed by the elbow bending at 90 degrees and the "L" formed by the racquet shaft and the forearm are clearly seen:

The first and second "L" positionings create a longer swing pattern that facilitates not only the continuous acceleration of the racquet head throughout the entire motion, but also the fluid transfer of energy through the kinetic chain.

The third "L"
The third "L" found in world-class forehands refers to the elbow positioning on the forward swing, which is bent typically at around 90 degrees. The exact amount of bending varies from stroke to stroke depending on height of the ball, tactical situation or balance, but the third "L" is consistently present in the majority of world-class strokes. This positioning of the elbow, which acts as a pivoting point, allows the stroke to be "driven" forward through the shoulder, elbow and palm of the hand solidly and with accuracy.

Note that the wrist is also bent, oftentimes at a 90-degree angle in what's commonly known as the "double bend." As discussed earlier, the first and second "L's" elongate the backswing, creating a tremendous amount of racquet speed at the point of contact. The "L"-shaped elbow, coupled with the bent wrist, provides a consistent angle on the racquet face, allowing the player to exert critical control over the high velocity of the racquet head and ball at the point of contact. Furthermore, having the ability to pivot on the bent elbow allows the natural rotation of the forearm, wrist and hand as the ball is struck (commonly known as the "windshield wiper"), imparting a tremendous amount of topspin to the ball. Virtually all world-class forehands use the windshield-wiper arm rotation action and the third "L" facilitates this biomechanical process.

In the following examples, please note that the elbow in the hitting arm is consistently pointing at the rib cage of the player. A common error that lesser players commit is to flare the elbow out (pointing it at the back fence) at the point of contact. That elbow positioning will result in significant loss of velocity and power on the stroke. Furthermore, the "elbow-out" position will impede the smooth rotation of the arm in the subsequent windshield-wiper follow-through. Many world-class players will have the elbow pointing at the back fence in the second "L" phase of the stroke as they take the racquet back (demonstrated in the earlier photos), but the majority of them tuck in the elbow and point it to the ribs immediately prior to the point of contact.

However, not all world-class players use the third "L" in their forehand. The two top players in the world, Rafael Nadal and Roger Federer, bend back their wrists 90 degrees, but straighten their elbow out as the racquet moves forward toward the contact point with the ball. Federer tends to adjust and bend the elbow slightly depending on the situation, whereas Nadal fully straightens the elbow, almost locking it. The athleticism and eye-hand coordination needed to strike the ball successfully with the arm straight is exceptional, but the fact that the two best current players in the world employ this technique perhaps reveals glimpses of the forehand of the future.

It is clear that in order to become a top performance player, developing the forehand as a weapon is a must. Top players have a variety of styles and techniques, but this article focused specifically on the biomechanical common denominators of a world-class modern forehand - the three "L's." Players wanting to improve their forehand should experiment with the concepts presented here, including the "straight arm" forehand, and incorporate what works and feels natural into their game.

39. ### julianHall of Fame

Joined:
Dec 20, 2006
Messages:
4,109
Location:
Bedford,Massachusetts,US
i meant the link listed by toly above

I meant the link listed by toly above
Systemic anomaly has posts overthere to read.
As I have said "I am out of this thread"

40. ### tolyHall of Fame

Joined:
Sep 2, 2010
Messages:
1,993
Hand and racquet operate as unit. So, how the hand can transfer energy to the racquet by using its deceleration? It’s impossible.

41. ### dominikk1985Legend

Joined:
Feb 11, 2011
Messages:
6,680
do they measure the actual hand or wrist joint?

42. ### tolyHall of Fame

Joined:
Sep 2, 2010
Messages:
1,993
It doesn’t matter. Rotation of the hand and racquet about wrist accelerates/decelerates together because they rotate as single unit.

43. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
This is just about what I would say. An exeption could be sometimes when you return a very fast shot, and you more counterpunch/block/lead the ball back.

Last edited: Jan 25, 2013
44. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Intuitively, I do not think its the stopping that causes the whip to crack, but the movement before, it is just delayed somewhat. But to crack a whip more, you can pull back a little, which might be in line with the pulling across the body.

45. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Which is why ofcourse the hand speed will also be slowed by the impact of the ball, I guess.

46. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Fair enough. Though I was curious to your answer to my post nr 27 , and also to which obeservation of Federer you were specifily referring to.

47. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Perhaps in a well timed shot you could consider the feel of the impact as a sign to stop accelerating, or to start going from acceleration to deccelleration. In that way you will have accelerated through impact, and of course you finish with a full followthrough, and no abrupt stopping.

Last edited: Jan 25, 2013
48. ### dominikk1985Legend

Joined:
Feb 11, 2011
Messages:
6,680
well physically energy is transfered by decelerating the prior body part. pulling back has the same effect as stopping.

successive accelerating and decelerating body parts is the foundation of the kinetic chain.

49. ### Povl CarstensenLegend

Joined:
Jun 14, 2004
Messages:
5,893
Allright, I am no expert in these matters. I do find it interesting and important though, that the body and racket is more than just a whip. Muscle action influence the movement of all the joints involved in minute and decisive ways. It is like you have the kinetic chain as the basis, and then the muscle control of the final resulting motion on top of that.
If that makes sense. I have been at the computer for too long...