Rotation Axes & Racket Head Speed

Chas Tennis

G.O.A.T.
If there is a rotation axis and an object is rotating around that axis,

the speed of the object is

r (radius) X rotation rate

Where the radius is found by first finding and drawing the axis, including extending the axis beyond the object. Then you just draw (or imagine) the radius perpendicular to the rotation axis. Much of racket head speed in tennis strokes is produced by an object rotating around one or more axes. The object may be above or below the body part with the axis, but still the important thing for speed is that same r, measured perpendicular to the rotation axis.

Frequent rotation axes for ground strokes are the
Spine (observe the line between the two shoulder)
Shoulder Joint (observe the upper arm)
Elbow
Wrist (observe the racket shaft)

These axes can be used together or sequentially, one after the other. For ground strokes, often the forward swing starts with spine rotation & its axis and then the shoulder rotation & its axis occurs with timing that can be clearly seen in high speed videos. The spinal rotation is usually the most significant for building racket head speed, it rotates the entire shoulder joint. For stroke details look at high speed videos.


Rec players typically use more shoulder and less spine for their ground strokes. They may not be clear about their main rotation axis and they may not be aware of the distance from their racket head to an important rotation axis.

Determine your main rotation axes that provide the most speed for your strokes. Observe the timing and racket positions for each axis in ATP and WTA ground strokes.

Remember that if you bring the racket head or some body part closer to a rotation axis, it will not pick up as much speed from the rotation. Notice that the pros don't bring the racket head close to their rotation axes and the rec players may.

This detailed post compares a pro player, Gasquet, and Mojo28 frame-by-frame. Note - the rotation axis through the neck area for Gasquet and the racket head's distance from the rotation axis.
This post from another thread shows a comparison and analysis of poster Mojo28's one hand backhand drive and Gasquet's from the start of the forward racket motion. Note the chest and upper arm of the high level backhand.

[ Note for new readers - It is necessary for this analysis to understand the defined joint motions of internal shoulder rotation (ISR) and external shoulder rotation (ESR). The upper arm between the shoulder joint and elbow does not go anywhere, it just spins like a top around the upper arm's center line.]

Pictures of each frame of Mojo's video. The time scales are in milliseconds with "0" milliseconds being impact. -267 milliseconds is about 1/4 second before impact.

I point out differences between better high level strokes and the poster's strokes. A poster can select a high level stroke and copy it or use some other stroke model. Or, go with instruction or on their own without a model or instruction.

Mojo's ball is lower than Gasquet's. Compare similar ball heights for better analysis.

Frame at -267 ms. It looks as if at 267 milliseconds before impact the OP has turned his shoulders back to about the same angle as Gasquet has. Compare also shoulder turn angles at impact, at Frame -0 ms. The positions of the arms and rackets are different. Gasquet's racket has not come down and is still in front of his body. Is Mojo copying some other backhand stroke? Mojo has also done pronation to bring the racket down. Impression is that Mojo is doing his own thing. ? (To see angles more accurately, the cameras for both backhands need to view the players and courts from the same angle. Wear tight fitting clothes or a short sleeve shirt to better see the upper arm, elbow angle, etc.)


Frame at -233 ms. Mojo has brought his racket farther down. Gasquet's racket has gone up slightly. Mojo's elbow looks bent more and his upper arm (between the shoulder and elbow) has more downward rotation (ISR). Compare ISR angle to ISR angle as these frames progress.


Frame at -200 ms. Mojo's racket is still lowering and low. Gasquet's is just starting to lower.


Frame at -167 ms. Mojo's upper arm is down from the shoulder joint. Gasquet's upper arm is more across the chest.


Frame at -133 ms. Mojo's racket still lowering. Gasquet's now lowering with more rapid drop.


Frame at -100 ms. Mojo's upper arm is down at the chest. Gasquet's upper arm is more across the chest. Gasquet now appears to have started more upper body turn. I believe that to produce this early arm and racket acceleration that Gasquet is pressing hard on his upper arm with his chest powered by the forces of turning his upper body. If a credit card were between his chest and upper arm, would it be pressed tightly? How much upper arm pressing Mojo is doing this is not clear (due to the obscuring shirt and arm angle). But his upper body does not appear to be turning as rapidly.


Frame at -67 ms. The racket head speed developed by any rotation depends on the location of the axis of rotation and the distance out from that rotation axis. Look at the arm and racket angle and the distance out from the location of the rotation axis (guessed for now). It looks as if Mojo's arm angle is not favorable for racket head speed. Also, Mojo's racket is already much more rotated toward the ball trajectory. Gasquet's racket is >180° back from the ball's trajectory. Gasquet's upper arm is pressed to his chest as discussed.


Frame at -33 ms. Look at the racket to ball trajectory angle for Mojo, 45°? Look at the racket to trajectory angle for Gasquet still >180°. The total turns of Mojo's and Gasquet's upper bodies from Frame -267 ms seem somewhat similar, similar average speeds. The upper arm and racket have been used differently. Another motion - now look at the elbow bones and estimate the angular position of internal shoulder rotation, or axial rotation of the upper arm in the shoulder joint. Compare ESR from -33 ms to -0 ms.


Frame at -0 ms closest to impact. The big differences from Frame -33 ms to Frame -0 ms are the angular movement of Gasquet's racket and the much larger movement of his hand in the forward direction in comparison to Mojo. Also, Mojo's racket is open and Gasquet's is closed at impact. Possibly the ball height was a factor in how closed the racket was.? Now look at Gasquet's elbow bones and compare them to Frame -33 ms. Gasquet has done rapid external shoulder rotation (ESR) from Frame -33 ms to Frame -0 ms. That has moved the racket up and added to the topspin that the upward hand path already would have produce without ESR. Because Gasquet brought down his racket earlier with a near straight arm, it caused rapid ISR and pre-stretched his ESR muscles, he is using those stretched muscles in this frame. (Search the Stretch Shorten Cycle).


Frame at +33ms after impact. Mojo's hand and racket go more forward. Gasquet's goes more forward and up. ESR has continued.


Frame at +67 ms. Comparison of the follow throughs.


Video.

Last edited: Mar 5, 2017"
What do you think about rotation axes?
 
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Raul_SJ

G.O.A.T.
The spinal rotation is usually the most significant for building racket head speed, it rotates the entire shoulder joint.
Just so that readers are clear. Rotation along the long axis (spine) is independent of rotation along the hitting arm shoulder.

Rotation along the long axis (spine) is simply rotation of both shoulder girdles. The rotation of the upper hitting arm is referred to external and internal shoulder rotation.

 

RobS

Rookie
Kinetic chain, length of lever, etc. This is good stuff. One of the key byproducts I have found when I can actually incorporate this and sequence properly is how relaxed I can maintain my shoulder, arm and wrist and how much harder I can hit the ball with minimal stress on my smaller muscle groups.
 

Chas Tennis

G.O.A.T.
Just so that readers are clear. Rotation along the long axis (spine) is independent of rotation along the hitting arm shoulder.

Rotation along the long axis (spine) is simply rotation of both shoulder girdles. The rotation of the upper hitting arm is referred to external and internal shoulder rotation.




If the spine accelerates to rotate at 300 degrees per second and the shoulder joint itself is not rotating, then the shoulder mass and upper arm are rotating at 300 degrees per second. Then the shoulder joint may also accelerate and rotate. Perfect illustration above. Serena does not seem to be doing much joint shoulder rotation before impact. Do not assume that all ground stroke techniques are the same for these spine & shoulder sub-motions. See the videos.

Federer one hand backhand. Early shoulder joint sub-motion technique, differs from Gasquet, Justine Henin and Wawrinka.

Could someone show some two hand backhands to see how they look?
 
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Raul_SJ

G.O.A.T.


If the spine accelerates to rotate at 300 degrees per second and the shoulder joint itself is not rotating, then the shoulder mass and upper arm are rotating at 300 degrees per second. Then the shoulder joint may also accelerate and rotate. Serena does not seem to be doing much shoulder rotation.
Presumably, the ISR of the upper hitting arm primarily drives the RH tip speed.
See the Toly chart...


Frame #RH Tip Speed
111 mph
28 mph
39 mph
412 mph
517 mph
619 mph
733 mph
859 mph
980 mph



Roughly which Frame# does Serena move from ESR to ISR?


 

a12345

Professional
Just so that readers are clear. Rotation along the long axis (spine) is independent of rotation along the hitting arm shoulder.

Rotation along the long axis (spine) is simply rotation of both shoulder girdles. The rotation of the upper hitting arm is referred to external and internal shoulder rotation.

Note theres is a 3rd variable of rotating around the shoulder that doesnt involve internal and external shoulder rotation.

Its basically doing the torso rotation pivoting around the right shoulder/right leg axis. Many ATP players do this.

However I believe that pivoting around the spine/head is better.
 

Raul_SJ

G.O.A.T.
If the spine accelerates to rotate at 300 degrees per second and the shoulder joint itself is not rotating, then the shoulder mass and upper arm are rotating at 300 degrees per second. Then the shoulder joint may also accelerate and rotate. Serena does not seem to be doing much shoulder rotation

Forget how these two different velocities are measured (two shoulder girdles rotating along with long axis spine rotation versus upper hitting arm shoulder rotation). And if there are any differences in measurement in long axis spine rotation versus the much faster internal shoulder rotation. But I believe the key measure is rotational velocity of the upper arm hitting shoulder, the ISR of the hitting shoulder.

I can drop feed, with very little long axis spine rotation, and generate great RH speed with hitting arm shoulder rotation!

This is from a serve study, but this principle applies to forehand as well.

The shoulder joint is integrally involved in the service action, with rotational velocities of approximately 3000°.s−1 developed through large ranges of motion (∼270° circumduction), believed to contribute ∼20% of the total force generated during the stroke.1
 
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Chas Tennis

G.O.A.T.
Note theres is a 3rd variable of rotating around the shoulder that doesnt involve internal and external shoulder rotation.

Its basically doing the torso rotation pivoting around the right shoulder/right leg axis. Many ATP players do this.

However I believe that pivoting around the spine/head is better.
Please show a video of the "right shoulder/right leg axis".
 

a12345

Professional
Tsitsipas here is using a right side rotation pivoting around the right shoulder/right leg.


Federer turns via his spine:

 

Chas Tennis

G.O.A.T.
Tsitsipas here is using a right side rotation pivoting around the right shoulder/right leg.


Federer turns via his spine:

This thread was to bring attention to rotations, axes and some things to understand, for example, how far the racket head should be from the axis and why.

Demo.

We a going to list several sources of rotation of the uppermost body, working up from the feet. Do each of these separately following instructions. Everything above the numbered body parts will rotate.
1) Feet. Take a racket in your hand, arm out to the side from the shoulder. Can you move your feet so that nothing else changes but that your uppermost body rotates around an axis through the neck area? (The neck and head can rotate too.)

2) Knees and hips. Can you move only your knees and hips in such a way that your uppermost body rotates around an axis in the neck area. Leg forces on the hips cause the pelvis to rotate and the bottom of the spine is attached to the pelvis. Note effect on uppermost body.

3) Abdominal & Spinal Muscles. Can you use only your abdominal and spinal muscles by twisting to cause your uppermost body to rotate through an axis in the neck area?

4) Shoulder Joint. Can you use only your shoulder joint to swing your upper arm forward around an axis through the shoulder joint?

5) Wrist Joint. Can you use your wrist to move the racket head forward. This is not to say the stroke should be powered by the wrist.

These sub-motions and others are available for racket head speed. Look at videos to see what is used.

The purpose of the thread is to point out the rotation axes, the location of axes, and the distances from the racket head to these axes.

Lots of details are left out to see the basic rotation rate vs racket head speed based on the radius. The radius depends on the angles of shoulder, elbow, wrist and racket shaft. Videos can show the angles and the radius. At the right camera angles, the radius can be measured.

When you look at an WTA or ATP player's uppermost body and see it rapidly turn your are seeing #1), #2) and #3) with a rotation axis through the neck area. The shoulder joint may also be used before impact, and then you see #4).

Dan Brown talking about the circular forehand vs the linear 'step forward' forehand. This video has a lot of information to listen to.
 
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Chas Tennis

G.O.A.T.
Rotation axes for a baseball batter.

Note the significant rotation axis through the neck area, the shoulder's chest-upper arm contact not changing much in forward swing, the use of the right arm, the additional rotation of the bat from a wrist area axis before impact.
 
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pencilcheck

Hall of Fame
This thread was to bring attention to rotations, axes and some things to understand, for example, how far the racket head should be from the axis and why.

Demo.

We a going to list several sources of rotation of the uppermost body, working up from the feet. Do each of these separately following instructions. Everything above the numbered body parts will rotate.
1) Feet. Take a racket in your hand, arm out to the side from the shoulder. Can you move your feet so that nothing else changes but that your uppermost body rotates around an axis through the neck area? (The neck and head can rotate too.)

2) Knees and hips. Can you move only your knees and hips in such a way that your uppermost body rotates around an axis in the neck area. Leg forces on the hips cause the pelvis to rotate and the bottom of the spine is attached to the pelvis. Note effect on uppermost body.

3) Abdominal & Spinal Muscles. Can you use only your abdominal and spinal muscles by twisting to cause your uppermost body to rotate through an axis in the neck area?

4) Shoulder Joint. Can you use only your shoulder joint to swing your upper arm forward around an axis through the shoulder joint?

5) Wrist Joint. Can you use your wrist to move the racket head forward. This is not to say the stroke should be powered by the wrist.

These sub-motions and others are available for racket head speed. Look at videos to see what is used.

The purpose of the thread is to point out the rotation axes, the location of axes, and the distances from the racket head to these axes.

Lots of details are left out to see the basic rotation rate vs racket head speed based on the radius. The radius depends on the angles of shoulder, elbow, wrist and racket shaft. Videos can show the angles and the radius. At the right camera angles, the radius can be measured.

When you look at an WTA or ATP player's uppermost body and see it rapidly turn your are seeing #1), #2) and #3) with a rotation axis through the neck area. The shoulder joint may also be used before impact, and then you see #4).

Dan Brown talking about the circular forehand vs the linear 'step forward' forehand. This video has a lot of information to listen to.
That Dan Brown's video is a reminder for me how NOT to hit.
 

Chas Tennis

G.O.A.T.
That Dan Brown's video is a reminder for me how NOT to hit.
In what regard?

The injured knee on the ground during the before forehand looks stressful to me. Is that what you mean?

Dan Brown mixes his description very well with clear high speed videos. He divides the forehand up into sub-motions and illustrates them clearly with high speed videos. He shows how identically the uppermost body turns for the linear and circular forehands by overlaying videos of each technique directly. I have never seen that.

This is the clearest description of the circular vs the linear forehand technique that I have seen - it probably is the only one.

The video was posted on Youtube in 2007. I wish that he were still making clear tennis stroke analysis videos.

Thread with posts discussing Dan Brown's forehand video.
 
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pencilcheck

Hall of Fame
In what regard?

The injured knee on the ground during the before forehand looks stressful to me. Is that what you mean?

Dan Brown mixes his description very well with clear high speed videos. He divides the forehand up into sub-motions and illustrates them clearly with high speed videos. He shows how identically the uppermost body turns for the linear and circular forehands by overlaying videos of each technique directly. I have never seen that.

This is the clearest description of the circular vs the linear forehand technique that I have seen - it probably is the only one.

The video was posted on Youtube in 2007. I wish that he were still making clear tennis stroke analysis videos.
Not only the knee, but also forced tennis elbow, also injured left leg.

This way of hitting is not that efficient, most likely will get blown away against high looping ball easily. It also has no power and cannot penetrate and put spin into the ball.

The only way to redeem using this technique is to practice a lot of calves movement, and then you will have injury in your feet pulling muscle there.

Basically this is a flawed, injury prone and useless technique. I wouldn't even try to learn it.
 

Chas Tennis

G.O.A.T.
Not only the knee, but also forced tennis elbow, also injured left leg.

This way of hitting is not that efficient, most likely will get blown away against high looping ball easily. It also has no power and cannot penetrate and put spin into the ball.

The only way to redeem using this technique is to practice a lot of calves movement, and then you will have injury in your feet pulling muscle there.

Basically this is a flawed, injury prone and useless technique. I wouldn't even try to learn it.
In the video, Brown is trying to correct a linear forehand that stresses the left knee and replace it with a circular forehand with less left knee stress. In the circular forehand, his foot is off the ground as his body & leg rotates, less stress to the knee. Which of the two ways are you discussing?

I can see his separation is not adequate. His lag looks as if it should be compared to ATP player's lags. Is the lag and coming out of it what you objected to, "forced tennis elbow"?

The player is a NTRP 4.5 that has transitioned from a linear forehand to a circular forehand.

He could be still be compared to 2021 ATP players and differences would show up. There may be some differences because the forehand technique taught in 2007 by Dan Brown is likely different than the ATP forehand techniques of 2021.

To describe your points in the video, you can identify frames by going to impact and counting back. For example, 'the forehand at 34 sec, 10 to 6 frames before impact, the elbow shows "forced tennis elbow".......'

Compare forehands frame-by-frame, one above the other. To single frame on Youtube use the period & comma keys. Always select the video using alt key + left mouse click, otherwise the video starts playing.
 
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pencilcheck

Hall of Fame
In the video, Brown is trying to correct a linear forehand that stresses the left knee and replace it with a circular forehand with less left knee stress. In the circular forehand, his foot is off the ground as his body & leg rotates, less stress to the knee. Which of the two ways are you discussing?

I can see his separation is not adequate. His lag looks as if it should be compared to ATP player's lags. Is the lag and coming out of it what you objected to, "forced tennis elbow"?

The player is a NTRP 4.5 that has transitioned from a linear forehand to a circular forehand.

He could be still be compared to 2021 ATP players and differences would show up. There may be some differences because the forehand technique taught in 2007 by Dan Brown is likely different than the ATP forehand techniques of 2021.

To describe your points in the video, you can identify frames by going to impact and counting back. For example, 'the forehand at 34 sec, 10 to 6 frames before impact, the elbow shows "forced tennis elbow".......' To single frame on Youtube use the period & comma keys.
Just try to play like him in any point rallies or point play you will know what I mean.

If you don't, that goes to show you need to play more tennis.

Hints:
1. narrow optimal contact points
2. running side ways
3. changing directions
4. high bouncing balls
5. related to 4, ball with no pace

Any of the above would result in more injuries as he will attempt to exert more on muscles that weren't intended to be stressed. Next thing you know, he will be out of tennis for 7-8 years the moment he pass 30-40+
 

Chas Tennis

G.O.A.T.
For learning new strokes, I believe that the player should have no pressure, little movement and try to hit a heavier paced shot. The 4.5 player appears to be doing that. After they have that they can add movement and high and low balls and adapt to those as best they can.

My standard for tennis stroke techniques is the top 100 ATP players with the variety that is out there to be handled with statistics (that I usually don't have on hand). I use high speed videos for comparisons so that the stroke positions are clearly seen.

I'd say that the 4.5 player is trying to hit a high pace shot, with his best technique and is using his right leg more forcefully than most ATP players in the compilation. The 4.5 player has stronger vertical motion than most in the compilation. I'll have to compare similar movements to the ball, similar pace struck, a hard hit. Disregard all low pace practice or warm up forehands. It looks like a lot of variety in the ATP foot work that disqualifies many forehands because of different movements to the ball. Nishikori has a strong jump to his forehand with feet often off the ground, maybe his forehand would make a good comparison.

My purpose in showing the Dan Brown video was not to say, 'hit your forehand like this 4.5 player', it was to show a linear vs a circular forehand technique and many other observations and insightful comments by Dan Brown.

I can't figure out what to look for by your points in post #14 or the "Hints" in post #16. If you could point out your video observations to support one of your points, I might understand more clearly.
 
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a12345

Professional
Not only the knee, but also forced tennis elbow, also injured left leg.

This way of hitting is not that efficient, most likely will get blown away against high looping ball easily. It also has no power and cannot penetrate and put spin into the ball.

The only way to redeem using this technique is to practice a lot of calves movement, and then you will have injury in your feet pulling muscle there.

Basically this is a flawed, injury prone and useless technique. I wouldn't even try to learn it.
The legs driving up to initiate the stroke is one of the most fundamental building blocks of every stroke.

Forehand , backhand, serve, the power starts from driving the legs up.
 

pencilcheck

Hall of Fame
The legs driving up to initiate the stroke is one of the most fundamental building blocks of every stroke.

Forehand , backhand, serve, the power starts from driving the legs up.
There are also many ways to do so. Dan Brown's way is but only one way.
 
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