Demo of Internal Shoulder Rotation vs Pronation

[Chas Tennis]

There is widespread ignorance among most tennis players about how the high level serve - as seen in the ATP - is being done.

These demos show the defined basic joint motions, without describing the complex motion of the serve.

Pronation - Bend your right elbow 90 degrees. Place your elbow on the arm of your couch. Rotate your wrist so that you see the back of your hand and then the palm. If your elbow is on the arm of the couch, then you are seeing only forearm Pronation & Supination. Pronation is caused by muscles and bones in the forearm.

Internal Shoulder Rotation ( Medial Shoulder Rotation in many countries)- With a straight arm, held straight out from your shoulder, rotate your wrist so that your palm faces up and then down. With practice, you can quiet down the pronation and do these motions only with Internal Shoulder Rotation & External Shoulder Rotation. Internal Shoulder Rotation is caused by muscles and bones in the back and not the arm. The upper arm bone, humerus, rotates.

Google: pronation Youtube

Google: internal shoulder rotation Youtube

In the 2022 Tennis Serve Nuthouse, most active tennis players do a different technique called a Waiter's Tray technique. Most serving instructional videos don't mention or demonstrate ISR.
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Analysis of high speed videos of ATP servers show the serving technique which is not described here.

 

[ballmachineguy]

The important thing is that regardless of the terminology, I do the same thing. I keep yelling at my dog “You’re a cat! You’re a cat!” Yet, he still barks.

 

[kaninfaan]

The important thing is that regardless of the terminology, I do the same thing. I keep yelling at my dog “You’re a cat! You’re a cat!” Yet, he still barks.

Language is for talking to other people. If youre just gonna talk to yourself you're free to make up your own words.

 

[TennisCJC]

Chas, does a high level serve have both ISR and pronation? Seems like they are closely related. I think there is movement in both my shoulder muscles and forearm when I rotate the palm out when serving. Tennis coaches have been using "pronation" for decades and ISR seems to be a fairly new way of teaching the serve. I've seen your videos and there is no doubt that the shoulder is a big driver of the arm rotation but to me even as I just take a shadow swing, it feels like both the shoulder and the forearm are working together. But, I can see where working on ISR can be a good concept to improve the serve.

 

[Chas Tennis]

Chas, does a high level serve have both ISR and pronation? Seems like they are closely related. I think there is movement in both my shoulder muscles and forearm when I rotate the palm out when serving. Tennis coaches have been using "pronation" for decades and ISR seems to be a fairly new way of teaching the serve. I've seen your videos and there is no doubt that the shoulder is a big driver of the arm rotation but to me even as I just take a shadow swing, it feels like both the shoulder and the forearm are working together. But, I can see where working on ISR can be a good concept to improve the serve.

Most of the service motion involves stretching muscles for ISR. If you do shadow swings that is not true.
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When the elbow is straight ISR and pronation produce the same effect on the wrist.

Wrist Rotation Angle = Pronation Rotation Angle + ISR Rotation Angle

(That is not true when the elbow is bent.)

If the entire arm is straight and ISR produced strong rotational acceleration and then the acceleration stopped before impact, ISR would then slow, pronation might then occur without the use of the pronation muscles, because of the inertia of the forearm and racket. That might happen anywhere and happens after impact with the 'fully pronated' follow through. I mostly ignore after impact.

Pronation vs ISR could be determined if you were able to measure both the wrist rotation angle and the upper arm rotation angle. If the wrist rotates at the same rate as the upper arm, that is all ISR. If the upper arm rotation rate was slower than the wrist rotation rate, wrist rotation would be both pronation plus ISR.

Why Don't We Know for Sure? In order to observe human motions, 3D Motion Capture Systems are used. These systems are also used to make video games look realistic. Reflective balls are placed on parts of the body and recorded by several video cameras. For human motions, reflective ball position data is processed in computers and used to make video games look realistic. These same 3D systems are used to measure tennis strokes at frame rates to 500 fps.

But there is a problem. In 2008, Brian Gordon published that measurements of long axis rotations for the serve had large errors. This was because the reflective balls were mounted on the skin and their rotation lagged behind the rotation of the bones. The bone motion defines the joint motions, not the motion of the skin. This is seen in serve videos as flesh flopping around in high speed videos. So 3D Motion Capture Systems have a problem in observing ISR rotation. Wrist rotation is easier to measure because the bones of the wrist have less muscle and minimal flesh so you can observe how the wrist is oriented.

Elbow Shadows. The elbow also had structures that rotate very much with the humerus of the upper arm. The high and low points of bones and some tendons cast shadows that indicate the upper arm's rotation angle. Some of these bone and tendon structures cast shadows that show ISR. But shadows change with rotation so measurement techniques need to be explored. Maybe some improvements have been made in 3D MCSystems for long axis rotations. ?

In other words, measuring ISR and pronation on the serve accurately may not be available yet.

But ISR can be demonstrated in high speed videos by elbow shadows. I think it might be feasible in videos to make estimates, for example, ISR to impact was between 40-60 or 70-90 degrees. The accuracy might be better with a calibration technique applied after the serve. But the server must cooperate and have a shadow to degrees calibration procedure done after the serve - no doing measurements from internet videos.

From high speed videos during the serve, I can observe ISR sometimes with elbow shadows. I usually can't see a difference between ISR and the wrist rotation. My estimated of angles are not very accurate. For example, 'That might have been 90 degrees of ISR from start to impact.' But I don't want to estimate the +/- .

Optics has a great capability of imaging the elbow and its shadows very close up that has not been explored.

 

[Dragy]

Chas, does a high level serve have both ISR and pronation? Seems like they are closely related. I think there is movement in both my shoulder muscles and forearm when I rotate the palm out when serving. Tennis coaches have been using "pronation" for decades and ISR seems to be a fairly new way of teaching the serve. I've seen your videos and there is no doubt that the shoulder is a big driver of the arm rotation but to me even as I just take a shadow swing, it feels like both the shoulder and the forearm are working together. But, I can see where working on ISR can be a good concept to improve the serve.

The question is what's the sequence and when pronation actually appears in the motion and how much it contributes to RHS. There's no reason to do ISR+pronation simultaneously, as this will make weaker forearm muscles work against the inertia coming from powerful twist by ISR. So as long as ISR is accelerating the racquet around, forearm better stay in stretched supinated position.

Here's good video of Fed close-up swing. On the still you can see that elbow pit flat faces the camera by the moment (which is close to full ISR, elbow points back and up now), while palm still faces mostly down, and stringbed - forward and down. This is just minor shift from full supination towards neutar - you can experiment with your own arm. This indicates, that all the way up to impact it's dominantly ISR-driven, with pronation happening through "release" brief instance, and into follow-through.

Video marked at 0:51

 

[Dragy]

Here forearm is pronated, while elbow position hasn't changed no more. It's how follow-through occurs

 

[socallefty]

Read these papers. My interpretation is as per the below post on what happens. Both pronation and ISR happens as per the Elliott paper.

The 8 stage model is a good paper for evaluating the serve by Mark Kovacs and Todd Ellenbecker.
Contributions of Upper Limb Segment Rotations During the Power Serve in Tennis by Elliot et al.
Long Axis Rotation: The missing link in proximal-to-distal segmental sequencing by Marshall and Elliot.

Thank you very much. The three papers you listed are exactly what I was looking for as they show pictures and descriptions including rotation/velocity/timing data of the shoulder/hand/wrist movements. The second paper by Dr. Elliott that you attached in particular is pure gold in terms of understanding what is going on.

As I interpret it, the twisting to make the strings hit the ball instead of the edge of the frame is forearm pronation and he shows timing and extent of forearm pronation in both his papers. Here is detail from Dr.Elliott - “Forearm pronation therefore plays a dual role in developing racket speed prior to impact while also positioning the racket head for impact”.

So, I think he is saying that forearm pronation is required to position the racquet properly for impact - from seeing the pics, I think the edge would hit the ball without this positioning using forearm pronation. There is a second stage of forearm pronation that happens after contact also during the finish as illustrated in Dr. Kovacs article which helps some players finish with the racquet away from the body with strings facing out - but, that is different from the pronation (with timing graphs shown) before contact in Dr. Elliott’s paper.

However, the papers show that internal shoulder rotation and wrist flexion generate most of the racquet head speed and power at contact especially if accompanied by shoulder abduction at the optimal 100+/-10 degree angle. (Detail from Dr Kovacs paper - ”The mean shoulder abduction just before contact is approximately 100° which is similar to the 100° ± 10° angle to produce maximal ball velocity and minimal shoulder joint loading in baseball pitching. This suggests an optimum contact point of 110° ± 15° for the tennis serve. At ball contact, ball velocity is determined by shoulder internal rotation and wrist flexion. Elbow flexion (20° ± 4°), wrist extension (15° ± 8°), and front knee flexion (24° ± 14°) are minimal at contact. Trunk is tilted 48° ± 7° above horizontal in Olympic professional tennis players”.)

Coaches are validated in using the term pronation to explain to students how to hit the ball with the strings after coming on edge with a continental grip as opposed to a pancake serve. Chas and others are correct in stating that to generate high pace, focus on having the proper sequence to maximize shoulder ISR - but, wrist flexion is key too at contact to generate power along with shoulder abduction at the optimal angle).

I highly recommend the scientifically inclined to read the three papers that @Digital Atheist attached as there are clear explanation for each segment of the tennis serve. I agree that coaches and players can teach and learn by being shown the proper motion in sequence and don’t have to understand all these terms. However, understanding them at least will prevent us from throwing the wrong terms around or giving wrong information. I think there was a lot of wrong information posted on this thread by posters incorrectly understanding ISR partly due to the position taken by some that only ISR is happening for the entire forward motion of the racquet - there is a lot more going on than that while ISR contributes to more than half of the racquet head velocity at contact.

Thanks, all!

 

[Dragy]

Read these papers. My interpretation is as per the below post on what happens. Both pronation and ISR happens as per the Elliott paper.

The 8 stage model is a good paper for evaluating the serve by Mark Kovacs and Todd Ellenbecker.
Contributions of Upper Limb Segment Rotations During the Power Serve in Tennis by Elliot et al.
Long Axis Rotation: The missing link in proximal-to-distal segmental sequencing by Marshall and Elliot.

It's important to understand that the values presented describe what happens at contact, with no reference to passive hinging vs active driving, as well all the shades in between. My take on it, which foundation comes from papers and then supported by high speed video observations and finally tested personally, to a degree I can deliver... My take on it is that there's the loading+acceleration phase (1) and then the release/pivot phase (2).
(1) happens through drop and coming up out of the drop. Here we inject max power from shoulder going around and over (cartwheel) and from arm twisting into ISR after being stretched. Racquet picks up speed as a whole, with minor rotation - racquet head is trailing behind the accelerated hand
(2) happens as arm straightens fully and continues into ISR, hence pulling the handle with change of direction. Relaxed (or moderately controlled) wrist and forearm allow racquet head to pivot with huge acceleration, up and around. This "smart" hinge combines wrist flexion, ulnar deviation and pronation to deliver the racquet pivot - rather than power it. I'm confident enough to say, that pronation here is more responsible for racquet head flattening for less spinny serves. There's a tad "longer" release phase for flat serves, while spin serves cut into the ball straight away, before ISR and further pronation open the stringbed too much.

 

[Chas Tennis]

Note - the words 'supination' and 'pronation' as well as ISR and ESR can be used to indicate both the angle of a joint OR the motion of a joint. Example, a joint may be at an angle of supination and be doing pronation (in the direction of maximum pronation). Confusing, yes, but that is how the joint terms are used. Consider the context.

If the racket is moving at 100 MPH and and impact occurs, then there is the follow through. 'Fully pronated' involves pronation.
All ATP servers do not do 'fully pronated'. I mostly ignore the follow through since the server has options that do not matter after impact.

When the arm is supinated prior to ISR start, it goes from a supinated angle by pronation motion while the elbow is still bent.

This shows the angle of supination while the motion of pronation is occurring leading to the first red arrow. Toly composite picture.

But at the lower red arrow, when the elbow is near straight, ISR starts and rotationally accelerates the entire arm, say, up to a racket head speed of 100 MPH. That is the significant part of the serve that was missed by all until 1995.

Now consider pronation during that strong ISR rotational acceleration and whether it is possible.

Effect of ISR Acceleration on Pronation. Consider an astronaut in a rocket. He is on a bench doing chest presses, and can press 100 lb. With earth's gravity of 1 G, he can press 100 lb. The rocket fires while he is pressing the barbell and the acceleration is then 3G. He can't press the weight any longer during rocket acceleration. For the serve, when ISR occurs strongly, is any pronation occurring? Then when strong ISR acceleration stops what would prevent pronation from occurring.

These thoughts are based on Newton's equation,

F = ma, Force equals Mass times Acceleration.

It seem questionable to me - that during strong ISR acceleration - that pronation could occur. ?

On the other hand, if strong ISR rotation forces stop before impact, ISR motion itself continues, and pronation might occur because of inertia or muscular pronation effort.

Getting measurements for the angular rotation rates of ISR and pronation rotation rates in this discussion has been shown to be difficult. We have discussed, that measurements with 3D Motion Capture Systems have a problem with long axis rotations. And that elbow shadows would require developing a technique and volunteer high level servers. (Some ATP players could help us out.)

I have shown many ATP videos that indicate strong ISR - start of ISR to impact - of the uppermost arm bone. I have tried to observe pronation during the time of the two red arrows above, but don't have anything yet.

Consider-
pronation during each phase of the serve. Pronation can be seen at times as discussed.
pronation during the ISR leading to impact
pronation after impact in the follow through including 'fully pronated'
pronation that occurs because ISR forces and acceleration has stopped, perhaps before impact.
pronation that occurs with muscular forces (of the pronation muscles) vs pronation that is occurring without pronation muscular forces.

Leading to impact, you can see that ISR is the most significant joint motion and pronation is hard to observe.

You don't know until you can measure pronation during the serve.

This thread suffers from each poster's understanding and usage of 'pronation'.

New Year's Resolution - avoid embarrassment, ditch the word pronation incorrectly used for the serve.

 

[Chas Tennis]

Demo of active range of pronation, ISR and both together. And same for ESR & Supination. (ISR - Internal Shoulder Rotation, ESR - External Shoulder Rotation)

1) Pronation - Stick arm out and hold elbow stationary with other hand, stick thumb out and rotate the hand fully in each direction using pronation and supination. Estimating by eye, my thumb indicates my wrist rotates about 170 degrees back and forth with pronation & supination.

2) ISR - Hold your arm straight out. Try to keep all pronation still, and use only ISR at the shoulder joint. Using only ISR & ESR, rotate the hand and estimate the maximum angle. Mine rotates roughly 180 degrees.

3) Pronation & ISR - Now release the elbow, do rotations with full ISR & pronation then full ESR & Supination. Estimate the full range for the shoulder plus forearm rotations. My full range is roughly 270 degrees.

Those are active muscle use ranges. During the serve, stretched muscles will extend these ranges.

The most important angle for the serve is the ISR angle from start to impact. On the high side of a strong serve, that might be ~90 degrees. ?

 

[matterer]

The reason professionals don't teach the serve using terms like ISR is because they know how to serve, and if you know how to do something, you won't teach it the same way as someone who doesn't know how to do it (you).

 

[Chas Tennis]

I do video analysis of tennis strokes, specifically of some sub-motions of tennis strokes, like the racket motions to impact. I have a research background in high speed imaging and give advice on videoing tennis strokes, what to do and what not to do. Make simple biomechanics comments of the most important sub-motions that I see.

I'm not a high level tennis player or an instructor. I don't know how to move my muscles to get many of the stroke sub-motions that I've seen and described.

If you want to discuss or disagree with any of my posts, please do. I enjoy discussing frames of videos and what they show.

 

[matterer]

That is not how you're supposed to learn tennis. You can't mimic a skill that takes hundreds of hours to develop. A waiter's tray serve is what happens when you try to do that. Jeff Salzenstein gives great lessons for free. TPA tennis too. Take their advice, it's correct. If you want to learn professional technique, put more effort into learning to serve than 99% of people are willing to, and never give up on improvement.

 

[Chas Tennis]

That is not how you're supposed to learn tennis. You can't mimic a skill that takes hundreds of hours to develop. A waiter's tray serve is what happens when you try to do that. Jeff Salzenstein gives great lessons for free. TPA tennis too. Take their advice, it's correct. If you want to learn professional technique, put more effort into learning to serve than 99% of people are willing to, and never give up on improvement.

This thread is about the
Demo of Internal Shoulder Rotation vs Pronation

Do you have anything to contribute? Can you find any material on ISR and pronation to make those clearer to the readers? My purpose was to demonstrate in a simple way these two joint motions for any interested reader.

Why? See the thread The Tennis Serve - What's True and listen to the examples. The communication of tennis facts is in shambles. Cutting and pasting a lot of muddle along with a little of what is true has been tried in The New Information Age and we aren't progressing very much here.

The Tennis Serve - What's True?

This serve video completely misses the significant part played by internal shoulder rotation (ISR) during the serve, as do most other serve instructional videos. Why is that? Is this because the most significant joint motion - Internal Shoulder Rotation - is widely misidentified as forearm...

tt.tennis-warehouse.com

 

[matterer]

I do internal shoulder rotation because I made it past the learning curve. I know what's involved in learning it, and why most people never learn it, and I told you where you can learn to do it. I think that's a great contribution.

 

[Chas Tennis]

This thread is not about learning the serve. It is about some important information that is relevant. The readers can do the demos from their couches.

Post what you have with specific links - with times in videos - to show what you mean. That way, interested readers can just click on the link to get your information. Talk forums are not so interesting if you tell that readers that they can search and might find whatever you are referring to.

I go into much more detail in videos than I see in nearly all instructional videos. The approach for me is to learn as much as I can and present it on the forum for those that are interested. (Hidden agenda is to do some pro or college video analysis, where the pro cooperates.)

My videos of ATP players are selected to clearly show sub-motions of strokes that are typical of what the ATP players are doing. Anyone can use my information to compare to their own strokes in videos as feedback. Showed the technique for comparing Youtube videos on the forum. I present the information that I would have wanted in the 1970s in order to understand the serve and other strokes. Instead of understanding, there was 35 years of muddled word descriptions. Was there any understanding of ISR, anywhere? No! Now I can see ISR clearly in strobe pictures from the 1950s and in the clear high speed video of Gerald Paterson from 1919. But I - for 35 years - was not using high speed video to determine what is true.

Ironically, I worked in high speed imaging for 36 years, using it to determine what is true. I took one serve 16 mm film in about 1980. But did not understand what it showed due to my ignorance. With the information that I post, that cannot happen.

With your approach, you are not going to have the video tools to tell you what is being done in strokes. Or whether what is being said is true.

The scientific approach, biomechanics, is the best thing that we have. For decades, ISR was ignored in tennis research. It's an amazing story. I hope that some of those that were involved will yet tell their stories.

If you have something good to tell, why don't you post the information that you think is important.

 

[Better_Call_Raul]

This shows the angle of supination while the motion of pronation is occurring leading to the first red arrow. Toly composite picture.

But at the lower red arrow red arrow, when the elbow is near straight, ISR starts and rotationally accelerates the entire arm, say, up to a racket head speed of 100 MPH. That is the significant

To confirm, I see just two red arrows in the Toly composite pic. A lower red arrow and an upper red arrow.

The upper red arrow, just at impact or very near impact, is when the elbow appears to be nearly straight.

This may be a typo that needs to be corrected.

 

[Chas Tennis]

I determined that you are a poster that has used AI and posted so that it was not clear that I was reading AI.

I asked you to answer two simple questions because AI was wasting my time again.

You did not reply.

Safety First-

I do not understand the "Google AI Bard" use in post #90. I do not understand if Better_Call_Raul: is an AI poster or posted Google AI Bard information in earlier posts. I spent a lot of time reading and explaining in this thread. This is a form of vandalism to spread false information.


Raul are you a person or an AI poster?

Please explain the AI in your earlier posts.

@Better_Call_Raul

These questions show the basic understanding of the poster or AI. Why not answer?

If posters have misrepresented AI as their own writing in the past and avoid answering questions in this post,

then how do we know if the post is from
1) a person or
2) a person copying AI or
3) an AI robot poster ?


What color are your shoes?

 

[Better_Call_Raul]

I determined that you are a poster that has used AI and posted so that it was not clear I was reading AI.

I asked you to answer a two simple questions because AI was wasting my time again.

You did not reply.

I already responded in the other thread about the elbow and the Elliot graph. With my opinion and background info generated by AI query. Most posters found the info useful. You are the only one that seems to think I am an AI robot.

My question here is very simple. Is that a typo in your "red arrow" description? If so, you will need to correct the typo. It is going to confuse readers.

 

[Chas Tennis]

The elbow appears "near straight" at 12 seconds.

 

[badmice2]

I like how this thread is trying to complicating serve motion without actually experiencing the action.

 

[Purestriker]

I like how this thread is trying to complicating serve motion without actually experiencing the action.

Welcome to TT. You must be new here.

 

[user92626]

I like how @Chas Tennis is very focused on his mission.