Serve mechanics - 90 degree elbow position

a12345

Professional
In order to get maximum racket head speed, as the racket drops, the elbow should remain at close to 90 degrees with the upper arm.

You must not bend the elbow in a scratch the back motion. The racket must not drop as a result of the elbow bending.

Instead you'll see that by keeping the elbow at 90 degrees, the racket goes around the shoulder as you turn the body.

Keeping the elbow at 90 degrees allows you to throw the racket with more force.

Fed 90 degrees



Roddick 90 degrees



Sampras 90 degrees



Warwrinka Bent elbow = loss of power

 

TennisDawg

Hall of Fame
Hope you have Joker level shoulder range of motion
Otherwise that 90 degree “rule”s gonna hurt you lol
Ah here’s one with clearly less than 90


I think that 90 deg bend is a general guideline. It refutes the old “scratch your back” with the racquet rule that was taught at one time. As a recreational player I try to maintain the 90 deg bend. It’s also important to keep the shoulders lined up in trophy pose.
 

mrmarble

New User
I think that 90 deg bend is a general guideline. It refutes the old “scratch your back” with the racquet rule that was taught at one time. As a recreational player I try to maintain the 90 deg bend. It’s also important to keep the shoulders lined up in trophy pose.
Doubt it’s a problem so long as you still have full external shoulder rotation which is possible even with a bent elbow
But if you just bend the elbow dropping racquet close to your back it’s no good
 

a12345

Professional
Hope you have Joker level shoulder range of motion
Otherwise that 90 degree “rule”s gonna hurt you lol
Ah here’s one with clearly less than 90


He gets pretty close at times.



It doesnt have to be rigid 90 its just a guideline. Its more about not collapsing the elbow.
 

mrmarble

New User
He gets pretty close at times.



It doesnt have to be rigid 90 its just a guideline. Its more about not collapsing the elbow.
It’s closer to full flexion than it is to 90 degrees
Reminder: full flexion of elbow is only like 120-130 not 180 lol
Try and see yourself
 

a12345

Professional
It’s closer to full flexion than it is to 90 degrees
Reminder: full flexion of elbow is only like 120-130 not 180 lol
Try and see yourself
The optimum position for power is a similar position to how a quarterback throws a football.

Heres Tom Brady throwing a football

 

SystemicAnomaly

Talk Tennis Guru
Hope you have Joker level shoulder range of motion
Otherwise that 90 degree “rule”s gonna hurt you lol
Ah here’s one with clearly less than 90

General guideline. Plenty of pro & rec players will keep the elbow flexion close to 90° during the racket drop. It does not take a superhuman ROM or flexibility to achieve this.

It does not appear that Nick's internal flexion angle is much less than 80°. This is an acceptable variation. From some perspectives, it is often an optical illusion that the internal angle is going much less than 90° degrees.

The old "back scratch" service instruction often had the elbow angle decreasing to 45° or less. Similar to what we see with the image below. In the 90s, I went from a backscratch-flexion serve to a constant 90° flexion that incorporated much greater shoulder rotation (ESR) rather than relying on a changing elbow flexion

 

mrmarble

New User
General guideline. Plenty of pro & rec players will keep the elbow flexion close to 90° during the racket drop. It does not take a superhuman ROM or flexibility to achieve this.

It does not appear that Nick's internal flexion angle is much less than 80°. This is an acceptable variation. From some perspectives, it is often an optical illusion that the internal angle is going much less than 90° degrees.

The old "back scratch" service instruction often had the elbow angle decreasing to 45° or less. Similar to what we see with the image below. In the 90s, I went from a backscratch-flexion serve to a constant 90° flexion that incorporated much greater shoulder rotation (ESR) rather than relying on a changing elbow flexion

Problem with Errani is not her flexed elbow but her nonexistent external shoulder rotation .
Although she could and should do that shoulder rotation despite the flexed elbow
 

SystemicAnomaly

Talk Tennis Guru
Problem with Errani is not her flexed elbow but her nonexistent external shoulder rotation .
Although she could and should do that shoulder rotation despite the flexed elbow
A lack of shoulder rotation was very common with the old backscratch serve implementations. In the very early '90s, I recall that I was using very little ESR because elbow flexion and extension were primary sources of power rather than shoulder rotation.
 

mrmarble

New User
A lack of shoulder rotation was very common with the old backscratch serve implementations. In the very early '90s, I recall that I was using very little ESR because elbow flexion and extension were primary sources of power rather than shoulder rotation.
Yeah that was wrong for sure
But again you can drop the racquet properly even with a flexed elbow so long as you rotate the shoulder externally
 

Chas Tennis

G.O.A.T.
In order to get maximum racket head speed, as the racket drops, the elbow should remain at close to 90 degrees with the upper arm.

You must not bend the elbow in a scratch the back motion. The racket must not drop as a result of the elbow bending.

Instead you'll see that by keeping the elbow at 90 degrees, the racket goes around the shoulder as you turn the body.

Keeping the elbow at 90 degrees allows you to throw the racket with more force.

Fed 90 degrees



Roddick 90 degrees



Sampras 90 degrees



Warwrinka Bent elbow = loss of power

You are looking at videos, correct?

Moment of inertia is a defined quantity - it can be Googled. It indicates resistance to rotation. If the elbow is bent at 90 degrees and the racket is griped in the hand as it is, the moment of inertia is large so that if the shoulder mass is accelerated forward the masses of the forearm and racket will cause the upper arm to rotate backward with external shoulder rotation (ESR). Watch those things occurring in a high speed video. It is difficult to describe in words as the body spins around and many sub-motions occur. But you can see them in high speed videos.

Look at other strokes, for example, forehands, where the moments of inertia of arms and rackets are being used. When the shoulder mass is accelerated in one direction - the arm and racket with large moments of inertia lag behind - and stretch muscles, often shoulder joint muscles.

Stretched muscles store energy and elastic energy in stretched muscles can shorten faster than active muscle shortening using Actin & Myosin in Sarcomeres. (I wish that I could find that stated in a biomechanics reference.)

As a demo of moment of inertia. Take a can of soup in your hand, elbow angle at 90 degrees and accelerate the shoulder mass forward and backward, gently, but feel the can of soup. Now put the can down. Do the same move and feel the difference. Moment of inertia around a specified rotation axis is found by considering each mass multiplied by the square of its distance out from the specified rotation axis. So the can of soup should have a big effect and it does. That is why the forearm and racket are held as they are for the serve, for a larger moment of inertia. You ask why not hold both the forearm and racket shaft at 90 degrees for even more MOI? Because that is uncomfortable for the wrist joint with the angle of the grip.

Another demo is to use a heavy hammer. Hold it by the handle and pronate and supinate your wrist, side to side. Now hold the head of the hammer and repeat. That illustrates how the location of the mass affects resistance to rotation.

In addition to the use of moment of inertia with a 90 degrees elbow, as described, the body is bending and then straightening the spine and moving the scapula around. This also stretches or slackens the muscles that run across the back, see Thoracic Extension, Thoracic Flexion, and Scapulothoracic joint motions that change the muscle length, particularly of the lat muscle. Each of the defined joint motions can be Googled, with pictures and videos to show how to measure joint angles.

If you only look at few pictures and word descriptions, you will miss the things mentioned here.
 
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a12345

Professional
Good point regarding the moment of inertia.

What is everyones thoughts about the next phase in terms of activating the internal shoulder rotation?

Im thinking in terms timing and the order of joint movements.

That is

1) body turn > internal shoulder rotation

i.e where is the line of the body facing as the ISR begins. When I slow the videos frame by frame it appears to me that for Fed and Sampras the body is still turning slightly as the ISR begins.

2) There is possibly 3 movements as we do the ISR.

The ISR of the hand going forwards, the straightening of the arm, pronation at the end.

My initial thought is the ISR of the arm and the straightening of the arm happen simultaneously together first and then pronation begins whilst the arm is still straightening not when its straight.

This is Fed, and the next frame is when he begins pronation. The trigger maybe when the butt cap is facing directly forwards so the racket is parallel to the court > pronation begins.

 

a12345

Professional
This is when Roddick begins his pronation.



It looks like it is when the racket reaches parallel to the court.
 

Chas Tennis

G.O.A.T.
There are variations, for example, when the elbow becomes near straight, or how far into the court the left foot lands (indicates a variation in body tilt and motion).

During the approach to impact the ball, everything is timed by the biomechanics. The closer to impact, the more all high level serves resemble one another. There are variations.

The timeline of the serve can be seen in high speed videos, but it should be based on statistical observations of what a number of ATP players do. I estimate that ISR starts about 25-30 milliseconds before impact. Kinovea allows you to put a timer on its videos and also a count down time line, where "0 ms" is impact. It's ideal for timing tennis strokes.

Relative time lines are available without time scales in all high speed videos by counting frames. Sometimes Youtube videos might skip a frame when the period and comma keys are pressed. Often, I believe, Youtube videos don't skip frames.

Observe & identify any sub-motion that you like and list it next to the time shown in the frame.

Giorgi has a high toss, and she stops and waits for the ball to drop in Trophy Position. The TP is well before impact and shows one of the significant variations among servers. Many other stronger servers move through Trophy Position, no stop.
 
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TennisDawg

Hall of Fame
Good point regarding the moment of inertia.

What is everyones thoughts about the next phase in terms of activating the internal shoulder rotation?

Im thinking in terms timing and the order of joint movements.

That is

1) body turn > internal shoulder rotation

i.e where is the line of the body facing as the ISR begins. When I slow the videos frame by frame it appears to me that for Fed and Sampras the body is still turning slightly as the ISR begins.

2) There is possibly 3 movements as we do the ISR.

The ISR of the hand going forwards, the straightening of the arm, pronation at the end.

My initial thought is the ISR of the arm and the straightening of the arm happen simultaneously together first and then pronation begins whilst the arm is still straightening not when its straight.

This is Fed, and the next frame is when he begins pronation. The trigger maybe when the butt cap is facing directly forwards so the racket is parallel to the court > pronation begins.

Elite servers toss the ball far into the court. If you’re trying to hit a flat serve for example, the average recreational player needs to began pronation much earlier. Most recreational players don’t toss deep into the court. Myself included.
 
I don’t think anyone ever meant for the racquet to touch, or try to get close to that, in the back in the “back scratch position.” It was to get servers to get the hand down to the level of the elbow at drop. Some misinterpreted it and took it literally. Unfortunately, some of those people were instructors.
 

SystemicAnomaly

Talk Tennis Guru
I don’t think anyone ever meant for the racquet to touch, or try to get close to that, in the back in the “back scratch position.” It was to get servers to get the hand down to the level of the elbow at drop. Some misinterpreted it and took it literally. Unfortunately, some of those people were instructors.
It was a whole lot more than just "SOME". Especially in the 1970s and much of the 80s. "Backscratch" was still a misleading instruction in the 90s onward. But many started to catch on -- if today we're given demonstration of a proper racket drop
 

Raul_SJ

G.O.A.T.
It was a whole lot more than just "SOME". Especially in the 1970s and much of the 80s. "Backscratch" was still a misleading instruction in the 90s onward. But many started to catch on -- if today we're given demonstration of a proper racket drop
Was practicing my serve and ran into a 65 year old coach. Said he played in college and that his serve used to be 120mph. No reason to doubt him as he was hitting forehands well... Told him that leg thrust (knee extension) should be timed when racquet head tip is pointed roughly vertical. But he insisted that racquet head tip should be pointed downwards (Macci calls this "racquet leak") when leg thrust begins...

Maybe it can work both ways? His method also might discourage Waiter's Tray as many rec players will tend to go palm up when the RH tip is vertical at trophy. But if RH is already somewhat behind the back when leg thrust begins, it might discourage palm up Waiter Tray.
 

Raul_SJ

G.O.A.T.
He gets pretty close at times.



It doesnt have to be rigid 90 its just a guideline. Its more about not collapsing the elbow.
90 degrees elbow flexed position is a good guideline. Believe the top ATP servers are pretty much dead on.

90 degrees externally rotated shoulder position is a good guideline for beginning of leg thrust.

But you want pics of the beginning of the leg thrust (knee extension).

(1) When the knees start to straighten, the elbow should be at a roughly 90 degree flexed position.

(2) When the knees start to straighten, the shoulder should be at a roughly 90 degree externally rotated position.

[/URL]



As @Chas Tennis has described, the leg thrust (straightening of the knee or knee extension) is simultaneously timed with thoracic extension and external shoulder rotation (when ESR reaches about 90d). This simultaneous timing of knee extension and thoracic extension helps to achieve a steeper racquet drop position.

Perhaps Chas can confirm the roughly 90d elbow flexion position and the roughly 90d externally rotated shoulder position, at moment of leg thrust, is a commonality with the high level ATP serves he has examined. Believe it is.
 
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mrmarble

New User
Those who think 90 degree elbow angle is ideal
Try it out and see at which angle your internal shoulder rotation will feel stronger 70 or 90 degrees?
Easy to do. Push something with your hand at different elbow flexion angles
Overhead that is
 

SystemicAnomaly

Talk Tennis Guru
I don't necessarily disagree with you, but your photo of Sampras does not exactly support your claim of 90 degrees. I thought 90 degrees meant perpendicular.
Optical illusion. I believe Pete is very close to a 90° (right angle). I do not believe that Pete ever has a flexion angle less than (75° or) 80°

As a teaching cue, I do not believe it is useful to suggest that the elbow is flexing more during the drop. If we encourage or dwell on increasd elbow flexion, we get students with elbow flexion angles of 45° to 60°. At these flexion angles they are probably employing insufficient ESR and stretching of the internal rotators.
 
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SystemicAnomaly

Talk Tennis Guru
Was practicing my serve and ran into a 65 year old coach. Said he played in college and that his serve used to be 120mph. No reason to doubt him as he was hitting forehands well... Told him that leg thrust (knee extension) should be timed when racquet head tip is pointed roughly vertical. But he insisted that racquet head tip should be pointed downwards (Macci calls this "racquet leak") when leg thrust begins...

Maybe it can work both ways? His method also might discourage Waiter's Tray as many rec players will tend to go palm up when the RH tip is vertical at trophy. But if RH is already somewhat behind the back when leg thrust begins, it might discourage palm up Waiter Tray.
Pointing downwards? Not understanding that. To my mind, pointing downward suggests the racquet position in the Novak image above. And "racquet leak" suggests something a bit different (video below).

Maximum knee flexion occurs during the trophy phase. Leg drive / extension starts as the racquet head is moved past the tradition trophy position. So is commences as the racquet head starts to drop after the trophy. Where exactly is this coach saying the leg drive starts?

 
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Raul_SJ

G.O.A.T.
Where exactly is this coach saying the leg drive starts?
Around the position below. Nicola says it is a 2mph-5mph difference, so it may not be a big deal.
Have not experimented with it but it might be a good progression drill for Waiter's Tray.
Accelerate (leg thrust) from that point and you might be less likely to go palm up into WT.
Accelerate from the second pic and there is tendency to go palm up into WT.


 

Raul_SJ

G.O.A.T.
Those who think 90 degree elbow angle is ideal
Try it out and see at which angle your internal shoulder rotation will feel stronger 70 or 90 degrees?
Easy to do. Push something with your hand at different elbow flexion angles
Overhead that is
We are discussing 90 degree elbow flexion angle on the drop, from trophy position, to behind the back. That is external shoulder rotation, not internal shoulder rotation.
 

mrmarble

New User
We are discussing 90 degree elbow flexion angle on the drop, from trophy position, to behind the back. That is external shoulder rotation, not internal shoulder rotation.
I know that. If drops with less than 90 degrees will also go up (ISR) with less than 90 degrees
Unless you want joker’s pre 2012 serve lol
 

Raul_SJ

G.O.A.T.
I know that. If drops with less than 90 degrees will also go up (ISR) with less than 90 degrees

Well actually joker took it to the extreme like 120 degree elbow lol

Not clear what is going on with 2010 Djoker. He looks to be dropping with a 30 degree elbow flexion angle. @Chas Tennis , if you drop with a 30 degree elbow flexion angle, instead of the ideal 90 degrees, does that 30 degree elbow flexion angle angle also hold all throughout the upwards swing? Or can the angle recover somewhat to normal during the upward swing?


Note that ISR occurs on the swing up, but ISR mainly occurs when the elbow is straight or near straight.







 
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SystemicAnomaly

Talk Tennis Guru
@Raul_SJ
I know that. If drops with less than 90 degrees will also go up (ISR) with less than 90 degrees
Unless you want joker’s pre 2012 serve lol
Novak's serve in 2011 & 2012 was actually pretty decent. He had fixed serve issues in 2010. First, with Todd Martin's attempt to teach him an abbreviated rhythm and then 2 other serving coaches later that year.

On the drop, when the shoulder is externally rotated, the internal rotators are stretched at that time -- for ISR release during the upward swing.
 

SystemicAnomaly

Talk Tennis Guru
Around the position below. Nicola says it is a 2mph-5mph difference, so it may not be a big deal.
Have not experimented with it but it might be a good progression drill for Waiter's Tray.
Accelerate (leg thrust) from that point and you might be less likely to go palm up into WT.
Accelerate from the second pic and there is tendency to go palm up into WT.
I was surprised to hear that claim of a 2-5 mph diff. But the high-level leak that he demonstrated was a rather modest / subtle leak compared to the "racket leak" seen with many club / rec players. He was demonstrating a modest / moderate RHS slow down after the traditional trophy position.

Amateurs who manifest a leak, often have a much more pronounced leak where the racket head rushes thru the trophy phase and then stops or significantly slows down behind the head. I suspect that the loss in the speed for these players is a significantly more than 5 mph. Maybe even more than 10 or 20 mph diff

The leak can possibly create other serious issues. It might be more conducive to a WTE. A significant slowdown behind the head requires a late acceleration that my be more stressful to the shoulder.
 

Chas Tennis

G.O.A.T.
Not clear what is going on with 2010 Djoker. He looks to be dropping with a 30 degree elbow flexion angle. @Chas Tennis , if you drop with a 30 degree elbow flexion angle, instead of the ideal 90 degrees, does that 30 degree elbow flexion angle angle also hold all throughout the upwards swing? Or can the angle recover somewhat to normal during the upward swing?


Note that ISR occurs on the swing up, but ISR mainly occurs when the elbow is straight or near straight.







Nice GIF display. Look at racket shaft to head clearance on the 2014 GIF.

The way to answer questions is to study ATP serves and note the stronger servers. Measure the elbow angles but first determine when the elbow angle is important, that, in my opinion, would be when he accelerates his shoulder mass to cause ESR. Earlier, who knows?

I notice that he also holds his racket shaft more straight to the forearm than most (I believe). From your GIF at 2014, I can see he does that to miss his head with the racket shaft, it's close. Normally, the grip places the racket shaft at more of an angle to the forearm. If Djokovic did that as others with a more neutral wrist, with his reduced elbow angle, he would hit his head with the racket. See 2014 GIF. Holding the racket more in line with the wrist as Djokovic does, moves the racket head farther from the ESR rotation axis and, therefore, increases the moment of inertia. If confirmed with some statistics on what ATP servers are doing, the elbow angle looks like a flaw. ??

Look at 10 ATP servers observing elbow angle when it counts, forearm-to-racket shaft angle (wrist angle or neutral wrist). Is Djokovic an outlier or the norm regarding his arm angles? His serve is very good but not the top group in performance.

-----------------------------------------------------------------------


This is the worst camera angle to choose to observe the elbow angle. The only way to use it is to measure the lengths of the upper arm and forearm and see if the ratio would indicate the elbow is straight or bent. Doesn't the upper arm appear shorter than it really is? The dimension toward or away from the camera is shrunken or hidden. Avoid trying to measure using it. If someone points a finger directly at a camera, how long is their arm?

Demo. Bend your finger and look at it with one eye as you rotate the hand. The best viewing angle to see the finger angle is obvious.

For a neutral wrist angle and a Continental Grip, what is the forearm-to-racket-shaft angle?

You are looking at the level of detail where there are differences among ATP players with high level serves.
 
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Chas Tennis

G.O.A.T.
90 degrees elbow flexed position is a good guideline. Believe the top ATP servers are pretty much dead on.

90 degrees externally rotated shoulder position is a good guideline for beginning of leg thrust.

But you want pics of the beginning of the leg thrust (knee extension).

(1) When the knees start to straighten, the elbow should be at a roughly 90 degree flexed position.

(2) When the knees start to straighten, the shoulder should be at a roughly 90 degree externally rotated position.

[/URL]



As @Chas Tennis has described, the leg thrust (straightening of the knee or knee extension) is simultaneously timed with thoracic extension and external shoulder rotation (when ESR reaches about 90d). This simultaneous timing of knee extension and thoracic extension helps to achieve a steeper racquet drop position.

Perhaps Chas can confirm the roughly 90d elbow flexion position and the roughly 90d externally rotated shoulder position, at moment of leg thrust, is a commonality with the high level ATP serves he has examined. Believe it is.
Please quote what I said.

The 90 degree elbow has variations. I suggest that you randomly pick 10 ATP better servers and observe their elbow angles. What percent have about a 90 degrees angle?

I don't estimate the max ESR angle ("MER" in some publications) since it is not easy to measure angles during a service motion. Video instructions on how to measure joint angles specify the body position and that does not include variable Thoracic Extension, etc. The leg thrust starts early, again see videos.

The word "simultaneous" refers to instants and the sub-motions take time and often one motion causes another. These motions are seen to overlap. It is too much work to figure out unambiguous words to describe a tennis stroke, by looking carefully at high speed video. Better to show a tennis stroke video and describe what is being seen with words. Then poor wording does not muddle what can always be seen by everyone. I did that in the video for Thoracic Extension, there is a timing scale and frames with text to explain events during TE & Thoracic Flexion. Post video post #19.
 
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Raul_SJ

G.O.A.T.
If confirmed with some statistics on what ATP servers are doing, the elbow angle looks like a flaw. ??
Do not think the 2014 Djoker motion is a flaw. Ryan advises to wear a birthday hat and knock it off with racquet. But be sure to wear the birthday hat towards the front like a unicorn. Djoker 2014 is knocking off the birthday hat. Ryan says some other servers, like Sam Groth do this. Others do not. But it is acceptable. Not clear why Djoker changed the 2014 motion with drop close to his dead.



 

Raul_SJ

G.O.A.T.
@Raul_SJ

Novak's serve in 2011 & 2012 was actually pretty decent. He had fixed serve issues in 2010. First, with Todd Martin's attempt to teach him an abbreviated rhythm and then 2 other serving coaches later that year.

On the drop, when the shoulder is externally rotated, the internal rotators are stretched at that time -- for ISR release during the upward swing.
Not clear why Djoker changed the 2014 motion. It looks acceptable. Similar to Groth.
Note that there is more of a lag with hitting arm in 2014. 2014 motion also goes more right to left while 2018 motion is more back fence to front. 2014 drops close to his head while 2018 drop does not come close to his head.
 

Chas Tennis

G.O.A.T.
I'd like to know what 7 or 8 better ATP servers are doing. I'd have to know that the camera angle was not making the racket appear close to the head while it was not. I believe that the forearm to racket shaft should have a smaller angle than I see with Djokovic's serve but need to consider camera angles. Need to know what the ATP players are doing, that is the reference standard.

If Djokovic's racket shaft is 5" from his head at its closest point and you walk around him in a circle, the racket will appear 5" away at two camera angles, then closer as you walk around in a circle, to touching his head or blocked by his head. All those possibilities for actually 5" separation. If you want to measure or estimate, select your camera angle. For many videos that I find on the internet, no control of recording, I find myself always thinking, maybe it's this or maybe it's that. ? It is almost always has to do with the camera's making a 2D image out of 3D space. If you have control of recording and the server and you can place the camera, you can get more accuracy for chosen angles.

You do realize for this issue, that for years people have believed that servers were 'scratching their backs' because many camera angles hide the dimension toward or away from the camera. That error seems to often be corrected recently.

I then try to find a more interesting project on my bucket list than an odd looking angle for an average serve.
 
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Raul_SJ

G.O.A.T.
I'd like to know what 7 or 8 better ATP servers are doing. I'd have to know that the camera angle was not making the racket appear close to the head while it was not
According to Coach Ryan, these are some of the servers that drop the racquet in over the head head: Djoker, , Federer, Groth, Kyrgios, Osaka.

Some servers that do not drop in over the head: Sampras, Barty, Shapovalov.

That list seems to establish that close to the head is acceptable. Most importantly, based on his experience coaching hundreds of rec players over 20 years, Ryan has observed that close to the head discourages waiter's tray. Would agree with this, as keeping the racquet closer to your field of vision discourages the palm up move.

"If you're ever teaching a beginning student who is struggling to avoid the palm up serve, I hope you'd consider putting a b-day hat on them and allowing them something physical to hit so they can learn the Federer-type (in over the head) swing path. It works wonders to help them avoid the waiter's tray."​
Groth drops in over his head. Groth drop looks very similar to Djoker 2014 drop over the head.

 
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a12345

Professional
Another consideration is that when making contact with the ball, there should be little to no shoulder extension at the point of contact.



That is, your arm must be close to inline with your shoulders, even if you toss the ball deep into the court.

Below is Roddick just after he makes contact but you can still see his arm in line with the shoulders.



Its his body that angles forwards not his arm at the shoulder joint.

And with Kygrios you could even argue his arm is slightly behind the line of his shoulder when he makes contact.



What this also means is that during a fast serve like these, in order to hit the ball with your arm in line with your shoulders, you must take your eye off the ball in order to commit to the swing.

This is the frame in which Kygrios takes his eye off the ball

 
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Raul_SJ

G.O.A.T.
He had fixed serve issues in 2010.
That 2010 motion looks painful. Dropping from a 30 degree elbow flexion angle. "Arming" the serve? Like a hand grenade toss instead of a proper throwing motion? Wonder if that led to shoulder surgery.
:unsure:

.
 

SystemicAnomaly

Talk Tennis Guru
Another consideration is that when making contact with the ball, there should be little to no shoulder extension at the point of contact.
Huh? Shoulder extension at contact? This is a puzzling statement. Shoulder extension has the arm down and behind the body (as shown by your posted image). How does this relate to the shoulder at contact?

What this also means is that during a fast serve like these, in order to hit the ball with your arm in line with your shoulders, you must take your eye off the ball in order to commit to the swing.

Not sure what you mean by having the arm in line with your shoulders. Typically, when we say the arm is (more or less) in line with the shoulders, we are talking about the relationship shown in my image above. That is, the arm is not at an extreme angle (like 60° or more), that would result in an impingement of the shoulder. But I suspect that you might be referring to something a bit different.

Anyway, both Kyrgios & Roddick fix their gaze up, with head up, on the ball and contact point for half of their upward swing or more. They are pulling their head down sometime between the inverted L (the Big L) and their contact.

There are some other top servers that do this as well. However there are plenty of images where Sampras, Federer, Murray and other big servers will usually have their head & eyes still up at impact. Their head has moved over somewhat to their left to allow their right shoulder to come up over the top. But they are still looking upward at impact.
 
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SystemicAnomaly

Talk Tennis Guru
That 2010 motion looks painful. Dropping from a 30 degree elbow flexion angle. "Arming" the serve? Like a hand grenade toss instead of a proper throwing motion? Wonder if that led to shoulder surgery.
:unsure:

.
Appears to be an error in this and an identical article I came across that must have come from the same source. This may have come from a Serbian or other source that was incorrectly translated. Notice how they say "shoulder" in the title but then refer to it as an elbow surgery in the article. Wiki also has Novak with an elbow injury in 2018 but no mention of any shoulder surgery.

In 2019, ND was talking about a shoulder injury. There was some speculation that he might have surgery on it that year. But I have not yet come across a source that the surgery ever took place.

Don't know if his pre-2010 motion was painful. I do not believe that he was actually dropping the racket head from the 30 degree flexion angle. It looks like he takes his racket back and his arm gets to that 30 degree angle prior to his trophy. However, as he moves thru the trophy phase the elbow goes from 30 to (nearly) 90 degree. But, as he goes thru the flexion action, his elbow drop drastically -- below his shoulder line. He is tucking that elbow into his body as he starts to drop the racket head. Look like the elbow is pretty close to 90 as he drops his racket head. This is pretty much the observations I was making ~2008 -- some 2 years before he fixed those issues.

 
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