How bad is elbow flexion for a good serve?

atp2015 · Mar 22, 2017

I know pros mostly use external shoulder rotation with a fixed elbow angle to achieve a good racket drop.
But how bad is elbow flexion in terms of the result, physical strain, injury potential, technique etc?
Is it something that needs to be avoided completely or a bit of flexion is okay from a long term impact to serve quality and injury potential?

Raul_SJ · Mar 23, 2017

Pic below is the point where the racquet begins to drop. And it's right around 90 degrees, which I believe is the approximate angle one needs to be.The Jeff Salzenstein course also mentions that the ~90 degree angle is important and common with elite servers. Anything else is not optimal and compromises the throwing motion.

Note: Since one one moves through the trophy position (it's not a static position), we are measuring the angle at the moment where racquet begins to drop behind the back.

The exercise site below also seems to suggest that one gets a bigger ESR stretch with a 95 degree angle.

SystemicAnomaly · Mar 23, 2017

atp2015 said:
I know pros mostly use external shoulder rotation with a fixed elbow angle to achieve a good racket drop.
But how bad is elbow flexion in terms of the result, physical strain, injury potential, technique etc?
Is it something that needs to be avoided completely or a bit of flexion is okay from a long term impact to serve quality and injury potential?

Don't know for sure. I served for 25+ years with minimal ESR. Instead, like many other servers, employed increased flexion (smaller angle) for my racket drop. I had 90 degrees during the trophy phase and decreased the angle (between forearm & upper arm) to something like 45 degrees for my racket drop.

When I switched to using more ESR on the racket drop and kept the elbow flexion close to 90 degrees, I found that access to power (or RHS) came much more easily.

Raul_SJ · Mar 23, 2017

SystemicAnomaly said:
Don't know for sure. I served for 25+ years with minimal ESR. Instead, like many other servers, employed increased flexion (smaller angle) for my racket drop. I had 90 degrees during the trophy phase and decreased the angle (between forearm & upper arm) to something like 45 degrees for my racket drop.

When I switched to using more ESR on the racket drop and kept the elbow flexion close to 90 degrees, I found that access to power (or RHS) came much more easily.

Not sure if there is a standard measuring convention... Would your "smaller angle" at racquet drop correspond to 45 or 135 degrees?

SystemicAnomaly · Mar 23, 2017

Technically, the angle I was referring to corresponds to 135 degrees of flexion. However, I felt that using the supplementary angle (the angle between the forearm and upper arm) of 45 degrees is easier to visualize and makes more sense to most readers.

atp2015 · Mar 23, 2017

SystemicAnomaly said:
Don't know for sure. I served for 25+ years with minimal ESR. Instead, like many other servers, employed increased flexion (smaller angle) for my racket drop. I had 90 degrees during the trophy phase and decreased the angle (between forearm & upper arm) to something like 45 degrees for my racket drop.

When I switched to using more ESR on the racket drop and kept the elbow flexion close to 90 degrees, I found that access to power (or RHS) came much more easily.

Are you saying you are achieving the racket drop mainly through ESR now and keep the elbow flexion fixed after passing through the "trophy" pose?

SystemicAnomaly · Mar 23, 2017

atp2015 said:
Are you saying you are achieving the racket drop mainly through ESR now and keep the elbow flexion fixed after passing through the "trophy" pose?

Yes.

Tennisanity · Mar 23, 2017

Imagine you were pitching a baseball, you probably would want to flex the elbow during the take back much beyond 90 degrees. The serve is basically an upwards pitch.

SystemicAnomaly · Mar 23, 2017

Tennisanity said:
Imagine you were pitching a baseball, you probably would want to flex the elbow during the take back much beyond 90 degrees. The serve is basically an upwards pitch.

Baseball pitchers employ a huge amount of ESR (& ISR). The elbow, for most elite pitchers, is pretty close to 90 degress as they are externally rotating the shoulder during their pitching motion.

Tim Lincecum:
http://media.gettyimages.com/photos...giants-throws-against-the-picture-id121087092

SinjinCooper · Mar 23, 2017

atp2015 said:
I know pros mostly use external shoulder rotation with a fixed elbow angle to achieve a good racket drop.
But how bad is elbow flexion in terms of the result, physical strain, injury potential, technique etc?
Is it something that needs to be avoided completely or a bit of flexion is okay from a long term impact to serve quality and injury potential?

Almost every good server (and pitcher) winds up somewhat off of the 90 degree mark as the shoulder rotates, probably mostly in accordance with how their shoulder feels moving through the motion.

Think of the 90 as the bullseye at the center of a target. Don't stray any further from it than you must, but listen to your body.

SinjinCooper · Mar 23, 2017

Super clear and super slow mo. Just about bang on 90 the whole way through that phase of the pitch.

Limpinhitter · Mar 23, 2017

atp2015 said:
I know pros mostly use external shoulder rotation with a fixed elbow angle to achieve a good racket drop.
But how bad is elbow flexion in terms of the result, physical strain, injury potential, technique etc?
Is it something that needs to be avoided completely or a bit of flexion is okay from a long term impact to serve quality and injury potential?

It's much easier, and more effective, to just employ a good throwing motion, or learn one if you haven't yet.

Limpinhitter · Mar 23, 2017

SinjinCooper said:
Super clear and super slow mo. Just about bang on 90 the whole way through that phase of the pitch.

His throwing motion seems a bit disconnected from his leg drive and upper body rotation. I prefer Koufax's throwing motion as a model. It would be nice if someone could invert the video to show him as a righty. In any event, Koufax looks like his arm is not quite to 90 degrees. But, most of the greatest servers seem to go a bit past 90 degrees during the racquet drop.

Tennisanity · Mar 23, 2017

SystemicAnomaly said:
Baseball pitchers employ a huge amount of ESR (& ISR). The elbow, for most elite pitchers, is pretty close to 90 degress as they are externally rotating the shoulder during their pitching motion.

Tim Lincecum:
http://media.gettyimages.com/photos...giants-throws-against-the-picture-id121087092

Yeah Djokovic get pretty close to the pitchers here.

atp2015 · Mar 23, 2017

Tennisanity said:
Yeah Djokovic get pretty close to the pitchers here.

130 means the angle between forearm and upperarm is 100 - which is more than 90 (ideal for great serves).

Tennisanity · Mar 23, 2017

atp2015 said:
130 means the angle between forearm and upperarm is 100 - which is more than 90 (ideal for great serves).

I don't think that's the angle OP was talking. I thought he was talking about the 90 degree angle between forearm and bicep, which in the above diagram is still about 90 degrees for Djokovic. The ESR angle is 130 deg.

Or if I misunderstood, why does 130 mean angle between forearm and upper arm is more than 90? I don't see any interdependence of ESR angle and forearm-upperarm angle.

Raul_SJ · Mar 23, 2017

SystemicAnomaly said:
Technically, the angle I was referring to corresponds to 135 degrees of flexion. However, I felt that using the supplementary angle (the angle between the forearm and upper arm) of 45 degrees is easier to visualize and makes more sense to most readers.

What would be the effect of having 135 and 45 degrees of elbow flexion at trophy, (instead of the optimal ~90), and completing the drop with that fixed angle? That is how I interpreted the OP "elbow flexion" question, as opposed to 90 at trophy, and then changing the elbow flexion angle during the drop. I am guessing that
45 would be preferable over 135, which IIRC would be somewhat similar to Djokovic's old motion (I think he was towards 45 elbow flexion using the reference below).

Also, was the common motion of modifying the elbow flexion angle during the drop a result of the "backscratch" cue that was commonly used in the 1970s? That "backscratch" cue has since been dropped because we want players to achieve the racquet drop more to the right side of the body rather than going into "backscratch"?

Tennisanity · Mar 23, 2017

Hmmm, is bending the knees and becoming lower than your height critical for activating the ESR?

SystemicAnomaly · Mar 23, 2017

atp2015 said:
130 means the angle between forearm and upperarm is 100 - which is more than 90 (ideal for great serves).

Yeah, as @Tennisanity indicates that 130 degrees of ESR is independent of the 90 degrees of elbow flexion.

Tennisanity said:
Hmmm, is bending the knees and becoming lower than your height critical for activating the ESR?

ESR can happen w/o a knee bend. However, a knee bend followed by a knee extension (and leg drive), will facilitate ESR. Easier to get a good ESR and a good racket drop with that leg drive. Have seen data that indicates the using leg drive to facilitate ESR appears to put less stress on the shoulder than attempting to generate ESR w/o leg drive.[/QUOTE]

SystemicAnomaly · Mar 23, 2017

Raul_SJ said:
What would be the effect of having 135 and 45 degrees of elbow flexion at trophy, (instead of the optimal ~90), and completing the drop with that fixed angle? That is how I interpreted the OP "elbow flexion" question, as opposed to 90 at trophy, and then changing the elbow flexion angle during the drop. I am guessing that
45 would be preferable over 135, which IIRC would be somewhat similar to Djokovic's old motion (I think he was towards 45 elbow flexion using the reference below).

Also, was the common motion of modifying the elbow flexion angle during the drop a result of the "backscratch" cue that was commonly used in the 1970s? That "backscratch" cue has since been dropped because we want players to achieve the racquet drop more to the right side of the body rather than going into "backscratch"?

Ok, just to be clear, the 135 degrees and the 45 degrees that have been referred to are the same amount amount of elbow bend. 135 degrees uses the extended (straight) arm as a reference, while 45 degrees is using only the upper arm as a reference.

My take is that the OP assumed 90 degrees of flexion at the trophy -- even for the "flexion" serve. @atp2015, can you confirm this?

As you surmised the "flexion" serve happened as result of the "backscratch" instruction we received in the 1970s (thru the 90s in many cases). Also beginning servers are often taught to start with the racket head behind the back -- with the elbow bent 30 to 45 degrees.

Raul_SJ · Mar 23, 2017

SystemicAnomaly said:
Ok, just to be clear, the 135 degrees and the 45 degrees that have been referred to are the same amount amount of elbow bend.

No. To clarify, I took the OP to mean arriving at trophy position with a greater/lesser degree of elbow flexion than the optimal 90, 135 vs 45. Greater elbow flexion vs Lesser elbow flexion at trophy. And beginning the drop from there.

But I was not sure which of the two "elbow flexion" positions at trophy OP was referencing.

SystemicAnomaly · Mar 23, 2017

Raul_SJ said:
No. To clarify, I took the OP to mean arriving at trophy position with a greater vs lesser degree of elbow flexion, 135 vs 45. Greater elbow flexion vs Lesser elbow flexion at trophy. And beginning the drop from there.

But I was not sure which of the two "elbow flexion" positions at trophy OP was referencing.

Don't believe, that I've ever witnessed a service trophy position with such extreme position for an elite server. For elites and many non-elites, it is usually somewhere in the 90 degree neighborhood.

Edit: However, there may be some that arrive at something of a "trophy" with the arm less bent. But I believe that they get to a 90 degree position by the time that they start the drop. Can you think of any examples where this does not happen?

SinjinCooper · Mar 23, 2017

Limpinhitter said:
His throwing motion seems a bit disconnected from his leg drive and upper body rotation. I prefer Koufax's throwing motion as a model. It would be nice if someone could invert the video to show him as a righty. In any event, Koufax looks like his arm is not quite to 90 degrees. But, most of the greatest servers seem to go a bit past 90 degrees during the racquet drop.

Yes, yes, I'm sure that the pitching, serving, and politics of those halcyon days left modernity in the dust. Notwithstanding all that, the Lincecum film is about a trillion times better for seeing what we're talking about, since it happened after the dawn of the digital world and can be viewed at insanely high resolution at creepingly low speeds.

Raul_SJ · Mar 23, 2017

SystemicAnomaly said:
Don't believe, that I've ever witnessed a service trophy position with such extreme position for an elite server. For elites and many non-elites, it is usually somewhere in the 90 degree neighborhood.

Edit: However, there may be some that arrive at something of a "trophy" with the arm less bent. But I believe that they get to a 90 degree position by the time that they start the drop. Can you think of any examples where this does not happen?

Yes, I agree anything other than starting the drop from ~90 feels awkward to me. But then again, the "backscratch" feels awkward to me as well as I was never taught nor practiced that motion -- modifying the 90 trophy angle and having more of an elbow bend on the "backscratch" drop. That is why I was not clear if OP was referring to greater or lesser elbow flexion.

Also, If I understand Ash's response to the same OP's question correctly, Ash bends elbow slightly more at trophy to achieve better drop.

Ash_Smith said:
It depends on how much you "close the gap" between forearm and upper arm and how much external rotation you use. If the racquet drop is found by just using flexion of the elbow, then yes I would say you may have an issue as you would ultimately be using the tricep to extend up to contact an not a lot else - which could cause some injury concerns.

If however, you are finding the drop position using external rotation from the 'trophy position', but you have a little elbow flexion I wouldn't be overly worried - your flexibility may not be such that you can achieve the position by external rotation alone - I can't and have a little flexion at that point - so unless you're trying to find that extra 1% I wouldn't be too worried if this is the case.

GuyClinch · Mar 23, 2017

atp2015 said:
I know pros mostly use external shoulder rotation with a fixed elbow angle to achieve a good racket drop.
But how bad is elbow flexion in terms of the result, physical strain, injury potential, technique etc?
Is it something that needs to be avoided completely or a bit of flexion is okay from a long term impact to serve quality and injury potential?

There are some scenarios here. It can either be bad or okay..

1) BAD - Excessive out of sequence Elbow Flexion

This is what you see with alot of rec players - they use elbow flexion to drop the racquet and then throw from that dropped position. This is because they have bad mental image about how the serve works and actually rob themselves of power with this 'technique'. But they do get racquet drop.

2) OKAY - Some slight elbow flexion DURING the ESR on the proper serve

If we study serves in slow motion we can see any elbow flexion beyond the 90 degrees - and importantly see when it happens.

Here is Murray serve elbow flexion is generally at 90 or so but it looks to me that it goes up a little during the drop portion of the serve. But importantly notice his addtional flexion is happening well after the throw motion has started. Its not 'drop then throw.' It's throw..and whatever drop you get is your drop..

Like alot of mediocre rec players I was stuck in 1 for a long time. Personally I don't even think its that useful to worry about racquet drop. Worry about your throwing motion and your flexibility and whatever drop you get - is what you get.. The goal is not drop - in scenario 1 you get plenty of drop but very little power.

The only caveat I think is actually the wrist. you have to relax the wrist to make sure your racquet can lag behind and your wrist will move appropriately.. This helps with drop some..

atp2015 · Mar 24, 2017

Limpinhitter said:
It's much easier, and more effective, to just employ a good throwing motion, or learn one if you haven't yet.

That's the question - does a good throwing motion involve elbow flexion and how much is desirable or tolerable for a quality serve and injury prevention?

atp2015 · Mar 24, 2017

Tennisanity said:
I don't think that's the angle OP was talking. I thought he was talking about the 90 degree angle between forearm and bicep, which in the above diagram is still about 90 degrees for Djokovic. The ESR angle is 130 deg.

Or if I misunderstood, why does 130 mean angle between forearm and upper arm is more than 90? I don't see any interdependence of ESR angle and forearm-upperarm angle.

You are right - my main concern/issue here was the angle between forearm and bicep. The ESR angle could be altered by the forearm-upperarm(i.e elbow) angle, even though 130 ESR angle does not necessarily mean 100 degree of elbow flexion.

atp2015 · Mar 24, 2017

SystemicAnomaly said:
My take is that the OP assumed 90 degrees of flexion at the trophy -- even for the "flexion" serve. @atp2015, can you confirm this?
.

I assumed 90 degree angle between forearm and upper-arm for an ideal serve where the most of racket drop is achieved by ESR. Now, my question was around eliminating any further angle reduction to achieve better racket drop.
Does better racket drop achieved through further elbow flexion help? either for quality of serve (with flexion I seem to get more speed increased inconsistency and less brushing effect/spin) or shoulder/elbow injury prevention.
I agree "elbow flexion" serve may see much narrower angle - probably close to 30.

atp2015 · Mar 24, 2017

Raul_SJ said:
No. To clarify, I took the OP to mean arriving at trophy position with a greater/lesser degree of elbow flexion than the optimal 90, 135 vs 45. Greater elbow flexion vs Lesser elbow flexion at trophy. And beginning the drop from there.

But I was not sure which of the two "elbow flexion" positions at trophy OP was referencing.

My concern/question is about the angle AFTER the trophy. It does not matter how we arrived at the trophy. What should happen after ? Is it good/bad to achieve more racket drop using elbow flexion after the ESR limit is reached? I had posted the question on "Ask the coach -2", my understanding of his response is that it's not bad if it cannot be eliminated completely, but should not be the primary mechanism to achieve the racket drop.

Dragy · Mar 24, 2017

atp2015 said:
I assumed 90 degree angle between forearm and upper-arm for an ideal serve where the most of racket drop is achieved by ESR. Now, my question was around eliminating any further angle reduction to achieve better racket drop.
Does better racket drop achieved through further elbow flexion help? either for quality of serve (which I have failed to see in my specific case due to increased inconsistency) or shoulder/elbow injury prevention.
I agree "elbow flexion" serve may see much narrower angle - probably close to 30.

Racquet drop is useful through muscles prestretch/range of motion, nothing more. Also, once forearm reaches parallel to the ground via ESR (not even talking DJ angles) elbow flexion will not increase the drop. It only works that direction if ESR is mild.
Now for the angle, most initial racquet upward acceleration is achieved by ISR (after ESR muscle prestretch). 90deg angle puts the racquet at farthest possible distance from the rotation axis maximizing torque effect and therefore acceleration - that's my opinion on why it's optimal.

atp2015 · Mar 24, 2017

Dragy said:
Also, once forearm reaches parallel to the ground via ESR (not even talking DJ angles) elbow flexion will not increase the drop. It only works that direction if ESR is mild.

Good point Dragy - it looks like the aim could be to get the forearm to become parallel to the ground via ESR keeping the elbow flexion fixed at 90??

Raul_SJ · Mar 24, 2017

atp2015 said:
My concern/question is about the angle AFTER the trophy. It does not matter how we arrived at the trophy. What should happen after ? Is it good/bad to achieve more racket drop using elbow flexion after the ESR limit is reached? I had posted the question on "Ask the coach -2", my understanding of his response is that it's not bad if it cannot be eliminated completely, but should not be the primary mechanism to achieve the racket drop.

Yes, but Ash says it is important to arrive at trophy with a ~90 degree angle. From there, the elite servers will generally keep that fixed 90 angle and proceed to drop to maximal ESR position. Ash's acceptable alternative (for those with less shoulder flexibility) is to get to 90 at trophy, slightly bend the elbow even more, and then proceed to maximal ESR drop.

But as Dragy suggests, I don't see much advantage to this alternative.

atp2015 · Mar 24, 2017

Raul_SJ said:
Yes, but Ash says it is important to arrive at trophy with a ~90 degree angle.

I can see how 90 degree can be achieved AT or just before the "trophy". I'm not sure how you can get there with 90 degree already formed.

Limpinhitter · Mar 24, 2017

atp2015 said:
That's the question - does a good throwing motion involve elbow flexion and how much is desirable or tolerable for a quality serve and injury prevention?

Without elbow flexion you can't have a throwing motion or a racquet drop on serve. Cricket bowlers don't use elbow flexion. In my view, the more elbow flexion the better. Some of the best servers go past 90 degrees of elbow flexion. In this video, you can see that Patterson, Budge, Laver, Sampras and Becker go past 90 degrees:

Raul_SJ · Mar 24, 2017

atp2015 said:
I can see how 90 degree can be achieved AT or just before the "trophy". I'm not sure how you can get there with 90 degree already formed.

Not clear on the question. My only point was that it was important to arrive at trophy and begin the drop behind the back with a ~90 degree elbow flexion angle and a ~90 degree ESR position (pic #1 "trophy position")...In pic#2, the 90 degree elbow flexion angle is formed earlier, but he also eventually gets to the same position ~90 elbow/90 ESR as pic #1. That might be what you are referring to.

Limpinhitter · Mar 24, 2017

atp2015 said:
I can see how 90 degree can be achieved AT or just before the "trophy". I'm not sure how you can get there with 90 degree already formed.

In my view, most good servers elbows are at more than 90 degrees of flexion at various times in the service motion.

GuyClinch · Mar 24, 2017

In my view, most good servers elbows are at more than 90 degrees of flexion at various times in the service motion.

Not much more though (10 - 15 degrees maybe) - and IMHO they don't really think about it. Neither should rec players...

Raul_SJ · Mar 26, 2017

Limpinhitter said:
In my view, most good servers elbows are at more than 90 degrees of flexion at various times in the service motion.

Yes, I agree Laver and others in that video flexes elbow past 90 as racquet begins to drop...

But to my mind, the only relevant time is when the racquet begins to drop behind the back to get the ESR stretch. I don't follow why other times in the motion are particularly relevant. Elbow flexion angles during other times of the motion are just idiosyncrasies. For example, Sampras will be at flexion angle of 0 degrees (neutral position. straight arm) early in the windup. Todd Martin will stay around 70-90 degrees elbow throughout his entire windup.

Likewise, the baseball pitcher below might have a straight arm early in the motion but will be at 90 as he drops behind back to get the ESR stretch (g).

[/IMG]

Raul_SJ · Mar 26, 2017

SystemicAnomaly said:
As you surmised the "flexion" serve happened as result of the "backscratch" instruction we received in the 1970s (thru the 90s in many cases). Also beginning servers are often taught to start with the racket head behind the back -- with the elbow bent 30 to 45 degrees.

Why was that "backscratch" instruction dropped after being used for so many years?

Chas Tennis · Mar 26, 2017

Raul_SJ said:
Yes, I agree Laver and others in that video flexes elbow past 90 as racquet begins to drop...

But to my mind, the only relevant time is when the racquet begins to drop behind the back to get the ESR stretch. I don't follow why other times in the motion are particularly relevant. Elbow flexion angles during other times of the motion are just idiosyncrasies. For example, Sampras will be at flexion angle of 0 degrees (neutral position. straight arm) early in the windup. Todd Martin will stay around 70-90 degrees elbow throughout his entire windup.

Likewise, the baseball pitcher below might have a straight arm early in the motion but will be at 90 as he drops behind back to get the ESR stretch (g).

[/IMG]

Raul_SJ, how are you aligning the angle indicator, especially regarding the upper arm bone.? Is the indicator fixed at only 90 d. ?

Raul_SJ · Mar 26, 2017

Chas Tennis said:
Raul_SJ, how are you aligning the angle indicator, especially regarding the upper arm bone.? Is the indicator fixed at only 90 d. ?

I try to measure the elbow flexion angle , align the protractor at elbow joint and set the 0 angle protractor reference as full elbow extention (neutral). This will be at approximately the point where knees begin to thrust upwards. This is approximately where the ESR stretch starts to move behind the back...

So Laver below has an elbow flexion of 107 degrees at trophy. Not sure about ESR measurement. If I set the protractor at racquet tip, he reaches 117 degrees ESR angle at drop.

Chas Tennis · Mar 27, 2017

I think that the angle you observe with the 'protractor' will depend on both the elbow flexion angle and the camera's viewing angle. Take a paper clip, straighten it and then bend a reference angle in it to simulate the elbow flexion angle. Hold the paper clip at arm's length and rotate it. Place the paper clip and view it from various angles. The reference angle bend stays the same but I believe the apparent angle you see will change. (This is the limitation of a 2D camera viewing the 3D world again.)

For ESR only use camera views looking along the axis of the upper arm bone, humerus. But I believe that 0 degrees is defined only for specific body positions.

Gazelle · May 8, 2017

Can someone explain what ESR exactly is (more than 'external shoulder rotation') and most importantly how to achieve it. I've heard this term so many times now but haven't managed to translate it into a better serve.

SystemicAnomaly · May 8, 2017

Gazelle said:
Can someone explain what ESR exactly is (more than 'external shoulder rotation') and most importantly how to achieve it. I've heard this term so many times now but haven't managed to translate it into a better serve.

ESR is shown in in the images in posts #2, #9, #14. What more do you need to know? This is also ESR:

Chas Tennis · May 8, 2017

Gazelle said:
Can someone explain what ESR exactly is (more than 'external shoulder rotation') and most importantly how to achieve it. I've heard this term so many times now but haven't managed to translate it into a better serve.

You need some of the biomechanical principles -

1) The main idea is that all athletic motions depend on the use of stretched muscles. Why?

2) Stretched muscles contain stretched Titin molecules and Titin is the rubber band of the body. Why do we want something like a rubber band?

3) Titin is the fastest system available in the muscle's microscopic sarcomere - it can supply force at higher speeds of muscle shortening. The other system in the sarcomere, the Actin and Myosin cross bridges system, is not so fast.

4) What does this have to do with the serve? You want high racket head speed and if you can get Titin effectively involved - by using a specific technique - you can get high racket head speed. Maybe more control too. ?

5) The way to get Titin involved is to use the stretch shorten cycle. You stretch muscles as you would stretch a Whamo sling shot. Then the Titin rubber bands are stretched and stretched muscles can shorten very faster. [More accurately, Titin can still provide shortening forces as the muscle shortening speeds increase.]

There is more than one way to stretch a muscle.........the part played by ESR is clear in high speed videos of serves.

Research, especially about 20 years ago, and reference books since describe the serve. Titin is a hot topic of current research........

ISR & ESR on the serve-
https://www.tennisplayer.net/public/biomechanics/chas_stumpfel/internal_shoulder_rotation/

How bad is elbow flexion for a good serve?

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