Internal Shoulder Rotation: Key to Serving Power

[bottle]

"Rotorded" is a Neologism for the Physical Limitation you have Repeatedly Described

So now I know less that before (and before was nothing...)

This is simple and not profound. Maybe it is so simple that you can't understand it. I don't understand this but it interests me.

You, Phil Picuri, did a your strokes article with John Yandell in which there was video of you serving. There was discussion too. The focus was on how far you do or don't get your racket tip to go down in the part of the serve that is behind your back and maybe a bit to your right side.

This is a universal problem with tennis players (not getting racket tip far down like Gonzalez, Sampras, Roddick or even Federer although he doesn't get as far as the three others).

It is a universal and important yet neglected by many tennis instructors aspect of our game. The test that seems best is to stand in serving position with arm bent at a right angle and see if you can wind humerus back until your forearm is parallel with the court.

This is ground that you and I have both covered many times in our various posts.

Just for fun I'll call anything less than parallel to the court "rotorded." That means that even Roger Federer is a bit rotorded, so maybe the rest of us shouldn't feel quite so bad.

But if you still are determined to misunderstand I'm sure you can. Maybe you would prefer to make up a different word. Before you abandon mine however please note that it is spelled with an "o" and not an "e." Or if you don't want to invent a better word or any word just say "I'm not as flexible as I like" or "A great tennis player ought to be able to point his racket tip at the ground on a perfect perpendicular at a certain point in his serve but I can't." Hmmm. Thirty (30) words.

Me, sorry but I'll use one.

Rotorded.

[bottle]

I'm not following this wording very well.

Could you point out the part of the article that you are referring to.

Sure.

Puerto Vallarte. Thanks for the response. I like your article-- especially the part about not recognizing something for many years but then turning on the light.

Unfortunately, if you think too much like me (but maybe on purpose), you may get smart, dumb, smart and dumb again.

Dumb again is maybe where I've been for a long time ever since, influenced by a posting guy named Bungalo Bill, I tried to centrifugate my spaghetti arm straight entirely from twisting the humerus or upper arm.

And when I read the Chas Stumpfel article here in Mexico-- your article-- I read it on my dumbphone and the furnitures didn't come up.

Now that I have it on a big computer I can see just where Isner's elbow starts to twist.

That doesn't answer your question.

The sentence that caused my reaction is, "This is followed by trained timing that shortens these pre-stretched muscles explosively over approximately the last 30 milliseconds before impact."

I have always tried for this explosive burst, achieve it once in a while for an ace or pressing second, would like to do that more often, am very interested to hear what ANYONE has to say on the subject.

Thank you very much for this article. In the future please write about the English game of skittles only if you want to.

I'm going to write about it though. Anything is worthy of discussion if it contributes to the "explosion" of speed we both are thinking about.

Note: Skittles is a game in which you spin a primitive top. The top looks like a section of tinker toy with a wooden disc on top. There are various compartments with pins in them. The top spins through holes in the walls that are exactly in the shape of the top. The bigger the spin the longer it keeps going to knock down more pins.

The fact that the upper arm gets spinning this way has got to be interesting. I love the Brian Gordon animations showing how it happens-- all about pre-stretch and stretch-shorten reflex, etc. But I didn't realize for many decades that a thing similar to the skittle spin happens inside the shoulder. Will this make me a better server? A worse one? Who the hell knows? But I sort of like to decide these things by myself. Especially when someone like Bruce Elliott refuses to go there.

I'm getting too complicated, I suppose, but on the other hand despise willful ignorance. I'm thinking the longest skittle spin I got was when I pulled on the string slightly before I pulled on it hard.

[stotty]

I am assuming a person's flexibility plays a key role here? I cannot lay my palm flat out because the tendons and muscles in my playing arm are so tight from years of coaching. I am guessing this would impair my internal rotation significantly?

I think the article breaks down internal (and external to extent) rotation well and makes it easy to understand. Like Chris says there are so many interconnected additional factors involved in the serve. The body has to get out of the way to maximise external rotation for a start...yet more flexibility required...you can see as we get older we're screwed.

I guess the key thing for coaches is how to go about teaching and improving external rotation to get better internal rotation, etc.

I just wonder if the best servers have ever given these things any thought? Were they ever taught these features and if so how...or do these things just routinely happen with the best?

The questions for Chris would be: How did you go about improving your own internal rotation? What "false beliefs" were you practising that you felt impaired your serve before you bumped into Bruce Elliot's theories?

[chastennis]

.................................................. ......................................
The sentence that caused my reaction is, "This is followed by trained timing that shortens these pre-stretched muscles explosively over approximately the last 30 milliseconds before impact."

I have not worked very much on measurements of the timeline of ISR.

But I am very much interested in the timeline of internal shoulder rotation (ISR) leading to impact, especially the separate timelines of it's forces, accelerations, speeds, etc.. to whatever level I can find. And, also, the issue - if and when any forearm pronation should appear.

On a 240 fps serve video that I consider typical, I see a clean, sudden twitch-like upper arm rotation that lasts about 7 frames or 29 milliseconds. That is, high rotation rate ISR racket motion leading to impact, and maybe a little after impact, lasts 29 milliseconds for that one serve. The acceleration is more difficult to observe than the racket movement. The acceleration seems very fast, high speed rotation seemed to occur in a frame or two, within several milliseconds? I have not yet attempted to look for acceleration or deceleration on millisecond timescales, serve statistics, etc.

You can do these same ISR timing observations yourself on high speed videos on Tennisplayer.net using the Quicktime arrow keys for single frame. I find that the shadows from direct sunlight at the elbow tend to act as markers and show you the upper arm rotation. It is still often hard to see but you probably will be able to see ISR and count the number of frames it lasts at high speed. Acceleration will be more difficult to observe. Joint rotations involve bones and sometimes the flesh lags behind, the bicep, in particular, flops around. Don't use the movement of the biceps, look for the bones at the elbow.

I can see the high speed upper arm rotation clearly but have not attempted to time the smaller arm movements earlier in the initial acceleration. The acceleration is closely related to the muscle shortening forces, the most interesting topic. The high speed upper arm rotation seen in the videos is timed mostly after the main acceleration.

In a 2000 report, by Marshall and Elliott, the individual joint motions are plotted vs time relative to impact. I have found that data and joint display very informative. See Researchgate for free online reports by Bruce Elliott. One issue with that data, I believe, is that the frame rates were 200 fps, a little slow, and the data presented, I believe, may have been averages from a number of servers and serves of elite young players. I'm not sure how the timing of the joint motions of a current high level server performing a single strong serve would compare. I would like to know. Suggest that you get the report and try to interpret the graph of joint motions.

But one thing on the Marshall and Elliott joint motion vs time plots was very interesting. The IRS seems to accelerate and then peak before impact, and decrease too. After the racket is accelerated by ISR to high speed, it could be that acceleration stops and the racket then cruises to impact, perhaps pronation allows the racket head speed to stay high if the ISR slows down - an interesting question. I decided to understand and confirm my interpretation of what was going with more recent data, still looking.

Here is what I think happens in sequence leading to impact, my opinion, still looking for measurements. The ISR muscles have been pre-stretched and begin to shorten. Some period of acceleration occurs. When the racket head speed is very high, this is what we are observing in high speed videos. The muscles are shortening at increasingly high speed. At some shortening speed and muscle length the muscles may no longer be capable of providing enough force to continue accelerating the ISR. At impact, over those few milliseconds, the racket may be still accelerating, maintaining speed or decelerating, to be determined.? Careful measurements on a representative number of high levels servers can provide the details and a timeline.

I have always tried for this explosive burst, achieve it once in a while for an ace or pressing second, would like to do that more often, am very interested to hear what ANYONE has to say on the subject.

............ In the future please write about the English game of skittles only if you want to.

Note: Skittles is a game in which you spin a primitive top. The top looks like a section of tinker toy with a wooden disc on top. There are various compartments with pins in them. The top spins through holes in the walls that are exactly in the shape of the top. The bigger the spin the longer it keeps going to knock down more pins.

The fact that the upper arm gets spinning this way has got to be interesting. I love the Brian Gordon animations showing how it happens-- all about pre-stretch and stretch-shorten reflex, etc. But I didn't realize for many decades that a thing similar to the skittle spin happens inside the shoulder. Will this make me a better server? A worse one? Who the hell knows? But I sort of like to decide these things by myself. Especially when someone like Bruce Elliott refuses to go there.

.................. I'm thinking the longest skittle spin I got was when I pulled on the string slightly before I pulled on it hard.

I looked for Youtubes and asked my English son-in-law about Skittles, I still don't know what the motion looks like but I can guess. Do you have a Youtube?

I'll look up the Brian Gordon animations that you mentioned.

If you are interested in the structure and how ISR functions, I suggest that you buy a reference on Kinesiology, such as, The Manual of Structural Kinesiology, Thompson .... an older edition such as the 15th is fine. It discusses the details and has crystal clear illustrations. With a $10 used copy and about an hour you will understand all there is about internal shoulder rotation.

The tricky feature is that the tendon of the lat muscle - on your back - attaches on the front of the upper arm. The lat tendon attaches right next to the pec's tendon on the front of the relaxed humerus. When you externally rotate and raise the arm and then shorten both the lat and pec muscles you pull on both tendons and produce internal shoulder rotation. Surprisingly, muscles located on the chest and back produce the same joint motion.

Here is a working demo for ISR - Take a soda straw designed with a line on it. Cut a wide rubber band in two equal pieces. Tape one end of each piece to the same spot on the straw (tape runs around the straw) about an inch from one end. Put the end of the straw on a nail to serve as a pivot, a small piece of wood helps hold the nail and attach the rubber bands. One rubber band represents the pec and the other the lat. Try to position the rubber bands as the lat and pec are held on your body, on the front and back. That set up makes for a working demo of internal shoulder rotation on the serve. Rotate the straw backward to simulate external shoulder rotation and let it go for ISR.

[don_budge]

Shoulder rotation...

Puerto Vallarte. And deserving of answer better than "YOU are rotorded!" or as my former Hungarian girlfriend used to say, "If you don't know, I can't tell you."

Xanadu X factor in lousy serving however may be too limited a subject, too self-referential and self-pitiful for mainstream elitist concern.

The author of this article, Chas Stumpfel, defines internal and external rotation ad infinitum and seems to understand the clotted pedestrianism of this hence his promise to titillate us through providing molecular level research.

Also, one would hope, he will stay close to earth by discussing the English game of skittles, which seems to offer the best explanation of how humeral twist works-- a string wrapped on something round.

Does the rotorded server have a short or stiff string as well as a short fuse? Or are the "adhesions" that everybody talks about little bumps on the round thingie? Or bumps on the string? Or conglomerations of scar tissue in the rotator cuff that have nothing to do with the top other than to slow it down?

Finally, precisely how do arm straightening and internal arm rotation combine with each other to produce maximum racket head speed and how does this relationship differ, if differ it does, for the Xanadu X server?

To me as somebody who has thought about this stuff before, Stumpfel's most provocative detail is the assertion that internal arm rotation is faster near the end of itself than at the beginning. How can this be true if everything is accomplished with initial muscle contraction? Or is one supposed to start spinning the top slowly and only add on speed at the end?

For those with "retarded shoulders"… a three week program with Ester. You have to admit that she is easy on the eyes. Improve your shoulder rotation…internal and external by doing these exercises religiously for three weeks. Warning…do not stretch beyond your comfort zone.

My thoughts on the article to follow.

https://www.youtube.com/watch?v=ppToA1N0CgE

[don_budge]

Thumb in…Thumb out. My Serve…the teaching paradigm. The Roller Coaster Serving

Let's discuss Chas Stumpfel's article, "Internal Shoulder Rotation: Key to Serving Power"!

Ok…you asked for it.

A thoroughly splendid article. Recently I translated a Swedish Midwife's research paper from Swedish to English. The gist of the paper was that the health care system provide the woman that has experienced a certain medical procedure with information that is comprehensive and translated from technical jargon into popular science speak. Get it? The information has to be able to be understood by the person reading it. I found this article to be a beautiful explanation that leaves the student to decide about what to do with the information.

From the article…Chas Stumpfel

Key to Serving Power

At that moment I realized that neither I, nor most players, nor even most coaches, understood the way racket head speed was maximized on the serve.

Internal Shoulder Rotation

The racket goes from this edge-on position to face-on to the ball at impact mainly and simply as the result of internal shoulder rotation. (A widespread misunderstanding attributes this edge-on to face-on transition to ‘pronation’, a poorly defined and misleading term in tennis usage.)

External Shoulder Rotation

The purpose of the wind up is to externally rotate the shoulder ending with the racket deep in the drop position.

The explanation in “The Demos” was certainly worth it’s weight in gold. Although I did have go back and forth several times to get it right as to which was “internal or external” rotation. Thumb in...Thumb out. I think that’s right. I was always concerned that 10splayer was more intelligent than me because he uses these terms at will...without having to reference back and forth. That is no longer a concern of mine. I realize that this isn't the case any longer…or at least the deal breaker is no longer the definition of internal or external rotation. Although I will guarantee that I will never use those terms in my teaching a serve to a student.

The serving motion is actually a roller coaster motion. Please allow me to explain:

The racquet is the roller coaster car and the path of the racquet is the track of the roller coaster. One prerequisite is a proper grip…backhand or at least a continental to the side of backhand. Australian?

Briefly the 6 steps are:

1. The set up position. A line is made at the end of both feet (the toes) to the target. The racquet is set on this same line. The track is from the precise target (example…the forehand corner of the deuce service box) all the way back to the wall behind the server.

2. Simultaneous drop of both hands to a lowest downward position. The roller coaster gets its initial impetus from this down hill motion on the "service" track. Keep the racquet on the track in this early phase of the ride.

3. The Upward climb in the backswing to the top of the hill…palm still down at the top of the hill. Wrist relaxed. After the initial impetus from the first downhill the racquet (the roller coaster car) must climb the track to the top of the hill. Arm, wrist and racquet position is unchanged from the set up position except perhaps a slight straightening of the arm from the gravity in the racquet head pulling the arm straight. Keeping the racquet on the track during the entire backswing to the very top of the hill.

4. The Key to Serving Power. The gist of step 4 is the contents of Chas' article. This is the loop behind the servers back. Once the roller coaster car gets to the top of the uphill climb in the backswing…at the top the car merely falls over the top and descends picking up speed very rapidly (free fall speed) and then roller coaster car has gone into a loop where it actually goes into an upside down loop and when coming out of that loop the speed has everyone in the roller coaster car screaming for mercy. Their faces are plastered against their skulls with the g-force. Here you have your external and internal shoulder rotation…in that order. I think. I hope. At the top of the backswing the racquet merely falls behind the server with a gentle leaning backwards…not to be confused with arching the back or is it...while turning the shoulders.

5. The Racquet screams into impact position. The track of the roller coaster leads the racquet to impact position. The edge of the racquet is screaming at the ball on the way out of the loop but with the relaxed wrist it naturally opens up without any manipulation from the conductor of the ride (the server).

6. The follow through. The last part of the track where the racquet finishes after expending all of its energy.

Two of the keys in this "roller coaster" analogy are the relaxed wrist and the ability to lift the ball onto the track at the to meet the racquet head at the point at the top of the track as it comes out of the loop. If you can throw the ball on the high point of the track and keep your car on the track at all times…you have a perfect service motion. One that is solely dependent upon the force of gravity. Well almost…the server learns how to exponentially engage the vectors in perfect timing of the different components of the swing.

This idea of the racquet coming out of the loop with the edge of the racquet at the ball is really cool. This was brought to our attention in a thread that Stotty started entitled the "Waiters Technique". Connect the dots…the dots as I see them are a track that the racquet head travels upon.

[don_budge]

The Key to Power in the Service Motion...

The key to power in the service motion is the servers ability to make that loop behind them and to make it as deeply as they can…while coming out of that loop building up as much speed as they possibly can. Apparently that means applying external and internal rotation in that order. Interesting…and the article does a fantastic job in explaining just that.

[bottle]

Back at Home in Michigan: Sorry I didn't Reply Sooner

If you are interested in the structure and how ISR functions, I suggest that you buy a reference on Kinesiology, such as, The Manual of Structural Kinesiology, Thompson .... an older edition such as the 15th is fine. It discusses the details and has crystal clear illustrations. With a $10 used copy and about an hour you will understand all there is about internal shoulder rotation.

The tricky feature is that the tendon of the lat muscle - on your back - attaches on the front of the upper arm. The lat tendon attaches right next to the pec's tendon on the front of the relaxed humerus. When you externally rotate and raise the arm and then shorten both the lat and pec muscles you pull on both tendons and produce internal shoulder rotation. Surprisingly, muscles located on the chest and back produce the same joint motion.

Here is a working demo for ISR - Take a soda straw designed with a line on it. Cut a wide rubber band in two equal pieces. Tape one end of each piece to the same spot on the straw (tape runs around the straw) about an inch from one end. Put the end of the straw on a nail to serve as a pivot, a small piece of wood helps hold the nail and attach the rubber bands. One rubber band represents the pec and the other the lat. Try to position the rubber bands as the lat and pec are held on your body, on the front and back. That set up makes for a working demo of internal shoulder rotation on the serve. Rotate the straw backward to simulate external shoulder rotation and let it go for ISR.

I applaud your open contribution to this great discussion, your ability and inclination to follow up, as it were. You didn't have to do that but you did.

Clearly, I thought there was only one stringy band attached to a bump on the humerus when in fact there are two bands and two bumps (I guess). I'll learn whether two bumps or one bump later.

This misconception (one band instead of two) made me think that God or whatever created this skittles-like spinning top must have been drunk. The two strings still seem a bit improbable but now one can conceive of stabilization though a pulling in the same direction from opposite direction.

You say to order this and try that-- very sensible-- but while I'm waiting for THE MANUAL OF STRUCTURAL KINESIOLOGY to arrive, I can place the smooth shaft of the Mexican cane I just bought in my palms and spin it in both directions.

The snake jaws on the curved end then spin wildly. The cane is a west coast Mexican rattlesnake with full markings tinged green.

I totally agree with Stotty that "as you get older you are screwed," but on the other hand, Chas, suddenly to learn that the interior of the shoulder is very different from what you imagined refers back again to your learning theme and conceivably could make a new difference in a genuine tennis student's serve if not that of the natural who serves 40 aces per match.

At the very least the person would become more aware of simultaneous twitch from pec and lat-- how could that hurt?

Where concentration goes, the energy flows, and that's what grows.

Or, as a tall Swede in Mexico said, "We don't see things unless we're looking for them, and then they show up. The human mind is a powerful thing."

So is this Swede's human body.

Apparently, she was sunbathing by the side of an infinity pool at the top of an old volcano above Puerto Vallarte (which is built on the Sierra Madre). I didn't see this, only heard about it, but did swim three times in that pool.

Not much was going on at the top of Puerto Vallarte, up past Gringo Gulch where the actors making NIGHT OF THE IGUANA stayed. An infinity pool is the kind where water goes to the very edge and appears to spill down into the jungle but collects in a gutter instead.

Anyone swimming in that particular development gets a lot of attention from 37 housing units towering above. Contrariwise, one can float on one's back and watch or imagine what is going on in all 37 units like Jimmy Stewart in Alfred Hitchcock's REAR WINDOW.

When the Swede lying on her stomach-- Camilla-- undid the back of her bikini-- the 37 housing units were knocked out or scandalized, depending.

I heard about this first, then found myself at the beach of Banderas Bay at Swell's just past Daiquiri Dick's.

Right in front of me was Camilla, sunbathing and eating something avidly with a big knife. Mussels? Who eats on the beach with such a big knife?

My friend (Hope, the friend, Jules Dassin and I all grew up in Middletown, Connecticut, I guess you could say) told me that Camilla owns her own house and always dresses to the nines and has a terrific job selling time shares for the best hotel.

She was talking to my friend but saying how she enjoyed talking to nobody (the Garbo thing). One thinks also of the Liv Ullman thing: "Sex never hurt nobody."

Right after Camilla made the statement about the human mind, my friend arranged an introduction for me.

"Hello Camilla," I said.

We went in the water then.

When we returned to our place, she was gone.

https://video.search.yahoo.com/video/play;_ylt=A0LEVr2_9tlUdzYAHbkPxQt.;_ylu=X3oDMTB0N25ndmVnBHNlYwNzYwRjb2xvA2JmMQR2dGlkA1lIUzAwNF8x?p=skittles+the+game&tnr=21&vid=F91FB4D9E2F4C816A258F91FB4D9E2F4C816A258&l=92&turl=http%3A%2F%2Fts2.mm.bing.net%2Fth%3Fid%3DUN.608053282360330109%26pid%3D15.1&sigi=11r71sitp&rurl=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DFNcyLUXMvsg&sigr=11b3nelp1&tt=b&tit=Skittles+The+Game&sigt=10ht3ftbj&back=https%3A%2F%2Fsearch.yahoo.com%2Fyhs%2Fsearch%3Fp%3Dvideo%2Bof%2Bskittles%252C%2Bthe%2Bgame%26type%3Dch.40.xp._.18-01.us.dis_ts._._%26param1%3DrVLLjtQwEPwVLvHNUfs9Ofgwj4200gqtYNBydWwnE9g81s4E-Hs6QcCVA4qV6mp3l7pL9n2whWk01IejYRfKaiGprI-GHjmraQ3qLGplxPGkCxNIsExUnAtgTAEACdkuGVhFXt3Y2TiSAfW84OACd9pUQZrAXBN5YNJ5H2WsoqZCKyVU0BJAtmyrg4rjJ0QTglHqYMAr0Qgyo1p2bezuLgUyJyRktexQshJKKQU531OK4_Lsuvjpw5O9LctcCFfwFs_wI0eX_K10a1f6acDUjHUZ8fdFnr8Xoo15XgsReMG17wNGBVfm9E-WYOEF24a97b_tjYqbnygZR4xDxmi3GcmckGS3pbeZgUkKnDIcXiEB3F4o_DGFFdtWf83amvc5_ziKmdzt--o3hLUPcdp1pnaH_LVfltfNMb_z5RZ37NwQyceY1pgeL_Z64vT6_kpf6gdgpJ-tPpSSlYaXDF_IlO1LP4bpW373-Zk09nxLE3Y3q5VQAvHRXtM9ki_5V_AT0%26param2%3Dunknown%26param3%3Dch.40.xp._.18-01.us.dis_ts._._%26hsimp%3Dyhs-fh_lsonsw%26hspart%3Davg%26ei%3DUTF-8&sigb=1mdt0c1co&hspart=avg&hsimp=yhs-fh_lsonsw

[bottle]

Thanks for the Reminder

For those with "retarded shoulders"… a three week program with Ester. You have to admit that she is easy on the eyes. Improve your shoulder rotation…internal and external by doing these exercises religiously for three weeks. Warning…do not stretch beyond your comfort zone.

My thoughts on the article to follow.

https://www.youtube.com/watch?v=ppToA1N0CgE

Thanks for the reminder (and don't be late!) of my three-week date with Esther. If we marry, she can be Esther Escher.

[waga]

Does shoulder rotation apply to forehand as well?

If so is there any content on tennisplayer.net that you can refer me to that demonstrates this please?

[stotty]

It certainly does. A good place to start is right here: http://www.tennisplayer.net/members/..._rotation.html

[bottle]

To me, one of the first ideas to learn should be that, although one rolls the arm, one tries not to sacrifice arm stability.

True instability likely would come from starting with the strings way open behind you and then closing them severely in the wild hope that they would get square or slightly beveled at contact and then continue to roll over.

Nice idea and you might hit a great shot once in a while, i.e., the pitch at contact be what you desired through sheer luck or because you are such a beautiful animal.

This unstable roll as well would likely direct energy to the side rather than the-forward-and-up that produces good "dwell."

A better percentage shot for most people comes from closing the racket behind you whether from choice of grip or other factors.

Now as racket starts to pass you and go out front it naturally can open to square or near square.

Combining this with arm roll means that you must re-balance all factors in relation to each other but at least you are within the realm of consistent possibility.

Ideally the natural opening combines with the various rolls to produce more verticality (racket wipes up rather than across).

Is speed of natural opening the same as speed of racket closing so that the two speeds cancel each other out producing verticality (again, racket going up rather than across)? I don't know. I only know I don't want to cross the ball.

Another factor is how much I as a right-hander placed the strings on right edge of the ball.

A huge factor lies in what proportion of arm roll is from upper arm compared to lower arm.

Lower arm produces more stability but less power. How much do Roger or Guga keep elbow pointed down until after contact? Could be different.

Balancing all the elements to combine desired pitch and dwell with shoulder twist power may be the big trick.

[stotty]

Power...

In some ways doesn't this article explain why many players can serve pretty much flat out just from just their stance...or even from the trophy position? This passage from external to internal rotation seems to be responsible for much of the power a server gets.

I am sure knee bending and driving upwards are power contributors also, but maybe less so than many coaches think?

I have been on courses where knee has been cited as delivering 30% of a server's power. Perhaps this was an exaggeration?

When I look at many servers today, the main thing that seems to be less prevalent than in previous generations (or given less attention to) seems to be weight transfer. In some cases it's hardly present at all; in others it's done in an odd way. Makes you wonder whether it is no longer considered a valid source of power...or even rhythm.

[gzhpcu]

Isn't the serve a complex kinetic chain of multiple factors? Some pros accentuate certain aspects more than others. I think it is impossible to incorporate all aspects optimally. Another factor is the physical attributes of the player: height, weight, arm flexibility, leg muscles, shoulder flexibility, etc. One will tend to attempt to achieve an optimal mix based on these.

[stotty]

Isn't the serve a complex kinetic chain of multiple factors? Some pros accentuate certain aspects more than others. I think it is impossible to incorporate all aspects optimally. Another factor is the physical attributes of the player: height, weight, arm flexibility, leg muscles, shoulder flexibility, etc. One will tend to attempt to achieve an optimal mix based on these.

I realise this, Phil, but my point was that an overwhelming percentage of power seems to come from internal shoulder rotation and, the way I understand it, the upper arm.