shoulder ISR in serves, bent arm and straight arm FH

[dominikk1985]

DIsclaimer: if you don't like technical discussion you don't need to participate so save comments on how little need there is for this thread for the general player section.

we all agree that shoulder ISR is very important in FH and serves. However I think that there is a misconception on what ISR does in serves and bent arm FHs.

most people think that in serves first the arm straightens and then ISR supports pronation in moving the rackethead around the hand.

however I don't think that this is the main effect of ISR in serves. ISR is also found to be a big contributor in throwing were long axis rotation of the arm only plays a minor role.

I believe that most of the ISR works before the arm is extended in accelerating the hand forward.

with a bent arm ISR doesn't rotate the arm around the long axis but moves the hand forward.

http://www.youtube.com/watch?v=x44CmqKFuMQ

that is what ISR does in the overhead throw:
http://www.youtube.com/watch?v=cJnm9bC2mag

I believe that aspect is a very underrated aspect of the bent arm FH. the bent arm FH will de-couple ISR and pronation, i.e first the shoulder will ISR while the forearm is still supinated moving the hand forward and then the forearm will pronate and move the racket around the hand.

with a straight arm FH both moves are coupled.

I think that is aspect is the explanation why both FHs produce the same ball and racket speeds. people always talk that SA FH is biomechanically superior because of longer levers and more stretch in the whole arm. that is true however you have to consider that the DB FH has another link in the kinetic chain. it cannot use the stretch reflex in the ISR muscles to generate RHS but it will use that stretch reflex to accelerate the hand which then stretches the forearm to accelerate the racket.

I have no data but I believe that BD FHs create higher maximum hand velocities but lower relative (to hand) racket velocities. the resultant velocities for both will be quite similar for both styles but only if you use ISR correctly (not externally rotate as the racket lays back but earlier so that the arm already IRs when the forearm starts to supinate) otherwise if you just drag the arm the SA FH will produce more speed.

I think that aspect is very underrated when studying SA vs DB FH and explains quite well why in reality both FHs produce the same ball velocities (although I believe that the SA FH might have a slightly better vertical component and thus spin potential while the DB FH might have slightly more horizontal component).

 

[toly]

Why pitcher always straightens his arm? The graph below shows that this “stupid” action decreases arm speed.

Azarenka keeps the bend elbow during forward swing. Her upper arm is basically vertical and this allows her using ISR very efficiently to maximize a racquet horizontal speed. That’s why a lot of old people serve with bent elbow.

See also video http://youtu.be/OQ_mXc9JMEQ

 

[Chas Tennis]

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See also video http://youtu.be/OQ_mXc9JMEQ

What do the red dots track? They move around on the racket.

 

[Topspin Shot]

A pitcher straightens his arm to maximize his fingertip speed at ball release. Your dots are tracking his wrist speed.

 

[toly]

What do the red dots track? They move around on the racket.

They should correspond to racquet tip coordinates.:-?

 

[Chas Tennis]

The pitcher probably keeps a bend in his elbow until he releases the ball. The ball travels with about finger tip speed at release.

Muscle shortening force has a velocity dependence. As the velocity of shortening goes up the shortening force goes down. His arm with an arm bent
at 90d has a large moment of inertia. He can still accelerate it at low ISR muscle shortening velocities. But as the upper arm rotates faster and the muscles shorten faster the available force decreases. Maybe he has to straighten his arm, reduce the moment of inertia, to keep the angular accelerating going.

BTW, if you look at the first arm position of the pitcher with the 90d bend and imagine a racket in his hand that is the position I used experimenting to attempt to increase the pace on my volley. I got an immediate Golfer's Elbow injury. I believe it was because the moment of inertia of the forearm and racket were too high for forceful ISR.

For Azeranka's forehand I'm sure the pros know what they are doing. But Golfer's Elbow injuries occur more for higher level tennis players than amateur players (the opposite of TE where the amateurs get TE more often than the pros). The serve and forehand are believed to be the stressful strokes for GE.

 

[toly]

A pitcher straightens his arm to maximize his fingertip speed at ball release. Your dots are tracking his wrist speed.

Can you elaborate? I really cannot understand why pitchers and the most of tennis servers apply straight arm at the end of the swing. :-?

 

[Chas Tennis]

The pitcher probably keeps a bend in his elbow until he releases the ball. (edited- I doubt it now, see replies below) The ball travels with about finger tip speed at release.

Muscle shortening force has a velocity dependence. As the velocity of shortening goes up, the shortening force goes down. His arm, with an elbow bent at 90d, has a large moment of inertia(resistance to rotation). He can still accelerate it at low ISR muscle shortening velocities. but as the upper arm rotates faster and the muscles shorten faster, the force available for rotation decreases. Maybe he has to straighten his arm, reduce the moment of inertia, to keep the angular acceleration going.

BTW - If you look at the first arm position of the pitcher, with the 90d bend, and imagine a racket in his hand, that is the position I used experimenting to attempt to increase the pace on my volley. I got an immediate Golfer's Elbow injury. I believe the injury occurred because the moment of inertia of the forearm and racket were too high for forceful ISR.

For Azeranka's forehand, I'm sure that the pros know what they are doing. But Golfer's Elbow injuries occur more for higher level tennis players than for amateur players (the opposite of TE where the amateurs get TE more often than the pros). The serve and forehand are believed to be the stressful strokes for GE. I can see that ISR with the bent elbow forehand would cause stress at the GE injury location. It would be nice to pin down the parts of these strokes that are associated with stress and injuries. Keep some statistics of the correlation between stroking techniques and injuries.

 

[Chas Tennis]

They should correspond to racquet tip coordinates.:-?

I see that on the 3 racket images most in front but then I can't make sense of it beyond those 3.

 

[boramiNYC]

Can you elaborate? I really cannot understand why pitchers and the most of tennis servers apply straight arm at the end of the swing. :-?

Triceps which extend the elbow is a very strong muscle for a properly trained arm. During the forward arm swing, the chain of internal rotation by pec and lat, extension of the elbow by triceps, and pronation and flexion at forearm and wrist are the major links that drive the palm and fingers to transmit force and generate velocity. In overhead throwing motion not fully extending elbow would be an inefficient technique.

 

[toly]

I see that on the 3 racket images most in front but then I can't make sense of it beyond those 3.

Here it is

 

[dominikk1985]

pitchers do both at the same time, ISR and extend the arm. both motions will move the hand forward/up relative to the elbow.

the straighter the arm gets the smaller is the influence of ISR but the bigger is the influence of the extension. thus the ISR should peak a tad earlier than elbow extension which will be the final acceleration. also the straightening will increase the radius which allows to still accelerate as the innertia decreases.

 

[Chas Tennis]

pitchers do both at the same time, ISR and extend the arm. both motions will move the hand forward/up relative to the elbow.

the straighter the arm gets the smaller is the influence of ISR but the bigger is the influence of the extension. thus the ISR should peak a tad earlier than elbow extension which will be the final acceleration. also the straightening will increase the radius which allows to still accelerate as the innertia decreases.

Thanks for the very clear explanation. You sound as if you have a pitching background.

I looked at the Red Bull Lincecum video to see release and arm elbow angle at release but could not find any angle. Seeing release when the ball and fingers have the same velocity is tough even with a HD 2,000 fps video. I did read that the fingers don't flex to add to the pitch speed with any last little push. I guess that's true.

Only good release at about 57.
http://www.youtube.com/watch?v=Y2PBLcp9tWM

There is some pretty fast straightening of the forearm-racket angle after impact for the tennis serve but always that angle exists at impact so that ISR rotation can drive the ball.

 

[Chas Tennis]

ISR for the Serve

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most people think that in serves first the arm straightens and then ISR supports pronation in moving the rackethead around the hand.

however I don't think that this is the main effect of ISR in serves. ISR is also found to be a big contributor in throwing were long axis rotation of the arm only plays a minor role.

I believe that most of the ISR works before the arm is extended in accelerating the hand forward.

with a bent arm ISR doesn't rotate the arm around the long axis but moves the hand forward.
....................................................................
stretches the forearm to accelerate the racket.
.............................................

For the serve the arm straightens and then the pre-stretched ISR muscles shorten to produce twitch-like ISR.
See the twitch-like ISR by carefully watching the elbow bones axially rotate. I believe that ISR gets up to speed very rapidly and that much of the joint motion occurs with little muscle shortening force but at a high rotation rate.
https://vimeo.com/27528701

In the first frame, he has completed arm extension. The edge of his racket is facing the ball. Twitch-like ISR rotates the entire straight arm to impact. The racket face turns from edge on to proper contact with the ball mostly from ISR. For this kick serve he is using a large angle between his forearm and racket at impact. A few millisecond later for some serve types this angle may become much smaller and maybe the racket and forearm tend to get straight if the wrist will allow.

None of these movements can be very well done using feedback by seeing or feeling what is happening during the service motion, during the 20 milliseconds over which they occur. Timing has to be trained with trial and error. 'Feel' is probably the most important feedback in training. How did it feel when the ball did what you were after? The position checkpoints that characterize most high level serves should be present in HS videos.

Do any of these points conflict with your view of ISR for the serve?

The commonality in the serve, most forehands, especially the DB FH, and the baseball pitch is that the largest muscles attached to the upper arm bone, the humerus, rotate it very forcefully - all by ISR.

 

[dominikk1985]

when you throw a ball ISR when the arm is already extended adds 0 (zero) MPH of throwing velocity because ISR with a straight arm only rotate the arm but doesn't move the hand in space. however we know that ISR contributes a lot to the overhead throw which means it has to happen while the arm is already bent.

I'm not sure whether the serve is different from the overhead throw but I believe most ISR is over before contact and the rest is mostly pronation.

I made a pete gif:
IMO it looks like the forearm is changing orientation much more than the upper arm (look where petes biceps point to). the frame after contact the biceps rotates a little more to pointing foward but most of the time the biceps is facing towards his head.

 

[dominikk1985]

I see around 90 degrees of ISR in those frames (biceps facing back to biceps facing inward). Maximum ESR is about in the first frame of this gif. that means that the stretch reflex is working that this moment with the arm bent 90 degrees.

I'm not saying there is no ISR after that but the strongest impulse comes after maximum ESR when the arm is still bent 90 degrees.

 

[Chas Tennis]

I see around 90 degrees of ISR in those frames (biceps facing back to biceps facing inward). Maximum ESR is about in the first frame of this gif. that means that the stretch reflex is working that this moment with the arm bent 90 degrees.

I'm not saying there is no ISR after that but the strongest impulse comes after maximum ESR when the arm is still bent 90 degrees.

The ISR is a joint motion where the humerus rotates. The joint motion is of the bones and not the soft tissue. You really can't estimate bone axial rotations from the biceps since the biceps has inertia and lags behind the accelerating bones. The biceps is pulled along with delay. The best thing to get an indication of the bones is to look at the shadowing of the bones around the elbow. This is not perfect since the shadows of the elbow bones require a little interpretation. Here is a serve video where the biceps flops around after the ISR is complete because the biceps is loose and its movement is delayed from the bone movements. You can see the identical biceps flop in the Tim Lincecum pitch video in reply #13.
Raonic serve, biceps flop.
https://vimeo.com/66720415

Raonic serve.
https://vimeo.com/53440915

Groth serve.
You can see ISR from the elbow bone shadowing.
https://vimeo.com/71730830

See ISR by the elbow bones and try to separate pronation.

When the arm is straight.
Wrist rotation = Pronation (between the elbow and wrist) + ISR (between shoulder & elbow indicated by the elbow bones)

I always have trouble even identifying pronation in the high speed videos. ISR is easy to see but I have trouble measuring ISR in degrees because the shadowing at the elbow bones varies in a complicated way. If the pros would wear markers this stuff would be a lot easier.

Most importantly, this conclusion comes from biomechanical research with high speed film cameras by Elliott and others.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2577481/

 

[dominikk1985]

I think I was wrong that ISR stops before contact. in fact pitching studies have shown that maximum ISR velocity is actually slightly after release.

the interesting thing is that maximum torque and maximum velocity are not occuring at the same time. maximum IR torque (the SSC phase) happens even slightly before maximum ER while maximum velocity happens late in the throw. probably because the innertia has to be overcome.

It seems like the ISR is happening during the whole acceleration phase (from max. ER which is about "backscratch" in tennis) and even through contact.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445080/

 

[dominikk1985]

I still believe that in the DB FH ISR and pronation have to be de-coupled. with a bent arm the ISR does this:

http://www.youtube.com/watch?v=x44CmqKFuMQ

could that mean that DB FHs have more horizontal velocity potential but less spin potential than SA FHs?

 

[Chas Tennis]

Have you seen this website and the references on baseball pitching?

The Tim Licecum pitch is slowed down farther and shows ISR perfectly. (The original video was recorded at 2,000 fps so this playback really slows down the motion.)

http://www.topvelocity.net/pronatio...locity-while-preventing-injury/#disqus_thread

(Substitute the words internal shoulder rotation for pronation.)