Poll: The Wrist Snap; autonomic or deliberate

[SystemicAnomaly]

^ As for the physics involved in pronation, consider moment of inertia. Pronation assists in producing racket head speed efficiently due to this "notational inertia". If a player were to try to to substitute an exaggerated wrist flexion (only) in lieu of pronation (in concert with other actions), the moment of inertia would be greater. This action might also be detrimental to the wrist...

I fully agree. Tennis is the art of compromises. Some pro players prefer results than health, but they can do that - they have good incomes, best doctors. In amateur tennis we should always choose health...

Yes, but the real point is that the lesser moment of inertia (with pronation) enables the server to accelerate the racquet head faster/more easily.

 

[sennoc]

Yes, but the real point is that the lesser moment of inertia (with pronation) enables the server to accelerate the racquet head faster/more easily.

Oh, ok. So if you want to talk about details, I'm not sure this is the best explanation. In my opinion (that's important, have not seen any papers about that topic) biomechanics here is much more important than physics.

During service motion, racquet rotates simultaneously around two axes. First one is in our wrist, second one is the axis of symmetry of the racquet. Pronation is responsible for rotation around the second one. In this case moment of inertia is relatively small and unimportant - we can rotate racquet around its axis of symmetry without any effort.

If you think about rotation around the wrist, moment of inertia is exactly the same no matter how you hold the racquet. The plane of racquet's head can be parallel or orthonormal to the vector of velocity, but moment of inertia will be almost the same in both cases.

So where is the source of power due to pronation? In my opinion - in the structure of our wrist.

There are huge accelerations at serves what means that large forces interact with the wrist. Here comes biomechanics: it is much easier to deflect wrist by extension than by radial deviation. Small angle of deflection at radial deviation is a perfect thing to deal with big forces, there is almost no place to loose energy here. Wrist works perfectly in this situation and we have feeling that the motion is powerful and under control. But if we try to challange huge forces by using radial deviation, we have to turn racquet's head just before contact - that's the real reason of pronation.

We can pronate consciously or nonconsciously, that's not as important as the fact that pronation should never block the flow of energy - and it always blocks it if you think about pronation as a source of energy (because you use muscles along kinematic chain in wrong time sequence).

BTW in my opinion pronation is always an action, not reaction. During service motion, it occurs naturally - but after the best moment of contact. So we have to pronate a bit earlier. Most of us do that unconsciously, but in my opinion this is not because "things happen", but because our brain introduces small corrections to the motion.

 

[thebuffman]

anybody else get lost in the forest with me?? you scientist talk some amazing stuff of which solely scientist can discern.

 

[sennoc]

I'm not a scientist. I'm physicist, but inactive, and my job - science journalism - is not a part of science. So, what you read above is just my opinion, based on everything I know and read about physics, biomechanics, tennis and cognitive science. I may be wrong (but I think I'm not ).

BTW I made small corrections in my previous post, it's more precise now.

 

[thebuffman]

It Gets Better - Internal Shoulder Rotation On The Forehand

I am still researching this but there seems to be information which eluded me dealing with the power add from properly performing internal shoulder rotation when executing the forehand ground stroke. I have always heard people say to finish the stroke as if you are trying to tell the time by reading a watch on your wrist. Well, this time telling method can be performed at least two ways by turning the wrist or by rotating the shoulder. You can tell if the shoulder is included in the stroke by how the elbow displaces. A high elbow finish equates shoulder rotation, low elbow finish equates no shoulder rotation but all wrist deviation.

I started researching to see if this concept actually exist where I can gain a lot more power from ISR on the forehand and stumbled upon this (emphasis added throughout):

Muscles Used in Forehand Strokes

....This energy is transferred into the lower legs (calves), then to the upper legs (quadriceps and hamstrings), gluteus maximus, hips (adductors and abductors), core (obliques and abdominals), upper body (pectorals), shoulder (deltoids), upper arm (biceps), forearm (brachialis) and finally hand. Any disruption in this link weakens the flow of power from the feet to the ball.

The forehand specifically relies on the pectorals, deltoids and biceps to provide much of the upper body and arm activity in a tennis stroke, with the forearm and wrist "following along for the ride" after the hips open and generate internal shoulder rotation.
Muscles Used in a Serve

The serve is similar to the forehand in its mechanics. In fact, the modern forehand has been described as "a sidearm serve." Internal shoulder rotation provides significant racket head speed at impact, according to research by Dr. Bruce Elliot of the University of Western Australia, similar to an open-stance forehand.

The serve relies more on shoulder muscles than a forehand does, with the rotator cuff more active on this stroke. The serve still starts in the feet and travels the kinetic chain in relatively the same order of muscles used as the forehand.

 

[tricky]

anybody else get lost in the forest with me??

Lost in the forest? I burn it down!! :twisted:

I'll post thoughts later today.

 

[thebuffman]

sennoc - now i see why you get into the biomechanics of sports. from what i am learning through study, it becomes apparent that unless you have a well studied coach training you, you might execute a motion with inefficient mechanics. a prime example is when one is told to finish the forehand as if you are telling the time. yes, i can finish this way but i might use extra wrist deviation to do it instead of shoulder rotation to do it. the latter being more powerful than the former.

i was watching coach kyril and mauro this morning. mauro was drilling kyril on finishing the forehand and he tells kyril to finish by "placing the racquet head inside of your imaginary backpack". when done this way, you are generating tons of internal shoulder rotational power not gotten from a more wristy shot. this is completely different from "finish as if you are trying to tell the time" which might or might not amplify the power from ISR.

 

[tricky]

The serve is similar to the forehand in its mechanics.

I would disagree with this pretty strongly, because a FH is not a shoulder-over-shoulder motion. The cartwheel motion means that you have a pivot motion around the hip that is unlike anything else in tennis. Different set of muscles with the kinetic chain (shouldn't feel the biceps or thumb during pronation.) Different stance. Wrist release through the contact point.

A lot of beginners try to build their serve with elements derived from their FH groundstroke, and that is why it's advisable to shadow serve using a sock.

In fact, the modern forehand has been described as "a sidearm serve."

Would also disagree with this. A shoulder over shoulder motion tends to put the arm in a 3/4 slot. Elliott amended his position in a later article,

The forehand specifically relies on the pectorals, deltoids and biceps to provide much of the upper body and arm activity in a tennis stroke, with the forearm and wrist "following along for the ride" after the hips open and generate internal shoulder rotation.

This is true: pectorals, front deltoids, and biceps. And remember that the serve emphasizes different muscles: pectorals, medial deltoids, and triceps.

You can tell if the shoulder is included in the stroke by how the elbow displaces. A high elbow finish equates shoulder rotation, low elbow finish equates no shoulder rotation but all wrist deviation.

Ehh, I actually have to disagree with that. It's like reading a racquet drop, a lot of factors go into the elbow finish, and if you know what to look for, you can make some educated guesses. For example, if you look at the angle of their forearm relative to the ground, you can guess how early their pronation was executed in the serve. If you look at the overall height of the upper arm against the shoulder, you can surmise how much "angle" (i.e. transversal adduction) they got in the service motion. It is however more useful (and easier) to evaluate a person's windup around the point they are in the trophy pose.

after the hips open and generate internal shoulder rotation.

Yeah, hip rotation loads shoulder rotation. However, hip rotation isn't the same thing as winding up the hips. Using the one foot drill helps you learn to use hip rotation in your strokes and your serves.

when done this way, you are generating tons of internal shoulder rotational power not gotten from a more wristy shot. this is completely different from "finish as if you are trying to tell the time" which might or might not amplify the power from ISR.

Actually, this isn't really true. Both a WW finish and an over-the-shoulder finish produce a lot of shoulder rotation. A lot of people associate turning the shoulder back as loading the shoulder, and actually this isn't quite true. Again, shoulder rotation really is about hip rotation, and that in turn reflects a person's overall footwork. Using a step-out pattern helps a lot with this. The one foot drill helps with this.

Your momentum and balance is important with the grounfstrokes. It is what your body uses to have the muscle stretch and load the kinetic chain. In terms of the video clip, the left arm is really a guide for that momentum. Ideally, as your momentum goes forward, you set up your left arm as a guide for your shot. Then when you initiate the forward swing, the left arm reacts as a brake to keep your torso aligned through the shot. The one foot drill enables you to learn the form this way, so all the dynamics are integrated as one.

 

[socallefty]

14 years later, still an interesting discussion.

Maybe it is someone‘s way of telling you to stop trying to pronate and use internal shoulder rotation (ISR) instead to generate more power. Read this article.

Beware of Pronation! | U.S. High School Tennis Association - 24 years!

One of the big breakthroughs in tennis teaching years about 40 years ago was the discovery of pronation, the outward turn of the forearm, wrist and palm at the end of the service motion that happened so quickly, most observers could not see it. For many years after (and, unfortunately, still...

ushsta.org

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

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

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

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

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

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

Thanks, all!

Thought I would list the three papers separately as I don‘t want them to get lost in the long posts above. Highly recommend bookmarking these links.

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

 

[Bagumbawalla]

The wrist should be kept loose and not used to force any action onto the service motion.
Think of the wrist as a simple chain connecting the arm and the racket
just as with nunchaku (martial-arts weapon) the greatest speed will be achieved
when the two sticks (think arm and racket) are in a line.

The other day I was thinking of something I read by "Pancho" Gonzales and
afterwards found this video that might help visualize the looseness of the wrist.