Update for those interested

[BrianGordon]

Sorry folks - been out of the loop for a couple days experiencing the joy of holiday travel etc. -

Don - excellent idea - ironic really because I've been searching for a trainer type to fully develop resistance protocols and interventions for all the intricacies I've discovered in the stroke mechanics as part of my web interface - have anyone in mind? - have to get back to you on the list - best to you.

Rosheem - seems you might be on to something - I applaud the depth of your thinking - let me know about progress - quantifying the strokes has led to many of those "ah ha" moments for me - but also a lot of "oops, my bad" moments.

tennisplayer - have not really looked at kick serves much - will say for elbow extension (triceps) the mechanics should not be that much different than for flatter serves - there the early part of the extension is generally due to muscular contraction (joint torque) - followed by a brief period of passive extension (motion dependent torque via joint forces) - ending with a final bout of joint torque - suggest you go to a graphic in my upward swing part 2 captioned "investigate the causes of joint rotation for yourself" (or something like that) - the graphic allows you to select a joint (elbow), and axis of rotation (flexion/extension), then allows stepping through where the bars on top tell you whether the joint rotation is caused "actively" (joint torque) or "passively" (motion dependent torque [joint force]).

[mntlblok]

In my recently defended dissertation, I developed a method to make this differentiation and reevaluated the final instants prior to contact – my method allowed accurate measurement up to 0.007 s prior to contact for the twist rotations of the hitting arm segments (upper arm and forearm) – interesting values at this time:

Shoulder twist rotation: 43% of racquet speed.
Forearm twist rotation: -5% of racquet speed.

The implication is that the rotation observed in the forearm (pronation) is purely a result of the internal rotation of the upper arm at the shoulder joint - independent rotation of the forearm is actually in the direction of supination RELATIVE to the upper arm – an important coaching cue in my opinion.

So, is it time to start addressing you as *Dr.* Gordon yet?

[QUOTE=BrianGordon;10273]
Scholarly is an artifact of the largely useless paper on the wall of my garage – detached is my nature and the legacy of my recently departed father (the true scholar in my family) – the language I use is a compromise to exist in dual worlds and an attempt to say the most with the least – admittedly it rarely works out – but it is what it is.

[QUOTE]

I get this picture of a composite of Mr. Spock, Sheldon Cooper, and Temperance Bones.

So ... with the extreme shoulder internal rotation speed seen in better servers, the fact that the forearm is supinating RELATIVE to the upper arm (even though it is internally rotating relative to the ground) could be due to the fact it simply can’t keep up, or it is being manipulated to ensure the entire hitting arm/racquet structure is not over rotated at contact. I don’t know which, but don’t think the purpose is to cushion the contact – I could be wrong.

Trying to see if I understand what "internal rotation" means, did you mean to say in the parenthetical portion "*pronating* relative to the ground"? That is, is "internal rotation" strictly a term used for the shoulder joint/humerus?

Also, to see if I understand the implications of what you've described, when looking "up" at the outstretched arm coming into impact for the serve, it has always *felt* to me like I was rotating the racket clockwise, and thus sliding the strings across the ball in such a manner as to be applying "slice"-type spin. Yet, video clearly shows that the racket is rotating counter-clockwise.

If this last observation is just way off the mark and out in left field, please have John just delete the whole post and I won't bother you guys anymore.

Kevin

[BrianGordon]

So, is it time to start addressing you as *Dr.* Gordon yet?

Absolutely not!!! - but it would not be technically incorrect.

I get this picture of a composite of Mr. Spock, Sheldon Cooper, and Temperance Bones.

Now that is freaky - exactly the image I was shooting for.

Trying to see if I understand what "internal rotation" means, did you mean to say in the parenthetical portion "*pronating* relative to the ground"? That is, is "internal rotation" strictly a term used for the shoulder joint/humerus?

This is where terminology becomes an impediment - any segment can internally rotate - pronation is typically used as an anatomical term - in this sense it indicates the forearm is internally rotating relative to the humerus.

In the results I put forth, the forearm is supinating relative to the humerus - so seen from a camera attached to the humerus the forearm would be seen to externally rotate; however, from a camera fixed to the ground the forearm would appear to internally rotate - that is, from the ground the internal forearm rotation linked to the internal rotation of the humerus at the shoulder is greater (far greater) than the external rotation (supination) of the forearm relative to the humerus.

Also, to see if I understand the implications of what you've described, when looking "up" at the outstretched arm coming into impact for the serve, it has always *felt* to me like I was rotating the racket clockwise, and thus sliding the strings across the ball in such a manner as to be applying "slice"-type spin. Yet, video clearly shows that the racket is rotating counter-clockwise.

If this last observation is just way off the mark and out in left field, please have John just delete the whole post and I won't bother you guys anymore.

Kevin

The internal twisting rotations of the humerus (shoulder) and/or forearm would create a counter-clockwise motion in the view you indicate - clockwise motion of the racquet face would result from other joint rotations - remember, the overall motion you see is the sum of ALL joint and segment rotations, what is seen or felt is the net for which the twisting rotations of the hitting arm are only a part.

The implication of my results is that pronation is a coaching cue used by many (including myself) to get the counter-clockwise motion you describe - however, it is critical in my view to know where the "pronation" is coming from as a guide to intervention - if for example I want you increase the CCW motion - if I tell you to focus on motion of the forearm relative to the humerus (pronation) I've attached a "ball and chain" to your progress - in my view.

Enough of that - good to hear from you Kevin - how have you been? Hope you are enjoying the holiday! - BG

[mntlblok]

Head pain

Absolutely not!!! - but it would not be technically incorrect.

Congrats on having the Ph.D. work behind you!


[QUOTE=BrianGordon;10299]


The internal twisting rotations of the humerus (shoulder) and/or forearm would create a counter-clockwise motion in the view you indicate - clockwise motion of the racquet face would result from other joint rotations - remember, the overall motion you see is the sum of ALL joint and segment rotations, what is seen or felt is the net for which the twisting rotations of the hitting arm are only a part. [QUOTE]

Dang it, I can't get this post to look all pretty with the "quote" thing. And, it's making my head hurt this Christmas morning to try to figure out where the clockwise of the racket face comes from, but I guess that's the price to be paid in order to deal with your sadistic explanations.

What I'm coming up with for the "other" joint rotations are maybe the unwinding of the torso (shoulder turn?) and probably a combination of both wrist flexion and ulnar deviation (always a fan favorite term). Am I getting close? Hmmm. . . As I think a little more about it, maybe it's just the whole "upward arc" thing initially contacting the right side of the ball (or at least a bit right of center). Dang. I can just feel the sadistic pleasure yer feeling from this.

At least I think I now know the meanings of internal and external rotations. Thanks.

Enough of that - good to hear from you Kevin - how have you been? - BG

This little recent thread on "Talk Tennis" should bring you up to date. http://tt.tennis-warehouse.com/showthread.php?t=303231 Mostly just having fun.

Kevin

[uspta990770809]

Internal/external...counterclockwise/clockwise...pronation/supination...help

[QUOTE=mntlblok;10300]Congrats on having the Ph.D. work behind you!

The internal twisting rotations of the humerus (shoulder) and/or forearm would create a counter-clockwise motion in the view you indicate - clockwise motion of the racquet face would result from other joint rotations - remember, the overall motion you see is the sum of ALL joint and segment rotations, what is seen or felt is the net for which the twisting rotations of the hitting arm are only a part.

I think it was the summer on 1968 when I was working in van der Meer's camp at Lake Tahoe that I first saw high speed films of Pasarel's serve(yeah, there were some high speed films back then, but they were rare, done with strobes). I knew I hit the right side of the ball like throwing a curve...I could feel the face of the racket rotating clockwise around the ball...at least I thought so...but here was the clear video evidence showing I was dead wrong. What I was feeling was the follow through, not the actual contact. And if you over think it, you'll never be able to hit it. It happens fast.

To visualize the clockwise/counterclockwise question, imagine a clockface in front of you at eye level at 9:15. Reach out with your arm horizontal and place the face of the racket on the hands of the clock. Now straighten the arm up reaching up to the contact point with the clock still attached to your racket. Now you have a good picture of clockwise vs counterclockwise. The spin of the ball is, of course, opposite the direction of the racketface rotation. Imagine the racket face as a ball spinning as it contacts the target ball. At contact the two balls are rotating in opposite directions.

By the way, this is one of the best and most informative threads I've seen in a long time. Hope I didn't confuse anyone any further. And my congrats as well on getting the Ph.D. done!

don

[mntlblok]

What I was feeling was the follow through, not the actual contact. And if you over think it, you'll never be able to hit it. It happens fast.



don

OK. I can pretty well follow the Tahoe explanation and even accept it. *But*, help me understand how the heck the "follow through" could "feel" like throwing a curve, with the racket face scraping across the right side of the ball. Ain't that when the pronation has caused the contacting face of the racket to be facing in exactly the wrong direction??

You'd be amazed at what all I can overthink. This *is* fun, though, isn't it?

Kevin

[mntlblok]

Sneaky attempt at a preview

The forearm can be rotated by twisting the upper arm using the shoulder internal rotating muscles (because the segments are connected); or it can be rotated independently by rotating the radius about the ulna using the forearm musculature (true pronation); or both. Problem was, until very recently I could not tell the difference when the arm was nearly straight.

Some of this is gonna turn up in yer upcoming forehand analysis, isn't it?

Kevin

[BrianGordon]

Some of this is gonna turn up in yer upcoming forehand analysis, isn't it?

Kevin

That's the goal - the upper arm and forearm relationship/interaction is infinitely more interesting viewed in the context of variations seen in the ground stroke mechanics.