question for Brian Gordon and John Yandell - timing of elbow extension in serve

[spacediver]

Over on talk tennis, there's an interesting thread that covers quite a few biomechanical concepts. On page 6, an issue came up about whether the elbow reaches full extension at contact, or before contact, when serving.

I originally thought that full extension occurs at contact, but am wondering whether this is true.

in the following images, it appears that full extension is reached well before contact. However, I'm aware that this evidence may be misleading, as to properly address this question one would need proper sensors that measure joint angles with a high temporal resolution.





I know that Brian's data claims that elbow extension contributes 35% of racquet head speed just before contact, but I'm not sure about the temporal window here.

Also, I'm a bit unclear as to whether elbow extension can actually contribute useful racquet head speed just before contact. As the shoulder continues to internally rotate, the circular path that the forearm traverses through space, due to elbow extension, rotates away from one that is conducive to useful racquet head motion. For example, when you fully internally rotate the shoulder, elbow extension drives the racquet head perpendicular to the target, rather than toward it.

Is it therefore possible that virtually all of the momentum experienced at the elbow joint gets transfered up the chain to wrist action (ulnar deviation and flexion), and possibly down the chain to internal shoulder rotation, right before contact?

Would appreciate any clarification or insights here.

Do we even know the answer to this question yet?

btw, here's the thread in case either of you decide to post there (John I know you've already posted earlier in the thread):

http://tt.tennis-warehouse.com/showthread.php?t=345688&page=6

[johnyandell]

I can't comment on whether the elbow is perfectly and completely extended but if not it is certainly very close a fraction before contact. Brian?

It's also possible that there is a man/women difference, as in the high speed video you usually see more rotation of the hand and arm at that point in the motion. Those frames are probably 1/10 of a second or so before contact.

You can see this in the Sampras clip.

http://www.tennisplayer.net/members/strokearchive/high_speed/High_Speed.html?PeteSampras1stServe.mov

Same thing in the other high speed clips in the forum:

http://www.tennisplayer.net/bulletin/showthread.php?t=1639

Or:

http://www.tennisplayer.net/bulletin/showthread.php?t=1624

Or:

http://www.tennisplayer.net/bulletin/showthread.php?t=1597

Like a lot of things in that thread, I'm not sure all the micro splitting of details is helpful or relates to hitting a good serve. The main guy pushing it there is obsessed with things that probably aren't within conscious control and dismissed Brian's work, I think because it differed with his agendas. That's why I lost interest.

[spacediver]

interesting - thanks for the reply John. The sampras clip was especially useful.

It appears that regardless of the exact timing of full elbow extension, elbow pronation and internal rotation seem to take care of the racquet head direction. So even though the elbow is extending away from target as contact point approaches, the racquet ends up going in the desired direction.

I'm trying to figure out whether the velocity of the racquet head due to elbow extension is wasted or not when its extending in a direction other than towards the target.

Bit of a tricky physics/biomechanics riddle for me.

My best guess is that elbow extension contributes a great deal of useful racquet head speed, up until the point at which it starts to deviate away from target. After that, internal rotation, wrist action, an elbow pronation are the primary drivers.

Brian, do you agree with this assessment?

btw this discussion has inspired a new way to practice/teach the mechanics of the later portion of the serve (the second half of the upswing):

Tell student to extend elbow, pronate elbow, and internally rotate shoulder (not at full speed, and can be done shadow swinging). Those three muscle activations appear to achieve the desired biomechanics beautifully. They can continue to experiment with the timing of these three activations until things start to really click

[uspta146749877]

Internal rotation

interesting - thanks for the reply John. The sampras clip was especially useful.

It appears that regardless of the exact timing of full elbow extension, elbow pronation and internal rotation seem to take care of the racquet head direction. So even though the elbow is extending away from target as contact point approaches, the racquet ends up going in the desired direction.

I'm trying to figure out whether the velocity of the racquet head due to elbow extension is wasted or not when its extending in a direction other than towards the target.

Bit of a tricky physics/biomechanics riddle for me.

My best guess is that elbow extension contributes a great deal of useful racquet head speed, up until the point at which it starts to deviate away from target. After that, internal rotation, wrist action, an elbow pronation are the primary drivers.

Brian, do you agree with this assessment?

btw this discussion has inspired a new way to practice/teach the mechanics of the later portion of the serve (the second half of the upswing):

Tell student to extend elbow, pronate elbow, and internally rotate shoulder (not at full speed, and can be done shadow swinging). Those three muscle activations appear to achieve the desired biomechanics beautifully. They can continue to experiment with the timing of these three activations until things start to really click

How do u explain a student how to rotate shoulder internally?

[uspta146749877]

A reference book

I would suggest to read a serve part of the following book
"Bbiomechanical Principles of Tennis Technique" by Duane Knudson

[uspta146749877]

Rainbow toss

interesting - thanks for the reply John. The sampras clip was especially useful.

It appears that regardless of the exact timing of full elbow extension, elbow pronation and internal rotation seem to take care of the racquet head direction. So even though the elbow is extending away from target as contact point approaches, the racquet ends up going in the desired direction.

I'm trying to figure out whether the velocity of the racquet head due to elbow extension is wasted or not when its extending in a direction other than towards the target.

Bit of a tricky physics/biomechanics riddle for me.

My best guess is that elbow extension contributes a great deal of useful racquet head speed, up until the point at which it starts to deviate away from target. ers.rsAfter that, internal rotation, wrist action, an elbow pronation are the primary drivers

Brian, do you agree with this assessment?

btw this discussion has inspired a new way to practice/teach the mechanics of the later portion of the serve (the second half of the upswing):

Tell student to extend elbow, pronate elbow, and internally rotate shoulder (not at full speed, and can be done shadow swinging). Those three muscle activations appear to achieve the desired biomechanics beautifully. They can continue to experiment with the timing of these three activations until things start to really click

Try to see whether your statements above are correct for a rainbow toss

[spacediver]

How do u explain a student how to rotate shoulder internally?

very easy. You have them perform the movement shown between the first and second poses in this picture:



You then ask them to activate those same muscles but from different positions.

[spacediver]

Try to see whether your statements above are correct for a rainbow toss

would a rainbow toss result in a different contact point?

[BrianGordon]

Sorry, been traveling - I’d add the following points:

1 – The images seen are pretty close in time to the “prior to contact” discussed in my early work (talked about in the first article).

2 – The images indicate varying degrees of available range of motion for elbow extension (not quantifiable from a 2D medium but rather based on my experience in correlating images of this type with 3D data) – as the cited contributions in that work were composites (temporally normalized averages of several players) they reflected variability in the timing of full elbow extension among individuals.

3 - This variability is indicative of the progression of skill acquisition in this type of serve – in general enhanced utilization of shoulder internal rotation indicates more advanced technique – those that show this trait must complete elbow extension (straight elbow) earlier than those who don’t. That is, if shoulder internal rotation is used extensively then complete elbow extension must be accomplished earlier – later if shoulder internal rotation is not as extensive in which case complete elbow extension is delayed until nearer contact.

4 – The full range of the skill acquisition spectrum can be seen even into the tour level and certainly at the college level – as I’ve mentioned before, the transition to a shoulder internal rotation dominated final period (near/at contact) can create problems as (IF) players make the transition – if elbow extension occurs too late, the final extension becomes a negative influence on forward racquet speed because internal shoulder rotation rotates the elbow extension axis to perpendicular to the baseline (or beyond).

5 – In the article for which data is cited, it is STATED that methodological issues (precise measurement of the orientation of the humerus about its own longitudinal axis) created problems in differentiating the relative contributions of pronation, shoulder internal rotation, and elbow extension when the elbow was close to straight. More recent work addressing the methodology at higher data acquisition rates showed indeed elbow extension peaked in the mid-portion of the upward swing and decreased to essentially zero (on the average) approaching contact – the trend implied in the earlier work.

6 – The kinetic implications (momentum, etc.) of this sequencing have been addressed in other parts of the series here – further analysis seems fruitless within the scope of a forum discussion and not something I have time to get into anyway – so… beyond what I’ve discussed in articles, I’ll have to let such kinetic theories serve as a basis of discussion for those so inclined – at least for now.

[spacediver]

thanks Brian - that's a very useful reply!

[uspta146749877]

For spacediver

You maybe interested in another thread

http://www.tennisplayer.net/bulletin/showthread.php?t=1633

It is related to serve components but in a different context
regards,
julian

[uspta146749877]

For spacediver

Please see

http://tt.tennis-warehouse.com/showthread.php?p=5103752&posted=1#post5103752

post #60