Interactive Forum: Extension

[lukman41985]

Relevant Rafa Pics

From Wimby '06...straight hitting arm, using some elbow flexion

[lukman41985]

Could it have to do with the angle of approach?

Perhaps these pictures will help your thinking...

His "angle of approach" seems pretty consistent to me. Though I don't know how to exactly define that term. Anyhow, that may be due to the fact the the ball heights in each picture are pretty similar.

[EricMatuszewski]

Beutifull photos lukman, make sure you don't forget that MCAT


Before you get back to studying...

Please comment more on what you conclude based on the excellent pics you're posting. I make this same mistake all the time, I assume that just because I see something so clearly that means everyone must see it. But we really need you to "spell it out for us".

So spell out your conclusions, and be as detailed as possible.

The image is so clear on the Rafa pic in the hand rotation post I can make out the mowing pattern in the grass and see the striations in his medial delts. Great camera work by somebody (give that photographer some credit please).

Someone should also comment on why Rafa's leaning back on that second pic, he does this often, what do you all think of that part of his technique?

[lukman41985]

Eric,
I can't really add anything that hasn't been said already. We've already talked a lot about the straight-arm position--especially Jeff. This is also the case with regard to elbow flexion. As per Rafa leaning back--I think this has to do with the fact that his grip is so extreme. Were he leaning more forward, the face would be too closed and the ball would likely go into the net. I see his leaned-back posture as a compensation. I don't think he's "falling backwards" or anything like that. Another factor that ties into the posture issue is how much upward he's going to go with the racquet path. I don't know if anyone finishes higher more consistently than Rafa. I wish I could give credit to the photographer of those photos, but there wasn't a copyright or name assigned to them. They are damn good though.

[crosscourt]

Try doing this and tell me what you think. First, go to the picture of Djokovic in post 11. Imitate Djokovic's stance -- uprightish, weight on the right foot but body balanced and able to be transfer its weight to the left foot, upper body rotated away from the ball, arm in whatever ready position you use, wrist laid back. Imagine a highish ball coming towards you and that you want to drive it through the court. Start your forward swing by shifting your weight forward and by intiating a shoulder turn and rotate your shoulder so that it is in front of you. Let your arm follow it. Imagine that you are throwing something like a roundhouse punch. Allow your arm to straighten out as it passes your body ie let the double bend loosen out at this point. Try to feel that you are using your hand to keep the top edge of your racket as the leading edge. (In fact the racket face will straighten up naturally to perpendicular as you hit the ball. But try to feel as if you are leading the racket through with a closed face.) As you go through contact allow the shape of the swing to take the racket across your body.

It is difficult to describe this, but that's how you get the very powerful straight arm type forehand.

Now try to do that with your body bent to play the lower ball that Federer is playing in the photos in Lukman's recent post. If you are doing what I have described above properly you should most likely fall over. You have to adapt your swing to the body planes in which you are hitting.

[BrianGordon]

Jeffrey, appreciate your contribution. I've been intrigued by the straighter arms of Nadal, who is totally straight as he comes forward, and Federer who is straighter than others, but whose arm length seems to vary with the shot. The theory which I am exploring has to do with the length of the lever. What I think I see with all who are sound on their forehand is a lever length that is stable as they come into and shortly after contact with ball. As I study more film this seems to hold true. Nadal and Federer seem to have a longer lever from hand through racket as they come finto the ball, and one that stays stable in length until after contact, although Federer's lever length may vary from shot to shot. Club players change the length of lever before, during, and/or after contact. Nadal and Federer do consistently have the single bend of the layed back wrist. So my theory is that one needs the bend at the wrist and a stable lever length on the forehand.
I also,believe that the longer lever produces a different action in the shoulder,
which moves the base of the arm up and forward toward the chin. It seems to involve external rotation of the upper arm but I think it's more than that, given the flexible nature of the shoulder joint. When this occurs I think the shoulder is loaded in a way that it isn't when the the double bend occurs, and adds to the spring and racket speed without giving up the all important stability.
Jody Rush

It appears Jody has turned down the golden path to the answer. However, I suggest the lever argument won't work here unless:

1. Proponents are arguing that the straight arm changes, for better or worse, one or more muscle moment arms with respect to particular joints they span - a tough road to travel.

or

2. The lever argument is meant to deal specifically with the torques at the various joints at the instant of ball contact - here you need to be more specific as to how distances change by style relative to the ball contact forces - which if defined might yield some difference in say, the elbow, and is likely more related to injury mechanics than shot outcome.

Perhaps by lever we are talking about distances between the joints and the racquet face center - this could hold some promise but it is not a lever - the distance does however dictate the velocity said joint rotations contribute to the speed of the racquet in various directions (velocity(racquet)=angular velocity(joint) X distance; commonly refered to as r for mechanics heads).

And this is certainly related to the final destination which entails how the various hitting styles change the way critical joint rotations contribute to racquet speed - If you think about it as Jody has (the shoulder thing not the lever thing) it all makes perfect sense - what racquet velocity do you want? and what is the best way to achieve it given the physiological constraints of an individual?

Just a few thoughts - gotta run - carry on - Brian

[crosscourt]

I agree with you Brian. The starting point is What is the source of the power in a shot? The next question is How do I best transfer that power into my shot?

[BrianGordon]

I agree with you Brian. The starting point is What is the source of the power in a shot? The next question is How do I best transfer that power into my shot?

Thank you crosscourt – this is indeed a rare occurrence I’ve found – and a good question that really can’t be answered by anyone but yourself and a highly qualified observer. It requires an assessment of your current approach and your physiological capabilities, particularly with respect to your RATE of force production capabilities in various muscle groups (which can be trained). Then you can easily construct a style that couples your racquet velocity goals (speed and direction) with the best combination of available joint rotations while at the same time allowing for the best contractile conditions for the muscles that ultimately produce those rotations. The observational gold standard is 3-D analysis – but any observer that really understands the goals will work – the type of people that chime in on this site clearly have thought through issues to extent that they are in the 99th percentile of stroke mechanics understanding – perhaps you live near one – good luck - Brian

[jeffreycounts]

Thank you crosscourt – this is indeed a rare occurrence I’ve found – and a good question that really can’t be answered by anyone but yourself and a highly qualified observer. It requires an assessment of your current approach and your physiological capabilities, particularly with respect to your RATE of force production capabilities in various muscle groups (which can be trained). Then you can easily construct a style that couples your racquet velocity goals (speed and direction) with the best combination of available joint rotations while at the same time allowing for the best contractile conditions for the muscles that ultimately produce those rotations. The observational gold standard is 3-D analysis – but any observer that really understands the goals will work – the type of people that chime in on this site clearly have thought through issues to extent that they are in the 99th percentile of stroke mechanics understanding – perhaps you live near one – good luck - Brian

Brian,

Your use of wire frame models of the serve is just incredible. Do you have any plans on publishing a forehand article like the serve one you wrote? Ever since that article came out, I was excited with the possiblity of modeling all the strokes the same way.

I think your 3D model of the serve is one of the best uses of technology in sports I have ever seen.
Jeff

[BrianGordon]

Jeff-

Thanks for the kind words - John and I have discussed such contributions - and this will happen at some point - available time is the nemesis right now. I've also enjoyed reading your stuff - you have clearly considered stroke mechanics to an impressive level - perhaps we should put our skills together and collaborate on a piece or two in the future - Brian

[jeffreycounts]

Jeff-

Thanks for the kind words - John and I have discussed such contributions - and this will happen at some point - available time is the nemesis right now. I've also enjoyed reading your stuff - you have clearly considered stroke mechanics to an impressive level - perhaps we should put our skills together and collaborate on a piece or two in the future - Brian

That would be awesome Brian.

One goal I have, and I don't know if it's possible, is to turn some of my video into 3D wireframes. I know you did yours by hooking up equipment to actual players, but I was wondering if you could use a program, like 3D Studio Max, to turn video into a wireframe?

Jeff

[lukman41985]

A collaboration between you guys would be awesome.

[BrianGordon]

That would be awesome Brian.

One goal I have, and I don't know if it's possible, is to turn some of my video into 3D wireframes. I know you did yours by hooking up equipment to actual players, but I was wondering if you could use a program, like 3D Studio Max, to turn video into a wireframe?

Jeff

Jeff-

Our wireframe programs (Fortran) require 3-D body/racquet coordinates. The coordinates are typically determined using high speed filming with video or film - this is the technique (16 mm film at 100 f/s) used for the subjects in my piece - it requires a minimum of two cameras.

Through a process called direct linear transformation (DLT) body points can be reconstructed in three dimensions by converting each 2-D film record into digital coordinates (digitizing). This process is brutally time consuming which is why I use a magnetic sensor based system which outputs the 3-D coordinates in real time in our training programs (and which has pros and cons).

Anyway - I believe you could convert your video into wireframes if you digitized them using available software (imageJ comes to mind). The output would be in 2-D (one view) and basic calculations could be produced if you have an object of known length visible in the plane you are filming (for scale).

As I'm sure Eric and John would like this forum section to return to hard core debate about stroke mechanics, you can contact me directly for more details if you wish - Brian

[jeffreycounts]

Jeff-

Our wireframe programs (Fortran) require 3-D body/racquet coordinates. The coordinates are typically determined using high speed filming with video or film - this is the technique (16 mm film at 100 f/s) used for the subjects in my piece - it requires a minimum of two cameras.

Through a process called direct linear transformation (DLT) body points can be reconstructed in three dimensions by converting each 2-D film record into digital coordinates (digitizing). This process is brutally time consuming which is why I use a magnetic sensor based system which outputs the 3-D coordinates in real time in our training programs (and which has pros and cons).

Anyway - I believe you could convert your video into wireframes if you digitized them using available software (imageJ comes to mind). The output would be in 2-D (one view) and basic calculations could be produced if you have an object of known length visible in the plane you are filming (for scale).

As I'm sure Eric and John would like this forum section to return to hard core debate about stroke mechanics, you can contact me directly for more details if you wish - Brian

Thanks Brian. I was actually going to ask you about this a long time ago, but then your article disappeared and I was very happy to see John get you back on tennisplayer.net.

Yes let's return to stroke mechanics!

[John Yandell]

Hey you gys can talk about anything you want! Personally I hope you figure out the wireframes Jeff!