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03-02-2013, 12:03 AM   #73
Chas Tennis
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Join Date: Feb 2011
Location: Baltimore, MD
Posts: 4,104

Quote:
 Originally Posted by thecode do you realize the arm is already straight in each of these frames?
Quote:
 Originally Posted by toly IMO you are right. When pros hit flat serve they often use intense wrist extension and then wrist flexion. The wrist extension brings the racquet in semi open position, so they cannot ‘swing up on edge’, see figure below and post http://tt.tennis-warehouse.com/showt...23#post5276723.
Duplicating these frames makes for a very nice demonstration of ISR and its relation to the "edge on" discussion. Stand anywhere holding a racket, no ball -

1) Tilt shoulders, one high and one low as the server is doing in all frames. (Important to minimize impingement risk as discussed earlier.)

2) Straighten the arm, keep straight throughout (as in all frames).

3) Racket 90° to arm to start and pointed back (as in frame #1) or as far back as it goes since you cannot get as much stretch in the demo as in a real serve. Racket is "edge on" to the imaginary ball position (as in frame #1).

4) Now internally rotate the shoulder as shown in frames 1-7.

5) As ISR rotates the upper arm for, say, ~90° of ISR, decrease the angle between the arm and racket from about the 90° of frame #1 to say, 30°, at impact (estimate of racket-arm angle in frame #7).

6) The racket had an approximate edge on orientation in frame #1 and with about 90° of ISR will be square to the back of the ball.

All angles are very approximate, will vary between serve types, etc. .

With No Wrist Motion. Notice that starting in the position of frame #1, without any wrist motion, that about 90° of ISR would take an edge on racket to flush on the back of the ball at impact.

Question - In frame #1 the ball must be closer to the camera than the racket head even though they appear to be in the same plane. Maybe the edge on racket location in that frame is not directly toward the ball but displaced to the side. ??

The frames also show the relative amount of forward hand motion and forward racket head motion.

Last edited by Chas Tennis; 03-02-2013 at 07:59 AM. Reason: reword