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Old 05-06-2013, 07:28 AM   #29
Chas Tennis
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Join Date: Feb 2011
Location: Baltimore, MD
Posts: 4,119

Originally Posted by GoudX View Post
Not entirely sure what you're getting at when talking about with the stretch shortening cycle. I'm guessing that you're using it to how the muscles generate fast speeds from the racquet head drop. Regardless, talking about this motion when trying to explain a serve is more likely to damage form, as it sounds like it will lead to tensing the arm.

The high racquet head speed on the serve only requires normal muscle movements and is due to the triple hinged pendulum movement of the arm, about the shoulder, elbow and wrist. The movement of the arm is a combination of a passive and active movement.

Passive movement: If you keep the arm loose and move it using only the leg, core and shoulder muscles from the dropped head position the arm will naturally unfold into the fast motion we use in the serve, due to the mechanics of a triple pendulum.

Active movement: The muscles in the arm do add extra power, however think how slow an arm only serve is (try hitting a serve from a sitting position if you don't believe me). Their main function of the arm muscles is to control the movement of the racquet in relation to this arm movement. The muscles control the planes along which the pendulum will travel, which is why you can hit flat serves, kick serves and slice serves with what is, for the most part, the same swing.

How does this mean?

-The racquet head drop is important for power, as it is the start of the pendulum movement.

-Power comes from relaxed joints, if the joint can move, it will. This is due to the centrifugal force acting on it as the arm accelerates. This includes forearm pronation, which must occur if the correct racquet head drop position and contact point are used.

-As the arm will naturally amplify the speed, you don't have to worry about really focusing on different muscles. You should relax the arm so that it can swing freely and use the arm muscles to ensure that the arm moves correctly through the contact point.

-Most of the racquet head speed is generated by the movements which accelerate the triple pendulum, the leg drive and core rotation. These are the areas where controllable power is available.

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A TW "thread" search of Chas Tennis Stretch Shortening Cycle gets 9 threads where I've discussed the stretch shortening cycle, mostly for the serve. If you select a "Reply" search it will highlight each reply.

I find 90% of my views directly from references. The most prominent biomechanical researcher on the tennis serve is, in my opinion, Bruce Elliott. His book Technique Development in Tennis Stroke Production, Elliott, Reid, and Crespo discusses the stretch shortening cycle and the part it plays in tennis strokes. The book is available from the ITF store for a very reasonable price. A summary of the ideas is in the shorter article, Biomechanics and Tennis.

You can also search the internet for stretch shortening cycle and find many descriptions.

"only requires normal muscle movements and is due to the triple hinged pendulum movement of the arm, about the shoulder, elbow and wrist."
How does internal shoulder rotation fit into this pendulum picture?

I am now reading the very interesting Cross article TW link on the double pendulum. I don't see internal shoulder rotation mentioned so far. ?

Last edited by Chas Tennis; 05-06-2013 at 10:22 AM.
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