Racket speed is essential on the serve. An important factor is the use of elastic energy in the stretch-shorten cycle. During the stretch phase energy is stored and released in the shorten phase. This must occur very quickly after the stretch phase, otherwise energy is rapidly lost.
An example is the bottom of the backswing, where maximum external rotation of the upper arm occurs. Leg drive, trunk rotation serve to further accentuate the MER, allowing an explosive internal shoulder rotation towards impact (stretch-shorten cycle). Pre-stretched muscles apply force better. Aiming high causes the arm to straighten and "stop", whipping the racket forward. The high elbow position after impact shows that one aimed high and not forward.
Correct timing pre-stretches the arm muscles for a fast serve.
Last edited by gzhpcu; 03-05-2011 at 06:54 AM.
Reason: replaced "major" with "important factor"