Correct muscle selection

The performer must select the muscle that are most effective for the task at hand.

Stability and the loss of effective force

A spotter must be stable before he/she can prevent a loss of force to the performer.

Effect of the angle of application on the force produced

In angular movements of body segments, the maximum effective force and velocity occur when the limb is at right angles to the direction in which the object is moved” (e.g., karate punches in which the arm straight forward, not up or down, so the arm is perpendicular to the body).

Of all the skills involved in tennis, the serve is the most individual.  Beginning players simply attempt to tap the ball into the appropriate court.  The more advanced players learn to place various slices and spins on the ball as it is struck; using appropriate muscle groups.  Although an effective serve is possible, the beginning player rarely serves with much power.  This important factor in the tennis game is most often the most difficult to learn as well as to teach or coach.

The power serve, as it is often called, is a skill that requires understanding of mechanical power gained through the laws of motion and force.  The technique is essentially the same throughout all individual variations and styles.  Through careful analysis of the applicable principles of motion and force, the performer of this serve should produce the desirable results.

Initial muscle tension

Placing muscle on stretch before contraction increases in the force of muscule contraction.