So during the windup, the pitcher moves his entire body weight back behind the pitching rubber. Then he thrusts it forward to deliver the pitch. This transfer of momentum from body to ball involves a biomechanical principle called sequential summation of movement. In baseball, the pitcher drives first with his legs, then his hips, shoulders, arm, wrist and fingers. As each part approaches full extension, the next part in the sequence begins to move, efficiently transferring momentum in a whip-like action.
Proper timing is necessary to produce speed and accuracy, and to avoid strain and injury.
A pitcher's body rotates around the foot he keeps planted firmly on the mound. The ball, held overhead in his extended arm, is like a rock whirling on the end of a string. And since the pitcher actually steps downhill, moving off the crest of the mound as he throws the ball, the height of the mound also affects the force of the pitch.