The speed of a thrown baseball is not determined exclusively by the strength and action of the arm. It is the culmination of kinetic movements involving the legs, pelvis, spine, shoulder girdle, upper arm, forearm and fingers. Former Chicago Cubs pitcher Steve Smith, on his instructional website The Complete Pitcher, writes: "An ideal pitching technique enables a pitcher to throw strikes consistently while using a fluid motion that distributes the stress of throwing throughout the body, thus reducing strain on the pitching arm."
Initial Motion
By starting in the "set" or "stretch" position--sideways to home plate--the pitcher can gather the entire the weight of the body through the leg thrust and coordinated rotation of the hips, torso and shoulders. The force of this weight moving forward and behind the baseball is what generates much of its speed. "The torso plays a key role in getting the arm in the proper throwing position," states The Complete Pitcher. "The speed of the trunk and late trunk rotation increase force applied to the ball."
Weight Shift and Hip Action
From the sideways stance, weight is shifted onto the rear foot, which is planted on the front of the rubber. According to instructor Chris O'Leary, this creates "linear momentum that will be converted into rotational momentum" to pull the shoulders around and toward home plate. The shift of weight to the rear foot naturally frees the pitching arm to be drawn back, out, up and ready to throw.
Forward Movement
At this stage, the glove arm is pointed directly at home plate. The stride of the glove-side leg toward the plate opens the hips, and the torso muscles are stretched. This increases the force with which the shoulders are pulled around, leading the long swing of the pitching arm. To maximize velocity, the shoulders should not rotate until the glove-side foot strikes the ground. "The longer you keep your shoulders closed with your glove pointing at the target," O'Leary says, "the more power you will get."
Arm Acceleration, Ball Release
The rotator cuff of the pitching shoulder enables the forearm to turn, or rotate, the palm of the hand down, or back, before facing home plate prior to release. A hard circular snap of the elbow, forearm and wrist apply the direct force that propels the ball from the fingers. The speed of the ball is intensified by the body weight marshaled behind it. "With the elbow circle break," says The Complete Pitcher, "the ball never travels out of a straight line with the plate."
Research
A 2001 study review by the Department of Kinesiology at the University of Hawaii revealed that 46.9 percent of an overhand throw's velocity is determined by leg stride and body rotation, and 53.1 percent by arm action. The Lexington Clinic found that the shoulder applied 21 percent of the total force to the ball, and the wrist 10 percent. High-velocity pitchers plant and extend their lead knee for stability in the pitching motion. Of the elite, The Complete Pitcher notes that "although each pitcher has different styles, all possess a certain rhythm that makes their movements look natural. Pitchers who practiced consistent mechanics created higher throwing velocity."
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