Advanced Biomechanics of the Pitching Delivery
Proper pitching mechanics are critical for both the success and health of a baseball pitcher of any level. Poor mechanics can lead to increased stress on the elbow or shoulder, increasing the risk of serious injury. Studies have shown that proper pitching biomechanics use proper motions and forces of all body parts in an optimal sequence. This optimal sequence is known in science as the "kinetic chain"; it is known in sports as "proper coordination." Proper pitching mechanics can reduce elbow and shoulder stress as well as maximize ball velocity. The purpose of this summary is to point out some key aspects of proper and improper pitching mechanics.
Research has shown few differences between the biomechanics of successful youth and adolescent pitchers and the mechanics of successful collegiate and professional pitchers. The major difference is that younger pitchers generate less joint force and torque, which of course is no surprise. Another difference is that younger pitchers are less consistent pitch-to-pitch. Research has also shown very few biomechanical differences between pitching from the windup and from the stretch. After the front foot lands, the motions are similar. The peak force and torque values are also similar between the two styles. Ball velocity is also similar between windup and stretch techniques. These findings are consistent with the fact that some pitchers are successful with both techniques and some other pitchers (mostly relievers) are successful always pitching from the stretch.
Proper Pitching Mechanics
While each pitcher is a different person and can display some individuality in his mechanics, everyone has similar anatomy (the same muscles, bones and ligaments in the same locations) and is throwing following the same laws of physics (force = mass x acceleration, etc.). Thus, research has shown common traits among healthy, successful pitchers. What follows is a description of proper mechanics, based upon three-dimensional high-speed automated analysis of thousands of pitchers by the American Sports Medicine Institute and other biomechanics labs. The photographs are a high school pitcher who displayed proper biomechanics during testing.
"Torque" is rotational force. Whereas a force pushes or pulls a body segment, a torque produces or resists angular motion. A simple example is that when you bend your elbow to bring your hand toward your shoulder, your biceps (and other muscles) are applying an elbow flexion torque. When pitching from the windup, the pitcher rotates his back foot parallel and in front of the rubber, whereas when pitching from the stretch, the pitcher's back foot starts parallel and in front of the rubber. The front leg is then lifted and the pitcher strides towards the plate. In the windup, the leg lift occurs first; from the stretch, the front leg is not lifted as high and the leg lift and the stride occur more at the same time (as a strategy to control the running game).
From its maximum height, the front knee drops and then starts to stride toward the plate as the throwing hand takes the ball out of the glove.
As the front leg strides forward, the two arms swing down, apart and then up. The throwing hand should be on top of the ball during this motion. This is difficult for some youth pitchers due to small hands and limited strength, but all grown (post-puberty) pitchers should be able to keep their hand on top of the ball.
At the instant the front foot makes contact with the mound, the throwing arm should be rotated up as shown. Specifically, the throwing elbow should be lifted high enough to create an armpit angle ("abduction angle") of about 90 degrees. In other words, if you drew an imaginary line through the two shoulders, the throwing elbow should be on this line.
Another critical aspect of the arm is the "external rotation." That is, the forearm should be at about a 45-degree angle above horizontal at the instant of front foot contact. If the forearm is already vertical or past vertical, then the arm is too "early." Conversely if the forearm is not up enough -- that is, the hand is not much higher than the elbow -- the arm is too "late." For some pitchers, the arm is so late that at the time of foot contact, the hand is below the height of the elbow. The colloquial expression for this is "Inverted W." Pitchers with a late arm or early arm have poor timing between their upper body and lower body, increasing the risk of arm injury and reducing their ability to generate velocity.
At the instant of foot contact, the stride length should be slightly less than body height. It is also important that the front foot should step slightly across the back foot, with the front foot rotated slightly inward. By foot contact, the pelvis (hips) has started to rotate to face home plate, while the upper trunk (shoulder) has not started to rotate. This allows the pitcher to stretch the core muscles in his trunk for extra energy. If you look closely, you can see the muscles stretched in these front view and side view pictures of foot contact. A pitcher who rotates his lower trunk and upper trunk at the same time is not using his trunk enough.
Next is the "arm cocking" phase. During this dynamic phase, the front knee is straightened a little, in order to stop the lead hip moving forward and allow the pelvis to rotate (that is, allow the belly button to face the plate). The upper trunk then rotates to face the plate, while the arm rotates back into a fully cocked position (maximum shoulder "external rotation"). The elbow should still be bent about 90 degrees; in other words, the forearm and upper arm should be in a "L" shape. Maximum torques are produced at the elbow and shoulder near the time of maximum external rotation. These torques slow down the arm cocking and initiate the arm's forward rotation (shoulder "internal rotation").
Next is the "arm acceleration" phase. During this brief explosive phase, the arm straightens at the elbow then "internally rotates" at the shoulder. The arm acceleration phase ends at the instant of ball release.
There are many different "arm slots" at ball release. Some pitchers are more overhand, while others are more "3/4 arm" or sidearm. Regardless of the arm slot, the shoulder abduction angle should be about 90 degrees. In other words, different pitchers can have different tilts to their shoulder-to-shoulder line, but the throwing elbow should be approximately on the shoulder-to-shoulder line at the instant of ball release. Having the elbow far below or far above the shoulder line is dangerous for the tendons and ligaments in the shoulder joint.
A good follow-through is important for a pitcher's health. The arms, trunk and legs need a good follow-through to dissipate the energy in the throwing arm. For a 3/4 style pitcher, the throwing hand should come across the lead thigh. The hand will come across more toward the lead hip for a sidearm pitcher and more toward the lead knee for an overhand pitcher. The trunk should become close to horizontal, with the back of the throwing shoulder visible to the batter. The pitcher should be in a prepared position to defend himself against a line drive hit at him.
Each pitcher should strive toward the positions and timing of proper pitching mechanics to maximize his performance without placing undue stress on his elbow and shoulder. Proper mechanics are described here in general. While professional teams have used biomechanical analysis for years, advances in technology now give amateur players opportunities to measure their mechanics. However biomechanical technologies are just tools for coaches and players to determine what to work on. Proper mechanics are achieved by players and skilled instructors working together.
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Fleisig GS, Barrentine SW, Zheng N, Escamilla RF, Andrews JR. Kinematic and kinetic comparison of baseball pitching among various levels of development. J Biomech. 1999;32(12):1371-5.
Fleisig GS, Chu Y, Weber A, Andrews J. Variability in baseball pitching biomechanics among various levels of competition. Sports Biomech. 2009;8(1):10-21. doi:10.1080/14763140802629958.
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Courtesy of Glenn S. Fleisig, Ph.D., Chairman of the USA Baseball Medical & Safety Advisory Committee, Research Director of the American Sports Medicine Institute, Advisor to Major League Baseball and Consultant to Little League Baseball.