Importance Of The Trunk/Core in Pitching

Written By Sherry Werner

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Importance Of The Trunk Core While Pitching

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Without a doubt, arm motion is important in the windmill pitch. And, most of us agree that the legs play a big role in pitching. My last two articles were devoted to the importance of footwork and the legs. Very rarely, though, do you hear much about the part of the body connecting the legs and the arms- the trunk/core. If the forces used in pitching originate through the feet and legs and are eventually imparted through the arm and hand to the ball, the trunk and core must be important, too. Unless the forces generated at the ground are transferred properly through the trunk to the pitching arm, the pitching motion is inefficient.

During the stride, motion of the pivot foot allows the hips and trunk to open toward third base. This, in turn, allows the arm to “windmill” more freely and puts the trunk in position so that as the hips close, they can contribute to ball speed. The muscles of the trunk are larger than those of the arm and legs. It only makes sense to use these muscles to assist in propelling the ball. Due to the quickness of the windmill pitch (average time from stride foot contact to ball release is about one-tenth of a second!), the hips should open and close as quickly as possible. As the hips and trunk rotate toward a closed position (square with home plate), the throwing shoulder moves with the configuration of the muscles, tendons, ligaments and bones to make this process extremely complex. Coordination of joint movements ensure efficient transfer of force is very important.

Force production first comes into play at the end of the stance phase. As the pitcher's center of gravity shifts from being centered over the back (stride) foot to being centered over the front (pivot) foot, the stride begins. The front foot then presses against the ground (and the ground pushes back with an equal and opposite reaction). This force acts to move the body forward through the stride. As the stride foot touches down it then assists the pivot foot in creating forces to close the hips and drive the body forward. Once the ball is released, hip rotation and the drive of the stride leg should cause the pivot leg to move forward, and the pivot foot steps up toward the stride foot. This step forward assists in dissipating the energy built up in the arm.

Principles of and flaws in the mechanics of the stride

Just as proper positioning of the feet is important during the stance, stride foot placement is also vital to pitching performance. For each athlete there is an optimal stride length depending on body height, leg length, flexibility, etc. Problems result in both underestimating and overestimating this optimal length. Under-striding creates timing and force generation problems. A short stride does not afford the arm enough time to go through its motion, and lower body movements get ahead of upper body movements. If coordination between the lower and upper body is compromised, efficient flow of forces from the legs through the trunk to the arm is also compromised.

Over-striding causes a multitude of problems as well. Pitchers who over-stride tend to land on a straight stride leg. A slightly bent knee is more advantageous because knee flexion can absorb some of the vertical force on the stride leg. Otherwise, this force could manifest itself in hip and/or low back injury. A pitcher who does not close her hips has to use shoulder muscles to move her arm toward the release point. For obvious reasons, it would be more advantageous to use a large body part (the trunk), with more muscle mass, to move a small body part (the arm).

Failure to close the hips also goes against a widely accepted principle in Biomechanics. Proximal to distal sequencing refers to a pattern of timing in human movement where the body part closest to the center of the body reaches its maximum speed, then the next closest body part reaches its maximum velocity, and so on until the body part furthest from the body ‘s center reaches its peak speed. In pitching, when the hips are open to third base and begin to close, maximum hip rotation speed will occur before maximum shoulder rotation speed. Then, once peak shoulder speed is reached, elbow flexion velocity is maximized followed by peak wrist speed.

This sequencing is thought to maximize joint coordination and ball speed. If the hips are not rotated toward a closed position, this timing pattern is adversely affected. Lack of coordination caused by not closing the hips also creates an inefficient flow of forces between the legs and throwing arm. Although failure to close the hips is a more common problem in pitching, closing the hips too early also creates unnecessary stress on the shoulder. Closing the hips prematurely decreases the trunk's contribution to the pitch. Any time the trunk and arm are out of synch, efficiency of movement is compromised.

Another detrimental effect of not rotating the hips toward home plate is seen during the follow through. If the hips close, the arm moves with the body, but if the hips remain open, the arm moves forward and across the body. This causes unnecessary stretch and stress on the shoulder joint. Any time that the arm moves as a separate unit from the body, stress occurs at the joint (the shoulder) between the arm and the body. Closing the hips also tends to pull the pivot foot forward during the follow through so that the pitcher is in a good position to field the ball.

Opening the hips to third base occurs without much effort as the pivot foot turns outward and the stride foot moves forward. Closing the hips, however, requires a forceful contraction of several muscles. Although these pelvic, stomach and back muscles which rotate the hips are large, they are usually weak, especially in females. Often times these muscles are overlooked in pitching. Strength training programs focus on the arm and, to a lesser extent, the legs. A strong arm and legs cannot overcome weak trunk muscles. You have heard the adage, “You're only as strong as your weakest link.” The trunk (core) is just that- an important link between the legs and the throwing arm.

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Sherry Werner: PhD is currently a biomechanics consultant with TMI Sports Medicine, and Tulane Institute of Sports Medicine, and a pitching instructor at the Sherry Werner Fastpitch Academy. She has held research positions at the United States Olympic Training Center. She received a MS degree in Biomechanics from Indiana University, and a PhD in Biomechanics from The Pennsylvania State University.
Dr. Werner's research has focused on the effects of throwing motions at the shoulder, elbow and wrist. Past projects include data collection and analysis of elite softball pitchers during the 1996 Olympic Games. Sherry also released an instructional pitching DVD with Jennie Finch in 2011.

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