Shoulder Stress

Written By Sherry L. Werner

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Shoulder Stress

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In 1996, I was lucky enough to lead a research team in collecting high-speed video of the pitchers participating at the first ever Olympic softball competition in Columbus, GA. From the high-speed (120 frames per second) video we were able to calculate kinematic (i.e. location, speed, acceleration) and kinetic (i.e. joint forces and torques) parameters of the pitches. In Biomechanics we use these parameters to better understand human movement. Sport Biomechanics strives to improve performance and reduce the risk of injury through such analyses. Not much quantitative information is available in softball, especially on highly-skilled pitchers, so this was an important study. This month I will share with you some of the relevant findings of our study.

From the video data we sought to better understand the mechanics and joint stresses in windmill pitching. Average ball speed for the riseballs thrown by the 24 pitchers we studied was 60 mph. We chose to study riseballs because all of the pitchers threw that particular pitch. If the ball was released 38 feet (it's probably more like 35 feet!) from home plate, the batter would have approximately 0.40 second (just under one half of a second) to react to the ball once it was released. The shortest time in which a human can react to a stimulus is 0.12 second!

The main emphasis of the Olympic study was to quantify joint stress. In particular, we were interested in elbow and shoulder loads in windmill pitching. A joint force is a representation of a “push” or “pull” on the joint. In Biomechanics we line these forces up with axes of the body to provide a more meaningful interpretation. For example, a force oriented along the upper arm tends to either push the upper arm into the shoulder joint (compression) or pull it away from the joint (distraction).

Forces are calculated as a percentage of body weight so that all pitchers, regardless of size, can be compared to one another. Maximum shoulder distraction force for the Olympic pitchers was 80% body weight. This corresponded to approximately 150 pounds of force acting to pull the upper arm away from the shoulder joint at ball release.

A distraction force was also found at the elbow near ball release. This force was directed along the forearm, and therefore acted to “pull” the forearm away from the elbow. Average elbow distraction force was 61% body weight. The average elbow angle at release was 30 degrees short of full extension.

Based on this data it seems that elbow and shoulder stresses are high during the windmill pitch. Over time, the loads that these pitchers are taking on their arms will certainly affect the muscles, tendons and ligaments of these joints. Although we need to carry out more research to be able to make more generalizable conclusions, it seems that pitching mechanics can affect these joint stresses. In particular, using the trunk and lower body to generate and transfer energy during the pitch to assist in propelling the ball can reduce the load on the arm. Proper follow through also aids in dissipating these loads after ball release.

For a long time it has been said that softball pitching is a “natural” motion and that it was much easier on the arm than overhand throwing. The joint stresses found for the Olympic pitchers do not support this contention. At this point we are just beginning to understand what goes on in pitching. Until we get more concrete conclusions it is important for young pitchers to learn pitching styles based on sound mechanical principles and to understand the importance of strengthening the arms, legs and trunk.

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Arm Motion

Written By Sherry Werner

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Arm Motion

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For the last few months I have talked about footwork and the legs, hips and trunk in pitching. You probably have gotten the message that I feel that it is important to use the whole body in pitching to assist the arm in delivering the ball. In order to ensure efficient usage of the leg and trunk contributions, proper arm motion is also important. The arm has to be in synch with the rest of the body and be in the correct position relative to the body throughout the pitch to maximize force transfer.

As the ball is taken out of the glove, the arm begins its “windmill.” Once the top of the motion is reached, the arm should be fairly straight to increase leverage. The longer the lever, the less muscle force is necessary to impart the same velocity to the ball. A straight arm also stretches the muscles of the arm and shoulder, which leads to greater force production.

Also at the top of the motion, the arm needs to rotate at the shoulder joint so that the hand and ball face third base (for a right-handed pitcher). This rotation allows the arm to continue through the rest of the “windmill.” If the arm does not turn outward, the geometry of the bones and muscles of the shoulder joint will not permit a smooth path of the throwing arm.

For the pitchers I have studied, the path of the ball is not circular, but more oval-shaped. This path occurs in a plane very close to the body. As the arm passes the ear at the top of the motion and again as it passes the hip near release, it should be in close proximity to the body. When the ball is moved through a plane near the body it is easier to control the release point. Control problems occur when the arm moves out of the plane and away from the body. This happens most often when a pitcher’s windup causes the shoulders to open ahead of the hips. A right-handed pitcher who brings the glove and ball to the right hip will tend to have this problem. It is important for the shoulders to stay square (closed) to the target as the pitch is initiated. If the arm stays in a plane close to the body and does not have to adjust back into that plane for release, the pitch has a “built-in” control mechanism.

As the arm nears the release point, the elbow begins to bend (flex) and the wrist should be cocked (extended) in preparation for a rapid wrist snap (flexion) at release. In Biomechanics, proximal to distal sequencing is a term used to describe an efficient pattern of movement where the most proximal (closest to the center of the body) joint reaches maximum speed ahead of the next most proximal joint, down the chain until the most distal (farthest from the center of the body) joint reaches its maximum speed. This sequence is smooth and the force transfer is very efficient. In pitching, the shoulder (proximal) joint begins to flex once it reaches the top of the motion. Next, the elbow begins to bend (flex) and finally wrist snap occurs as the ball is released.

Wrist and elbow flexion should continue through release and the follow through. Although the ball is headed toward the catcher’s mitt as the follow through occurs, this is a critical phase of pitching. The energy and forces produced throughout the pitch remain in the throwing arm after ball release. This energy must be dissipated by the arm and body during the follow through. Continuing to bend the elbow and wrist after ball release shortens the arm lever and acts to decrease shoulder stress.

During the delivery phase of pitching, the anterior (front) shoulder muscles contract to propel the ball. Once ball release occurs, however, the posterior (back) shoulder muscles come into play to slow down and stop the arm’s motion. Strengthening of the pitching arm is important, but the posterior muscles are often overlooked. Strong posterior shoulder muscles can minimize shoulder flexion after ball release, which in turn decreases shoulder stress.

In past issues I have stressed the importance of strengthening the musculature of the feet, legs, hips and trunk. Because of the loads placed on the elbow and shoulder joints in pitching, it is equally imperative to strengthen the arm and shoulder girdle. In the studies that have been carried out on windmill pitching so far, the magnitude of force pulling on the shoulder joint at release has been, on average, 100 percent body weight. Reducing this stress with proper pitching mechanics and increasing the joint’s ability to absorb these loads through strength training are our only avenues to reduce the chance of chronic overuse injuries in pitching.

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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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Use Your Legs

Written By Sherry Werner

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Use Your Legs

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Last month I stressed the importance of footwork during the initial stages of the windmill pitch. To recap: Proper foot placement in the stance phase allows for good balance, which is critical to rhythm and coordination, and efficient force generation. The feet are the only body parts in contact with the ground, and the force produced as the feet push against the resistance of the ground are ultimately imparted to the ball.

To elaborate on how the forces flow from the ground to the ball, I will use the analogy of several cars in a train representing “segments” of the body (i.e. the foot, lower leg, thigh, etc.). If a force is imparted to a car at one end of the train, a chain of events will occur. Part of the initial force will in turn be imparted by the first car on the next car through their point of connection (i.e. a joint, such as the ankle, knee or hip). The orientation of the two cars relative to one another will determine what effect the force has on the second and each successive car of the train. Although this example is very simplified, it does reflects what happens in the body.

In pitching, the muscles of the leg contract in order for the foot to push against the ground. In reaction, the ground provides resistance and a push, equal and opposite, is imparted to the foot. Part of this force, plus additional forces due to motion of the foot, are then passed to the lower leg through the ankle joint. Likewise, force is passed from the lower leg to the thigh via the knee joint, from the thigh to the trunk via the hip joint, etc. This description is also oversimplified. The orientation and configuration of the muscles, tendons, ligaments and bones make this process extremely complex. Coordination of joint movements to 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. Understriding 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.

Overstriding causes a multitude of problems as well. Pitchers who overstride 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 stride that is too long also reduces the range of motion of the hips as they rotate from an open to a closed position. As the distance from the pivot foot to the stride foot increases, so does the stretch across the muscles at the front of the hips. Eventually the limits of these muscles’ lengths are reached and hip rotation is stopped short of full rotation. The longer the stride, the harder it is to close the hips.

A third problem that occurs in overstriding is movement of the center of gravity down and backward in relation to the stride foot. The longer the stride, the lower the center of gravity and the farther the distance from the center of gravity to the stride foot. If the goal of the movement is to move the body forward, the center of gravity should be high and forward in relation to the stride foot. “Sitting back” does not allow the body to assist the arm in propelling the ball forward.

Overstretching of the muscles of the stride leg also makes it difficult for the muscles to push against the ground. When a muscle is at maximal length it does not have good leverage, and can therefore create little force. All in all, overstriding minimizes the contribution of the lower body since hip rotation is hindered and force generation is minimized. This places the burden of force production on the throwing arm. Striding toward the target is the most efficient path.

Lateral position of the stride foot is also important. If we use a straight line from the center of the pivot foot to the apex of home plate as a guideline, placement of the stride foot too far to the left or right of this line will result in inefficient hip rotation. The farther to the left of the line the foot is placed (for a right-handed pitcher), the more closed the hips are at stride foot contact, thus reducing the potential for hip rotation during the delivery phase. Conversely, if the stride foot placement is too far to the right of the line, the hips tend to remain open and do not contribute to ball speed. Stride foot orientation follows the same logic. If the foot points toward first base, the lower leg and thigh will also rotate in that direction tending to close the hips prematurely. A stride foot pointing toward third base causes rotation in the opposite direction and makes it difficult to close the hips. Optimal orientation of the stride foot is half way between completely open and completely closed.

The legs act to generate force, rotate the trunk and absorb energy throughout the pitch. Considering these lower body contributions, it seems imperative for pitchers to strengthen the muscles of the feet, lower legs and thighs. The trunk (back and stomach muscles) needs to be strengthened as well since it is the link between the lower body and the arm. The shoulder, elbow and wrist joints cannot do it alone. Use of the legs in pitching is all-important.

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Footwork Is Critical

Written By Sherry Werner

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The importance of initial Foot Position

Footwork is a critical element in the windmill softball pitch. Considering that your feet are the only body part to make contact with an external source (the ground), the force used to propel the ball ultimately starts with the feet as they press against the resistance of the ground. Force is generated through the feet and moves through the ankles, knees, hips, trunk, shoulder, elbow, wrist, fingertips and is eventually transferred to the ball. Forces are passed through the joints via the muscles, tendons, ligaments and bombs of the limbs and trunk. Efficient flow of the forces is enhanced by smooth and coordinated movement patterns.

The feet form the foundation or base of support for the body in most athletic movements, softball included. This foundation is the fundamental component of balance, rhythm and timing, which are all necessary for safe and efficient pitching. A wide base of support (i.e. standing with feet spread wider than shoulder-width apart) creates a very stable position. The drawback of a wide base of support is that it can restrict proper joint action and make it difficult to initiate movement. For example, forward striding, walking, or jumping motions are more difficult to execute when the feet are spread wider than shoulder-width apart.

Conversely, a narrow base of support, with the feet to close together (or in the extreme, standing on one foot), allows for easier body movement, but body balance is compromised. An unstable foundation makes coordination of force production very difficult. If a pitcher begins off balance, force generation at the ground will not be optimal and force flow through the joints will not be well coordinated. This combination of reduced leg drive and poor joint interaction could result in shoulder injuries because arm stress is increased.

A suggested pitching stance for young pitchers is one with the feet about shoulder-width apart and the legs are relaxed and comfortable. This allows for freedom of joint movement, yet still maintains sufficient balance and stability. Staggering the feet on the rubber provides additional stability. Figure 1 shows a staggered position with the toes of the stride foot (the left foot for a right-handed pitcher) in contact with the back edge of the pitching rubber and the pivot (non-stride) foot extending over the front edge of the rubber.

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Footwork and the Initial Weight Shift

Once the pitcher find a comfortable position with her feet staggered on the rubber, most of her weight should be centered over her back foot. First movement of the pitch is a weight shift or transfer forward over the pivot (non-stride) foot. The placement of this foot, extending over the front edge of the rubber, enables the foot to push more efficiently during the stride. You may have heard the Physics adage, “For every action there is an equal and opposite reaction.” This is exactly what happens between the ground and the pitcher's feet. As the feet push against the ground (and the rubber, which is fixed to the ground), the ground pushes back with an equal and opposite reaction. This is the origination of much of the initial force which moves the body forward and which is ultimately transferred to the ball. Ball velocity is highly dependent on how quickly the non-stride foot pushes backward against the ground/rubber. The quick, backward push results in an explosive stride towards the target.

With the pivot foot out over the front edge of the rubber, the ankle can extend somewhat, putting the foot in a better position to push against rubber and ground with the ball of the foot. Although “digging a hole” with the pivot foot allows the foot to generate more force backward, it is not advisable since it can hinder the foot's ability to pivot effectively.

In Biomechanics there is a term “degrees of freedom” (DOF). This refers to the number of body parts or joints allowed to move in a skill. The more DOF, the more difficult it is to control and coordinate body movement.

Extraneous motion makes the movement pattern more complicated and in a sense the brain becomes overloaded, resulting in diminished performance. When accuracy is an issue, as it is in pitching, coordination and control are extremely important. Pitchers with a lot of pre-pitch “pump” motion are those who start with their stride foot far behind the rubber, requiring more body part to move in order to initiate the pitch, are many times more susceptible to balance, control and accuracy problems.

It is clear that the lower body plays a vital role in pitching. The muscles of the legs push the feet against the ground to generate force which is passed through the trunk to the throwing arm and eventually to the ball. Foot placement, proper weight transfer to the ball of the pivot foot and explosive push towards the target are paramount in order for leg power to be produced efficiently.

Next month I will talk more about the stride and the importance of the legs in pitching.

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Windmill Wisdom

Written by Sherry Werner

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Windmill Wisdom

Recognizing the need for a scientific basis in softball pitching, Fastpitch Softball Magazine has asked me to write a monthly column devoted to the science of pitching. I will use this first column as an introduction to give you an idea of my background and softball research experience.

I have been addicted to softball since I was eight years old. Growing up in southeastern Pennsylvania, my summers were consumed with softball. My mother was my biggest fan and “team mom” for all of my teams (including college, I think!). My father was the coach for every team I was on and he was a pitching coach, relying on very little information out there at the time. They continue to be my biggest fans and “coaches” today. Thanks, Donna and John!

We were involved in Little League, Big League and ASA competition. As a pitcher and shortstop in high school I was first team all-league and named to the all-decade team. In college, I played second base and was a four-year letter winner at Slippery Rock University. After my junior year I was selected as an Academic All-American.

Although I pitched when I was young, I did not know much about the windmill pitch until I went to college. As a Physical Education major I began learning how to teach skills like pitching, and at the same time my father was attending pitching clinics. Through him I learned a lot about the windmill pitch. When I went to Indiana University to pursue a Master of Science in Biomechanics, the obvious choice for my thesis topic was the windmill pitch.

One of the first steps in a research project is a review of related literature. My review of softball research did not take long. Although many books, articles and videotapes exist that are written by coaches, only a handful of scientific studies had been undertaken. This emphasized in my mind the need for solid research in softball. Two years later, I had completed the first ever three-dimensional analysis of windmill pitching. My thesis investigated the timing of the pitch, the path of the ball, factors contributing to ball velocity and stresses on the shoulder.

When I graduated from Indiana, I was offered a research assistantship at the Olympic Training Center in Colorado Springs, CO to work in the Sport Science Department. Sport Science consists of Biomechanics, Exercise Physiology and Sport Psychology. Biomechanics, which is my area of expertise, is the study of human movement. The goals of Sport Biomechanics are to improve performance and reduce the risk of injury. Basically, we apply Physics, Biology and Engineering principles to athletics. High-speed videography, force measurement and computer analysis are used to evaluate sport skills. In my opinion, it is our job to carry out research and be able to bridge the gap between high-tech science and the coaches and athletes.

From Colorado I moved to Birmingham, Alabama, where I worked at the American Sports Medicine Institute with James Andrews, MD. Because I worked with a group of orthopedic surgeons, our research was geared toward prevention, detection, and rehabilitation of athletic injuries. Although I did have a chance to evaluate a few injured windmill pitchers, most of my time was spent analyzing the stresses on the elbow in baseball pitching. Never one to stray too far from softball, I also coached a Dixie Youth team and ran informal pitching clinics for seven to twelve year-old girls.

Although coaching has provided many memorable moments, my biggest thrill came in a phone call from my former boss, Head of Biomechanics at the Olympic Training Center. She asked if I would assist her staff and act as a softball consultant in collecting data at the Pan Am softball tryouts. Once softball was officially declared an Olympic sport for 1996, ASA (the National Governing Body of softball) had better access to the Training Center and asked for biomechanical testing. We collected high-speed video data on six of the top pitchers at the tryout. We also collected force data on the stride foot of one pitcher (whose last name was Fernandez!). Along with the stride foot force analysis, I calculated the loads on the shoulder and elbow joints from the video data.

Since my first experience with elite pitchers, I have gotten a PhD in Biomechanics from Penn State, carried out a study on the pitchers at the 1996 Olympics, worked at Steadman-Hawkins Sports Medicine in Vail, CO, Tulane University in New Orleans LA, TMI Sports Medicine in Arlington, TX and now am a private biomechanics consultant and pitching instructor. Recently I collaborated with Jennie Finch and her dad, Doug, on 2 instructional DVD's based on science and medicine.

The need for a scientific basis in pitching is obvious. We need to know if the “proper” mechanics we are teaching young girls are safe and efficient. Gradually, more and more interest is being shown in getting the facts on pitching. I will attempt in future columns to share with you the results of my research, studies that are done by other scientists and the science behind the art of pitching. I hope you are as excited as I am that Fastpitch Softball Magazine is giving us this opportunity.

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