95 miles per hour: Physiology of Pitching (Technical)

Introduction

Nationals_Rockies_Baseball-00baa-27438Recent technological advancements through scientific research have had an impact on nearly everything we know, including sports. Research is constantly undertaken in physiology and the basic sciences to develop training protocols that maximize physical gains through optimal training protocols. Additionally, experts using high-speed cameras and sophisticated software programs evaluate technique and movement to find the most efficient way to perform a movement. All this and more is done to improve performance at all levels of athletics.

At the Major League level, pitchers throw at extreme velocities with precise control. No one exemplifies this trend better than the young star in Washington D.C., Stephen Strasburg. In his first 127 innings this season, he leads the league in average fastball velocity at 95.9 mph (FanGraphs Pitching Leaderboard 2012). Not only that, he is also able to effectively change speeds by throwing a curveball at an average speed of 80.5 mph and a change-up at 88.8 mph, leading to a third best 160 strikeouts (FanGraphs Pitching Leaderboard 2012, Major League Baseball Statistics 2012). Furthermore, his control is remarkable as shown by only giving up 34 walks to this point (Major League Baseball Statistics 2012). A common metric for individual pitching performance is the strikeout to walk ratio; Strasburg is third in the league at 4.71 (Major League Baseball Statistics 2012). Clearly, he is one of the most dominant power throwers in professional baseball right now.

Although pitchers do have an advantage in baseball, their job still comes with obstacles.  Strasburg must throw a 9-ounce baseball 60 feet and six inches into what is called the strike zone. The strike zone, as defined by Major League Baseball, is only 17 inches wide and runs upward from just below the kneecap to the midline between the shoulders and the belt (Major League Baseball Commissioner’s Office 2012). Not only is it difficult to throw the ball in this zone consistently, but also the batter at the plate is trying to make contact with the ball whenever it gets close. Experienced pitchers know a combination of throwing hard, changing velocities, and being accurate are the keys to maximizing the chances the ball will miss the sweet spot of the bat. Although Strasburg is an elite athlete who has learned how to do all these things extremely well, the principles behind his ability to throw the ball and be successful are ones that can be applied to any pitcher at any level.

In order to understand the more complex mechanisms at play in the throwing motion, a basic background into the fundamentals of anatomy and physiology is necessary. Many people know that muscles are the functional units that allow the body to move, but most know little else about what a muscle is composed of and how it works to achieve movement. Additionally, few people understand what the body must go through to fuel the movement of muscles.

The human body contains 400 skeletal muscles which work to achieve movement (Fox 1987). At a fundamental level, muscle is made up proteins (Seeley et al 2006). Muscles work by burning energy in order to create contractile force, which shortens the length of the muscle.  Muscle shortening can easily be seen when the arm goes from straight to bent by flexing at the elbow. Contraction occurs in the biceps brachii during this movement, but there is more than just that occurring.

If only one muscle group were associated with that part of the body, once a person flexed their biceps the arm would remain in that position; thankfully, this is not the case.  An antagonist group of muscles, the triceps brachii, which relaxed and extended when the biceps contracted, is now able to contract, straightening the arm. Most muscles within the body have this agonist-antagonist duality that allows us to function in a practical manner (Seeley et al 2006).

In order for triceps, biceps, or other muscles to move the body, they have to be attached to the skeleton in some manner.  This is the function of tendons, which are a type of fibrous connective tissue that have the strength to withstand tensile forces (Medline Plus Dictionary 2012). When a muscle contracts, it exerts a force on the tendon which pulls on the bone, creating movement (Plowman and Smith 2008). The direction of movement is determined by the direction the fibers are orientated and where the tendon is anchored(Plowman and Smith 2008).

What most people consider a single muscle is actually composed of many smaller units called myofibrils or muscle fibers (Plowman and Smith 2008). Each muscle fiber is composed of myofilaments, T tubules, and sarcoplasmic reticulum, among other things (Plowman and Smith 2008). Figure 1 gives a visual of the hierarchy of the muscle fiber.

The smaller myofilament houses the functional unit of the muscle, the sarcomere. The sarcomere consists of two major filaments: a thick filament composed of the protein myosin and a thin one composed of actin and tropomyosin, two proteins (Huxley and Hanson 1954, Seeley et al. 2006, Plowman and Smith 2008, Medline Plus dictionary 2012). A series of steps must take place in order for a signal from the brain to make a muscle contract.  First, calcium is released inside the cell, which changes the alignment of the tropomyosin, exposing sites where the heads of the myosin filaments can attach (Plowman and Smith 2008). After the myosin heads attach to the actin, forming a cross-bridge, they perform a power stoke to shorten the length of the fiber (Plowman and Smith 2008). A simple way to envision this ratchet type movement is to hold the forearm out straight and flex at the wrist. Now, adenosine triphosphate (ATP), the fuel source of cells, attaches to myosin, releasing the cross-bridge bond (Plowman and Smith 2008). The myosin heads return to their initial position so the process can repeat again to continue shortening of the muscle.  This process happens extremely fast and takes place many times over the length of contraction. The number of myofibrils that are recruited to carry out this action depends on the force required by the activity.

The ATP required for muscle contraction is produced in the body through three different systems. Although it is important to note that the three systems are not mutually exclusive, each system is the prime energy producer in different intensities of exercise.  Aerobic cellular respiration takes place when oxygen is present in the system, which generally occurs during long and light exercise like jogging or bicycling (Baechle and Earle 2008). The second system, anaerobic glycolysis, functions at higher intensities and shorter durations, like running a 200-meter sprint or biking up a steep hill (Baechle and Earle 2008). Finally, the ATP-PC system activates during high intensity activities that last only a few seconds (Baechle and Earle 2008). Simply based on this information, it is easy to see that pitching requires the use of the latter two energy systems to supply fuel.

Muscles Involved With the Pitch

When it comes to pitching, the muscles used to throw can be thought of as residing in two main categories: accelerators and decelerators. Of course, the accelerators are the ones that produce the high-speed velocities seen from Strasburg and others. However, decelerators are just as important in the throwing motion. A simple analogy is to think of having a car with a working gas pedal, but lacking any braking system.

During the delivery of the pitch, the muscles in the rotor cuff fire at a moderate intensity (Jobe et al. 1983, Escamilla and Andrews, 2009). Since these muscles function to keep the joint in place, their activity during this stage should be expected (Escamilla and Andrews, 2009). Furthermore, the deltoids show a moderate level of activity, which is attributed to the need for shoulder stabilization during the delivery (Escamilla and Andrews, 2009). Once the ball is released and the deceleration process beings, these muscles increase their activity to aid in injury prevention (Jobe et al. 1983, Escamilla and Andrews, 2009). Since the arm acts as a whip during the acceleration stage; these muscles assist in braking at the shoulder and preventing the ball of the humerus from coming out of the socket.

Moving to the upper arm, the biceps brachii show most activity after release of the ball (Jobe et al. 1984, Escamilla and Andrews, 2009). The biceps work in conjunction with the rotator cuff muscles to keep the shoulder in place.  The opposite is the case with the antagonist group, the triceps brachii.  Since this muscle group functions by extending the arm at the elbow, it should make sense that high muscle activity can be seen during acceleration and low activity during deceleration.

The last two upper body areas of activity that will be examined are the chest (pectoralis major) and the back (latissimus dorsi and the upper part of the subscapularis).  The pectoralis major has a high level of activity during the acceleration phase and a lower moderate level during the deceleration phase (Escamilla and Andrews, 2009). In the back, both aforementioned muscle groups exhibit extremely high levels of activity during acceleration.  Therefore, it can be concluded that these two groups play an important role in force generation. Although their activation levels are still considered high during deceleration, the forces are almost half of what is produced during the acceleration phase (Escamilla and Andrews, 2009).

Although data is somewhat sparse when it comes to force generation in the legs and core, some studies do indicate that these areas are important for force production and injury prevention (MacWilliams et al. 1998, Willardson 2007, Coleman 2009, Lehman et al. 2012). In his 2009 article, Dr. A. Coleman estimates that 50% of the power produced by a pitcher comes from the legs, with 30% initiating in the core and only 20% coming from the shoulder (Coleman 2009) Essentially, both the push off and landing phases have the ability to transfer energy up the trunk and impart force on the baseball.  This means that for as wiry as Strasburg is, he has the ability to generate tremendous amounts of force from his lower body and core.

Implications for Pitchers

Proper care must be taken in any sport to aid in avoiding injury.  For pitchers, the most delicate place is the glenohumeral joint in the shoulder.  Therefore, it is absolutely imperative that the musculature in this region be trained with carefully thought-out protocols (Escamilla and Andrews, 2009). Additionally, shoulder problems can start with inconsistencies in other locations.  For example, some throwers may experience anterior shoulder instability due to weak latissimus dorsi muscles and an overcorrection in the rotator cuff (Escamilla and Andrews, 2009). This indicates the need for strong back muscles to allow for proper muscle recruitment during maximal recruitment.

As stated above, the legs and core can be thought of as contributing approximately 80% to the force production in the throw.  Prepared athletes will use this knowledge to improve flexibility and strength in all aspects of the core.  This means that not only do the abdominal muscles need to be strengthened, but the lower back and hip muscles (flexors, extensors, adductors, abductors) do as well. Since so much power is generated in the legs, total lower body strength should be emphasized during training to create velocity and reduce the reliance on the shoulder (Perelli 1996, Coleman 2009). In a study soon to be published by Lehman et. al., they describe that lateral to medial jumps (side to side) have the highest correlation to an increase in velocity in comparison to other common lower body strengthening techniques (Lehman et al. 2012).

Training the muscles is not enough; the athlete must also train the appropriate fuel systems for optimal performance. It is the author’s opinion that since the duration of the pitching activity falls within the ATP-PC system and anaerobic metabolism, that these are the energy producing systems that should be trained. Although aerobic conditioning is necessary to build endurance, maximal force production likely comes from the other two energy producing systems and should be trained accordingly. This means a training regimen should include many short duration explosive activities done many times to simulate the short explosive nature of a pitch. It is important to remember that any training program should be done under the guidance and direction of trained professionals.  There is no magic formula that will maximize strength while eliminating the risk of injury, as exemplified by Steven Strasburg himself.

By: Josh Silvernagel, Graduate Student, Bioengineering, University of Utah
Josh Silvernagel received undergraduate degrees in Exercise Science and Mathematics from Bemidji State University (BSU) in Bemidji, MN.  During his undergraduate studies, he was a four year starter in baseball for the BSU Beavers, where he both pitched and played infield.  In addition to providing sport specific training for ametuer and professional athletes following school, Josh spent two years coaching the sport at both the collegiate and high school levels.  He is currently working on a Ph. D. in Bioengineering at the University of Utah, where he studies cardiac electrophysiology in the CARMA Center.  Josh and his wife, Danielle, are recently married.

References

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Coleman, A E. 2009. Training the power pitcher. Strength and Conditioning Journal 31: 48–58.

Escamilla, R.F. and J.R. Andrews. 2009. Shoulder muscle recruitment patterns and related biomechanics during upper extremity sports. Sports medicine (Auckland, N.Z.) 39: 569– 90.

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Fox, S. I. 1987. Human Physiology. William C Brown, Dubuque, Iowa, USA.

Huxley, A. F., and R. Niedergerke. 1954. Structural changes in muscle during contraction: Interference microscopy of living muscle fibres. Nature 173: 971–973.

Huxley, H. and J. Hanson. 1954. Changes in the cross-striations of muscle during contraction and stretch and their structural interpretation. Nature 173: 973–976.

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Jobe, F.W., J.E. Tibone, J. Perry and D. Moynes. 1983. An EMG analysis of the shoulder in and pitching throwing preliminary report . American Journal of Sports Medicine 11: 3–5.

Lehman, G., E.J. Drinkwater and D.G. Behm. 2012. Correlation of throwing velocity to the results of lower body field tests in male college baseball players. Journal of Strength and Conditioning Research / National Strength and Conditioning Association 3979.

MacWilliams, B., T. Choi, M.K. Perezous, E.Y. Chao, and E.G. McFarland. 1998. Characteristic ground-reaction forces in baseball pitching. The American Journal of Sports Medicine 26: 66–71.

Major League Baseball Commissioner’s Office. (2012). Official rules of major league baseball. Retrieved from http://mlb.mlb.com/mlb/official_info/official_rules/foreword.jsp

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Medline Plus Dictionary. (2012). Tendon. Retrieved from http://www.nlm.nih.gov/medlineplus/mplusdictionary.html

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Plowman, S. and D. Smith. 2008. Exercise Physiology for Health, Fitness, and Performance. Kippincott Williams and Wilkins, Philadelphia, PA, USA.

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Willardson, J. 2007. Core stability training: applications to sports conditioning programs. Journal of Strength and Conditioning Research 21: 979–985.

Articles by Josh Silvernagel.

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