Using the principles of biomechanics, explain how a starting pitcher in baseball gains maximum curve, power and accuracy when throwing a 'Curve ball'

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How can the pitcher accurately throw the ball to the desired target?

In order for a pitcher to achieve optimum accuracy with their pitch they need apply perfect summation of forces through the six distinctive phases of the pitch. The six phases are: Wind up, stride, arm cocking, arm acceleration, arm deceleration and the follow through. (Figure 1)





Figure 1: Six distinct phases of a biomechanically correct baseball pitch



The Wind up phase puts the pitcher in a good starting position making sure that the pitcher is perfectly balanced by keeping the pelvis straight and still plus putting your weight on the back foot rotating the body 90 degrees and the front leg is bent and has a high hip thrust to end this phase. This is the phase where the pitcher creates potential energy as they are storing this energy to use for their pitching motion. The stride phase begins when the front leg begins to fall and move towards the desired target, the front foot lands with a stride length of 80-90% of the pitcher's height with high braking and vertical impulses which is an example of Newton's Third law 'For every action there is an equal and opposite reaction' with the foot producing a vertical force on the ground; the ground then exerts an equal and opposite force back into the foot stopping the foot from sinking into the ground.  With this large step the pitcher is now creating a larger centre of mass and lower centre of gravity in order to maintain optimum balance. (Hay, 1993). The arm cocking phase begins after the foot makes contact with the ground creating a horizontal ground reaction force which leads to the pitcher rotating their  hips and upper body therefore twisting until facing front on with the batter, the shoulder begins to extend while the elbow is still remains flexed. This phase is where the pitcher begins to produce maximum kinetic energy from the potential energy stored in the wind up phase.The phase ends with the pitcher applying angular velocity externally rotating their shoulder to maximum capability of 180 degrees. The optimum angle for a pitcher to cock their arm should be between vertical and horizontal (approximately 70 degrees) which will severely affect the accuracy of the pitch plus putting too much force on the elbow and shoulder ultimately leading to injury.  The arm acceleration phase is the shortest phase of the sequence taking approximately 50msec to complete as it requires the production of large impulses. The phase starts from the maximum shoulder rotation around an axis, then the pitcher will use their hip and torso rotation as well as their shoulder and elbow to create as much angular momentum as possible in the shoulder. The pitcher's angle and height of release needs to be at the optimum angle and height for maximum accuracy and speed which is called the three quarters arm slot (figure 2).  If the release angle or height becomes too high or low then accuracy will be sacrificed in order to compensate for the poor mechanics created. The end of the arm acceleration phase is where all the kinetic energy created is imparted onto the ball and released with maximum kinetic energy. (Houglam, 2010). The Arm deceleration phase starts when a braking impulse is applied to the arm after the ball has been released and ends when the pitcher has completed the internal shoulder rotation movement. During the deceleration and the follow through phase the Law of Conservation of Momentum takes place 'The total (angular) momentum of a system remains constant unless external forces influence the system.'  The pitcher's arm will be constantly rotating unless the braking force is applied which allows the arm to influence the momentum and decelerate. The back leg begins rotating around an axis as the pitcher is following with the momentum and preparing to balance themselves for the follow through creating a propulsive impulse with the front foot. (Blazevich, 2010). The follow through begins when the maximum internal shoulder rotation has ended. The pitcher will now regain their balance by lowering their centre of gravity and widening their centre of mass. The phrase 'timing is everything' applies to pitching not only the summation of forces but of the ball release. Cross describes the different outcomes behind a late ball release and an early ball release which severely affects pitching accuracy.

"The pitcher must release the ball at a very precise moment during his throwing action. If he releases the ball a fraction too early, the ball will travel toward or above the batter's shoulders. If the ball is released too late, the ball will travel toward or below the batter's knees."  (Cross, 2011, p.75.)

 



Figure 2: Diagram of the three quarters arm slot.

 



 



 

 

 

 

Video 1: Detroit Tigers pitcher Justin Verlander biomechanically perfect pitch

 

 

 

 

 

How is maximum acceleration achieved?

 

The curveball is not a pitch that requires a high amount of speed however, the quicker the curveball the greater chance of pitching a strike. On average the curveball ranges from speeds of 60-80mph. Many biomechanical and technical factors can influence the velocity of a pitch. To maximise your pitching velocity the pitcher needs a lot of kinetic energy in the energy output of the skill, also the weight transfer during the stride phase is very important in terms of a pitcher's centre of mass and momentum. Perfect timing of the sequence is essential in order to obtain maximum velocity from the pitch. It is very important for the pitcher to not spend too much time on the back leg in the wind-up stage due to a high chance of the back leg collapsing and the production of momentum and velocity is severely reduced. The most common mistake made by pitchers is that the arm cocking stage begins before the transfer of weight on to the leading hip and leg therefore losing large amounts of velocity. The pitcher's stride needs to be around 80-90% of their height because if the pitch is too short the arm acceleration is reduced dramatically therefore affecting the force imparted on the ball. pitchers will increase their velocity when they get the arm involved later so that the body can build more forces that end up as arm speed later at ball release. If you do not move fast enough or create enough kinetic energy moving from the back leg to the front leg then there will not be enough energy to transfer from the legs to drive hip rotation and to the trunk to drive trunk rotation which is what whips the arm through at high speed.

"the lower extremity, pelvis, and trunk are the larger segments that produce the muscular torques that accelerate the smaller distal segments. These base segments have greater moments of inertia meaning they exhibit smaller angular velocities as they rotate. The smaller distal segments  have smaller moments of inertia, but move with greater angular velocities." (Hurd. et.al., 2011, p.292.)

 Elbows are always fully extended and their elbows are just below the level of their shoulders regardless of the arm slot that they throw from. The extension velocity of the wrist and fingers create high acceleration and velocity on the ball until it leaves the fingers which is an example of Newton's first law of motion where 'An object will remain at rest or continue to move with constant velocity as long as the net force equals zero.' The object at rest is the ball and it will remain at rest until the external force of the throw turns it into a projectile.

A large amount of torque and forces are required to pitch a baseball at high speeds which puts stress on the shoulder, elbow and forearm. In the elbow and forearm there are two torques applied: flexion torque and varus torque. The flexion torque occurs during the arm acceleration phase and requires approximately 50 Nm (Newton metres) and the varus torque occurs during the arm cocking phase which requires 52 Nm. There are three forces applied to the elbow and forearm which are the medial force, peak anterior force and the proximal force. The medial force occurs during the arm cocking phase and produces 250 N (Newtons), the peak anterior force is applied during the arm acceleration phase and produces a force of 300 N.  The proximal force which produces the most force of the whole movement occurs right after the ball release during the deceleration phase, it produces a force of 800 N.  The shoulder of a pitcher applies a number torques which is why injury is common when poor mechanics are applied. The torques applied to the shoulder are abduction torque, horizontal adduction torque and internal rotation torque. Three of the torques occur during the arm cocking stage: abduction torque is applied with 45 Nm which is lowest torque or force applied in the movement. Horizontal adduction torque applies 65 Nm and the internal rotation torque applies 52 Nm. The two torques adduction torque and horizontal abduction torque are applied during the arm deceleration phase. The horizontal abduction torque applies 63 Nm  and the adduction torque applies 70 Nm to the shoulder. There are three large and distinct forces applied by the shoulder during the arm cocking and arm deceleration phases: anterior/posterior, superior/inferior and proximal forces. The anterior shear force and superior force are both applied during the arm cocking phase. The anterior shear force produces 280 N and the superior force produces 250 N. The posterior and inferior forces are produced during the arm deceleration phase. The posterior force produces 295 N and the inferior force produces 230 N. These are the maximum forces required in order to achieve maximum angular momentum, acceleration and velocity. As you can see from the values the correct summation of forces is needed for optimal force and torque production with the larger muscles moving first in order for the smaller muscles to gain maximum speed and momentum. (Sabick. et.al. 2004.).

 

 

How does a Pitcher achieve maximum curve through the air?

 

To throw the curveball and impart maximum curve on the ball the correct grip is one of the most important aspects otherwise there is a high chance the throw will be unsuccessful. The pitcher places the middle finger on and parallel to one of the long seams, and the thumb just behind the seam on the opposite side of the ball such that if looking from the top down, the hand should form a "C shape" with the horseshoe pointing in towards the palm following the contour of the thumb. The index finger is placed alongside the middle finger, and the other two extraneous fingers are folded in towards the palm with the knuckle of the ring finger touching the leather. (Brancazio, 1997). (figure 3).

 

Figure 3: An example of the curveball grip.

 As previously discussed the six phases of a pitch are applied but with slight modifications to impart the required spin. The phase that requires the modification is the arm acceleration phase as the release of the ball is crucial towards the success and failure of the pitch. The pitchers arm will be at a 90 degree angle through the arm acceleration phase and the wrist is rotated facing inwards towards the pitcher for both left and right handed pitchers. At the top of the acceleration phase the pitcher will snap the arm and wrist in a downward motion. The ball first leaves contact with the thumb and tumbles over the index finger thus imparting the forward or "top-spin" characteristic of a curveball. The result is the exact opposite pitch of the four-seam fastball's backspin, but with all four seams rotating in the direction of the flight path with forward-spin. The amount of spin that the pitcher can impart depends on the kinetic energy imparted into the ball and how hard they can snap their arm and wrist over the ball, the harder the snap the greater spin imparted. Majority of the force and torque comes from the elbow, biceps and forearm which is why safety and correct mechanics are crucial to avoid injury. Due to the unnatural action of the curveball the pitcher has to sacrifice some velocity in order to gain more spin. (Briggs, 1959).

When thrown correctly with maximum accuracy and controlled velocity, the ball could break from 7 to as much as 20 inches in comparison to the same pitcher's fastball.  the Magnus effect describes the laws of physics that make a curveball curve. A curveball, thrown with topspin,

creates a higher pressure zone on top of the ball, which deflects the ball downward in flight. Instead of counteracting gravity, the curveball adds additional downward force, thereby gives the ball an exaggerated drop in flight. (figure 4). (Adair, 1995).  

 

Figure 4: Magnus effect of a curveball

 

 

 

 

 

 

 Video 2: How to throw a curveball (putting it all into practice)

 

 

 

 

 

 

 

Reference List:

 

Adair, K., The physics of baseball. Physics today, 1995. Harper Collins, New York.

 

Blazevich, A.J. (2010). Sports biomechanics the basics: optimising human performance. Bloomsbury, London, UK.

 
Brancazio, P. (1997). The Mechanics of a Breaking Pitch. New York:  Department of Physics, Brooklyn College,


Briggs, L. J. (1959). Effect of Spin and Speed on the Lateral Deflection (Curve) of a Baseball; and the Magnus Effect for Smooth Spheres.  Washington D.C:  National Bureau of Standards. 

Cross, R., (2011). Physics of baseball and softball, Springer. New York. 


Ferrer, R & Watts, R.G (1986). The lateral force on a spinning sphere: Aerodynamics of a curveball. New Orleans:  Department of Mechanical Engineering.

 

Fleisig G.S, Kingsley D.S, Loftice J.W, Dinnen K, Ranganathan R, Dun S, Escamilla RF, Andrews J.R. (2006). Kinetic comparison among the fastball, curveball, change‐up, and slider in collegiate baseball pitchers. The American Journal of Sports Medicine 34(3) pp.423‐430.

Fortenbaugh, D,  Fleisig, G., & Andrews, J.R., (1995). Baseball pitching kinematics, joint loads, and injury prevention, Journal of Sport and Health Science, vol. 23(2) pp. 233-239.

 

Hay, J.G., (1993). Biomechanics of Sports Techniques, Prentice-Hall. New Jersey.

Hurd, W.J.,  Kaplan, K.M., Neal, S.,  Jobe, F.W.,  Morrey, B.F,  & Kaufman, K.F .(2011). Glenohumeral Rotational Motion and Strength and Baseball Pitching Biomechanics, Journal of Athletic Training, Vol. 46(3) pp.289–295.

Sabick MB, Torry MR, Kim YK, Hawkins RJ. (2004). Humeral Torque in Professional Baseball Players , American Journal of Sports Medicine, Vol. 32(4), pp.892-898.

Stodden DF, Fleisig GS, McLean SP, Andrews JR. (2005).  Relationship of Biomechanical Factors to Baseball Pitching Velocity: Within Pitcher Variation, Journal of Applied Biomechanics. Vol. 21(1) pp.44-56.

Whiteley, R. (2007). Baseball throwing mechanics as they relate to pathology and performance-A review,  Journal of Sports Science and Medicine  Vol.6, pp.1– 20.  

 

Video 1: Justin Verlander pitching mechanics, 2009.  http://www.youtube.com/watch?v=mbVQc2gYjFQ accessed on: 8/4/13

 

Video 2: How to throw a curveball. (2007). http://www.videojug.com, or http://www.youtube.com/watch?v=yK-v7B0H4wM . standard youtube licence, accessed on: 8/4/13.

Figure 1: Fleisig,G.S,  Barrentine,S.W, Zheng, N, Escamilla, R.F,  Andrews, J.R.  (1999). Kinematic and kinetic comparison of baseball pitching among various levels of development. Journal of Biomechanics, American Sports Medicine Institute. Vol. 32(12), pp. 1371–1375.

 

Figure 2: Three quarter arm slot diagram, accessed on: 9/4/13  http://www.chrisoleary.com/projects/PitchingMechanics101/Essays/PitchingMechanics.html

 

Figure 3: Curveball grip example, http://baseball.about.com/od/curveball/ss/curveball1.htm 

accessed on: 10/4/13

 

Figure 4: Magnus effect of a curveball, http://www.stevetheump.com/HR_physics.htm accessed on: 15/4/13.