Biomechanics of Baseball Pitching

By, Sean Light CSCS

SLStrength.com

Pitching is one of the most complex and stressful movements in all of sports. As baseball strength and conditioning coaches, pitching presents a unique challenge for training. Bodily stress, fatigue and muscle imbalances are all big concerns when training a baseball pitcher. Specifically, the shoulder endures a tremendous amount of stress during the pitching motion.

Throughout the six stages of throwing, the shoulder will go through three basic movements. Flexion, abduction, and rotation.

Flexion is the act of raising your arms straight out in front of you at a ninety-degree angle. An example of shoulder flexion can be found in many horror films when zombies rise from the dead and slowly walk with their arms straight out in front of them.

Abduction is the act of raising your arm to ninety-degrees. If you made yourself into the human form of the letter “T,” then you will have abducted both of your shoulders.

Rotation has two different forms, internal and external. If you abduct your arms with your palms down, the act of switching to palms up would be external rotation. The switch from palms up to palms down is conversely, internal rotation.

The combination of these three movements will allow you to throw an object.

There are three bones that are primarily used in the pitching movement. The clavicle (collar-bone), humerus (upper arm; bone between elbow and shoulder) and the scapula (shoulder blade).

We can’t talk pitching without mentioning the rotator cuff and the labrum.

The rotator cuff stabilizes the shoulder. It is made up of four different muscles, the subscapularis, supraspinatus, infraspinatus and the teres minor.

The labrum also helps stabilize the shoulder. The glenohumeral joint (where your humerus connects to the scapula) is very shallow and unstable thus creating instability. The labrum is a ring of cartilage surrounding this joint which deepens the socket and allows for greater stability.

The pitching motion is broken down into six different segments.

The first is the wind-up. This is when the pitcher begins his motion until he reaches the height of his leg kick. This segment is primarily used to create a rhythm and prepare the body for the ensuing pitch. The lower body is the primary mover here.

The second segment is the stride and early cocking. This is when the front foot begins to advance towards home plate and the hands separate and the throwing arm is dropped.

Next we have late cocking. This is when the torso rotates towards the target, the lead foot makes ground contact and your shoulder reaches maximal abduction and external rotation. This phase produces the most rotator cuff activity. Depending on your arm slot will also determine the amount of force placed on your deltoid and supraspinatus as these two muscles work to abduct your arm past ninety-degrees.

Another term pitchers and their coaches should know is valgus. Valgus is the pressure that forces your hand out and your elbow in. The momentum during late cocking will produce some valgus force.

During late cocking, several muscles act as restraints in order to prevent the arm from cocking too far.

At the end of late cocking, your lumbar spine (lower back) will extend forward in order to increase the amount of force that your throwing arm can produce.

The fourth segment is acceleration. This is when your arm converts from eccentric to concentric action or when your arm stops going backwards and begins to move forward. During this phase, your arm achieves extremely fast internal rotation. During this phase, your scapula protracts, or moves forward, along the scapulothoracic articulation. The serratus-anterior (rotates and protracts the scapula) and the pectoralis major (largest chest muscle) are highly active here. The subscapularis and latissimus dorsi (the muscles that create the V shape in your back) also contract during this motion.

The fifth phase, deceleration, is the most stressful on the arm. Deceleration is when the all is released and the arm begins to slow down. The arm is slowed by a great deal of eccentric (muscle lengthening) force. The rotator cuff, especially the infraspinatus and teres minor combat momentum in order to slow down the arm. The biceps also is put to work to minimize stress on the elbow.

The final motion is the follow through. This is where many injuries to the rear shoulder occur. During this motion it is important that the pitcher complete a full follow through so that the arm can minimize the amount of force it must absorb to slow down the arm. The stride leg can soak up some force and a good follow through can decrease the amount directed at the shoulder.

Because of the excessive stress on the shoulder, a plethora of injuries are possible. They include impingement, which is contact between the greater tuberosity and the acromioclavicular (AC) joint and scapula dyskinesis, which is the lack of full retraction of the scapula during cocking.

SOURCES:

Maranowski PhD, Michelle, “The Biomechanics of Pitching,” http://www.sciencebuddies.org/science-fair-projects/project_ideas/Sports_p053.shtml

“Biomechanics of the Shoulder and Throwing,” http://wings.buffalo.edu/eng/mae/courses/417-517/Orthopaedic%20Biomechanics/Biomechanics%20of%20the%20Shoulder%20and%20Pitching.pdf

Houglam PhD, ATC, PT, Peggy A. “An Analysis of the Biomechanics of Pitching in Baseball,” http://www.humankinetics.com/excerpts/excerpts/an-analysis-of-the-biomechanics-of-pitching-in-baseball