Coaching Baseball Pitchers By Michael G. Marshall, Ph.D. Copyright 2008
     2.  Chapter Fourteen:  The Shoulder Joint

         a.  Shoulder Joint Bones

     The Humerus bone is the bone of interest in the Shoulder Joint.  The head of the Humerus bone articulates with the Glenoid Fossa of the Scapula bone.  The Glenoid Fossa has a very shallow fossa.  While the shallowness of the Glenoid Fossa decreases the stability of the Shoulder Joint, it also increases the range of motion of the Shoulder Joints.  This means that the Humerus bone has a three hundred and sixty degree full circle range of motion.

     Anteriorly, the Gleno-Humeral ligaments stabilize the head of he Humerus bone in the Glenoid Fossa.  Superiorly, the Coraco-Humeral ligament suspends the head of the Humerus bone.

     A circular band of connective tissue called, the ‘Labrum,’ attaches to the rim of the Glenoid Fossa.  Its purpose is to stabilize the head of the Humerus bone in the Glenoid Fossa.  The long head of the Biceps Brachii muscle attaches to the Labrum on its superior border and the posterior head of the Triceps Brachii muscle attaches to the Labrum on it inferior border.

         b.  Shoulder Joint Kinesiological Joint Actions

     The movements of the Humerus bone define the kinesiological actions of the Shoulder Joint.  The Humerus bone moves forward and backward, up from and down to sides, forward and backward from shoulder high positions and rotate inwardly and outwardly.

1)  Abduction:  When the Humerus bone upward from the sides of the body.
2)  Adduction:  When the Humerus bone down to the sides of the body.
3)  Extension:  When the Humerus bone backward from the sides of the body.
4)  Flexion:  When the Humerus bone forward from the sides of the body.
5)  Horizontal Extension:  When the abducted Humerus bone moves backward.
6)  Horizontal Flexion:  When the abducted Humerus bone moves forward.
7)  Inward Rotation:  When the Humerus bone inwardly rotates.
8)  Outward Rotation:  When the Humerus bone outwardly rotates.

         c.  Shoulder Joint Muscles (09)

     Shoulder Joint muscles attach to the Humerus bone and the Scapula.

             01)  Coracobrachialis

     The Coracobrachialis muscle arises from the Coracoid Process of the Scapula bone and inserts into the middle of the medial side of the mid-shaft of the Humerus bone.  Therefore, when the Coracobrachialis muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Coracobrachialis muscle adducts and flexes the Shoulder Joint.

     During the acceleration phase of the baseball pitching motion, the Coracobrachialis muscle inwardly rotates the Humerus bone of their pitching upper arm.

             02a)  Deltoid, Anterior

     The Anterior deltoid muscle arises from the lateral one-third of anterior surface of the Clavicle and inserts into the deltoid tuberosity on the lateral side of the mid-shaft of the Humerus bone.  Therefore, when the Anterior Deltoid muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Anterior Deltoid muscle abducts and flexes the Shoulder Joint.

     During the acceleration phase of the baseball pitching motion, the Anterior Deltoid muscle inwardly rotates the Humerus bone of their pitching upper arm.

             02b)  Deltoid, Middle

     The Middle Deltoid muscle arises from the superior surface of the acromion process of the Scapula bone and inserts into the middle portion of the deltoid tuberosity of the Humerus bone.  Therefore, when the Middle Deltoid muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Middle Deltoid muscle abducts the Shoulder Joint.

     During the deceleration phase of the baseball pitching motion, the Middle Deltoid muscle outwardly rotates the Humerus bone of the pitching upper arm.

             02c)  Deltoid, Posterior

     The Posterior Deltoid muscle arises from the superior surface of the spine of the Scapula bone and inserts into lateral portion of the deltoid tuberosity of the Humerus bone.  Therefore, when the Posterior Deltoid muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Posterior Deltoid muscle abducts and extends the Shoulder Joint.

     During the deceleration phase of the baseball pitching motion, the Posterior Deltoid muscle extends and outwardly rotates the Humerus bone of the pitching upper arm.

             03)  Pectoralis Major

     The Pectoralis Major muscle arises from the medial one-third of the anterior surface of the Clavicle, the Sternum and the anterior surfaces of the first through seventh ribs (R1-R7) and inserts into the lateral lip of the bicipital groove on the anterior surface of the head of the Humerus bone.  Therefore, when the Pectoralis Major muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Pectoralis Major muscle flexes and inwardly rotates the Shoulder Joint.

     During the acceleration phase of the baseball pitching motion, as the antagonist muscle to the Trapezius I muscle, the Pectoralis Major muscle must not contract at all.

             04)  Subscapularis

     The Subscapularis muscle arises from the entire internal surfaces of subscapular fossa of the Scapula bone and inserts into the lesser tuberosity of the head of the Humerus bone.  Therefore, when the Subscapularis muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Subscapularis muscle adducts and inwardly rotates the Shoulder Joint.  The Subscapularis muscle is the anterior-most of the four rotator cuff muscles.

     During the acceleration phase of the baseball pitching motion, the Subscapularis muscle inwardly rotates the Humerus bone of their pitching upper arm.

             05)  Infraspinatus

     The Infraspinatus muscle arises from the infraspinatus fossa on posterior surface of the Scapula bone below its spine and inserts into the middle facet on the posterior surface of the head of the Humerus bone immediately below the attachment of the Supraspinatus muscle.  Therefore, when the Infraspinatus muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Infraspinatus muscle extends the Shoulder Joint.  The Infraspinatus muscle is the third anterior-most of the four rotator cuff muscles.

     During the deceleration phase of the baseball pitching motion, the Infraspinatus muscle extends and outwardly rotates the Humerus bone of the pitching upper arm.  The Infraspinatus muscle is the second posterior-most muscles of four rotator cuff muscles.

             06)  Latissimus Dorsi I

     The Latissimus Dorsi II muscle arises from the spinous processes of the seven through ninth thoracic vertebrae (T7-T9), to the posterior/superior surfaces of the nine through twelfth ribs (R9-R12) and to the superior surfaces of the Iliac Crest and inserts into the medial lip of the bicipital groove on the anterior surface of the proximal end of the Humerus bone.  Therefore, when the Latissimus Dorsi II muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Latissimus Dorsi II muscle extends and inwardly rotates the Shoulder Joint.

     During the acceleration phase of the baseball pitching motion, the Latissimus Dorsi I muscle powerfully inwardly rotates the Humerus bone of the pitching upper arm.

     During the deceleration phase of the baseball pitching motion, the Latissimus Dorsi I muscle horizontally extends the Humerus bone of the pitching upper arm.

             07)  Supraspinatus

     The Supraspinatus muscle arises from the supraspinatus fossa on the posterior surface of the Scapula bone above its spine and inserts into the first facet on the top of the head of the Humerus bone.  Therefore, when the Supraspinatus muscle contracts, these structures move closer together.  This means that, in the anatomical positin, the Supraspinatus muscle abducts the Shoulder Joint.  The Supraspinatus muscle is the second anterior-most of the four rotator cuff muscles.

     During the acceleration phase of the baseball pitching motion, the Supraspinatus muscle powerfully inwardly rotates the Humerus bone.

     During the deceleration phase of the baseball pitching motion, the Supraspinatus muscle outwardly rotates the Humerus bone.

             08)  Teres Major

     The Teres Major muscle arises from the inferior one-third of posterior surface of the axillary border of the Scapula and inserts into the medial lip of the bicipital groove of the Humerus bone immediately outside of the attachment of the Latissimus Dorsi I muscle.  Therefore, when the Teres Major muscle contracts, these structures move closer together.  This means that, in the anatomical position, the Teres Major muscle extends the Shoulder Joint.

     During the acceleration phase of the baseball pitching motion, the Teres Major muscle powerfully inwardly rotates the Humerus bone.

     During the deceleration phase of the baseball pitching motion, the Teres Major muscle horizontally extends the Humerus bone.

             09)  Teres Minor

     The Teres Minor muscle arises from the middle one-thirds of posterior surfaces of axillary border of the Scapula bone and inserts into the third facet on the posterior surface of the head of the Humerus bone immediately below the attachment of the Infraspinatus muscle.  Therefore, when the Teres Minor muscle contracts, these structures move closer together.  This means that, in the anatomical positin, the Teres Minor muscle outwardly rotates the Shoulder Joint.  The Teres Minor muscle is the fourth anterior-most muscle of the rotator cuff muscles.

     During the deceleration phase of the baseball pitching motion, the Teres Minor muscle outwardly rotate the Humerus bone of the pitching upper arm.

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Free Coaching Baseball Pitchers Book!!!                          Chapter Fifteen