The Shoulder: Biomechanics of Pitching

Anatomy Review of the Shoulder: Bones

• Bones of the shoulder include the clavicle, scapula and the humerus

Anatomy Review of the Shoulder: Joints

• The shoulder consists of 5 articulations: The sternoclavicuar, acromioclavicular, coracoclavicular, glenohumoral, and the scapulothoracic

Movements of the Shoulder

• The shoulder is a highly unstable joint, allowing for extreme ranges of motion

• Pitching involves movements of the shoulder pertaining to all three planes of motion: saggital, frontal, and transverse

• Movements involving pitching include variations of abduction and adduction, flexion and extension, and internal and external rotation.

Movements of the Shoulder: Abduction and

Adduction• Abduction of the shoulder is controlled by

the supraspinatus and the deltoid

• Adduction of the shoulder is primarily controlled by the pectoralis major

Movements of the Shoulder: Flexion and

Extension • Flexion of the shoulder is primarily

controlled by the pectoralis major

• Extension of the shoulder is primarily controlled by the latissimus dorsi

Movements of the Shoulder: Internal and External Rotation

• Internal rotation of the shoulder is controlled by the subscapularis and teres major

• External rotation of the shoulder is controlled by the infraspinatus and teres minor

The Rotator Cuff

• There are four muscles that comprise the rotator cuff: The supraspinatus, the infraspinatus, teres minor, and the subscapularis

• In association with the deltoid, the four rotator cuff muscles are responsible for stabilization of the shoulder

The Rotator Cuff: Supraspinatus

• origin: medial 2/3 of supraspinatus fossa above spine of scapula

• insertion: superior surface of greater tuberosity of humerus and capsule of shoulder joint

• action: abduction of humerus at GHJ: stabilization of glenohumeral joint

• supraspinatus muscle contributes to GH stability, demonstrating peak activity in late cocking phase of throwing mechanics.

The Rotator Cuff: Infraspinatus

• origin: infraspinatus fossa of scapula

• insertion: posterior aspect of greater tuberosity of humerus, capsule of shoulder joint

• action: extension, horizontal extension and lateral rotation of humerus at the shoulder joint

• the infraspinatus is the primary muscle force resposible for external rotation

The Rotator Cuff: Teres Minor

• origin: middle half of the lateral scapular border

• insertion: inferior aspect of greater tuberosity of the humerus, capsule of shoulder joint

• action: lateral rotation of humerus at the shoulder (responsible for 45% of power of external rotation)

• aids in adduction and extension of humerus

The Rotator Cuff: Subscapularis

• origin: entire anterior surface of the subscapularis fossa

• insertion: lesser tuberosity of humerus and capsule of shoulder joint

• action: main action: glenohumeral head depressor and in certain positions allows extension, adduction and medial rotation of humerus at shoulder

• stabilization of the glenohumeral joint

The Six Phases of Throwing

• The pitching motion can be divided into six phases: windup, stride, arm cockingarm cocking, arm acceleration, arm deceleration and follow-through

The Windup Phase

• The windup phase initiates movement when the pitcher steps back with his front foot and positions his back foot against the rubber.

The Windup Phase

• During the windup phase, the activity of all shoulder girdle muscles are below 21% maximal muscle tension

• Injury appears unlikely during this phase

The Stride Phase

• During the stride phase, a pitcher moves his front foot toward home plate as the two arms swing down and apart from each other

The Arm Cocking Phase

• During the arm cocking phase, the pelvis and then upper trunk rotate to face home plate as the throwing arm externally rotates at the shoulder.

The Early Cocking Phase

• During the early cocking phase, the trapezius and serratus anterior muscles actively position the glenoid for the humeral head as the arm moves to 104 degrees of abduction, forming a force couple to upwardly rotate and protract the scapula, while the deltoids and supraspinatus abduct the arm

• Without proper positioning of the scapula, impingement results

• Without normal supraspinatus function, the deltoid is in a position to lever the head out of the joint with abduction

The Late Cocking Phase

• In the late cocking phase, the scapula provides a stable base for the rapid external rotation of the humerus

• The rotator cuff, pectoralis major, and latissimus dorsi are most active during late cocking, replacing deltoid activity

• The teres minor and infraspinatus fire concentrically, while the subscapularis fires eccentrically to stabilize the humeral head

The Arm Acceleration Phase

• The arm acceleration phase begins from the instant of maximum shoulder external rotation until ball release

The Arm Acceleration Phase

• The highest joint compression force (860 N) is seen at this time

• The pectoralis major contracts for adduction and internal rotation, while the teres minor offers a posterior restraint

• The latissimus dorsi generates the greatest internal rotation muscle activity, followed by the pectoralis major

The Arm Deceleration Phase

• The arm deceleration phase is from ball release until the arm stops internally rotating

The Arm Deceleration Phase

• The most violent phase of the throwing motion, and the one during which the shoulder is most vulnerable to injury

• The trapezius, serratus anterior, and rhomboids are all active, as are the deltoids

• The teres minor has the highest activity of all glenohumeral muscles

The Follow-Through

• The follow-through begins with maximum shoulder internal rotation and ends when the pitcher regains a balanced position.

• The follow-through phase has been described as a noncritical motion, since all shoulder girdle and upper extremity muscles exhibit activity below 42% maximal muscle tension

Contributing Works

• Thomas J. Gill, MD, Sherry Werner, PhD, Tricia Murray, Scott D. Mair, MD, and Richard J. Hawkins, MD: Pitching remains a prescription for injury. BioMechanics Magazine, August 1999

• Glenn S. Fleisig, PhD: Biomechanics of Throwing. American Sports Medicine Institute. February 17, 1998

• JHU Biomechanics Laboratory Projects: http://dodo.med.jhu.edu

• Wheeless’ Textbook of Orthopaedics: http://medmedia.com/05/182.htm

The Big Train

• He pitched for 21 years for the Washington Senators.

• Career record of 416 wins (second best in history) and 279 losses.

• Career ERA of 2.17 which is seventh best of all time.

• Ranks fifth all time in complete games wit 531. Ranks third all time in innings pitched with 5923.2 Ranks first all time in shutouts with 110.

• In 1913, pitched 56 consecutive scoreless innings, a record that stood until 1968 when it was broken by Don Drysdale.

• Eleven times his ERA was under 2.00.

• Led the American League in ERA five times. Led the American League in strikeouts twelve times.

• Led the American League in shutouts seven times.

• Led the American League in wins six times.

• In his career, he lost 27 games 1 - 0, and his team was shutout in 65 of his losses.

• Had a lifetime winning percentage of .599.

• He was one of the first five players elected to the Hall of Fame in 1936.

Walter Johnson