This document provides an overview of shoulder biomechanics as they relate to pitching a baseball. It begins with an anatomy review of the shoulder bones and joints. It then describes the various movements involved in pitching, including those in the sagittal, frontal, and transverse planes. Specific muscles that control shoulder abduction, adduction, flexion, extension, and internal/external rotation are identified. The six phases of pitching - windup, stride, arm cocking, arm acceleration, arm deceleration, and follow-through - are outlined. Details are provided on muscle activity and stresses on the shoulder during each phase. The rotator cuff muscles and their actions are defined. Biomechanical factors that can lead to shoulder injury during

1. The Shoulder:
Biomechanics of Pitching

2. Anatomy Review of the
Shoulder: Bones
• Bones of the shoulder include the clavicle,
scapula and the humerus

3. Anatomy Review of the
Shoulder: Joints
• The shoulder consists of 5 articulations:
The sternoclavicuar, acromioclavicular,
coracoclavicular, glenohumoral, and the
scapulothoracic

4. 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.

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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

11. 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

12. 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

13. 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

14. 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.

15. 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

16. 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

17. 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.

18. 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

19. 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

20. The Arm Acceleration Phase
• The arm acceleration phase begins from the
instant of maximum shoulder external
rotation until ball release

21. 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

22. The Arm Deceleration Phase
• The arm deceleration phase is from ball
release until the arm stops internally
rotating

23. 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

24. 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

25. 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

26. 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.

27. Walter Johnson