Kinesiology of the Shoulder and Scapula:

by Brent Brookbush DPT, PT, MS, PES, CES, CSCS, ACSM H/FS

Scapulohumeral Rhythm: The actions of the shoulder are paired with actions of the scapula. This serves to both increase the available range of motion of the upper extremity, and allows the glenoid fossa to be positioned in a more stable position in relation to the humeral head. For example, shoulder abduction is accompanied by upward rotation - this increases the amount of gleno-humeral abduction available by moving the acromion process “out of the way,” and this positions the glenoid fossa partially under the humeral head providing mechanical stability to downward force. The analysis below pairs each shoulder joint action with the accompanying scapular movement.

Shoulder Horizontal Adduction and Scapular Protraction:

Shoulder Horizontal Adduction (Horizontal Flexion)

• Prime Mover: Pectoralis major
• Synergists: Anterior deltoid
• Antagonists: Posterior deltoid
• Neutralizers: Posterior deltoid , infraspinatus, and teres minor neutralize internal rotation force created by the anterior deltoid and pectoralis major . Middle deltoid , latissimus dorsi , teres major , and coracobrachialis neutralize ancillary motion in the frontal plane.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Protraction

• Prime Mover: Serratus anterior
• Synergist: Pectoralis minor
• Antagonist: Mid traps , rhomboids
• Neutralizers: Upper and lower trapezius muscle acts to prevent downward rotation, and the lower trapezius muscles act to prevent elevation, and downward rotation.
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Shoulder Horizontal Abduction and Scapular Retraction:

Shoulder Horizontal Abduction (Horizontal Extension)

• Prime Mover: Posterior deltoid
• Synergists: N/A
• Antagonists: Pectoralis major , anterior deltoid
• Neutralizers: Anterior deltoid and subscapularis neutralize external rotation force created by agonists and synergists. Middle deltoid , latissimus dorsi , teres major , and coracobrachialis neutralize ancillary motion in the frontal plane.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Retraction

• Prime Mover: Middle trapezius
• Synergist: Rhomboids
• Antagonist: Serratus anterior , pectoralis minor
• Neutralizers: Upper and lower trapezius muscle  acts to prevent ancillary motion in the frontal plane (elevation and depression).
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Shoulder Flexion and Scapular Upward Rotation:

Shoulder Flexion

• Prime Mover: Anterior deltoid
• Synergists: Pectoralis major (clavicular head) , coracobrachialis , biceps brachii
• Antagonists: Latissimus dorsi , posterior deltoid , teres major , long head of triceps
• Neutralizers: Posterior deltoid , infraspinatus, and teres minor neutralize internal rotation force created by the prime mover and synergists. Middle deltoid may contribute to flexion if the arm is internally rotated, or it may act to neutralize adduction forces created by the prime mover and synergists if the arm is in a neutral position.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Upward Rotation

• Prime Mover: Serratus anterior
• Synergist: Upper and lower trapezius
• Antagonist: Pectoralis minor , rhomboids , levator scapulae
• Neutralizers: Lower trapezius muscle acts to prevent elevation caused by upper trapezius .
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Shoulder Extension and Scapular Downward Rotation:

Shoulder Extension

• Prime Mover: Latissimus dorsi
• Synergists: Posterior deltoid , teres major , long head of triceps
• Antagonists: Anterior deltoid , pectoralis major (clavicular head) , coracobrachialis , biceps brachii
• Neutralizers: Posterior deltoid , infraspinatus, and teres minor neutralize internal rotation force created by the prime mover. Middle deltoid may neutralize adduction force created by prime mover.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Downward Rotation

• Prime Mover: Pectoralis minor
• Synergist: Rhomboids , levator scapulae
• Antagonist: Serratus anterior , upper and lower trapezius
• Neutralizers: Lower trapezius muscle acts to prevent elevation force created by synergists, and the anterior tipping force created by pectoralis minor .
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Shoulder Abduction and Scapular Upward Rotation:

Shoulder Abduction

• Prime Movers: Anterior and middle deltoid
• Synergists: Supraspinatus
• Antagonists: Latissimus dorsi , pectoralis major (sternal head) , teres major , coracobrachialis , long head of triceps, infraspinatus, teres minor , subscapularis
• Neutralizers: Posterior deltoid , infraspinatus, and teres minor neutralize internal rotation force created by the anterior deltoid .
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Upward Rotation

• Prime Mover: Serratus anterior
• Synergist: Upper and lower trapezius
• Antagonist: Pectoralis minor , rhomboids , levator scapulae
• Neutralizers: Lower trapezius muscle acts to prevent elevation caused by upper trapezius .
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Shoulder Adduction and Scapular Downward Rotation:

Shoulder Adduction

• Prime Mover: Latissimus dorsi
• Synergists: Pectoralis major (sternal head) , teres major , coracobrachialis , long head of triceps, infraspinatus, teres minor , subscapularis
• Antagonists: Anterior deltoid , middle deltoid , supraspinatus
• Neutralizers: Posterior deltoid , infraspinatus, and teres minor neutralize internal rotation force created by the prime mover and synergists.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Downward Rotation

• Prime Mover: Pectoralis minor
• Synergist: Rhomboids , levator scapulae
• Antagonists: Serratus anterior , upper and lower trapezius
• Neutralizers: Lower trapezius muscle acts to prevent elevation force created by synergists, and the anterior tipping force created by pectoralis minor .
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Shoulder Internal and External Rotation:

Note: Shoulder rotation is not strictly paired with a specific movement of the scapula

Internal Rotation:

• Prime Movers: Subscapularis
• Synergist: Anterior deltoid , pectoralis major , latissimus dorsi , teres major
• Antagonists: Posterior deltoid , infraspinatus, teres minor
• Neutralizers: Biceps brachii, long head of triceps, middle deltoid , and coracobrachialis neutralize ancillary motion in the sagittal and frontal plane. The supraspinatus prevents neutralizes the adduction force created by the prime movers.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

External Rotation:

• Prime Movers: Infraspinatus, teres minor
• Synergist: Posterior deltoid
• Antagonists: Subscapularis , anterior deltoid , pectoralis major , latissimus dorsi , teres major
• Neutralizers: Biceps brachii, long head of triceps, middle deltoid , and coracobrachialis neutralize ancillary motion in the sagittal and frontal plane. The supraspinatus prevents neutralizes the adduction force created by the prime movers.
• Stabilizers: Rotator cuff – supraspinatus , infraspinatus, teres minor , subscapularis
• Fixators: Scapular muscles, intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Elevation and Depression:

Note: Scapular elevation and depression are not strictly paired with a specific shoulder movement or another scapular action. They likely function to allow movement of the glenohumeral joint in various transverse planes, or to extend movement in the frontal plane.

Scapular Elevation

• Prime Mover: Upper trapezius
• Synergist: Levator scapulae , rhomboids
• Antagonists: Lower trapezius , pectoralis minor
• Neutralizers: The serratus anterior and rhomboids must carefully balance upward and downward rotation to prevent excessive motion in either direction caused by the prime mover and synergists.
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

Scapular Depression

• Prime Mover: Lower trapezius
• Synergist: Pectoralis minor
• Antagonists: Upper trapezius , levator scapulae , rhomboids
• Neutralizers: The lower traps and stabilizers of the scapulae neutralize the anterior tipping force created by the pectoralis minor .
• Stabilizers: Serratus anterior , rhomboids , levator scapulae
• Fixators: Intrinsic stabilization subsystem , rectus abdominis , internal and external obliques , quadratus lumborum , erector spinae

© 2011 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged -