Kinesiology of the Shoulder and Scapula:
by Brent Brookbush DPT, PT, MS, CPT, HMS, IMT
From the Course:
Additional Courses
- Lesson 7: Scapular Muscles (Introductory Course)
- Lesson 8: Introduction To Deltoids (Introductory Course)
- Sternoclavicular (SC), Acromioclavicular (AC), and Scapulothoracic (ST) Joint Anatomy (Advanced course)
- Shoulder Joint Anatomy (Glenohumeral Joint) (Advanced Course)
Definitions:
- Prime Mover : The muscle that can produce the most force for a joint action. Generally, this is the muscle that will generate the most force during a joint action when exerting force against an external load.
- Agonist : Muscles that perform a joint action, including the prime mover and synergists. That is, unlike the terms prime mover and synergist, agonist refers to all of the muscles that can perform a joint action.
- Synergist : Synergists are muscles that assist the prime mover in performing a joint action. By definition, all agonists that are not the prime mover are synergists.
- Antagonist : Muscles that oppose the agonists (including the prime mover and synergists) for a given joint action. That is, all of the muscles that can perform the opposing joint action.
- Neutralizer : During a joint action, neutralizers are muscles that oppose the unwanted or ancillary joint motions that result from the force generated by the prime mover and/or synergists.
- Fixator : Fixators are muscles that act to reduce or prevent movement of joints proximal to the joint in motion.
- Stabilizer : The role of a stabilizer is to improve arthrokinematics by maintaining optimal alignment of joint surfaces during joint actions. Most often, these muscles are the most intrinsic muscles of a joint. For example, the muscles of the rotator cuff of the shoulder.
Kinesiology of the Shoulder and Scapula
Scapulohumeral Rhythm: The actions of the shoulder are paired with the actions of the scapula. This serves to 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 -