MOT548 Shoulder Muscles and Movements

Prime Movers

Shoulder flexion prime mover

Anterior deltoid

Shoulder extension prime mover

Latissimus dorsi

Shoulder abduction prime mover

Supraspinatus

Shoulder horizontal adduction prime mover

Pectoralis major

Shoulder protraction prime mover

Serratus anterior

Shoulder internal rotation prime mover

Subscapularis

Shoulder external rotation prime mover

Infraspinatus

Muscle Functions

Trapezius function

Stabilize, elevate, depress, rotate, and retract the shoulder blades (scapulae)

Biceps function

Elbow flexion, forearm supination

Supraspinatus function

Shoulder abduction

Scapular movements

Scapular elevation and depression movement

Shrugging the shoulders

Scapular elevation muscles

Levator scapulae, upper trapezius, and rhomboids

Scapular depression muscles

Pectoralis minor, lower trapezius, ACJ, and latissimus dorsi

Scapular protraction and retraction movement

Reaching forward and pinching shoulders

Scapular retraction muscles

Rhomboids and lower/middle trapezius

Upward and downward scapular rotation

Inferior angle of scapula rotating up/lateral or down/medial

Scapular upward rotation muscles

Serratus anterior and trapezius

Scapular downward rotation muscles

Rhomboids, levator scapulae, and pectoralis minor

Scapulohumeral rhythm

Coordinated movement of the scapula and humerus

Scapulohumeral rhythm ratio

2 degrees of humeral movement for every 1 degree of scapular movement

Scaption

Lifting arms in scapular plane, halfway between flexion and abduction

Benefit of scaption

Reduces stress in the shoulder

Winged scapula

Medial border does not stay anchored to thorax, causing a protruding scapula

Winged scapula cause

Weakness of serratus anterior, causing scapula to fail to glide on ribcage

Pec major

Pec major

Origin: medial half of clavicle, sternum, cartilages of first 6 ribs

Insertion: crest of greater tubercle of humerus

Rotator Cuff Muscles

Supraspinatus

Elevates the shoulder joint out to the side

Origin: supraspinous fossa of scapula

Insertion: greater tubercle of humerus

Infraspinatus

Externally rotates the shoulder joint; helps pull arm back

Origin: infraspinous fossa of scapula

Insertion: greater tubercle of humerus

Teres Minor

Externally rotates the shoulder joint; provides stability

Subscapularis

Allows humerus to move freely during elevation of the arm

Origin: subscapular fossa of scapula

Insertion: lesser tubercle of humerus