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
- 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