18/02/2026
The shoulder joint is one of the most mobile joints in the human body, capable of moving through multiple planes to allow functional reach, lifting, and rotational control. The image illustrates three primary shoulder motions — abduction, flexion, and internal rotation — each involving coordinated activity between the glenohumeral joint, scapula, clavicle, and thoracic spine.
Arm abduction occurs in the frontal plane and begins with activation of the supraspinatus, which initiates the first degrees of movement. As elevation continues, the deltoid becomes the primary mover, generating upward force to raise the arm. To maintain joint stability, the rotator cuff compresses the humeral head into the glenoid fossa, preventing superior migration. Simultaneously, the scapula rotates upward through the coordinated action of the upper trapezius, lower trapezius, and serratus anterior. This scapulohumeral rhythm preserves subacromial space and prevents impingement.
Arm flexion occurs in the sagittal plane and involves the anterior deltoid, clavicular head of pectoralis major, coracobrachialis, and biceps brachii. As the arm elevates forward, the scapula protracts and upwardly rotates to maintain optimal alignment. Thoracic extension contributes to full range of motion, while the rotator cuff stabilizes the humeral head to ensure smooth joint motion.
Internal rotation of the arm occurs around the longitudinal axis of the humerus. The primary muscles responsible include the subscapularis, pectoralis major, latissimus dorsi, and teres major. This motion is essential for functional tasks such as reaching behind the back, tucking in clothing, and stabilizing the arm during pushing activities. Proper scapular positioning ensures efficient rotational movement and prevents anterior shoulder stress.
Biomechanically, these movements depend on the maintenance of joint congruency and muscular balance. The rotator cuff provides dynamic stabilization, while the scapular stabilizers ensure a stable base for humeral motion. Without this coordination, excessive humeral translation may occur, increasing the risk of impingement and soft tissue injury.
Thoracic spine mobility and posture significantly influence shoulder mechanics. Restricted thoracic extension or forward shoulder posture can alter scapular positioning and reduce available motion, forcing compensatory movements that increase strain on surrounding tissues.
Efficient shoulder movement requires harmony between mobility and stability. Strengthening the rotator cuff, enhancing scapular control, and maintaining thoracic mobility are essential to preserve shoulder health, optimize performance, and prevent injury.
