Shoulder Joint Movements: Flexion, Extension, Rotation, and More

What are the movements possible at the shoulder joint?

The shoulder joint, specifically the glenohumeral joint, is a highly mobile ball-and-socket joint that permits an extensive range of motion in multiple planes, crucial for the arm's versatility in daily activities and athletic performance.

Understanding the Shoulder Joint's Mobility

The shoulder joint, or glenohumeral joint, is formed by the articulation of the head of the humerus (upper arm bone) with the glenoid fossa of the scapula (shoulder blade). Its shallow socket and loose joint capsule, while contributing to its remarkable mobility, also make it inherently less stable than other joints, relying heavily on surrounding muscles, tendons, and ligaments for support. The movements possible at this joint are primarily dictated by its anatomical structure and the actions of the rotator cuff and other periarticular muscles.

Primary Movements of the Glenohumeral Joint

The shoulder joint allows for movement in three primary planes: sagittal, frontal (coronal), and transverse (horizontal).

Flexion and Extension (Sagittal Plane)

• Shoulder Flexion: This movement involves lifting the arm forward and upward, away from the body.
  • Example: Raising your arm to point straight ahead or overhead, as in an overhead press or a front raise.
  • Muscles Involved (Primary): Anterior deltoid, coracobrachialis, pectoralis major (clavicular head), biceps brachii (long head).
• Shoulder Extension: This movement brings the arm backward and downward, or from a flexed position back towards the anatomical position, or even further behind the body.
  • Example: Bringing your arm down from an overhead position, or pushing it backward as in the end phase of a triceps pushdown or a rowing motion.
  • Muscles Involved (Primary): Latissimus dorsi, teres major, posterior deltoid, triceps brachii (long head).

Abduction and Adduction (Frontal Plane)

• Shoulder Abduction: This movement involves lifting the arm sideways and upward, away from the midline of the body.
  • Example: Raising your arm out to the side, as in a lateral raise or the upward phase of a jumping jack.
  • Muscles Involved (Primary): Middle deltoid, supraspinatus.
• Shoulder Adduction: This movement brings the arm sideways and downward, back towards or across the midline of the body.
  • Example: Lowering your arm from an abducted position, or pulling it across the body, as in a cable crossover or a pull-up (though the latter also involves extension).
  • Muscles Involved (Primary): Pectoralis major, latissimus dorsi, teres major, coracobrachialis, triceps brachii (long head).

Internal (Medial) and External (Lateral) Rotation (Transverse Plane)

• Internal (Medial) Rotation: This movement involves rotating the humerus inward, bringing the forearm and hand towards the body' when the elbow is bent.
  • Example: Placing your hand on your lower back, or the downswing phase of a tennis serve.
  • Muscles Involved (Primary): Subscapularis, pectoralis major, latissimus dorsi, teres major, anterior deltoid.
• External (Lateral) Rotation: This movement involves rotating the humerus outward, moving the forearm and hand away from the body when the elbow is bent.
  • Example: Throwing a ball, or the cocking phase of a throwing motion.
  • Muscles Involved (Primary): Infraspinatus, teres minor, posterior deltoid.

Horizontal Abduction and Adduction (Transverse Plane)

These movements occur when the arm is positioned at approximately 90 degrees of shoulder flexion (i.e., straight out in front of the body) or 90 degrees of shoulder abduction (i.e., straight out to the side).

• Horizontal Adduction (Horizontal Flexion): Bringing the arm across the body from an outstretched position.
  • Example: The pressing motion in a bench press or a chest fly.
  • Muscles Involved (Primary): Pectoralis major, anterior deltoid.
• Horizontal Abduction (Horizontal Extension): Moving the arm away from the midline of the body, backward, from an outstretched position.
  • Example: The pulling motion in a reverse fly or a face pull.
  • Muscles Involved (Primary): Posterior deltoid, infraspinatus, teres minor.

Circumduction

Circumduction is a complex, multi-planar movement that combines flexion, abduction, extension, and adduction in a continuous sequence, allowing the arm to move in a circular or conical path. While not a distinct movement on its own, it showcases the comprehensive range of motion available at the glenohumeral joint.

• Example: Drawing a large circle in the air with your arm, or the arm action in freestyle swimming.

Interdependence with Scapular Movement

It's critical to note that while these movements describe the glenohumeral joint, full, uninhibited shoulder complex motion also relies heavily on the coordinated movement of the scapula on the thoracic cage (scapulothoracic joint). This intricate relationship, known as scapulohumeral rhythm, ensures optimal positioning of the glenoid fossa for the humeral head, preventing impingement and maximizing force production. Understanding these distinct but interconnected movements is fundamental for effective training, rehabilitation, and injury prevention.