The shoulder joint, while exceptionally mobile, is often described as having seven primary actions. However, considering nuances and components, we can clarify and expand upon this to better understand the complexity of shoulder movement. While the provided reference lists seven actions, a more comprehensive breakdown reveals nine distinct actions through which the shoulder joint operates:
- Flexion: Moving the arm forward, increasing the angle between the arm and the torso (e.g., raising your arm straight in front of you).
- Extension: Moving the arm backward, decreasing the angle between the arm and torso (e.g., moving your arm backward from a forward position).
- Abduction: Moving the arm away from the midline of the body (e.g., raising your arm straight out to the side).
- Adduction: Moving the arm towards the midline of the body (e.g., lowering your arm from a raised, side position).
- Horizontal Abduction (Transverse Abduction): Moving the arm away from the midline of the body in a horizontal plane, typically from a flexed position (e.g., moving your arm out to the side from a position where your elbow is bent and at shoulder height).
- Horizontal Adduction (Transverse Adduction): Moving the arm towards the midline of the body in a horizontal plane, typically from a flexed position (e.g., bringing your arm across your body from a position where your elbow is bent and at shoulder height).
- External Rotation (Lateral Rotation): Rotating the arm outward, away from the body's midline (e.g., with your elbow bent at 90 degrees and close to your body, rotating your forearm outward).
- Internal Rotation (Medial Rotation): Rotating the arm inward, towards the body's midline (e.g., with your elbow bent at 90 degrees and close to your body, rotating your forearm inward).
- Circumduction: A circular movement that combines flexion, abduction, extension, and adduction in sequence. It describes a cone-shaped motion of the arm.
It is important to note that these movements often occur in combination, and the shoulder joint works in conjunction with the shoulder girdle (scapula and clavicle) to achieve its full range of motion. The interaction between the glenohumeral joint (shoulder joint) and scapulothoracic joint (scapula gliding on the ribcage) allows for more complex movements and greater stability.
