Five contributions to one motion
The shoulder is among the most mobile regions in the body because several elements cooperate. Glenohumeral flexion lifts the arm forward, abduction lifts it to the side, external rotation turns it outward, and internal rotation turns it inward. None of these works well in isolation: the scapula must glide, rotate, and post against the rib cage to keep the socket positioned under the moving arm.
This coordinated movement between the upper arm and shoulder blade is called scapulohumeral rhythm, and a roughly two-to-one ratio of glenohumeral to scapular motion is often cited as a reference pattern.
Why mapping all five matters
Overhead pressing, throwing, and hanging each demand a different blend of these ranges. A deficit in any one, internal rotation is a frequent culprit in overhead athletes, can quietly limit performance or shift stress onto neighboring tissue. Mapping the components separately helps locate which one is the bottleneck.
Reading restriction conservatively
Reduced range can stem from joint capsule, muscle, or training history, and the cause shapes the remedy. Persistent shoulder pain, clicking with pain, or sudden loss of range deserves assessment rather than self-treatment. This is general educational information, not medical advice.