What occurs after the initial 30 degrees of motion in scapulohumeral rhythm?

In scapulohumeral rhythm, the coordination between scapular and humeral movement is crucial for full shoulder abduction and flexion. During the initial phase, the first 30 degrees of movement primarily occurs at the glenohumeral joint. Following this initial motion, for every 2 degrees of motion that occur at the glenohumeral (GH) joint, there is typically 1 degree of upward rotation at the scapulothoracic (ST) joint.

After the initial 30 degrees of motion, as the arm continues to elevate beyond this range, the contribution from both joints changes. Typically, after the first 30 degrees, the movement continues with a combination of additional degrees contributed from both the GH joint and the ST joint.

In this case, 30 degrees of additional motion comes from the GH joint, while the ST joint contributes an additional 30 degrees as well, leading to an effective movement that is well-balanced between both joints. Thus, the answer indicates a continued motion from both joints stabilizing and facilitating the elevation of the shoulder complex.

Understanding this rhythm is vital for rehabilitation and functional movements, ensuring optimal shoulder mechanics during activities.