Which muscle group performs extension and lateral rotation at the glenohumeral joint?

The posterior deltoid fibers are primarily responsible for extension and lateral rotation at the glenohumeral joint. The deltoid muscle is divided into three functional parts: anterior, middle, and posterior fibers, each contributing to different movements of the shoulder.

The posterior fibers, specifically, assist in extending the arm backward and rotating it laterally. This is crucial for various movements that require the arm to be positioned behind the body or rotated outward, such as in certain sports or rehabilitation exercises.

In contrast, the anterior deltoid fibers predominantly facilitate flexion and medial rotation, while the middle deltoid fibers are primarily involved in arm abduction. The supraspinatus is also involved in shoulder abduction but does not contribute significantly to extension or lateral rotation. Understanding the specific roles of these musculature fibers aids in comprehending shoulder mechanics and is vital for effective massage therapy and rehabilitation approaches.