Final answer:
The muscles responsible for external rotation at the GHJ are primarily the infraspinatus, teres minor, and the posterior portion of the deltoid muscle.
Step-by-step explanation:
The muscles responsible for external rotation at the glenohumeral joint (GHJ) include the infraspinatus, teres minor, and the posterior portion of the deltoid muscle. These muscles are part of the rotator cuff and shoulder muscle groups that enable multidirectional movement of the arm.
Specifically, the infraspinatus is a key player in external rotation, working alongside the teres minor to rotate the humerus laterally in the glenoid fossa.
The posterior deltoid, while primarily known for its role in arm abduction, also assists in external rotation of the shoulder. These muscles ensure the smooth and controlled movement of the upper limb, highlighting the complexity and versatility of the shoulder girdle’s musculature.