Which muscle primarily aids in shoulder flexion and adduction?

The pectoralis major is the primary muscle involved in shoulder flexion and adduction. This large, fan-shaped muscle is located in the chest and has a critical role in arm movements. It originates from the clavicle, the sternum, and the cartilage of the first six ribs, and it inserts into the humerus. This arrangement allows the pectoralis major to effectively perform shoulder flexion, which is raising the arm forward, and adduction, which is bringing the arm towards the body’s midline.

In addition to its primary functions, the pectoralis major also assists with shoulder internal rotation. Its action is particularly prominent when performing movements that involve lifting the arms upwards in front of the body or bringing them down towards the torso.

Other muscles listed, although important in different shoulder functions, do not primarily specialize in these two actions in the way the pectoralis major does. For instance, the deltoid muscle primarily enables shoulder abduction and contributes to flexion and extension, but its main role is not specifically in adduction. The rhomboids primarily retract the scapula, stabilizing the shoulder blade rather than moving the arm. The subscapularis, while involved in internal rotation of the shoulder, does not