What muscle is the prime mover for adduction, flexion, and inward rotation of the humerus?

The deltoid muscle is the prime mover for adduction, flexion, and inward rotation of the humerus. It is a large, triangular muscle located on the upper arm and shoulder, playing a crucial role in arm movements. The anterior fibers of the deltoid are particularly involved in flexing the humerus and aiding in inward rotation, while the muscle as a whole contributes to adduction when the arm is positioned away from the body.

Other muscles like the trapezius mainly assist in positioning the shoulder and do not directly perform these actions on the humerus. The coracobrachialis contributes to flexion and adduction but is not the prime mover for these actions due to its smaller size and specific location. The supraspinatus, while it plays a role in initiating arm abduction, is not involved in adduction or inward rotation, thus making the deltoid the most significant muscle in these combined movements of the humerus.