Extremities Exam 1 – Muscles Practice

Deltoid anterior action?

Adducts arm Extends and laterally rotates arm Flexes and medially rotates arm Abducts arm after first 15º

Correct Answer:

Flexes and medially rotates arm

Explanation:

The anterior part of the deltoid is oriented to move the arm forward and rotate it inward. Its fibers originate from the lateral clavicle and insert on the deltoid tuberosity, so their main action is shoulder flexion and medial (internal) rotation, with some help in horizontal adduction. The middle fibers do the primary abduction once the arm has cleared the initial range (the first ~15 degrees of abduction is driven by the supraspinatus). The posterior fibers extend the arm and rotate it laterally. So describing the anterior deltoid as flexing and medially rotating the arm accurately captures its main function.

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