When medially or internally rotated, the fibers of the first segment (I) of the anterior deltoid will actually contribute to adduction, or returning from being raised in the scapular plane.Ĭhew on that for a moment: Anterior deltoid fibers perform shoulder flexion, transverse adduction, abduction, and adduction. In fact, it becomes the primary shoulder abductor in this position. These fibers also assist the subscapularis and latissimus dorsi with internal rotation.īut that’s not all! When working in unison with the middle and posterior fibers, the anterior delt also performs shoulder abduction, especially when the humerus is externally rotated, as in an overhead press. It inserts into the deltoid tuberosity on the lateral aspect midway down the humerus.įunction: The anterior deltoid works as a synergist to pectoralis major for shoulder flexion and transverse (or horizontal) adduction (as in a chest press).
Origin: The anterior, superior surface of the lateral third portion of the clavicle. This suggests, and was supported by testing, that each segment’s fibers can separately perform a distinct motion from the remaining fibers. PET scans indicate the anterior deltoid can be divided into two segments and the posterior deltoid can be divided into four distinct segments (the middle deltoid remains a solitary unit) for a total of seven (I-VII) compartments. What’s remarkable here, however, is that at least two studies of cadavers and healthy volunteers indicate that each head invests into the insertion via separate tendons. – en:Anatomography ( setting page of this image), CC BY-SA 2.1 jp, Link
Each fiber has a separate origin and but they share one point of insertion. The deltoid muscle, otherwise known as the deltoideus or shoulder muscle, consists of three distinct “heads” with very different joint actions that, when engaged simultaneously, work together to produce shoulder abduction: the anterior deltoid, the middle deltoid and the posterior deltoid.
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