Action: Anterior: abduction, flexion and medial rotation of the humerus
The deltoid is located on the lateral superior part of the shoulder. It creates the rounded look of the shoulder and is one of the primary movers of the arm. Because of its location, its primary movement is abduction of the arm. The origin is located on the lateral 1/3 of the clavicle, acromion process, and the lateral 1/3 of the spine of the scapula. From there it travels down the humerus and attaches on the deltoid tuberosity. There is a bursa sac that is important to be aware of. If the bursa is inflamed it can be painful to client and cause irritation. The deltoid is also considered a shock absorber for the shoulder that protects it from impact. When the deltoid becomes tight it can create many dysfunctions in the shoulder such as should impingement. If the superior fiber becomes tight it can compress the shoulder and rotate the scapula downward. When the anterior fibers become tight it will medially rotate the arm. The posterior fibers are typically used in extension and will be usually eccentrically contracted unless the person has used it a lot in sports activity. The deltoid is a superficial muscle that will usually have referral from other muscles deep to the deltoid. For instance, if the rotator cuff muscles have become injured or have developed trigger points (TrPs) those TrPs will refer into the deltoid. It is important to also look at the muscles that attach under the deltoid in order to thoroughly work the muscle. Understanding the function and how to properly work and release the deltoid can be beneficial for shoulder injuries and for postural discrepancies.
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