The deltoid is the the muscle that is most often thought of as the “shoulder.” It is the diamond shaped muscle that caps the shoulder joint. It originates on the clavicle, the acromion, and the spine of the scapula. It inserts on the deltoid tuberosity of the humerus. As a whole unit the deltoid laterally abducts the humerus at the glenohumeral joint. The anterior portion of the delt forward flexes the arm, as well as horizontally flexing the arm across the chest. Since the deltoid is involved in almost all shoulder movements it is especially prone to trigger points. Points in the anterior deltoid refer into the anterior and lateral shoulder. Trigger points in the posterior deltoid refer pain into the posterior shoulder with spillover down the lateral arm.