The trapezius muscle is located in the upper shoulder. Trigger points may refer pain both in the local area and/or to other areas of the body. Trigger points are like small blisters under the skin and when a muscle becomes tight the trigger points can be painful to touch and more prominent.
The trapezius is a synergist to the deltoid (together with the serratus muscle); the trapezius is responsible for moving the shoulder blade and supporting the arm. He elevates, depresses, rotates and retracts the scapula.
Trigger points usually occur in muscles when they have to compensate and as a result are constantly overused. Trigger points in the Trapezius may result from poor posture, overuse due to poor shoulder biomechanics or stress.
Applying pressure massage or inserting an acupuncture needle into the trigger point can help to relieve overall tightness into the muscle.
Levangie P.K. and Norkin C.C., 2011, Joint Structure and Function: A Comprehensive Analysis, 5th Edition, F.A. Davis Company, Philadelphia, PA, p:264