Trigger points are focused areas of spasm and inflammation in the skeletal muscle. The trapezius and rhomboid back muscles, located in your shoulder area and upper back, are common sites for trigger points. Trigger points may also occur in the lower back and are less common in the arms and legs. There are palpable nodules in the muscles where the trigger point is located. This area is tender, painful to the touch, and radiates around the local area of the trigger point. These areas are where the trigger point injections are done in order to provide pain relief.