Infraspinatus is one of my favorite muscles to work on. Clients rarely know about it, but almost everyone has some trigger points there, and people are often amazed by the intensity of sensation when it gets worked on.
“Infraspinatus muscle” by Anatomography – CC BY-SA
One of the deep shoulder muscles in the rotator cuff, infraspinatus covers almost all the of the shoulder blade below the spine of the scapula. It helps to laterally rotate the arm, like when you pull your arm back to throw a ball. Anyone who uses their arms a lot in their work will like getting work done on their infraspinatus, because when the arms stay overhead or out in front of you for long periods of time, the muscle works overtime trying to keep the arm up. Both driving a car with both hands on top of the steering wheel and working at a computer keyboard without elbow support can abuse the muscle as well.
Though the muscle is located on the shoulder blade, usually the pain is not felt there. Mostly it refers to the front or outside of the shoulder, though it can also be felt down the arm or along the inside border of the shoulder blade. Stiffness in this muscle can make it difficult to reach behind you, and can cause the other muscles in the rotator cuff to tighten, which can in turn lead to what is known as “frozen shoulder,” but can generally be treated successfully through trigger point massage.
Davies, C. (2004). The Trigger Point Therapy Workbook (2nd ed.). Oakland, CA: New Harbinger Publications, Inc