Dr. Janet Travell, author of Myofascial Pain and Dysfunction, identifies a trigger point (TP) as a hyperirritable neuromuscular point that is painful when compressed, and is associated with dysfunctional neurological reflex circuits. Translated into English, this is an area that gets so irritated that the body misinterprets the signal, causing the person to feel as if the pain is coming from somewhere else. About 70% of the time an area will refer pain to a predictable spot, and these are shown on trigger point charts. But each of us is different, and many times people will have unique referral patterns. Unique referral patterns can be caused by a facilitated pathway. This means that when a person has a long term area of inflammation, the body will become used to sending and receiving nerve signals from that area. With a facilitated pathway, new injuries will refer pain to the old injury. Trigger point therapy can help reduce facilitated pathways, returning the nerve pathways to a more normal functioning.
Trigger points are found in muscle tissue or its associated fascia, located in a taut band of fibers. Deactivating a trigger point relieves the local impaired mobility and pain due to muscular and vascular restriction, and reflexively improves the associated referred pain and dysfunction. In english this means that by pushing on a trigger point area, the referral pain goes away, and the tight muscle under your thumb softens and relaxes.
Knowing about trigger points is important because where people feel pain is not always where it is originating. For example people usually feel infaspinatus pain deep in the front of the shoulder, while they feel subscapularis pain in the posterior shoulder. It is also important to use resistance tests to assess the muscle & tendon, and range of motion tests to test the joint capsule.