Trigger points have been a subject of study by a small number of doctors for several decades although this has not become part of mainstream medicine. The existence of tender areas and zones of induration in muscles has been recognized in medicine for many years and was described as muscular rheumatism or fibrositis in English; German terms included myogelose aned myalgie. However, there was little agreement about what they meant. Important work was carried out by J.H.Kellgren at University College Hospital, London, in the 1930s and, independently, by Michael Gutstein in Berlin and Michael Kelly in Australia (the latter two workers continued to publish into the 1950s and 1960s). Kellgren conducted experiments in which he injected saline into healthy volunteers and showed that this gave rise to zones of referred pain lower down the limbs.

It was however an American physician, Janet Travell, who was responsible for the most detailed and important work. She published more than 40 papers between 1942 and 1990 and in 1983 the first volume of The Trigger Point Manual appeared; this was followed by the second volume in 1992. A second edition of this work has now been published. In her later years Travell collaborated extensively with her colleague David Simons.

In spite of all this work, the trigger point concept is unknown to most doctors, who still learn little or nothing about the subject at medical school. Other health professionals, such as physiotherapists, osteopaths, and chiropractors are generally more aware of these ideas and many of them make use of trigger points in their clinical work.

The main innovation of Travell's work was the introduction of the myofascial pain syndrome concept. This is described as a focal hyperritability in muscle that can strongly modulate central nervous system functions. It needs to be distinguished from fibromyalgia, which is characterized by widespread pain and tenderness and is described as a central augmentation of nociception giving rise to deep tissue tenderness that includes muscles. It is consideraby more difficult to treat.

Trigger points can be classified as latent or active, depending on whether they are giving rise to symptoms. Latent trigger points can cause muscle shortening and weakening but not spontaneous pain. The causes of activation include acute or chronic muscle overload, indirect activation by other trigger points, visceral or joint disease, emotion, and radiculopathy. The radiation effects include pain and also other sensations; the affected muscles may also be weak.

Diagnosis of trigger points is mainly by manual palpation. There are changes in the "feel" of the tissues and the patient will report local tenderness, sometimes with radiation effects. There may be a twitch in the affected muscle.

Treatment of trigger points may be by local compression, injection of corticosteroid, or "stretch and spray" using a cooling spray. Practitioners of medical acupuncture often use trigger points as the basis for their treatment and studies have shown a considerable similarity between the locations of trigger points and classic acupuncture points.