Trigger Point Illustration
A Above you can see the cross section of a muscle with its attachment at either end, represented by the diagonal lines. The dark line in the middle is the taut band the trigger point resides within. ATrp means "attachment trigger point" and they are exactly that -- trigger points that form where the muscle or tendon meets the bone. CTrP is a central trigger point, which is one that is in the belly of the muscle (the most common).
B Here you can see an expanded view of a central trigger point. As you can see it is not just one big "knot", but a series of trigger points intermingled with the individual muscle fibers. Notice the "normal fibers" that the diagram points to and that the sarcomeres, which are the units of contraction for a muscle, are divided into evenly spaced segments. Now look at a fiber that contains a trigger point and see how the sarcomeres are contracted in the middle at the site of the trigger point and stretched on the outsides. This property is what creates the taut band, which is clinically characteristic of a myofascial trigger point.
Myofascial Trigger Point Therapy is not just the treatment of trigger points that develop in skeletal muscles, but the examination of the factors that cause the condition (precipitating factors) as well as the factors that keep pain and dysfunction ongoing (perpetuating factors).
Myofascial Trigger Point (Clinical Definition): A hyperirritable spot in skeletal muscle that is associated with a hypersensitive palpable nodule in a taut band. The spot is painful on compression and may give rise to characteristic referred pain, referred tenderness, motor dysfunction, and autonomic phenomena.
Types of Trigger Points
Trigger points can exist in one of two states, active or latent.
Active trigger points cause referred pain which is felt somewhere else in the body as well as a decrease the range of motion for that muscle.
Latent trigger points do not cause pain except when compressed, but they will restrict range of motion.
Example
Tension headache caused by a trigger
point in the upper trapezius muscle.
In this case the trigger point (always distinguished as the X) in the upper trapezius muscle is referring pain up the side of the neck and into the temple area. This trigger point may also refer pain into the jaw. The dark, solid red areas are the most common areas of pain and the lighter areas represent areas in which a person may feel pain, but not as common.
So it can be seen in this example that if you were to have only the dark red areas treated (where you feel the pain) then treatment does nothing for the trigger point (X) that is actually causing the problem.