The drawing above is a representation of several muscle fibers within a trigger point. It’s based on a microscopic photograph of an actual trigger point. This particular trigger point would cause a headache over your left eye and sometimes at the very top of your head.
Letter A is a muscle fiber in a normal resting state, neither stretched nor contracted.
Letter B is a knot in a muscle fiber consisting of a mass of sarcomeres in the state of maximum continuous contraction that characterizes a trigger point. The bulbous appearance of the contraction knot indicates how that segment of the muscle fiber has drawn up and become shorter and wider.
Letter C is the part of the muscle fiber that extends from the contraction knot to the muscle’s attachment (to the breastbone in this case). These overstretched segments of muscle fiber are what cause shortness and tightness in a muscle.
Normally, when a muscle is working, its sarcomeres act like tiny pumps, contracting and relaxing to circulate blood through the capillaries that supply their metabolic needs. When sarcomeres in a trigger point hold their contraction, blood flow essentially stops in the immediate area.
The resulting oxygen starvation and accumulation of the waste products of metabolism irritates the trigger point. The trigger point responds to this emergency by sending out pain signals.