The following is an excerpt of Pain Relief with Trigger Point Self-Help:
When pressed, trigger points feel like “knots” or tight bands in the muscle, and are usually very tender. Healthy muscles usually do not contain knots or tight bands, are not tender to pressure, and when relaxed, they feel soft and pliable to the touch, not hard and dense, even if you work-out. When trigger points are present, on the microscopic level, part of the muscle fiber is contracted into a small thickened area, and the rest of the fiber is stretched thin. Several of these muscle fiber contractures in the same area are probably what we feel as a “knot” in the muscle. These muscle fibers are not available for use because they are already contracted, which is why you cannot condition (strengthen) a muscle that contains trigger points. The sustained contraction probably leads to the release of sensitizing chemicals, producing the pain that is felt when the trigger point is pressed.3 Eventually some of the structural changes may be irreversible if trigger points are left untreated for long enough.