Hubbard D R, Berkoff G M
Department of Neurosciences, University of California, San Diego.
Spine (Phila Pa 1976). 1993 Oct 1;18(13):1803-7. doi: 10.1097/00007632-199310000-00015.
Monopolar needle electromyogram (EMG) was recorded simultaneously from trapezius myofascial trigger points (TrPs) and adjacent nontender fibers (non-TrPs) of the same muscle in normal subjects and in two patient groups, tension headache and fibromyalgia. Sustained spontaneous EMG activity was found in the 1-2 mm nidus of all TrPs, and was absent in non-TrPs. Mean EMG amplitude in the patient groups was significantly greater than in normals. The authors hypothesize that TrPs are caused by sympathetically activated intrafusal contractions.
