UNDERSTANDING AND MEASUREMENT OF MUSCLE TONE AS RELATED TO CLINICAL MUSCLE PAIN

Measurable sources of muscle tension include viscoelastic tone, physio logical contracture (neither of which involve motor unit action potent ials), voluntary contraction, and muscle spasm (which we define as inv oluntary muscle contraction). The latter two depend on motor unit acti on potentials to generate the tension. Total muscle tension is most ac curately measured as stiffness. Thixotropy of muscle is an ubiquitous and functionally important phenomenon that is not commonly recognized. A clinical pain condition associated with increased muscle tension is tension-type headache, which is largely muscular in origin; it is oft en caused by myofascial trigger points, but not by a pain-spasm-pain c ycle, which is a physiologically and clinically untenable concept. Cli nical conditions associated with painful muscle spasm include spasmodi c torticollis, trismus, unnecessary muscle tension, nocturnal leg cram ps, and stiff-man syndrome. (C) 1998 International Association for the Study of Pain. Published by Elsevier Science B.V.