Muscle tension with tenderness may be localized or generalized as in fibromyalgia. Wartenberg's pendulum test might be appropriate for quantitating muscle damping, at least in generalized cases.
Damping values provide a quantitative measure of muscle tension and of the response to various treatments.
According to recent anatomic and experimental works, intrafusal muscle fibers are double-innervated by gamma motoneurons and sympathetic fibers. With electromyograph recording, the activity of extrafusal fibers and gamma motoneurons (reflexes) can be assessed and separated from the action of the sympathetic system.
An electrogoniometer registers the movements of the freely swinging leg. On the oscilloscope, the patient's nodular curve is compared with an ideal calculated dampened curve to find the damping value. Electromyograph surface electrodes from the knee extensors and flexors detect the activity of extrafusal fibers and the occurrence of reflexes.
In longstanding severe fibromyalgia, damping values are almost always elevated, at least in one leg. Half or more of patients with chronic lumbago and cervical syndrome present with increased damping. The surface electromyograph remains silent (in contrast to spastic patients).
The findings support the hypothesis that muscle tension in rheumatic patients results from overactivity of the sympathetic system (or part of it). Even in clinically localized pain syndromes, muscle damping is often increased in the legs. The test is valuable for quantitating muscle tension and the effectiveness of therapeutic methods.