Elastic properties of muscles measured at the elbow in man: II. Patients with parkinsonian rigidity.

A method is described to measure reproducibly stiffness, and therefore "tone", at the elbow of patients with Parkinson's disease using a torque motor. In Parkinsonian versus normal patients (previously reported) it was observed that: the neutral angle in Parkinson's disease patients was significantly smaller (92 degrees +/- 15 degrees) than in normals (107 degrees +/- 10 degrees), and in Parkinson's disease patients, even with relatively mild symptoms, the upper limb was stiffer than normals in the totally relaxed state with no electromyographic activity present. Our results suggest that changes in the passive mechanical properties of the upper limb affected by Parkinsonian rigidity may have taken place, accounting for the more flexed neutral elbow angle and greater passive stiffness. Using this technique, response to antirigidity therapy and natural progression of illness can be quantitatively assessed and followed.