Shortening reaction in normal and parkinsonian subjects

Angel, Ronald W.

Department of Neurology, Veterans Administration Medical Center, and Stanford University School of Medicine, Palo Alto, CA. Supported by the Medical Research Service of the Veterans Administration.

Please address correspondence and reprint requests to Dr. Angel, Department of Neurology, Veterans Administration Medical Center, 3801 Miranda Avenue, Palo Alto, CA 94304.

Accepted for publication August 18, 1981.

Neurology 32(3):p 246-251, March 1982.

Article abstract

During passive extension of the elbow, the triceps shows a shortening reaction (SR), which is manifested by a burst of EMG activity. The SR and the velocity of passive movement (VPM) were measured in parkinsonian patients and control subjects. The mean SR was larger and the mean VPM was smaller in the parkinsonian group. An unexpected finding was that “reinforcement” caused an increase of the SR in normal subjects but not in the patients. The VPM is considered to be a measure of rigidity, and the SR provides a quantitative approach to the pathophysiology of muscle tone.