Assessment of human hemiplegic spasticity by a resonant frequency method.

The resonant frequency of the wrist has been measured in hemiplegic subjects and was higher on the spastic side, indicating greater stiffness. The increased stiffness is associated with stretch reflex activity, which is absent in normal subjects. The increased stiffness of spasticity in most of the patients did not exaggerate the sharpness of tuning as there was a compensatory rise in damping. Increased damping will contribute to the subjective assessment of muscular hypertonicity. Measurements of resonant frequency and damping are essential in assessing muscular hypertonicity.