Spasticity, Rigidity, Tone: What’s It All Mean?



Spasticity is a word that describes a state in which the muscles are in a persistent state of increased involuntary reflex activity in response to a stretch. You may observe the following in a person with spasticity: hypertonia, hyperactive deep tendon reflexes, clonus, and a spreading of the reflex response beyond the muscles that were stimulated.


The term rigidity is used to describe an involuntary increase in resistance of a muscle to passive stretch that is uniform though out the range of motion (ROM) of the muscles being stretched and which is not velocity dependent. Rigidity and spasticity are often confused and are very hard to tell apart but they are tow separate and distinct phenomena. In rigidity deep tendon reflexes are not hyperactive as they are in spasticity.


Tone is the passive resistance to stretch offered by a muscle group to external manipulation. If a person has hypertonia this means that they have an above normal level of tone. If a person has hypotonia they have a below normal level of tone. If a person has atonia this literally means being without tone. Atonia is usually present in ataxia.


Clonus is used to describe when the application of a sustained stretch to a muscle group results in repetitive contractions, relaxation, and contractions again.


Dystonia is a term that describes a slow sustained movement that is a result of an involuntary contraction. The contraction that occurs in dystonia also results in maintaining a dystonic joint posture in which there is increased resistance to a passive stretch in the direction of the resting position. Dystonic moments can occur involuntarily or as a result of an initiated action.


In athetosis you can generally see slow, writhing movements of the trunk and extremities. When used to describe cerebral palsy athetosis may also include such phenomena as variability of resting tone, and persistence of primitive reflexes.

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This page was last updated 06/25/00