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
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.
1995-2000 page contents by Anee Stanford
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page was last updated 06/25/00