Hyperreflexia Clonus Involuntary rhythmic muscular contractions and relaxations SNOMEDCT_US:36649002 A series of rhythmic and involuntary muscle contractions (at a frequency of about 5 to 7 Hz) that occur in response to an abruptly applied and sustained stretch. Clonus is a manifestation of spasticity that can occur with lesions of the corticospinal tract. Only sustained clonus (5 beats or more) is considered abnormal. HP:0002169 UMLS:C0009024 Involuntary movements