clonus (n.), clonic (adj.)

https://doi.org/10.1351/goldbook.11683
  1. Alternate involuntary muscular contraction and relaxation in rapid succession.
  2. Continuous rhythmic reflex tremor initiated by the spinal cord below an area of spinal cord injury, set in motion by reflex testing.
Source:
PAC, 2015, 87, 841. (IUPAC Glossary of terms used in neurotoxicology (IUPAC Recommendations 2015)) on page 857 [Terms] [Paper]