myotonia

https://doi.org/10.1351/goldbook.11904
Prolonged contraction or delayed relaxation of a muscle after mechanical or brief electrical stimulation.
Note: Myotonia is indicative of an abnormality of ion channels of the muscle membrane, and is often an example of an ion channelopathy.
Source:
PAC, 2015, 87, 841. (IUPAC Glossary of terms used in neurotoxicology (IUPAC Recommendations 2015)) on page 885 [Terms] [Paper]