This is called tone or spasticity (spastic-ity). I call it %@2S/T!
A spastic biceps (big arm muscle) might always be “on,” always bent up. The arm cannot straighten. It is annoying to have an arm bent all the time. It also gets really sore.
For awhile, until it was calmed down with stretching, strengthening of the opposite muscle, poison injections and luck, I had a really butch biceps on my stroke side. Flex my stroke biceps and it looked like that of a strongman.
I am happy to report that I am back to my wimpy self.