I went with a friend to have this procedure. She would go about every six months, if she didn't her hands would be in a constricted painful fist. It's an office procedure, fairly quick. The place a needle in the suspected muscle to listen to a machine that makes the spasms audible. The they inject the diluted botox or myobloc. Her doctor's office began using myobloc because it has less tendency to migrate. My friend was very happy with the procedure.
Your muscle will be stronger and you'll have better luck with strengthening it further.
best wishes