I'm not sure if this is exactly it, but there's a condition called akathisia that meds like Abilify can cause. While I was in the hospital I was constantly being assessed to see if I was developing it, even though I have Tourette's so it was difficult to tell. Akathisia is a potentially permanent disorder that causes involuntary movements and feelings of restlessness that lead to these movements, and often includes tensing of the muscles.
I'm not sure though if it only happens while you're manic. I would definitely recommend seeing a GP about it.