Because vanadium dioxide experiences a sudden phase change at 67° C, instead of trying to make small changes to gradually contract or expand muscles, could an alien instead have many smaller muscles, like a bunch of separate smaller muscles connected to the bone, each one is a little weaker than the one above it, and the placement on the bone makes it so that certain ones can't put very much force into moving the arm.
I imagine that this would make their movement fairly robotic, as to move the arm to a specific spot a certain number of muscles would be heated, contract, and then the arm would suddenly snap to a position. The more muscles activated the stronger the pull kind of thing. Is this more plausible than having one larger muscle?
(If you have any questions I'll do my best to answer them.)