If by "coming up" you mean that your back goes into it's normal lordosis (curve), then that isn't necessarily a back thing. Some more recent workouts (like those by Charlene Prickett, who gives EXCELLENT form advice and keeps up with the latest fitness info and safety info) say that instead of flattening the back to the ground, one should try to "lock in" the natural curve of the back and keep it throughout the move, which requires some tension to do.
If, on the other hand, you mean "coming up" as arching beyond the natural curve, then you should modify the moves so that your back will stay in a safe position.