Posted in: Workouts / Workout Programs

how do I keep my lower back flat on the mat during ab routines?

In a lot of the videos the trainer will mention keeping your lower back flat against the mat during ab workouts, like scissor kicks, bicycle, crunch style stuff. I can't keep my lower back flat to the mat at all, even in the easiest version of any exercise. How (and what) do I strengthen whatever needs to be strengthened to do that?