It could be reverse crunches to tuck the lower abs but I think that it is more important to teach lower abs to work in a stabilizing sense. What I mean by that is for example when people run, cycle, jog, walk whatever the case may be they have weak lower abs and lower abs that are not working in a stabilizing functional sense. The pelvis is going to kind of rock back and forth and little bit whenever the hip flexors do their motions. And by doing that it's putting stress and pressure on the lower back and that's one of the reasons why people struggle with lower back issues. Their lower abs is not working in a stabilizing functional sense. So as far as I am concerned when it comes to lower abs it's very important to teach it to work that way. Ironically one of the better ways of doing that is to do leg lifts lying on the floor keeping the lower back flush against the floor. In most cases I start people with one leg or one leg with the bent knee and then gradually get to the point where they can raise and lower both legs at the same time while keeping the lower back flush.
