If you do a search for lower ab exercises, you will find numerous training methods that would supposedly help you to chisel this problematic area of your body.
However, most people don't realize that what they really need is not a better exercise, but a better nutrition plan that would eventually make them burn even the stubborn fat.
Your body has a genetically programmed pattern by which it determines how the stored fat is used for energy.
And guess what? The fat cells below the navel are much more reluctant to give away their fat content than the ones located in other parts such as the upper abs (it wouldn't be called stubborn for no reason).
Once you get to 10-12% body fat, the abdominal muscles above the navel usually become visible, but you still won't see the full six pack.
It shouldn't be that difficult to get to this level of leanness because your body has to cashier first the fat located in areas that are more accessible. So stop blaming cortisol or genetics for your potbelly.
Strength training added to your regular diet (calorie control and adequate protein) will normally get it done without too much of a headache.
However, the real struggle begins when you attempt to get to even lower body fat levels. That's what you have to do if you ever want to see how lower abdominal muscles look like.
At this point, your diet and exercise plan have to be adjusted because the remaining fat is more stubborn, which means that it doesn't respond very well to whatever you did before.
Doing more reverse crunches or any other lower ab exercises (like the girl in the picture) won't help you that much because your abdominal muscles are already strong from your regular weight training.
Really, it's just a matter of fat distribution, so stop looking for special exercises that would supposedly make you look like a fitness cover model.
My assumption is that you are not that naive to believe in spot reduction or other similar absurd myths that refuse to die. But who knows? You would be surprised to find out how many people still believe in this bullshit.
Some gyms give even special classes for sculpting the core, where everybody is doing crunches, bicycles, leg raises, etc for one hour long.
I know, this is retarded, but if you attend such a program (maybe you want to see some chick in lycra bending in front of you), pay close attention to the trainer.
Most of them are totally out of shape, so it should be obvious that doing tons of ab exercises is a complete waste of time.
Although it's not mandatory, your program should include some specific ab work such as reverse crunches. But if you are looking for more lower ab exercises, maybe you should read a physiology book instead.
You would spend the same amount of time, but at least you would get some useful knowledge.