Listen to this: there is no lower abdominal muscle.
Listen to this: there is no lower abdominal muscle. It does not exist. The abdominal muscles are continuous muscles that begin at the base of the rib cage and end at the pubic bone of the pelvis. You can't train one end of your muscles more than the other. The whole muscle works evenly.
When someone says, "It works the lower abdomen," they are either seriously wrong or lying for marketing reasons. Firstly, you cannot lose fat under the belly, it is impossible to spot reduce. Second, you can't just exercise the lower abdominal muscles (the rectous abdominus, aka the six pack), because this muscle is not a separate muscle. You also cannot add notches to your abdominal muscles. The shape of your notches and the number of grooves your abdominal muscles shows are fixed (set in stone). It is determined by genetics. It is a fibrous divider that is there,or not since birth. All you can do is accentuate what you already have ( hiding under your fat layer, if you aren't yet lean) by thickening those muscle fibers with abdominal exercises, and reduce the fat that covers them, with diet and good overall exercise plan that lowers your total body fat