The abs exercise in this part of the butt and abs workout targets your obliques. For maximum benefit it is important to keep the weight in your heels and drive up through your heel when you come out of the lunge. You will feel the muscles in your leg respond immediately when you shift the balance of your weight to your heel as you perform this exercise. Proper form always creates better results. The other thing that you want to watch is to make sure that you are bending your knee to a 90-degree angle, and keeping the top of your knee behind your toes.
Best,
Zuzana