As I always say, when you work the abs, work as many of the abs muscles as possible. The muscles that help give you that definition in the sides of your waist are called the obliques. Several movements that involve rotation and twisting help work the obliques. I tried out this one where you incorporate the plank, but you twist out your waist as well. Want to try it?
All you need to do is to start in an elbow plank looking down. Keeping your upper body straight, slowly rotate your lower body into a twist (like you would do for a side plank) so your waist is kind of wrung out. i.e. the torso is facing downward and the legs are facing one side. Return to center, and then rotate to the other side.
Confusing? Watch the video below for a demonstration.
Try out 4 sets of 10 on each side to really feel it in your abs.
Cheers Eights & Weights!