Go for twist exercises like the Russian twist ... Put your right arm on the mat and your left hand behind your head. Crunch up in a V, getting up on your hip and butt. Keep your legs straight.

this Russian twist ensures that you are working your transverse abdominus (TA) muscles. Lie down on your back with your head straight on the floor and your arms stretched out to the sides.

You place your hands behind your head and just pull elbows down ... And a variation of this exercise would be, just a twist and lift your knee, and pull the elbow towards the knee as you twist.