Lie flat out on your back with your legs out flat on the ground.
Cross your right ankle over your left ankle and put your hands behind your head.
Press your lower back down into the mat and pull your head up and off of the mat in a crunching motion. Complete your repetitions then switch legs so that the left ankle is on top of the right ankle; repeat.
Targeting the abdominal and oblique muscles is one of the best ways to get a slim waist, and this surprisingly challenging move does just that. Crossing one ankle over the other engages both the abs muscles and the side oblique muscles, trimming the waistline and strengthening the core.