Lie on your back with your hands at your sides and your knees bent (almost like a regular abdominal crunch.) But in this one, bring your knees slightly up and toward your head (so your feet are in the air.)
Use your abs to lift your legs up until your hips come up slightly off the floor. Hold for one second and repeat.
Be sure to remain stable. Don’t use momentum to rock back and forth.
Repeat for 2-3 sets of 10-20 reps.