How to do it:
Lie faceup with arms by your sides, palms down. Extend legs at 90 degrees and cross your right leg on top of your left, toes pointed.
Brace your abs in tight to your back and start to trace a circle with your legs, moving from the right down and around to the left. As you bring your legs in and up to complete the circle, press your arms into the floor and lift your hips, bringing your legs as high overhead as you can at the top of the circle (as shown).
Slowly lower your hips and your legs back to your starting position and then cross your left leg over your right and reverse the circle.
Do as many reps as you can with control for 1 minute, alternating legs each time.
Bonus burn: If done correctly, the corkscrew is a great move to help activate the lower part of the abdominal wall (since you have to control your leg circle with your core strength). Get even more out of it by keeping your navel drawn into your spine the entire time.