So this one is kind of tough. But it does really work your core. Lie on your back holding a dumbbell with your two hands over your head. Lift your legs until they are straight up and perpendicular to the floor. This is position 1. Get into position 2 by lifting the dumbbell to try to reach your toes. Your shoulders should come off the floor in the process, but make sure you are not putting a lot of pressure on your neck. Return to position 1 still keeping your legs up. That is 1 rep. Repeat this for 3 sets of 15 reps. And do not rush it. Do it slowly so you really work those ab muscles.
You can use a dumbbell from 5 to 15 lbs. But using one too heavy could restrict your motion so take note of how you feel.
Cheers Eights & Weights!