Lie on your back in a crunch position, with your legs bent at a 90-degree angle, as shown.
Rather than keeping your arms down at your sides, hold one end of a medium to heavy dumbbell with both hands, and stretch your arms up and back, so the dumbbell hangs over or behind your head. The further back you hold the dumbbell, the more difficult the exercise will be.
Keep your core tight as you drive your knees toward your chest, lifting your hips off the ground in the process. Return to the starting position.