The exercise works the abs and quadriceps.
Lie down on a bench so that your thighs are on the edge.
Hold on the bench and extend your legs.
As you exhale, slowly raise extended legs until they form a 90 degree angle with the floor or a little bit closer to the head.
Do not pause and, as you inhale, return to the starting position.
At the top you can bend your torso bringing your legs over the head to increase the load.
You can also perform this exercise on an inclined bench. The bigger the incline angle, the more difficult the exercise becomes.
You can also add weight by putting on weight cuffs.
People with back issues should avoid this exercise.