Hang from a chin-up bar with both arms extended at arms length in top of you using either a wide grip or a medium grip. The legs should be straight down with the pelvis rolled slightly backwards. This will be your starting position.
Raise your legs until the torso makes a 90-degree angle with the legs. Exhale as you perform this movement and hold the contraction for a second or so.
Go back slowly to the starting position as you breathe in.
Repeat for the recommended amount of repetitions.
Caution: Perform this exercise slowly and deliberately as it takes some getting used to. Also, do not be hasty and try to use weights on the first time; you'll have enough in your hands by holding your weight and also learning how to balance yourself so that you avoid swinging your torso. As you get more advanced you can hold a dumbbell in between your feet. However, you have to be very careful when adding weight to this exercise as if you add too much too quickly you could get a hernia.
Variations: This exercise can also be performed using a vertical bench that makes the exercise easier by supporting your upper back in place and by allowing you to hold yourself by placing your elbows and arms on the side pads.