Grip bar with hands or use hanging assist pads at shoulder width. Keep body in good alignment (abs tight, chest up, back straight). Bend knees before beginning exercise. In a controlled motion, curl lowerbody up by drawing legs to the chest. Contract ab muscles fully without compromising form. While maintaining the controlled motion, return body to starting position. Do not allow body to swing. Do not allow muscles to relax before next repetition.
Here are a few suggested alternative exercises:Ab CrunchAb Crunch ObliquesBall Crunch TraditionalDouble CrunchDumbbell Side BendsLateral Bend with Barbell