Adjust seat and sit in good body alignment (abs tight, chest up, back straight). Grip bars and lock feet under foot pads. In a controlled motion, twist body left or right. Contract abdominals fully without compromising form. While maintaining the controlled motion, return to starting position. After completing one side, perform the same motion to the opposite side.
Here are a few suggested alternative exercises:Ab Crunch ObliquesBall Crunch TraditionalDumbbell Side BendsLateral Bend with Barbell