The side oblique crunch exercise is extremely useful for those looking to tighten and strengthen their abdominal muscles. It allows you to stretch and tense those muscles which will give more definition. If you turn sideways for the starting position, place your two legs straight out, laid on top of each other, and place your hand and forearm on the ground. You will be supporting yourself at the elbow, placing your other arm around the back of your neck. The arm around the back of your neck is not meant to support your neck or stretch it in any way.
Then you simply bend your body so that your hips are touching the ground and then lift your hips as high as possible bending your head towards the floor. Then simply lower yourself so that your hips are on the floor again and then lift as high as possible. Repeat and increase the number of repetitions as you become more used to the exercise.