The alternating (twisting) oblique crunch with workout ball is a relatively simple exercise. It's similar to the traditional ball crunch. But a twisting motion is added to actively incorporate the oblique muscles.

Instructions:

Position the stability ball on the middle/lower back area. Lie flat on the ball. Your hands can be used to support the head or they can be placed across the chest. Crunch your abs while twisting to either side. Return to the starting position, then crunch and twist to the opposite side. Be sure to exhale as you perform the twisting motion. Ab exercises should typically done slowly. Consider holding the muscular contraction for 2 or 3 seconds. The aim is to simultaneously crunch, twist, and breathe out.

The twisting abdominal "crunch" is different from a sit-up. The range of motion is much shorter than a sit-up, where you literally end the movement in an upright position. Accordingly, the torso should elevate to about the halfway point.