YES, Isolation WORKS!......
A lot of people believe in separating abdominal work into exercises that focus mainly on the upper abs such as crunches, and exercises the focus more on the lower abs such as hanging leg raises and reverse crunches. Some research has made the claim that it is impossible to focus on just the upper or just the lower abs and that both areas are used equally wether you perform crunches or reverse crunches. If you train your abs frequently then you most likely know this is false, as you cancel the ab area that is being focused on when training. New research suggests that this is correct.
RESEARCH:
Researches from the University of Sao Paulo in Brazil had male subjects perform the crunch and reverse crunch while they measure the muscle activity of the upper rectus abdominis (upper abs) and the lower rectus abdominis muscel fibers.
Based on the muscle-activity data, the upper abs are definitely used more than the lower- ab muscle fibers during the crunch and the lower-ab muscle fibers are used more than the upper-ab muscle fibers during the reverse crunch. Research showed that the different portions of the abs are innervated by different nerves.
So we know that it is in fact possible to focus on the upper abs or the lower abs by doing specific exercises that emphasize each area.
To build well-balanced abs from top to bottom, incorporate a variety of exercises that focus on the upper abs and exercises that focus on the lower abs as well.