Top 10 Questions About Abdominal Exercises

By Elizabeth Quinn, About.com Guide

Updated May 12, 2008

About.com Health's Disease and Condition content is reviewed by the Medical Review Board

Answer: Although it may feel as though you can "isolate" the upper and lower abs (the rectus abdominis), you actually can't contract one section independent of the other. Research that looked at the muscle activation while performing a basic crunch exercise found that you may feel more contraction in the upper abdomen because the muscle fibers in the upper part of the rectus abdominis shorten more than in the lower part of the muscle, but the entire muscle is, in fact, activated during the movement.

When you perform a reverse crunch (lifting the hips), the opposite happens; you feel more contraction in the lower part of the rectus abdominis even though the muscle fibers in the upper rectus abdominis are also contracting.

Additionally, when you stabilize the hips and only lift the torso during the crunch, there is greater muscle involvement in the upper rectus abdominis as well as the internal obliques. When you perform reverse crunches, there is more activation the lower part of the rectus abdominis and more involvement of the external obliques.