Researchers from the University of Wisconsin-La Crosse rounded up eight men and eight women between the ages of 18 and 24 and had them test out a variety of ab exercises, including basic crunches, planks, and stability ball moves. They also tested out popular as-seen-on-TV equipment like the Ab Rocket, the Ab Wheel, and the Perfect Sit-Up.
The researchers attached electrodes to different muscles on the subjects' skin to determine the effectiveness of each exercise on each muscle. The results showed that, while certain moves and gizmos (like the bench curl-up and the Ab Wheel) were better at working out the obliques, the basic crunch produced the greatest muscle activation overall. In other words, that crunch you learned in gym class is the most efficient ab exercise you can do.
Of course, these findings hinge on doing the move properly. Study author John Porcari says, "We had people do the traditional crunch very deliberately and correctly, and I think we had fairly high activation from the abs because of that."
While a crunch may not be No.1 for oblique toning, it's certainly No.1 for all-purpose abs. So, if you're looking to consolidate your ab workout, your best bet may just be plopping your butt on the ground and crunching it out — in a deliberate, form-focused way, of course.