Believe it or not, one of my favorite ab exercises includes one of those cheap infomercial gadgets, "the ab wheel". You can pick one up at Walmart for under 20 bucks, and it works your abs hard without crunches.
But do other ab gadgets hold up?
Researchers (from the Mayo Clinic, of all places) tested the "Ab-Slide" device and compared it to the ab crunch, the supine double leg thrust (seated knee tuck-in), and side plank.
J Strength Cond Res. 2008 Nov;22(6):1939-46.
An electromyographic analysis of the Ab-Slide exercise, abdominal crunch, supine double leg thrust, and side bridge in healthy young adults: implications for rehabilitation professionals.Youdas JW, et al.
Ten young men and twelve young women did all the exercises. The tests showed that the Ab-Slide, a contraption fairly similar to the Ab Wheel, worked the abs the hardest. On the other hand, the seated knee tuck-in required a lot of hip flexion, and the doctors believed it could cause low back problems in people prone to low back injury.
Personally, I'm going to stick with the Ab Wheel, but as usual, I'm going to keep crunches out of my program, and add the Seated Knee Tuck-in to my list of ab exercises to avoid.
Craig Ballantyne, CSCS, MS
Turbulence Training for Abs