They tested against non weighted crunches? That's like "revealing" that 80% 1rm activates more than 20% 1rm....DUH!
100lb weighted crunches beats the front plank. The RKC plank more than triples the activation of the front plank. As you can guess, the best "isolation" exercise for lower abs is the hanging leg raise, otherwise chinups work them very well. The ab wheel is one of the best overall ab exercises. If you want to know where your favorite exercise stands, just Invalid Link Removed