In their ab workouts study, the researchers compared 30 men and women performing "traditional crunch, modified crunches, partial body weight exercises and exercises using both home [including the Torso Track, Ab Roller, and AB Rocker] and gym exercise equipment [including the captain’s chair]". They measured muscle activity to quantify how much the exercisers were working (and if they were working the proper muscles), and found that the bicycle maneuver (a floor exercise), captain's chair (a piece of gym equipment), and crunches on an exercise ball were the best exercises (see here for instructions on how to do the good exercises, including images).
The home ab exercise equipment didn't fare too well:
"[T]he Torso Track appeared to be marginally more effective than the traditional crunch. However, this training benefit is likely offset by the lower-back discomfort reported by a significant number of subjects while using the Torso Track.Their other studies make for interesting reads as well, though they generally show results that any good skeptic would already have hypothesized.
The Ab Roller was proven to be virtually no more effective than the traditional crunch while the AB Rocker was shown to be up to 80 percent less effective."
[cross-posted at The Gym at Rhosgobel.]