Tim Ferriss wrote two influential books called The 4-Hour Work Week and The 4-Hour Body. In both books Tim explores ways to get maximum effect from minimum input, both in terms of life-style design and fitness.
Tim references a study about abdominal exercises and their relative impact on muscle development. He uses an EMG to measure the amount of muscle activation of 13 abdominal exercises, and compares them to the traditional crunch. The traditional crunch is given a value of 100% for comparison. Of the 13 exercises the bicycle crunch is the best, measuring 248% or 2 and half times more muscle activation than the traditional crunch. The Ab Rocker scored the lowest with 21%. In other words you would need to do five times as many reps with the Ab Rocker as you would a traditional crunch to get the same effect!
Turning this question on organizational performance improvement, what kinds of interventions are getting the greatest results? What are the Ab Rocker equivalents?