Until recently, athletes using Passive Elastic Running Prostheses (PERPS) were clearly at a disadvantage compared to those with fully functional biological legs. The remarkable accomplishments of a few prominent athletes (e.g. Oscar Pistorius, Amy Palmierio-Winters) have raised the issue of advantage/disadvantage and stimulated a recent flurry of misinformation and scientific experiments. Although an initial measurement and suggested that PERPS enhance running economy, a growing body of evidence demonstrates equivalence. Yet, distance running performances are still much slower for athletes using PERPS. Athletes using PERPS cannot/do not apply ground reaction forces as great as those with biological legs. That limits maximum running speed and thus, sprint performance. The low mass and inertia of PERPS would seem to allow more rapid leg swing, but athletes using PERPS do not exhibit unnaturally fast swing times. Further, it is not clear that it would be advantageous if they did. Although we have learned a great deal about the science of PERPS in the last few years, the database, especially for runners using bilateral PERPS, is inadequate. I will outline the next most important experiments in this area of research.