A year or more ago I mentioned a study on powerlifters which demonstrated that former steroid users gained strength much more quickly than athletes who'd never used steroids. AW just drew attention to a similar study on mice demonstrating that those given steroids develop more nuclei in their muscle cells and retained them for 10% of their remaining life, also retaining the ability to respond much more robustly to training. After 6 days of exercise, the former roid-users gained 31% muscle gain vs. 6 percent for the mice that had always been drug free.
Two things:
1. Runners such as Bolt, Powell, Blake, Gatlin, and Gay will ALWAYS have advantages over clean runners. This advantage will last for the rest of their careers, even if they go clean.
2. Athletes who cheat in high school or college when they are not tested gain a career-long advantage as well. There is, in effect, everything to gain from cheating while young and unknown.