Doping

How? if you continue to train then surely you are still getting the benefit from the period of higher training?

If someone stops taking steroids, the muscles don't simply disappear do they? they can be maintained after that with normal "legal" training.

I'm far from an expert, but to my understanding, to keep muscle development at a consistent level you need to keep training at that level. So when the person stops doping, they can no longer train at such a level, and as such their physical capabilities would drop to what they can do naturally.