During yesterdays versus coverage of the Liege-Bastogne-Liege, and after Vinokourov won it, Bob Roll asked the question "how come racers that come back from a suspension perform so well?" (or words to that effect).
The AAAS Science Journal had one possible answer (I don't have the issue to hand but it was shortly before the Beijing Olympics); there is no evidence that many of the proscribed products and practices enhance performance, in fact they may even degrade performance, or have no effect at all. Apparently, when a substance or practice is rumored to being used by athletes, then that substance or practice is added to the proscribed list without any scientific research being conducted.
The AAAS Science Journal had one possible answer (I don't have the issue to hand but it was shortly before the Beijing Olympics); there is no evidence that many of the proscribed products and practices enhance performance, in fact they may even degrade performance, or have no effect at all. Apparently, when a substance or practice is rumored to being used by athletes, then that substance or practice is added to the proscribed list without any scientific research being conducted.