Haven't they proved that the long term effects of some drugs stay in your system for years?
Not sure which ones off the top of my head, but one of the arguments levelled at Gatlin is that he is able to still run at the same level he did when doping because of the long term effects of the drugs he was using a lot of earlier in his career!
This is muscle memory, they claimed about two or so years back that having platelet rich plasma infusions with surgery actually made you stronger then pre-injury. The same for testosterone, ever notice guys in there mid-20s who run say 10.25-say for 100m who never qualify for any major champs all of a sudden jump to 9.89-94 in one year but then never improve? Because athletes in the wilderness aren't tested, but afterwards they are subject to out of competition testing.