This may sound a stupid question, but why did WRs continually fall and average elite times continue to come down through the 90s right up to around 2004/05 after which stricter testing was introduced?
I mean does EPO have long term benefits, or was there simply more and more athletes getting on the EPO bandwagon? Otherwise you'd expect the WRs and average times to be more staggered based on the random luck of the talent pool at the time, unless it was just a conincidence that the best runners appeared towards the end of the EPO era.
Take El G for example. He had his best years around aged 29 in 2003/2004 running a ridiculous 3:26 and 12:50 or something for the 5000m. This is highly unusual for a middle-distance runner. When was the last 1500m runner before him who peaked at age 29? Nearly every great before him peaked at 24 or 25 or even earlier if they had the misfortune of injury or health problems.
Doesn't this suggest that El G (and likely most of the Africans) were not just doping themselves silly with EPO but doing so since their teens? El G would have been able to start taking EPO from the age of 16 or 17 in the early 90s which would explain his junior success too. The reason why we say El G is the 'King of EPO' is entirely down to fortunate timing. His career began just when EPO was becoming available and ended just when the curtain was about to come down on it with better reliable testing. That's why he peaked at 29/30.
http://sportsscientists.com/2017/05/recalibration-world-records-brief-thoughts/