So when will athletes start hitting the limits?

[littlebabyjesus]

Drug cheating in athletics started long before the 80s. I vaguely remember reading that drugs used to enhance the performance of pilots in WW2 were used in athletics in the 50s. Britains own David Jenkins (400m) admitted that he'd been using drugs since the mid-70s and later went to prison for manufacturing or importing steroids.

In women's athletics at least, the stats suggest that it became far more prevalent/effective from the start of the 80s. Don't doubt that it started before that, but athletes/teams became properly good at it around then.

Drug cheating is also more effective for women. They can gain a bigger advantage through taking drugs that give them a more 'male' physiology. Some of the records for women set in the 1980s may never be broken.