This would make for such great viewing. Only athletes who have consistently been taking performance-enhancing drugs are allowed to enter, plus obviously they've been training really hard too. It'd be awesome to see just how far the human body can be pushed. Imagine how fast someone with the natural ability of Usain Bolt would be able to do the 100m sprint if they'd been on a course of steroids? Or how high they'd be able to jump, or what time they'd be able to do the marathon in. Amazing.
I guess the competitors hearts exploding in their chests at the age of 32 would be a potential downside, but omlette / eggs / break etc.