The way people on here talk, you'd think the use of illegal substances among athletes is clear as day.
1.Have you ever seen, with your own eyes, Dibaba injecting EPO?
2.Has she ever failed a drug test?
3.Has anyone close to her made accusations, with clear, concrete evidence, of her doping?
If the answer to those questions is no, you must give her the benefit of the doubt! Same goes with any professional athlete. Since when is a good performance evidence of doping? That would be like saying, Bill Gates is so rich and successful, he must've made the money illegally, no other explanation.
There is another explanation. Hard work, brains, and talent. The very things that make this sport enjoyable to watch and compete in.