Olympic champion Usain Bolt believes it will take a couple of years to convince some people he is breaking world records without doping.

The 23-year-old Bolt broke his own marks in the 100 and 200 metres in August at the Berlin World Championships. He had originally set those two at last year's Beijing Olympics, along with the world record in the 4x100 relay with Jamaica.

"I'll continue running fast, I am clean without a doubt," Bolt said Thursday at a conservation event in London. "As soon as you start running fast, there's going to be a problem. It's going to take a couple of years for people to start believing that you're actually clean.

"If you continue running fast and doing it clean and then, over a period of time, all the tainting will go away. People will continue to say it until that period of time."

What hasn't helped Bolt convince doubters are doping convictions in recent years for sprinters Marion Jones, Tim Montgomery and Justin Gatlin.

"People always say things, the sport has been through a lot. But it's changing, definitely," Bolt said. "The IAAF is doing a very good job of cleaning up the sport."