Usain Bolt, who shattered the world record each time to capture Olympic gold in the 100 metres, 200 and 4x100 relay, dismissed speculation his sudden rise to supremacy was aided by doping.
"I know I'm clean. I work hard for what I want," the Jamaican told Reuters in a telephone interview on Friday.
The 6-foot-5 (1.96-metre) sprinter clocked 9.69 seconds for the 100 in Beijing last month to carve 3/100ths of a second off the previous record he set in New York on May 31.
Bolt had previously run only a handful of 100s and his performance raised eyebrows among some observers.
Carl Lewis, a nine-times Olympic champion who won one of his titles when Jamaican-born Canadian Ben Johnson tested positive for steroids at the 1988 Seoul Games, raised questions about Bolt in a recent interview in Sports Illustrated magazine.
"I'm still working with the fact he dropped from 10-flat to 9.6 in one year," American Lewis was quoted as saying.
"I think there are some issues ... countries like Jamaica do not have a random (dope control) programme so they can go months without being tested."
Bolt felt such speculation came with the territory.
"I know what he said," said the Jamaican. "To me it doesn't really matter what he said, a lot of people were saying that.
"When you run the 100 metres that's what you get. As long as you're fast they start saying that.
"It's like a trend. I'm trying to change that. It's a bad image for the sport.
"Carl Lewis can say whatever he wants. That's just his opinion."
HARD TRAINING
Bolt said his 100 breakthrough was earned by hard training.
"The 200 is also sprinting, that was key," he said. "The only thing I had to do was get my start right and I got my start right.
"That's why my last 50 metres are so good because I've got speed and endurance."
The 22-year-old also rejected Lewis's comments about the amount of testing he had to go through back home.
"For sure we get tested in the Caribbean," he said. "They like to come to your house early in the morning.
"It's not cool getting up at six, seven in the morning when you're just trying to enjoy your sleep. But I know what it's for and it's fair. We get tested all the time.
"When you're in the top 20 in the world you get random tested. They get to know your whereabouts."
Bolt said he would continue to run the 100 and 200.
"In the future I'll probably step up to 400 metres," he said. "But it's a lot of work. I'm not ready for that kind of work."
Bolt also said he was looking forward to defending his titles at the 2012 Olympics.
"I'll be in London ... I hope it isn't cold," he said. "I'm looking forward to that.
"I can be champion again. I'll be 26 then. I have a lot of time on my hands. All I have to do is stay focused, train hard and be ready."
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