Confident of 100m gold
"I said a couple of years ago it had to get really bad, when there's nowhere else to go but up.
“Doping is always a bad thing and it's never pleasant because you put in the hard work and the sport starts going forward and then you have other guys bringing it back, it's hard.
"It's going in the right direc- tion so hopefully it will continue in that direction." Bolt has raced only three times this season, and last month appeared to be struggling with a back injury, but he insisted he was still the man to beat in the 100m, the qualifying rounds for which start on Friday.
“For some reason I am the underdog,” he said. “That is what my team keep telling me so I have to prove myself once more. But I am confident in my abilities, always. When I go out there I am fully confident and ready to go – 100 per cent.
“The last 100m race I ran was a 9.95sec which shows I am going in the right direction. It is all about who can keep their nerves. I have been here many times and I know I am ready. It is go time.”
Bolt, who turns 31 later this month, also gave an emphatic answer when asked how he would feel on Saturday night after the 100m final. “Unbeatable,” he said.
“Usain Bolt has retired unbeatable over that event. For me that will be the biggest headline. Unbeatable and unstoppable.”
The men's 4x100m relay race - which will mark the end of Bolt's career - is on August 12.
The Jamaican also insisted that he had been provided with extra motivation to win yet another world title following the tragic death of his close friend Germaine Mason, the Olympic silver medal winning high jumper, in a road accident in April. “It was a rough time,” he said. “I have never had someone who passed away so close to me. I didn’t train for three weeks. My coach gave me my space, he gave me my time to get over it.”
Jamaica's Usain Bolt gestures during a press conference in London, UK, on Tuesday