Jamaican sprint star Usain Bolt expressed his sadness that doping issues rather than track talk were dominating the build-up to the world championships that start in Beijing on Saturday.

Athletics' world governing body IAAF has recently been mired with allegations over doping, while Bolt's main sprint rival is Justin Gatlin, the controversial American who has served two doping bans, the latter for four years after testing positive for testosterone.

"It's really taken centre stage," Bolt said of the doping issue. "All I've been hearing over the past couple of weeks is doping, doping, doping.

"The majority of questions are about doping, it's definitely sad."

But Bolt played down suggestions that he was the "saviour" of track and field, saying he alone was not capable to turning the tide.

"Initially I'm running for myself, that's what I do," he said. "People say I need to win for the sport, but there are a lot other athletes who are running clean.

"It's not only on me because I can't do it myself.

"I think it's the responsiblity of all the athletes to take it upon themselves to help save the sport and show the sport can go far, without drugs cheats or athletes who've taken drugs."

- Ready to defend -

Bolt, the six-time Olympic gold medallist and world record holder in both the 100m and 200m, added: "I just try to do what's right by the rules of the IAAF, WADA and everybody. We all know the rules and we just have to abide them.

"It's not only up to me because I can't do it by myself because I'm not the only one in the sport.

"It's up to all the athletes to understand the rules and abide by them and just work hard to be the best: it will make sports a better place."

Bolt might have endured a stop-start season debut, but he vowed he is ready to defend his double sprint titles at the world champs.

The towering Jamaican gets his campaign under way in heats for the 100m on Saturday, the opening day of the competition that runs until August 30.

For Bolt, it will signify a return to Beijing's iconic Bird's Nest stadium, where he first made his name with a thrilling golden treble in the 2008 Beijing Games.

Since then, bar one hiccup in the 100m at the Daegu world championships in 2011, Bolt has won every sprint and relay title at world and Olympic level.

Bolt last month roared back from an early season pelvic joint issue that saw him miss six weeks of competitive action with back-to-back 100m times of 9.87sec at the London Diamond League meeting.

That left him sixth in the 2015 list of the fastest sprinters over 100m, with Gatlin atop the group of elite athletes, having run a personal best of 9.74sec in Doha in May, having also clocked 9.75 twice and 9.78.

- Great memories -

"I've been training hard these past few weeks to put myself in the best possible condition to run well and defend my titles over the next week," Bolt insisted.

"Coach (Glen Mills) is happy and that's always key because when he's happy I know I'm in good nick.

"Everyone knows that the championships are the most important for me. That is what I train for. The one-off races are important but the medals and titles are given out at the championships.

"My racing season wasn't ideal this year but I have great confidence in my coach and his ability to get me into shape at the right time."

Bolt added that memories of seven years ago were not lost on him.

"Beijing was where it all started for me at the Olympic Games in 2008. I have great memories of this city and the stadium. It's great to be back here, I'm looking forward to getting on the track on Saturday."