Jamaican sprint legend Usain Bolt labelled himself the underdog as he seeks to round off his glittering individual track career with the defence of his world 100m title this week.

"That's what I keep reading and what my team keeps telling me, so I've got to prove myself again," the 30-year-old said in a warning shot to pretenders to his crown in the blue riband event of the IAAF World Championships.

Bolt started this season in sluggish form, running two 10sec-plus times before finally hitting some form at the Monaco Diamond League.

"The last race I ran was 9.95sec, which shows I'm going in the right direction," he said.

"It's a championships and the two rounds always help me. I've been here many times. It's go-time, so let's go!"

He added: "Usain Bolt has retired unbeaten in an individual event, unbeatable, unstoppable -- for me that would be the best headline!

"If I show up at a championships you know I'm fully confident and ready to go, and my coach, I'm ready to go."

Bolt refused to single out who would be his closest rival for the 100m, with heats on Friday before the semi-final and final on Saturday at the same stadium in east London where he won treble gold at the 2012 Olympics.

"The seven people who are going to be in that race with me, they're the biggest challengers," he said.

Bolt has dominated sprinting since taking double individual gold at the Beijing Olympics in 2008, going on to win a further six Olympic golds and also picking up 11 world titles.

He also holds world records of 9.58 and 19.19sec in the 100 and 200m, both set when winning at the 2009 Berlin worlds.

Bolt admitted that he hoped his records would last.

"I want to brag to my kids when they're 15, that I'm still the best," he joked.

- 200m in 2008 the best -

In a glitzy press conference organised by his long-term sponsors Puma and hosted by Welsh ex-hurdler Colin Jackson, Bolt picked out his then-world record breaking victory in the 200m at the Beijing Olympics in 2008 as the stand-out performance of his career.

"It's definitely Beijing (Olympics), the 200m, because I never knew I could break the world record," he said.

"That was my main dream growing up -- I always wanted to be Olympic 200m champion. When I broke the record I didn't know how to react."

And he insisted that motivation was not lacking despite having devoted his life to the track since the age of 10.

"Every year you find something else to motivate you," he said. "I love competition, I thrive on competition, and I want people to run fast to push me.

"I'm comfortable saying I'm a legend because I've proved myself.

"I didn't know I would be 100m world record holder growing up, I had no idea.

"Anything's possible, you've just got to put it in your head and work for it. There are no words to explain what I've done over the years, and I'm really proud of myself."

Sprinting has been mired by doping over the years, and track and field's governing body the IAAF has been on the back foot over widespread state-sponsored doping in Russia, whose athletes were barred from the Rio Olympics and will also miss London, although some have been cleared to compete as neutrals.

But Bolt insisted the sport was on the right path.

"You can't be happy about doping, but we're doing a better job and are catching up and if you cheat, you will get caught," he said.

"After the scandal on Russia, it doesn't get any worse than that. It's on its way back up now.

"Hopefully, athletes will see what they need to do to make the sport go forward."

Source: AFP