Usain Bolt says he is fit and ready for the London Olympics and is convinced his defence of the 100 metres title could trigger one of the fastest ever races in the blue riband sprint.

The 25-year-old Jamaican said he had been training well after a minor hamstring problem and reiterated his desire to become a "legend" of the sport by defending his 100m and 200m titles.

Concerns about the fitness of the biggest name in track and field arose when cameras were banned from his training sessions and he was pictured receiving treatment on his hamstring.

Bolt dismissed those concerns, saying a stiff back causing some problems for his hamstring had been fixed.

"I'm always ready," the 100m and 200m world record holder told a news conference on Thursday.

"I keep telling you guys, it's all about the championships, it's not about the trials, it's not about one run, every athlete knows this.

"My coach determines whether we train in front of cameras or not, he doesn't like the cameras. I had slight problems but nothing too serious, I got that fixed and I've been training great.

"I'm ready to go, I came into the camp today and felt that chill, that's a good vibe so I'm happy."

Bolt's aura of invincibility was dented earlier this month when he was beaten over both 100m and 200m by training partner and world champion Yohan Blake at the Jamaican trials.

"I've been beaten before the Olympics before, Asafa (Powell) did it in '08, it's always a wake-up call to be beaten in the season but it's better at the trials than at the Olympics," Bolt said.

"It opened my eyes, I sit down and rethink a few things. But for me it's just about getting it right on the day. I'm alright."

World champion Blake's time in the 100m at the trials, 9.75 seconds, was the fastest of the year but he is not the only challenger to Bolt's crown who has been in impressive form this season.

Justin Gatlin, the Athens Olympic champion, returned from a four-year doping ban to run 9.80 to win the U.S. trial while his compatriot Tyson Gay has also run under the 10 second barrier.

The man who has run under 10 seconds more than any other runner, former world record holder Powell, was alongside Bolt on the stage on Thursday and is also likely to be in the final on Aug. 5.

"Hands down, for sure, I'm thinking this could be one of the fastest 100 metres anyone has ever seen because these guys have been showing potential all season, a lot of guys have been running fast because it's an Olympic year," said Bolt.

Powell, who has admitted to having psychological problems when he races the likes of Bolt and Gay, said he was confident he would contribute fully to the occasion.

"It's just going to be very exciting. I don't know what is going to happen in the finals," he said.

"All I know is a lot of people are expecting Usain to win way out in front but it's not as easy as you think.

"If I don't make the podium, I'll be very disappointed. I know I have what it takes to go out there and put in on the track and a lot of guys will eat my dust."

Bolt said whatever happened in London, he would continue to run track and field after the Games but would try to do it in a way that was less stressful.

He left no doubt, however, of his goal in London, where he will carry Jamaica's flag at the opening ceremony on Friday.

"Usain can become a legend so I'm on it," he said.