Usain Bolt brushed aside fears of injuries hampering his Olympic challenge, saying he is fit and raring to go.

Bolt goes into the London Olympics, as the defending champion in both the 100 and 200 meters, but has seen injuries to his back and hamstring, quell his progress in the last few months. Fears over his fitness grew when the previously unbeatable Bolt, lost to compatriot Yohan Blake in the 100 and 200 meters Jamaican Olympic trials, the loss in the latter event, coming as particularly surprising.

However, Bolt has said he has overcome the problems, and is feeling fine going into what many consider one of the greatest 100M showdowns in recent history.

"I think I am probably 95 percent fit, but I am in great shape," Bolt told BBC Sport.

"This is the moment that is going to define my entire life. A lot of people say I am a legend, but this is going to define me as a legend.

"It's a big occasion, I strive on challenges so I'm really looking forward to it and I am just going out there to get it done."

"It's always a wake-up call to get beaten. It opened my eyes and I sat down to rethink a few things."

Bolt won three gold medals in Beijing, and will definitely go for the treble yet again, but hinted he might also be a part of the 4x400 relay team.

"If I feel like I'm up to it after the 200m, then why not? For my country, I would do it, if it was necessary."

The Jamaican, who will be his country's flag-bearer at the opening ceremony later on Friday, said he was not too concerned about speculation over his injuries, and was just concentrating on working hard and doing his best for the Olympics.

"The vibe is good and I am happy," Bolt told reporters at an event.

"I am always ready. For me, I keep telling you guys it's always about the championships; it's never about one run, never about the trials."

The enigmatic Bolt, known for his broad smile as much as his performances on the track, admitted it has not always been easy to put up a happy front. "I've been through so much, with niggles and problems and I have to do a lot of sponsorship stuff as well," he said.

"There are so many different things that I have to do and I have got to keep focused on going out there and competing and training every day.

"It's getting harder and harder just to smile because there is so much on my mind, worrying if everything is going to come together and a few other things.

"But I think I am more confident now that everything is feeling better, so I can smile more now and I am looking forward to it."