Usain Bolt says he has overcome back and hamstring problems and is ready to defend his Olympic titles in London.
The reigning 100m and 200m champion was beaten in both events at the Jamaican trials by training partner, Yohan Blake.
"I think I am probably 95% fit but I am in great shape," Bolt told BBC sports editor, David Bond.
"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."
He added: "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."
Bolt, who will be Jamaica's flag bearer at the opening ceremony, also hinted he may go for four golds by running in the 4x400m relay, as well as the 4x100m.
"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," he said.
Bolt's fitness has been a source of speculation following his defeats by Blake.
But the 25-year-old says he is fully focused on the Olympics.
"It's always a wake-up call to get beaten. It opened my eyes and I sat down to rethink a few things," he said.
Bolt was speaking four years to the day since he smashed the 100m world record at the 2008 Beijing Games with a time of 9.69 seconds, despite slowing to celebrate yards from the finish line.
He broke his own record a year later with a time of 9.58 secs at the World Championships in Berlin, before losing the world title to Blake in 2011 after a false start.
Bolt, who was speaking at a media conference in east London alongside team-mate Asafa Powell, added: "The vibe is good and I am happy.
"I am always ready, for me I keep telling you guys it's always about the champs, it's never about one run, never about the trials."
The smile was back on the face of the sprinter, as he entertained the world's media, but he admitted it has not always been easy to keep it there.
"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."