Jamaican track star Usain Bolt on Thursday acknowledged he has had a rocky build-up to the London Olympics, but declared himself "ready to go" in his bid to defend his double sprint titles.

"I'm always ready," said Bolt. "It's all about championships. I've had slight problems, but I'm ready to go."

Fitness concerns, an early morning car crash and losing over both the 100 and 200m to training partner and compatriot Yohan Blake in the Jamaican Olympic trials raised serious doubts about Bolt's ability to defend his titles.

But Bolt, speaking at his first pre-Olympic press conference alongside fellow sprinter Asafa Powell, said: "I'm going to focus on going out there to win.

"My back was a little stiff and it affected my hamstring but I'm over that. I've been training for the past two-and-a-half weeks and everything is alright."

The 25-year-old added: "I don't think it will be the end of the world if I lose."