"I am back in the saddle," Montgomery told reporters at a U.S. team press conference on Friday.

He said the allergy to peanuts and related products had taken down his immune system, prompting poor performances in Stockholm and London. That had caused many to question his fitness for the championships, which begin on Saturday.

"But after the second round you are going to be saying 'Wow'," said Montgomery, who set his world record of 9.78 seconds in Paris last September.

Montgomery said that he was unsure whether he would even make the world championships.

"I was done," he said. "Emotionally I was fried. ... If the doctor had said you are perfectly fine, I would not have come here.

"I didn't want to come out here and make a fool of myself. I am only human."

But tests back in North Carolina confirmed the allergy had affected his immune system, causing fatigue. He slept for 14 hours the day before the race in Stockholm.

He ran so poorly there, finishing sixth, that Montgomery told organisers he would be back for free next year.

The London event was even worse. He failed to make the final and he abandoned the rest of his European season before the world championships and returned to the U.S.

However a course of antibiotics seemed to alleviate the problem and he recently ran a time trial, which boosted his confidence and convinced him he was ready to run.

"I'm not going to say what the time was," he said. "But that's why I am here.

"I am not going to let no one say stay home and do this and do that. I am here to fight. I am a fighter.

"I came in to Paris last year and Dwain Chambers was going to be ranked number one in the world and I wound up breaking the world record."

"Now...I don't have anything to lose. I'm focused and I'm ready to go out there."

While Montgomery said he is now focused, he hadn't always been that way recently.

"I had put track on the back burner. I wasn't focused. I wasn't hungry. I was race rusty," said Montgomery, whose girl friend, triple Olympic champion Marion Jones, gave birth to their first child last June.

"It has been a joy," Montgomery said. "I've got a girl friend that is wonderful, that gave up her season for me to have my child and I gave up my season to be beside her.

"Now the child is here, Marion is back beside my side and we are ready to run."

Jones will serve as a television commentator for the championships though she had warned Montgomery not to perform badly.

"She told me that if I ran bad, 'I am going to saying you are running bad. Don't make me do that'," said Montgomery of Jones's advice.