The 18-year-old made her surprise announcement to a crowd of 8,000 area elementary students at Hy-Vee Hall in her hometown of Des Moines.

Johnson said: "I got caught up in the moment.

"And what better way to do it than to inspire 8,000 kids."

There had been doubts over whether the teenager would return in time for London because of a knee injury she suffered in a skiing accident and also the success of her post-Olympic life.

Johnson earned nationwide attention after Beijing when she won the ABC-TV reality show Dancing With The Stars last year and has also appeared in a series of television adverts for her sponsors.

But, in the end, the lure of competing in another Olympics proved too big a temptation for Johnson, who also won three silver medals in Beijing, including in the individual all-round.

She said: "[There's] something about it that called me back.

"I'm a little kid at heart.

"I can't get away from it and I missed it a lot."


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