The First Lady, who campaigns against child obesity, said she
hoped watching the US athletes would encourage children at home
to "get off the couch".
"Our goal is to get all kids in our country and across the world
in a better state of health, and that starts with getting up and
moving," she said.
"As you all compete here, think of your fellow competitors back
home -- all those young kids who are going to be thinking of
visions of you as they go spike a ball or put their toe in that
She said she hoped the US athletes would have fun in London, but
added, "Winning is good."
The First Lady, who will be attending the opening ceremony, told
the team: "You've got a country back home that is rooting for you
every single second, so you've already won."
Ahead of the ceremony, Obama was due to host a sporting event at
the US ambassador's residence in London for around 1,000 US
military children, along with US and British students.
Her arrival in London comes a day after Mitt Romney -- the
Republican who will challenge her husband Barack Obama for the
presidency in November -- had to backtrack after questioning
whether London was ready for the Games.