DES MOINES, Iowa Wild arm swings, sharp robotic turns, pulsing fist pumps.

Michelle Obama busted out a few new moves Thursday to mark the second anniversary of her campaign against childhood obesity with a few new friends - 14,000 or so, it turns out.

The first lady rocked out with thousands of sixth- to ninth-graders at a Des Moines arena on the first stop of a three-day trip to highlight her "Let's Move" campaign. It was a giant pep rally for eating right and exercising, complete with a towering birthday cake of fruit.

The first lady and crowd revved up by doing the Interlude, a dance that started in a dorm room at the University of Northern Iowa.

The first lady took on the issue of childhood obesity because almost a third of U.S. children are at least overweight and about 17 percent are obese.

In the two years since she launched her campaign, she has brought substantial new visibility to the childhood obesity issue and has prodded schools, families, restaurants, and others to do more to tackle the problem.

Robert Blendon, a Harvard professor who tracks public opinion on health care, said the first lady has given people tangible ideas on how to eat better and exercise more rather than talking in broad concepts.

The first lady herself said recently she's "pretty much willing to make a complete fool out of myself" to get kids moving and eating better.

To that end, she's done push-ups with South Africa's Desmond Tutu, danced the Dougie with school kids, fed veggie pizza to Jay Leno and competed in an East Room potato sack race with Jimmy Fallon.

Thursday, she added the Interlude to her repertoire.