We now know the secret of first lady Michelle Obama’s fab arms. During an event that she hosted at the White House on Monday to promote physical fitness among military families, she participated in a series of exercises and dance movements with a group of renowned athletes that included Olympic gold-medal gymnast Dominique Dawes, ice skater Michelle Kwan and tennis player Billie Jean King. Her personal trainer, Cornell McClellan, who serves on the President's Council on Fitness, Sports & Nutrition, also participated in the event.

“If anybody wants to know who’s responsible for these arms—it’s that guy,” Obama said. “And it is always helpful to have somebody else pushing you—because let me tell you, there are times when my rational mind says it’s enough, and he says no it’s not.”

The first lady announced three new “Let’s Move” initiatives that will provide immediate family members of actively deployed National Guard and Reserve members with access to gym memberships and personal training so they can pursue a healthier lifestyle. The International Health, Racquet and Sports Club Association is offering more than 100,000 free memberships and the American Council on Exercise has agreed to provide at least one million hours of free personal training and fitness instructions to the families. In addition, the President’s Council on Fitness, Sports & Nutrition will host a special series of events with military families across the country.

“We know that when our troops serve, you all serve.  And I think that it’s time that we started serving you in return,” she told the families attending the event. “It’s time we started doing everything as a country that we can do to show our gratitude for your contributions to this nation.”

Obama also stressed the need for all families to become more physically active, which doesn’t always require spending money on gym memberships.

“The truth is, is that movement doesn’t have to be complicated or expensive,” she said. “It’s a walk in the park. It’s a run around the park. It’s dancing around the living room.”

(Photo: AP Photo/Evan Vucci)