Michelle Obama Michelle Obama

The Biggest Loser has all the elements of a covert operation: contestants train at a secret location under close supervision until they're lean, mean machines. The only thing missing has been Secret Service — until now. For the Season 13 makeover episode — split into two parts, airing tonight and next Tuesday, April 10 — the competitors aren't just rewarded with new haircuts, snazzy clothes and a chance to see their families: they also get to visit Michelle Obama at the White House.

But before they got their audience with the FLOTUS, stylist Jeannie Mai and hair guru Ken Paves spruced them up. For former pro wrestler Kim Nielsen, it was a chance to revisit how she looked before a sports injury sidelined her seven years ago. "It was like getting the old Kim back," she says. The transformations came as a shock to the contestants' loved ones. "My son started to cry," says Kim. "My daughter's mouth dropped open. I was like, 'Why are they so stunned?'"

Still, the biggest surprise of all was reserved for Obama, who, after the tearful reunions, participated in a group workout led by trainers Bob Harper and Dolvett Quince. And if you think they gave her a pass on their tough love, think again. "I'm yelling at her, she's yelling back. As I'm yelling, I'm looking in the corner of my eye at the Secret Service men," recalls Quince. Confirms Obama, "I don't think it's in Bob's or Dolvett's natures to 'take it easy.'" Thankfully, a national crisis was averted. "It was such an incredible experience to work out with the trainers," says Obama. "They really put me to the test, and I'm happy they did!"

The Biggest Loser airs Tuesday at 9/8c on NBC.

Subscribe to TV Guide Magazine now!