Jordin Sparks cuts a slimmer figure during her Planet Hollywood Handprint Ceremony held Tuesday in NYC.

The singer, 19, whose album Battlefield is in stores now, is cheerful and giddy. She attributes her smaller size to the rigors of the road. And what a tour — the youngest American Idol winner joins the Jonas Brothers every night!

“I’m literally drenched every night when I get off the set because the stage for this world tour I’m on is so massive,” she tells me. “I’m constantly moving, and I do have my trainer out on tour with me this time around. He just got here last week, and it’s been a lot of fun. Any time I find time – or I’m not sleeping – he’s like ‘let’s work out, let’s do something.’ I’m like ‘nooo,’ but he gets my butt up and I’ve gotta do it. It’s fun to do that.”

Her regimen relies on a mix of techniques.

“We do a whole bunch of different things,” the Arizona native says. “He doesn’t keep the same thing every time, so he shocks the body so you’re running, you’re doing throw-downs, you’re doing stairs, you’re doing lunges. I’ve done all of those in the past four days, and I will tell you that my butt hurts very badly.”

How has Jordin changed her diet?

“It’s not really different. I don’t deprive myself of anything. If I want to have a brownie, I’m going to have a brownie, but it’s all about food proportion.”

Pick up the OK! on newsstsands this week for a beauty feature all about Jordin. Rob and Kristen: “Steamy Nights Together” is the cover line. Catch Jordin with the Jonas Brothers performing in a city near you. And, her sophomore album, Battlefield, is in stores now.

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