While she was on tour with Jason Aldean, Lauren Alaina got to fill the shoes of another American Idol alum…

The country rocker would invite Lauren to the stage to sing Kelly Clarkson’s part on their smash single “Don’t You Wanna Stay.” Lauren called the opportunity “a life changing experience.”

“My stage presence got better,” Lauren says, “and I feel more comfortable in front of people.”

And these days she should be feeling more confident in front of concert crowds.

The reason? The Idol runner-up has slimmed way down since the show ended, and it’s all thanks to a workout program called “Insanity.”

“It definitely gets you in shape. I can tell a difference on stage since I’ve been working out, I can hold my notes longer and don’t get out of breath as easily.”

Lauren continues her tour with Sugarland through the summer.