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Whatever Carrie Underwood is doing to maintain her svelte physique, it’s certainly working. Which is precisely why we turned to the star’s trainer and author of The 4x4 Diet, Erin Oprea, for the scoop on how she stays in shape.

In the video above, Oprea shows me a full body move she does on Underwood that works everything from the arms to the legs (with some core thrown in for good measure!).

To begin, go into a lunge and hold it, then straighten both legs, extending your arms out in front of you. Then, twist your body, making sure not to let your elbows bend. Next, take it back to the center, then stand up straight.

Oprea recommends 12 to 15 reps for 3 rounds, 2 to 3 times a week, starting out with lighter weights (she recommends 3 pounds) and working your way up to 10 pound weights as you progress with the move.