Carrie Underwood Trains Intensely to Prep for Her 'Physical' Concerts: 'I Have to Keep Up with Myself'

Between life on the road as a country music superstar and a mom to two young sons, Carrie Underwood's schedule is packed with places to be and people who need her. So when she fits in her workouts — an essential part of her day that she considers "therapy" — Underwood has a little trick to switch her mind over into thinking about exercise.

No matter the workout, Underwood, 39, likes to start out on the treadmill, she tells PEOPLE.

"I'll walk on the treadmill for 10 to 15 minutes, because I feel like if I do the same thing before I work out, my body's going to be like, 'OK, we're about to work out,' " she says. "In my brain and in my body, and I'm telling my body I'm about to work out."

From there, Underwood gets right into her workouts with her trainer Eve Overland — and these regimens aren't for the faint of heart. Anyone who's seen the "Before He Cheats" singer's legs knows that she has serious muscle strength, and Underwood says that keeping up her fitness is essential to make it through her concerts.

"I'm a very physical performer in that I feel like I use my whole body to sing. I don't sing easy songs, and I don't want to. So I have to keep up with myself," she says.

"I'm 39 years old now," Underwood, who is also a spokesperson for all-natural sports drink BODYARMOR, continues. "I have to make sure that I can give the fans the best show that I possibly can and feel good doing it. I don't want to feel exhausted when I get off stage … I want to be ready for it, and I want to be able to give it my all."

That means Overland is structuring Underwood's workouts to hit each part of the body throughout the week, with some extra conditioning that she knows the singer can handle.

"We always stick to the basics, the basic squats and the dead lifts and the pushups and the pull-ups," Overland says. "Everything is full-body, but then the next day would be upper body pull, lower body push, that kind of thing. And then I can detail it. So we can stick with the major exercises and deviate from there. Because Carrie's so conditioned all the time, I actually have the luxury of getting more detailed work with her."

As Underwood has gotten older, she's also noticed that she can't push her body quite as much.

"Things are easier when you're in your 20s. You feel like you can do anything. You probably can," she says. "I feel like I'm a little more conscious just about my body and not overdoing things."

That's where Overland comes in, and can adjust her workouts to rest one area while strengthening another. Their goal is to "work out smarter, not harder," Underwood says.

RELATED VIDEO: Carrie Underwood Announces Her Las Vegas Residency After the 'Forced Slow Down' of the Pandemic

"She knows her body so well, and so actually slowing down and taking that time, actually, I think has helped improve her overall physique as well as conditioning," Overland says, before quickly adding: "But don't get me wrong. We have maybe slowed it down, but I challenge anyone to work out with her!"

And as Underwood prepared to lead, alongside Overland, a HIIT workout in Austin, Texas on a 100-degree day, she points out that hydration and refueling — she usually goes for BODYARMOR LYTE's coconut and orange clementine flavors — are essential to staying safe and letting the body recover.

"I love it," Underwood says of the heat. "I love being outside. But once you sweat and lose all of that, you have to replenish," she adds, pointing to the BODYARMOR LYTE. "You have to have your electrolytes."