When Carrie Underwood and Keith Urban showed up together this week on Twitter, they did so from a sort of boxing ring. It was all about the new video they've made for his song, "The Fighter."

And in addition to that, I'd also just seen a Self magazine story about Underwood keeping some workout basics at home -- like a Bosu ball. (That one, I think, is not so basic. I had to Google it. It's that thing that looks like you cut a round plastic ball in half. The Bosu people call it a balance trainer.)

So with my curiosity piqued, I read on to find out what kinds of exercises she's doing now that keep her in such great shape now that her tour is over.

There are walks with her almost-2-year-old son Isaiah when the weather's nice.

“He enjoys just being outside and looking around. It’s good for both of us,” she says.

There are weights.

“I’ve been getting more and more into doing more stuff with weights,” she said.

And there is strength.

“I’ve noticed a big difference in the past year on things just being easier, where I’m like, ‘Ooh, I can lift that!’ I love it.

"I just love seeing that forward progress," she said, "and I like feeling strong."

Spoken like a true fighter.