Selena Gomez (Pic: Reuters)

Selena Gomez works out in her underwear if she's just training at home.

The 'Bad Liar' hitmaker - who recently underwent a kidney transplant - keeps things "intimate" if she's exercising at home, but of she's out and about, she wants her gym gear to feel "sexy".

Asked what she works out in, she said: "When I'm at home, it can be very intimate. Maybe just a sports bra and maybe some little spanky kind of cute things. 

"And when I'm out, then it's the typical: something slouchy that feels sexy that I can take off. It's about layering and cute little socks.

"I add little chains to my socks because it adds a little charm, a little sparkle to it. Little anklets, actually. Me and my assistant got a bunch from Japan when I was on tour."

However, Selena admitted she often misplaces her beloved anklets.

She added to Vogue.com: "I went through this whole phase where I would just wear the anklet around and shower in it. It's effortless. I lose things--for me, it's got to be on me, you know what I mean?"

The 25-year-old star favours comfortable footwear and claims she enjoys wearing sneakers so much, she's "forgot" how to walk in high heels.

Selena Gomez for Puma. (Pic: Supplied)

She said: "[Sneakers] have been so changing my life. I actually forgot how to walk in heels, you guys. I've been figuring out the past few events I've gone to, I've forgotten how to walk in heels just a little bit. I'm like Bambi, trying to figure out how to get my legs under. 

"It's the craziest thing because you get so comfortable [in sneakers], and now you can just wear them everywhere. Now that I'm in the city--I'm going to be here for a little while--it's even better. I can walk anywhere, I can put on a cute dress with them. My entire closet is sneakers and cute boots and now a few heels."