Credit: Astrid McGuire.

When it's 6 a.m. and 30 degrees outside, the thought of getting out of bed and breaking a sweat can make you want to burrow deeper under the covers and whimper. My quickest way to banish all of that? Music.

I recently dropped by Barry's Bootcamp in West Hollywood, Calif. To say that the instructor that day, Astrid McGuire, kicked my butt would be doing her a disservice. She engineered a workout so brutal that I wanted to throw a weight at her. (A light one, 5 lbs.) Of course, I was grateful for the opportunity to sprint at 9.0 mph and "recover" at a 7.0 … five times in a row. What got me through: A killer soundtrack featuring Rihanna, Avicii, Flo Rida, and more high tempo pop stars that turned torture into a dance party.

Afterwards, I talked with Astrid about her top 5 tips for picking tunes to make the burn feel so much better:

1. Mix it up. Remixes are the bread and butter of a blood-pumping playlist. "My clients Doug and Derrik Perry make my playlists for me," Astrid says. "They try to mix it up with current songs, newer remixes of older songs, and anything with a good build-up. We use songs that are upbeat and make you feel their high energy level, like Rihanna, Nicki Minaj, David Guetta, LMFAO, Afrojack, Swedish House Mafia, Lady Gaga, Pitbull, Tiesto, Laidback Luke and of course, my favorite, Enrique Iglesias!"

2. You don't need a pro. While having DJ friends is nice, a computer can do pretty much the same thing for you. "When I'm looking for new music, I use iTunes as my staple," Astrid says. "Search for a song you like, then check out the remixes that come up and listen to the previews. Once you find someone that you like, you can search by their name to find more remixes they've done. I'll also Google a song that I like and see what DJs are doing with it. A lot of them will offer free downloads from their sites."

3. Don't waste time searching for songs. Make a playlist and stick with it from the moment you start you work out 'till you cool down. Scrolling through that iPod just wastes time. "I always create the workout and the playlist before hand and I let the power of the music fill the room," Astrid says. "The way I do it, when you start feeling the burn, the beat will pick up and you'll get a burst of energy."

(Fun fact: Astrid grew up dancing. When she first came to Barry's as a student, she "couldn't even do a mile." "I couldn't run past five miles per hour," she said. "I think that's part of the reason I'm so crazy in class, because I know that if you try a little bit harder, you can go a little bit more.")