Average calories burned: 400
Cost per class: $25
Cost per calorie: 6.3 cents
Class time: 1 hour

This workout consists of three stations: the treadmill, the rower and strength training. The goal: to spend 12 to 20 minutes in the orange zone, aka at least 84 percent of your maximum heart rate. This helps your body continue to expend energy once you're done working out -- resulting in extra calories burned.

Upon entering the studio, you'll be hooked up to a heart rate monitor, and your numbers will be projected onto a screen in the studio (the fact that everyone can see your numbers -- even if they're likely focused on their own -- is surprisingly motivating). When the class is over, they email you a printout of your workout performance.

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Average calories burned: 600
Cost per class: $34 class
Cost per calorie: 5.7 cents
Class time: 1 hour

Were it not for the dozens of stationary bikes in the room, you might think you were at a nightclub. The lights are dim; the music is loud. There's a raised platform in the front of the room with a lone bike and a turntable, the other bikes surrounding it worshipfully. The hour-long spin class will push you to go harder, faster. Your teacher might jump off her bike to dance and yell motivational quotes. And by the end, your legs will feel like jelly (in a good way). Expect the endorphin rush to last throughout the day.

Do not expect to preserve your blowout during this class.

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Average calories burned: 800
Cost per class: $30-$40, depending on location
Cost per calorie: 3.8 to 5 cents
Class time: 1 hour

Barry's Boot Camp alternates between intense treadmill action and weight training, so you get the best of both worlds -- you build muscles while you burn calories. The low lights and rows of treadmills may seem intimidating at first (especially if you don't consider yourself a runner), but a glance around the room at the superfit people will show you that something, clearly, is working.

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Average calories burned: 660
Cost per class: $26
Cost per calorie: 3.9 cents
Class time: 30 minutes

A favorite among celebs like Emma Stone and Ashley Greene, this boutique climbing studio boasts a 30-minute workout that burns calories and tones muscles. (Seriously, if you want a killer upper body this is the place to go.) The lights are low, and the music is loud and pulsing, keeping you motivated as you climb to the beat. Since this slightly-tortuous-but-worth-it class combines cardio with muscle building, you'll continue to burn calories long after the workout is over.

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Average calories burned: 500
Cost per class: $16
Cost per calorie: 3.2 cents
Class time: 1 hour

A combo of Pilates, kickboxing and dance, this class packs a fat-torching punch while toning your muscles. Translation: You get the lean-muscle-building benefits of Pilates and boxing -- not to mention the abs workout of both -- plus, the cardio burn of high intensity intervals. A note: If you don't like to dance (in public, anyway), you may want to skip this. There are definitely some Zumba-esque moments.