The Class Burn
Where Healthworks (healthworksfitness.com)
What it is A group class that alternates between seven minutes of walking and running on a treadmill and three minutes of continuous strength-training moves for up to 50 minutes.

The Class Barton Biking
Where David Barton Gym (davidbartongym.com)
What it is A one-hour session, during which you'll power through a biking interval and grab a pair of dumbbells to do a few sets of arm or shoulder exercises; then repeat until you've strengthened your entire body and burned more than 500 calories.

The Class Chaos
Where Equinox (equinoxfitness.com)
What it is A boredom-busting hour and a half of cardio drills and strength-training exercises. The class also involves make-believe, such as sprinting across the "street" (a.k.a. the studio) when you hear a "horn" (whistle) to avoid a "car" (stability ball). You'll work your body and mind in a variety of ways—kind of like you do in real life—and have a blast in the process.