Some of the hottest new exercise trends are actually just updates on yesterday's classics. See how new classes compare to old-school favorites.

Then: Boot Camp

Now: CrossFit

What they have in common: Both utilize military drills like push-ups and jumping jacks.

Why new is better: "CrossFit is more intense," says Carol Espel, senior director of group fitness and Pilates for Equinox.

Then: Jazzercise

Now: Zumba

What they have in common: They're both dance-based, low-impact aerobic classes.

Why new is better: "Zumba moves faster, so you get even more cardio conditioning," Espel notes.

Then: Lotte Berk

Now: Physique 57, Barre3, Figure 4

What they have in common: Exercise moves are done on a ballet barre.

Why new is better: According to Espel, "Classes use light weights and body-weight moves like push-ups and planks to tone."

Then: Body conditioning

Now: Metabolic training

What they have in common: Both use weights to improve strength and endurance.

Why new is better: "Metabolic training is faster and more athletic," Espel says.