1. CrossFit

Don't Hate It Because It's Popular

Join This Craze if: You're into old-school workouts minus the 'roid rage

Lifting weights is kind of like smoking. You love doing it in your twenties, but at some point it starts to feel a little silly and vain. The problem is, strength training is good for things such as, but not limited to, being able to pick up your children; not dying at an early age. What you need is an excuse to do it. Have you heard the good word about CrossFit?

If that last sentence sounds like proselytizing, deal with it. Because getting into CrossFit—a regimented system with licensed gyms—requires one to accept that it's a craze! Developed in Santa Cruz in 2002, it's perhaps the signature fad of the past decade; there are now more than 6,000 outposts.

Part of the craze: the CrossFit vibe. The gyms are bare-bones and manly. The workouts are simple, badass, low-tech: jumping rope, body-weight ercises, some weight lifting. It adheres to sound fitness theory—that whole-body movements are more effective than isolated ones, that your heart rate needs to get jacked up, etc. The most important part of the class is the Workout of the Day, a five-to-fifteen-minute session based on the idea that short, high-intensity workouts are the most effective. It may be three rounds of rowing 500 meters on a machine, followed by ten pull-ups and twenty-one kettlebell swings. But it will involve muscle failure and the desire to barf. And it gets addictive, because the best fitness fads often become fads because (1) they're fun and (2) they work. Which is more than I can say for running two and a half times a month—my previous routine._—Devin Friedman _

Intensity: 9

Price: Approx. $215/month for twelve classes