And you're up next for Karaoke Spinning, the hot new trend among L.A. fitness fanatics

Imagine breaking into a high-resistance stint in your Spinning class as "When Doves Cry" blasts over the sound system. Suddenly, a microphone is shoved into your face, and your demanding instructor expects you to sing The Artist Formerly Known as Prince's falsetto part. Sure, Spinning is the best way to get into condition for spring cycling, but it's also stationary, monotonous, and, well, boring. All of which might explain (but not defend) the latest fitness craze: Karaoke Spinning.

In the battle to attract new students to their classes, health clubs like Crunch and Bally Total Fitness generate buzz by applying ever-more baroque twists to the concept of the theme-based workout. September 1998 saw the emergence of Urban Rebounding, in which exercise buffs bounce up and down on mini trampolines to a disco beat. A few months later, Cardio Thai Boxing debuted, melding hip-hop sound tracks and martial arts moves. Neither of these routines, however, achieves the hybridized weirdness of Karaoke Spinning, conceived last fall by Stacey Griffith, a 32-year-old instructor at Crunch in Los Angeles who sidles up to her students during "climbs" and high-cadence pedaling "runs" and holds a cordless mike to their lips. Taking their cues off a large screen at the front of the room, the students alternately gasp and belt out lyrics. "Brass In Pocket" and "Love Will Keep Us Together" are mainstays. At the chorus, the entire class chimes in.

Currently the most popular class at the L.A. Crunch, Karaoke Spinning has migrated to Miami and New York—where it is meeting with mixed reviews. "I think it's hilarious," says Mary Noonan, a producer for CBS's 48 Hours who works out at Manhattan's 38th Street Crunch. "Of course, I myself wouldn't do it in a bazillion years."

Dubious as the trend may be, karaoke can actually help you determine how hard you're working out: As long as you can sing clearly, you haven't exceeded 70 percent of your maximum heart rate, which is where you should be for much of your training. Try to wail "Purple Rain" if you've gone beyond that threshold, however, and—questions of taste notwithstanding—you'd better stick to lip-synching. —GRANT DAVIS