Every time you lift your head to finish yet another crunch, you see them: two go-go dancers in hot pants, fishnets, and leg warmers, bumping and grinding to A-ha. They shimmy while you swing kettlebells. They flip their hair while you do countless chest presses on a TRX band. This isn't working out in a club, per se, but an approximation of one at Chaos Conditioning. The small but effective interval-training gym is well known for hosting bootcamp-style workout classes—think modified jump-roping, digs, squats, and push-ups—that leave you trembling and toned. But on an occasional Saturday night, owner and instructor Jeff Baird turns the place into Club Chaos, an invite-only workout party with thumping music, flashing lights, fog machines, and dancers. With its keep-your-muscles-guessing mix of strength training and cardio, the sixty-minute class is incredibly tough. But the ambience and Baird's energy make it—dare we say?—fun.