survival of the fittest; Based on the theory of chaos, the latest exercise craze shakes up the average gym routine.

Byline: Betsy Berne

The idea of taking an exercise class called Chaos is not exactly enticing. As a single parent who harbors a young daughter who is a cross between a stubborn mule and a human cyclone, I already have enough in my life. Yet in the interest of longevity, I figure, why not try it?

I arrive at Equinox, home to the 2007 fitness phenom Chaos Training, gussied up in my finest pink-and-orange Stella McCartney workout clothes, to find a swarming mass of type-A muscular bodies dressed in black. These are serious gym rats, and this is serious business. In my prime I, too, was a gym rat. I, too, worked out religiously at gigantic, gleaming gyms with state-of-the-art high-tech equipment. Fifteen years later, I am a slovenly type-D personality who prefers sweating it out twice a week at the neighborhood boxing gym.

Before the class begins, Lashaun Dale, our head coach, explains that the 90-minute class, while designed around the theory of chaos (defined in my dictionary as "utter confusion"), is really about finding order within a seemingly random setup of eclectic props-medicine balls, drinking straws, and balloons, for example-as you unwittingly achieve a stellar cardio and strength workout. Your mind-body skills will also improve. "It's like the real world, the unpredictability of life," says Dale. "It's about problem solving; the idea is to get more fit and smarter at the same time."

Orange traffic cones and X spots are strewn about the studio, yoga blocks line the perimeter, and a cluster of balloons hovers menacingly above as we each choose a playing card to divide us into groups. Our first drill: Move around the edge of the studio performing exercises that include the "inverted hamstring arabesque" (a storklike balletic semi-leap) and the "inchworm walk" (a moving downward-dog maneuver).

Next up, a series of fairly straightforward mini-workout sessions-lunges and ...