Sometimes I wonder if the fitness industry is secretly having a laugh at our expense. I wonder whether the big-wigs of the gym world sit on exercise bikes in some glossy aerobics studio, brainstorming the most outlandish ideas for new fitness crazes that will leave us looking as ludicrous as possible. Last year they had us trying erotic aerobics (pole dancing and stripping), kangaerobics (on bouncy boots) and vibrating platforms (power plates); and now they present us with Chaos Training, a workout that, as its name suggests, is somewhat off-the-wall in its approach.

Billed as "an exercise craze to shake up the average gym routine" by this month's US Vogue and currently a sell-out fixture in New York's trendy Equinox gyms, it turns on its head the current concept of gym-based sessions as orderly, choreographed and instructor-led. Were you to peek through the door when this class was being held, you would be greeted with utter mayhem. Its creators - an exercise physiologist called Dr Paul Jurvis and the national creative manager for Equinox, Lashaun Dale - claim that it is loosely based on the scientific theory of chaos, namely that apparently random actions can ultimately enable you to reach a predetermined goal. Exercise, they propose, can benefit from being very chaotic - ever changing from one workout to the next - yet predictable in its direction and purpose. "There is no order and no two classes are the same," Dale says. "Your mind and your muscles never know what to expect. It's about problem-solving as much as anything - the idea is to get fitter and smarter at the same time."

Certainly, you might not expect to find workout tools such as drinking straws, traffic cones, helium-filled balloons or builder's ladders in an exercise studio, yet all have been used in a 60-90 minute Chaos Training class. A session begins with some running or skipping before taking a more disorderly turn. "The majority of the class consists of what we have called 'chaos tasks' that change by the week," Dale says. "Each drill is followed in quick succession by another that is completely different." One of the tasks involves 30 helium balloons being released to the ceiling and participants being asked to get them down as quickly as they can. "They need to use their initiative - some get on each other's shoulders, others run to the store-cupboard to borrow a ladder; it doesn't matter how they do it because it all works their bodies and minds."

The seemingly random collection of props is used to great effect. Drinking straws are breathed through when abdominal exercises are being performed ("it helps to focus the effort on the deeply embedded core muscles", Dale says) while the raising of a yellow flag signals a "suicide run" in which class members must sprint to one side of the room and stand on a letter X on the floor. Those who fail to make it in the designated time are required to perform a hamstring-quivering squat against the wall for the duration of the next drill. When the studio lights are turned out everyone must drop to the floor in a "plank position" (with only elbows, forearms and toes on the floor) which is designed to strengthen the core muscles. They also incorporate a "human ladder" in which two rows of people each hold a weighted, tubular "body bar" so that someone can climb across the top.

There are intermittent bouts of lunges, squats, sit-ups and crunches performed with and without weights, but many of the moves are unlike anything even the most ardent gym-goer will have seen or tried before. There's the "inchworm walk" - a yoga-style downward dog manoeuvre with your hands and feet on the floor and bottom in the air; the "inverted hamstring arabesque" - a balletic leap across the room; and, perhaps most punishing, the "body drag" in which you inch across the floor on your stomach while pushing a heavy medicine ball. "Workouts like this can be great confidence builders," says Dearbhla McCullough, sport psychologist at the University of Roehampton, Surrey. "You start by thinking: 'I'll never be able to do that' but realise you can with a bit of determination. They are also good for people with a low boredom threshold as, like circuits, their content changes so often."

Robin Gargrave, director of YMCA Fitness Industry Training in the UK, says the underlying principles of Chaos Training are not new. "It is the kind of approach athletes use all the time - testing different muscles and challenging reaction times and spatial awareness - to simulate the unpredictability of sport. If you always do the same workout, your mind and your muscles get bored. Sport is different - you never know which direction or plane your body is going to be required to turn, jump or run. This class is attempting to simulate that, and it can only be a good thing."

Brian Johnston, director of the International Association of Resistance Trainers, a government-recognised education institute for fitness instructors in America, agrees, adding that progression can be incorporated by getting people to use heavier weights, perform more repetitions and take shorter recovery time between drills. "The dramatic alteration of the stimulus makes exercise at the very least more enjoyable and interesting. It's ideal for instilling motivation and, in spite of its variation, it does have some structure." Dale says that 12 core movements (including the lunges, abdominal crunches and squats) are contained within each class and "that you would get fit if those moves were all you did".

Chaos Training, which has been trademarked by Equinox, is to be launched by the group in the UK later this year at a yet-to-be-decided gym chain. But is the rather more reserved British gym member ready for such a class? Gargrave thinks so. "It sounds like a brilliant idea," he says. "It is basically a multi-command type circuit that combines all the principles of cross training in one crazy class. You could get the benefits from going out to play a sport, but people love the pre-packaged element of a class. I predict it will be a resounding success."