When I was young, I owned a much-loved pair of Noddy shoes that had marked on the toe ''Right'' and ''Left''.

Right now, I'm wishing desperately that I still had those red-and-blue shoes as I demonstrate my legendary lack of co-ordination to the other 60-or-so members in a group exercise class.
It's my first group class. I've never been one for exercising with others, preferring my own company, either running or cycling.

Worryingly, the gym management has put me right in front of the stage from which fitness instructor Yvette Cattana is leading the class. She is a small woman, wearing not much more than a bikini top and short shorts that show off a tanned, extraordinarily toned body. As well as her chiselled abs and boundless energy and enthusiasm, I can't help but notice she is hefting about twice as much weight on her barbell as the embarrassing amount I'm using.

But, in general, I'm not in a frame of mind to think about much at all other than trying to follow Cattana's graceful and fluid moves as she powers through the class, somehow maintaining a generous smile throughout.

She's extraordinarily encouraging - even to someone with my galumphing ineptitude - and it's clear she genuinely cares that the people in her class have a good and productive time.
The class she is teaching is legendary in the fitness business. Called BodyPump, it has demonstrated unusual staying power, still packing them in at more than 14,000 gyms around the world after more than 20 years. If BodyPump were a rock group, it would be the Rolling Stones.
Exercise is obviously a ''together'' thing for a lot of people, and BodyPump somehow fulfils that need more than most other classes.

It's owned and licensed by fitness behemoth Les Mills, a Kiwi company founded by Phillip Mills and named after his father, a four-time Olympian.

One of the secrets to BodyPump's staying power is the degree to which it is standardised. Attend a class in Tokyo, London or Manila and you will get exactly the same experience - the same moves, the same music, even the same exhortations from the trainer.

For instance, today Cattana is teaching the 88th official release of BodyPump in Australia. Each release has its own specific music and moves, which instructors spend hours memorising from extensive notes provided by head office in New Zealand.

Mills makes no apologies for this formulaic, cookie-cutter approach on which he has built an empire.
''People like standardised products,'' he says. ''It's a terrible comparison to make but [it's] your McDonald's concept. If you can standardise the components it guarantees a good experience.''
And with such success comes the inevitable slew of imitators, which Les Mills spends a lot of time and effort closing down.

''We spend millions protecting our IP and trademarks,'' says Mills. ''We have a service that we use around the world that takes down illegal postings of our stuff. In the first two months we employed them they took down 7000 listings of people trying to sell our stuff illegally, mainly in China.''
The longevity of BodyPump is a clear exception in a fickle industry governed by trends and fashions that come and go almost with the seasons. Almost as soon as news reports touting ''This year's hot new exercise trend'' appear, the lycra crowd moves on in search of something new.
No one seriously expects, say, AntiGravity Yoga (you hang upside down in something like a giant nappy suspended from the ceiling) or Aqua Cycling (yep, bikes in a pool) to stick around for long. Even the mad craze for Zumba that for a while threatened to take over the world appears to be on the wane.

Exercise physiologist Kate Pumpa, from the University of Canberra, says once you strip away the frills, group exercise classes can be separated into two categories.
''There are the ones that work you aerobically, like your riding or running classes or step,'' she says. ''The other side is more resistance and strength-based classes. They all boil down really to these two things. Some classes have a combination of both.''

Mills agrees that activities that stray too far from the basics are unlikely to last.
''When the classes get too wildly creative and different they often won't pick up on a big enough following to maintain them over time and a lot of classes tend to come and go.''

But regardless of the bells and whistles, one overarching trend that most of the fitness industry agrees is here to stay is exercising with others, be it in large or small groups.

''You don't have to go to a gym to do exercise but for some people it's a means to have a commitment,'' says Pumpa. ''If you hopped on a treadmill you might walk for 10 minutes then leave, but when you are in a class dynamic and everyone is working out together, you may feel a bit more guilty if you leave halfway through.''

For other people there is also a social aspect to group classes that draws them in.
''A lot of people are captivated by classes because it entertains them for an hour or so and also builds a rapport with the instructor,'' she says.

''The social aspect is also important because when they go regularly they make friends there.''
After the 45-minute Sydney class the room empties quickly as people hurry back to their desks. Talking to Cattana before she rushes back to her own ''day job'' (she's a corporate lawyer), her passion for group exercise is clearly heartfelt.

''It gives me so much pleasure when my participants start to see results, and when I have the same people who might come to my classes no matter where I'm teaching,'' she says. ''It's really nice to know that all the hard work I put into delivering their workout is effective for them and appreciated by them. That is such a delight.''