THERE'S only one thing wrong with cycling as a form of exercise, I've always thought - and it's nothing to do with the bikes themselves. It's the fact that, at least as often as they go downhill, roads will insist on going up again. No matter how many gears you may have, there's no getting away from it. Riding up hills isn't much fun.

Or so I'd always believed until I tried riding up the ones in the Barbican Centre.

No, it's not some weird new indoors BMX track I'm talking about. It is spinning. And not the kind dear to the hearts of New Labour political advisors, either.

Spinning is a form of cycling group exercise that's done indoors, lasts for about 30 minutes, involves you riding up and down imaginary hills until you're absolutely knackered - and is great fun.

Spinning bikes developed, explains fitness instructor Anne Lucas-Storrie, from the machines used by professional cyclists to train indoors when the weather was bad.

They're basically like the 'bikes' you find in a gym - wheel-less contraptions with a comfortable saddle, handlebars, and pedals. Tucked away neatly on the handlebar is a 'gearstick' which enables you to alter the resistance in the pedals. Flick it up to high, and it immediately feels as though you're cycling up a steep gradient. Turn it down to low and you're speeding down a long downslope, your imaginary wheels 'spinning' (hence the name).

Sounds like your idea of hell? You'd be wrong.

The spinning sessions at Total Leisure Fitness (TLF) in the Barbican Centre are run in small classes of up to six. The bikes are arranged in a group in the gym, facing inwards so there's a real feeling of shared effort.

There are a few looks of trepidation among the beginners in my mixed class when I go along to try it out, so Anne, our instructor, takes things gently to begin with. She shows us how to adjust our seats, how to fit our feet into the pedal clips, how to work the gearstick that changed the gradient - and then we're away.

It is easy at first, the seven of us spinning merrily along, gears set to zero resistance, a thumping dance track on the stereo.

But just as I am beginning to think I must be fitter than I thought, Anne informs us, with a wicked grin, that the warm-up is over. Time to try increasing the resistance, she says: just a little at first.

We do so, flicking our gearsticks upwards. Suddenly, it is as though we are cycling up a long, gradual slope. The tempo slows as the resistance increases. But still it is easy enough. Then Anne ask us to increase the resistance a bit more. Then a bit more.

Before long, I feel as though I am cycling up Ben Nevis. By now, on Anne's instructions, we are all standing in the pedals, really putting our backs into it. After a short, hard pull, she counts us down - 5,4,3,2,1 - and then we sit down and flick the gearsticks back to zero resistance.

It is like cresting the top of a hill. Suddenly it is easy again, the wheels spinning. We relax in the saddle, blowing, hands on hips. "Only another 25 minutes to go..." says Anne.

The next 25 minutes are hard, there's no gainsaying it. Anne splits us into two groups, and we alternate between standing up in the pedals with high resistance and spinning along on low. There are gradual increases in gradient - followed by gradual decreases, as we move the gearstick slowly up and down.

The good thing about it is that, because we ourselves are in control of how stiff a resistance we set, nobody is forced to do more than they want.

And being in a group somehow takes the pain out of it. We laugh and joke, encouraging each-other, commiserating when the going gets hard.

The session finishes with a cooling down spell on minimum resistance, followed by leg stretching exercises.

Afterwards, over a coffee, Anne and her colleague, TLF manager Ann Sunderland who is also a spinning instructor, talk me through the health benefits.

It is essentially a good cardio-vascular workout, excellent for the heart, lungs and circulatory system, Ann Sunderland says. But there are other benefits as well. "General fitness, to start with," says Anne Lucas-Storrie, who barely raised a sweat while leading us through our half hour routine. "And it is very good for weight loss, weight control, and toning."

"Particularly the lower body," interjects the other Ann. "It will improve muscle tone in the legs and bottom."

As with most regimes, it is best to vary types of exercise, Ann says - spinning once or twice a week, say, with some swimming, aerobics or yoga at other times.

If you only do one sort of exercise, Ann says, your body adapts to it and learns to 'cheat', so you don't get so much benefit. "Also, doing the same thing day in, day out, you are more prone to injuries," she says.

The real beauty of spinning, she says, is that you do vary the types of exercise during a class. Also, even though it is a group exercise, everybody can work at their own level because each person controls the amount of resistance in their pedals. So you can have a good workout, spurred on by others in the group, without ever having to push yourself too far. "You can work as hard as you want," says Anne Lucas-Storrie. "It doesn't have to hurt."

Even better, because it is a 30 minute workout, it's the kind of exercise you can do in your lunch break.

"After you've had a shower, it feels really invigorating," says Ann Sunderland. "It really sets you up for the rest of the day!"

I can vouch for that.

Spinning classes at TLF at the Barbican are held mornings, lunchtimes and evenings on various days of the week, including a morning session on Sunday. Classes are free to TLF Total members. Membership costs £31 a month (£25 a month if you sign up for a minimum of 12 months), which entitles you to unlimited use of the gym, swimming pool and fitness classes.

You can pay for individual sessions as a casual member, which will cost £3.20 with a York card, but you will have to pay an initial one-off £12.90 fee for casual membership and an introduction to the gym facilities.

Because places at spinning classes are limited, you should book in advance.

To find out more, call the Barbican on 01904 630266.

As with any exercise regime, if you have a heart condition you should seek medical advice first. If you have any other medical condition you are worried about, you can speak to a TLF instructor.

Updated: 09:28 Monday, August 12, 2002