These days, if you want to get fit, it seems you have to get high-tech. After the success of Nintendo’s Wii Fit home console, which has sold more than 600,000 in the UK and Ireland since its launch in April, the hot new way to work out is online. Whether it be web-based diet clubs, virtual gyms or even online personal training, a host of health and fitness websites — such as VirtualGym TV (virtualgym.tv), which has 3,000 private and 23,000 corporate users — are drawing people in droves.

At first glance, the website Superchick (iamsuperchick.com) doesn’t look as if its aim is to help you get fit and lose weight. It is super-girlie, super-pink and founded by Georgie Thompson, the Sky Sports News presenter, and her perky personal trainer, Cat Dugdale. With tips on the calorie content of cocktails and which Pret sandwich has the most fat, as well as workouts such as the Break Up-Wake Up, designed to “pick you up when you’re at your lowest ebb”, it is aimed at glam girls about town.

Superchick is one of many new health sites that have jumped on the internet bandwagon. Now that you can buy beauty products and fashion from Topshop to Tom Ford online, it isn’t too big a leap to imagine dieting, getting fit or even being personally trained on the net — or is it?

The celebrity trainer Matt Roberts, who has sculpted Naomi Campbell’s body, admits that his new personal-training website — although it gets 25,000-40,000 hits per day — is never going to be as good as seeing him in person. “The best thing in the world is to see a trainer,” he says. “But if you can’t afford one, you can get my training philosophy online for just £15 a month.”

Once signed up to mattroberts.co.uk, you provide detailed information about your body, medical history and goals. The programme then provides a personalised workout, complete with videos to demonstrate the exercises. After four weeks, you report your progress and get an updated programme.

Another celebrity trainer launching herself into cyberspace is the GMTV fitness expert Nicki Waterman. She fronts VirtualGym TV, which offers a selection of 45- to 60-minute workouts from top trainers, which are available to download. Just logging on makes you feel tired. Underneath the picture of a glowing Waterman is a preview video of a personal trainer bopping around and shouting: “Work those thighs, guys! Push!”

Richard Davis, the site’s managing director, explains: “Our instructors record new exercise classes every day, which you can watch whenever it suits you. We appeal to those who may not be able to afford a personal trainer, or who don’t want to go to the gym because they feel self-conscious. Gyms are expensive, and the class times and locations can be problematic.” VirtualGym TV charges £15 a month, or you can pay £20 for the year, then pay for each video at a cost of 60p-£1.

Yet no matter how technologically brilliant these websites are, they still don’t offer that crucial ingredient: motivation. Rob Williams, a London-based personal trainer, has mixed feelings about the online fitness revolution. “If someone is at home, you can’t spot if they’re doing the exercise wrong or adjust the programme,” he says. “And if you are motivated, great. But how many people do you know with Cindy Crawford’s workout gathering dust on the shelf?”

Of course, the same problem applies to gyms, whose business model relies on the majority of those who sign up dropping out within a few weeks, but continuing to pay. Superchick tries to boost motivation by adding useful extras to keep women logging back on. As well as the alcohol-calorie counter and calorie info on lunch options from most food chains, it also sends a weekly “motivation Monday” e-mail.

Lucy Evans, 28, a Superchick subscriber, has found the focus on drink useful. “My alcohol calculator was quite scary, and, naturally, I cut down once I was aware of what I was drinking.” Superchick also offers group training sessions in London parks, which Evans attends. “If you’re not that motivated, the park training is brilliant.”

Encouragement from others helps dieters stay focused, and this is the principle behind the huge growth in online diet clubs. Big players such as Weight Watchers, Rosemary Conley and Slimming World have a significant presence online, and new clubs, such as Tesco’s, have burgeoning memberships.

The theory is that by encouraging each other, you can all boost your willpower. Many have found success that way, but it didn’t work for Natalie Smith, 37, who is several stone overweight and firmly believes you need direct contact. “I’ve tried every diet and ended up putting all the weight back on.

My problem is that I emotionally overeat, and none of these diets dealt with that. The only thing that has helped is seeing my personal trainer five times a week. I’ve lost 3st.”

Cary Cooper, professor of organisational psychology and health at Lancaster University Management School, agrees that online dieting might be less effective than a weekly weigh-in. “The power of group conformity and peer pressure can really help you stick to the objectives you set,” he says.

Where online health sites can really deliver, however, is in offering technology that makes life easier. A good example is mapmyrun.com, which allows runners to measure their favourite run along roads or parks.

Similarly, nutracheck.co.uk offers a sophisticated online food-diary service. A recent American study showed that just the act of keeping a food diary can double a person’s weight loss. The technology counts how many calories a day you need to achieve your target weight, taking into account alcohol and exercise. It costs from just £1.16 a week.

Samantha Tracey, 42, has lost 2½st since joining Nutracheck in January. “There is no elimination of food types, so I haven’t felt deprived. It is a simple equation — if you take in less than you use, you will lose weight. Everything works, as long as you are committed,” says Tracey.

The online health revolution offers great opportunities to join clubs and receive information on exercise and diet at bargain prices. Now you just have to work out how to turn down that chocolate biscuit and go for a run.

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