A world without the gym: a glorious Utopia, or the road to (yet more) national slothfulness? Whichever your view, the death of the treadmill has arrived. For the first time since gyms muscled their way into the public consciousness in the Eighties, there has been a sharp decline in the number of people joining them.

Open a copy of Grazia or heat and you will find confirmation. A decade ago we were bombarded with images of celebs on their way to and from the gym (typified by the Princess of Wales's love of the Harbour Club in Chelsea). Now we are more likely to learn about Geri Halliwell's love of swinging kettleballs in the park.

Five years ago, when gyms and health clubs were at the peak of their popularity, 8.7 million of us in Britain were members. But statistics from the accountancy firm Deloitte reveal that 54,000 fewer people took out gym membership during 2007 than they had 18 months previously. In some parts of the country, including Northern Ireland, the West Midlands and the North East, the dropout rate has risen to 8 per cent, despite joining fees falling by an average of 17 per cent. And there is worse to come, according to business analysts, who point to falling profits and share prices of many clubs over the past two years. Gyms, they say, have fallen into a price battle to woo new custom.

Thanks partly to changed lifestyle choices and partly to the economy, the gym's heyday has come and gone. Just as Jane Fonda and her legwarmers were superseded by the treadmill in the late Eighties, so in the new millennium the gym has been elbowed aside by yoga, Pilates and outdoor boot-camp-style programmes such as park circuits.

It may be odd to contemplate for under-35s who can't recall a high street without tracksuits, but it was only 20 years ago that physical activity was remodelled into daily “fat-melting” workouts and promoted as something that would make participants feel - and, crucially, look - younger and healthier. The number of gyms soared, and we joined them in droves.

In the late 1980s there were fewer than 200 gyms in the UK. Now, according to the Fitness Industry Association (FIA), there are 5,714 - more than 3,000 of them private health clubs, of which the bigger names such as Fitness First and David Lloyd Leisure have branches nationwide. “You are never more than 20 minutes from a public or private fitness facility in the UK,” says Howard de Souza of the FIA.

Yet we have started avoiding them. Partly, we have realised that they don't work. Research last year at the University of Leicester confirmed that the fitness-industry boom has had little impact on the nation's girth. Dr Jennifer Smith Maguire, the study's author, says: “Many Western countries have experienced this strange situation, with fitness and exercise industries expanding alongside problems of inactivity.”

Almost a quarter of British adults are judged to be obese and, if current trends continue, 60 per cent of men and 50 per cent of women will be clinically obese by 2050.

There is a growing realisation, too, that gyms are sterile environments, and that their clinical approach to working out becomes simply boring after a while. This may help to explain why, alongside the gym's demise, alternative forms of exercise are flourishing. Dedicated yoga and Pilates studios are on the increase, more people are running now than during the jogging boom of the 1980s, and participation in activities as varied as ballroom dancing, ice-skating and triathlons is rising. It has become obvious to consumers that there are other, more appealing, means of burning calories - and that even walking the dog or cycling to work can be considered battling the bulge.

According to Dr Smith Maguire, gyms focus on “image rather than health”, which tends to mean that their customers' commitment is sustained for only a limited period. Psychologists are convinced that the ploys used by the fitness industry to attract new members will have short-lived health benefits, if any, for those they attract. “Gyms feed into people's insecurities about their weight and appearance, and get them to join in the belief that they can change those things,” says Martin Hagger, a social and health psychologist at the University of Nottingham. “Yet it has been shown time and again in studies that extrinsic motivational factors - such as improving the way you look, or losing weight - are unlikely to achieve the desired results.

“If people exercise simply to shed fat, not because they enjoy it, they will either give up before they achieve their goal or will think ‘job done' when it is finally reached, then revert to their old habits of inactivity.”

Another reason, though not a new one, why gyms are not fulfilling their promise is that, while we have paid up, we haven't always turned up. Many surveys have indicated that, six months after joining, the dropout rate among new gym members is about 60 per cent. One Mintel report suggested that 20 per cent of health club members work out there no more than once a month.

“Gym membership is altogether different from gym attendance,” says Dr David Haslem, a GP and clinical director of the National Obesity Forum (NOF). “People join and feel a degree of smugness about having a gym membership card in their wallet - but what's the point if they never set foot though the door?”

What has been lost, it seems, is an accurate perception of what activity means. “People think you need to join a gym to get fitter, but activity doesn't have to be done in a single 60 to 90-minute session,” says Dr Colin Waine, chairman of the NOF. “The real key is to build exercise into your daily life. You can become much more active without spending anything, and walking farther or taking stairs instead of escalators are approaches that could benefit a greater number of people.”

Dr Beckie Lang, of the Association for the Study of Obesity, agrees. “You don't need to make big changes to your lifestyle, such as going to a gym every day,” she says. “Consistency is what matters - and that means that activity must become a habit. So if doing the school run on foot is something you are more likely to keep up, that is better than a step class once a week.”

Many studies have linked moderate daily activity - the kind that can be achieved without donning Lycra - to more significant and longer-lasting improvements in health than the occasional gut-busting session at a gym. In a 2001 study, Professor Klaas Westerterp, of Maastricht University in the Netherlands, found that people who did moderate amounts of daily activity burnt more calories than those who performed short but intense gym sessions at lunchtime or after work. “After a tough workout, people typically limit their activity and either go back to their desk or relax for the evening, assuming that they have done enough,” he says.

Another study, at the University of Ottawa, suggested that, the harder the workout, the more calories people were likely to consume afterwards. It followed that a more relaxed approach to activity could result in greater long-term weight loss. A group of women were invited to eat as much as they wanted at a buffet lunch after a morning gym session of between 60 and 90 minutes. Those who pushed themselves to the limit in high-intensity workouts, such as running at a pace too fast to hold a conversation, or high-impact aerobics, gobbled up “in excess of 90 per cent of the calories they had just burnt” in the post-workout meal. Conversely, says Professor Eric Doucet, who led the research, those who adopted a more leisurely approach, such as brisk walking, replaced only about a third of the calories they had used.

Dr Waine says that the fitness industry has complicated exercise so much that we make absurd attempts to achieve what could easily be integrated into our day. “People drive to fitness centres, and gyms have installed escalators and lifts to save people walking,” he says. “They just need to be more active each day and obesity levels would drop.” Since the 1950s we have lost, on average, about two-and-a-half hours of calorie-burning activity a day. Back then, fewer labour-saving devices meant that people covered between three and five miles each day in the course of their ordinary lives. Now we barely manage that distance in a week.

Activity need not be done in a single burst. Current government recommendations suggest that 30 minutes of moderate exercise is enough to make an impact on health, but more is obviously better. “This eliminates the common excuses of not having the time or money to exercise,” says Dr Lang. “Do whatever you enjoy and you are likely to want to do more - gardening, walking, cycling to work, playing football with the kids. Just get moving.”

Integrated Exercise by Peta Bee is published by Kyle Cathie Ltd at £14.99; available from Times BooksFirst at £13.49: 0870 1608080, timesonline.co.uk/booksfirst

How to lose more weight for no money

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