It's always assumed that new year's resolutions cause the biggest increase in people signing up to a gym but, according to the Fitness Industry Association, September is by far the biggest month for business: apparently, people have “a desire to sustain the sense of healthy wellbeing experienced during a summer of activity and fun”.

Yeah, right. For me, it is the humiliation of watching tanned, muscular beach bums strut their stuff while I lie on the sand worrying that if I don't keep my hat on a Japanese whaling ship will come and cut me up for blubber. I suspect that I am no different to most people filling out direct debit forms in the dead light of gyms across the country. We are motivated by a deep dissatisfaction with our bodies.

This is, I know, not a particularly fashionable thing for a man to admit. I'm meant to say that I'm interested in getting fitter for sport, or that I go to the gym to keep healthy. In fact, I want to look like one of those Olympic gymnasts who swings on the hoops, although that's not what I wrote in the “goals” section during my assessment with my personal trainer. A woman may receive support if she stands in front of a mirror saying “I wish I was thinner”. A man who says “I wish I had a six pack” in public invites ridicule.

Dr John Morgan, an eating disorder expert, says that many young men suffer “extreme distress” over the appearance of their body. The preliminary results of his research, which was carried out on male students aged 18 to 25 at Surrey University and is due for publication next year, found that one in five worry about their physiques. Morgan, who is head of the Yorkshire Centre for Eating Disorders, says that, for every man with an eating disorder, another ten desperately want to change the way they look. “One in five men have some degree of quite extreme distress,” he says. This can result in anything from obsessive dieting to spending vast amounts of time in the gym, or simply worrying a lot about how you look. “Not all these people are ill, but true illnesses do arise from this fermenting cocktail of anxieties,” he says.

Of course, male body anxiety is not necessarily all that new, nor limited to “metrosexuals”. In the 1950s, the literary macho man Ernest Hemingway was preoccupied with his weight and would record its fluctuations on his bathroom wall; the early bodybuilder Charles Atlas earned his fortune preparing men's bodies for the beach as long ago as the 1920s.

But as the latest issue of Men's Health magazine attests, this preoccupation is on the rise. A survey of its readers shows that 62 per cent of them worry about their daily calorie intake. And Men's Health has bucked the trend in men's magazines by increasing sales for seven consecutive years.

An ICM study for Norwich Union in 2006 found that 36 per cent of men exaggerated how much they could lift. One in five men also lied about his weight - once considered a solely female preserve.

The rise of male body anxiety is harder to spot than the female equivalent as it's more complex, says Dr Stephen Edwards, a lecturer in psychology at Swansea University. “In women it's very straightforward - they want to lose weight. Men fall into three broad categories: those who want to gain weight, that is put on muscle; those who want to lose fat; and those who don't care.” There are also competing body ideals. Thin is in for most women, but would all men like to look like Jarvis Cocker, Arnold Schwarzenegger or David Beckham?

Deborah Schooler, a body image researcher at Brown University, Rhode Island, says that there is little research into the rise of male body anxiety. “Twenty years ago, we weren't asking the right questions. We'd ask about anxieties around weight loss, for instance, not recognising that many men have the opposite concern - putting weight on.”

I seem to have both concerns at the same time. If I look around my desk I can see a tub of muscle-building powder, creatine muscle-building pills and several books on weight training. In my drawer I have body fat calipers, testosterone-boosting pills, conjugated linoleic acid pills that are supposed to strip away fat and a vitamin complex that is meant to do something similar. Don't get me started on the press-up bars, weights, and exercise videos under the stairs. I'm not even an extreme case. I quit and go back on the pies after about three months of overdoing it. Other men take it much farther.

At the far end of the scale this appears as “reverse anorexia”, where men - despite spending most of their time in the gym and, in some cases, taking anabolic steroids - become convinced that they are not muscular enough.

Anna Paterson, author of Fit to Die: Men and Eating Disorders, and herself a former anorexic, says: “Muscle dysmorphia is a syndrome seen in both men and boys who feel dissatisfied with their body. They do not believe that they are muscular enough. This will lead them to try to work even harder to build their muscles, and dangerous patterns of overexercising begin to develop.” She says that, when they look in the mirror, sufferers of this condition see someone who is small and frail, even though in reality they are usually very muscular. The condition is also known as “bigarexia”.

The male preoccupation with their physique could, says Paterson, be to do with the changing appearance of such role models as wrestlers, movie stars and even action figures. “In 1974, a GI Joe doll, the American equivalent of Action Man, had a 44in chest, 31in waist and 12in biceps. The GI Joe of today has a 50in chest, 28in waist and 22in biceps. It seems that an increase in musculature, especially on the upper body, is the new ‘desirable' shape.”

However, a study published in the American Journal of Psychiatry in 2005 found that in the US and Europe men are more likely to overestimate female desire for muscular mates. One reason for the difference could be that Western males, unlike Asians, are bombarded with images of muscular men in advertisements. From 1958 to 1998, about 20 per cent of US print ads showed undressed female models, according to the researchers' analysis of two leading American women's magazines. The share of undressed male models rose from 3 per cent in the 1950s to 35 per cent in the 1990s.

Andrew, 43, says that worrying about his weight made him less attractive. “When I was in my early twenties I was very skinny, and a bit short, but I had no problem meeting attractive girls. Then, I got into weight training because I felt self-conscious about my weight and transformed my body completely. I put on about 30lb of muscle but I ruined my looks. People started calling me ‘Mr Potato Head'. Now I've got injured and stopped training and, when I'm on the beach, I remind myself of one of those former Soviet leaders at a Black Sea resort.”

There is no doubt that the ideal male body image has changed in the past 30 years. Take James Bond. Now, we are treated to the sight of Daniel Craig emerging from the water, six pack rippling as the result of an intense workout that you could follow only if it was your job to do so. In the 1970s we had the more achievable figure of Roger Moore. It used to be the Bond girls who emerged dripping from the sea with the camera lingering on every curve. Now it's Bond himself.

As men are judged more and more as sex objects, male body anxiety is only going to increase. It looks as though I'll be renewing my gym membership every September for many years to come.