When blokes sign up to join a gym, they generally have a secret image of how it's going to make them look.

After a few weeks behind the weights bench, you're bound to look like Arnold Schwarzenegger's twin – or so you tell yourself.

Of course, for most of us, it doesn't work like that. After a couple of frantic sessions on the treadmill, you fail to make it to the gym for another 18 months, until you finally give up and remember to cancel your membership.

But some men are made of sterner stuff, and one Bristol gym is currently awash with Popeye-like biceps.

Fitness First in Longwell Green can boast not just one but three competitors at the British finals of the National Amateur Body Building Association (NABBA) on May 30 in Southport.

The two Herculean Bristolians, Dave Guest and Dan Barry, will be joined by woman body builder Gina Ford at the show, where they will pit their muscular frames against the rest of the 60 finalists.

The top six from the show will then be able to go on to challenge for the title of Mr Universe or Miss Universe.

The contestants first have to do a one-minute posing routine choreographed and set to music, then their bodies are carefully inspected by judges who are checking things like tone, shape and symmetry.

Dave Guest, 31, of Ashton, a property developer by day, is a former weight lifter, who has now turned his attention to body building.

"I used to be heavily into weightlifting," he said. " I won the British finals for nine years in a row and was able to participate in the Commonwealth Games. But when I hit 30, I thought I should call it a day because it's a discipline that's not good on your joints.

"So I thought I'd try my hand at body building instead, which is a very different thing. It's not about physical strength, it's entirely about looking right. You're exercising to break the muscle down, which allows it to grow back bigger.

"For body building you have to be very lean, and it's mostly about dieting and eating the right food. Carbohydrates are off the menu completely. You just try to take on as much protein as possible. So I get through lots of chickens each week."

Dave trains for 1.5 hours each morning and two hours each evening.

"I have a very patient girlfriend," he says.

It's not quite as difficult for fellow finalist Dan Barry, 20, of Kingswood, as he works as a personal trainer at the gym.

"It's great for me, because I'm constantly training as part of my day job," he said.

"I only started a couple of years ago. I was 19 stone, so I wanted to get trim, and once you start, and see the progress in the way you look, it can become quite addictive.

"Body building is all about sculpting the physique. It's a very considered process. You have to eat every two hours, in order to speed up your metabolism – because this allows you to burn up fat.

"People think you get in shape by dieting, but it's not the case. You do it by eating the right things. I eat a lot of meat, egg whites, broccoli and vegetables. But rice, pasta, potatoes and bread are all out.

"It can be very difficult to watch what you eat to that extent – you end up feeling dreadful.

"Then when it comes to getting up on stage, you dehydrate yourself for a few hours, because by making yourself dehydrated you make your skin tighten – which enhances the shape of your muscles.

"By the time you're on stage you may look like the picture of health, but in reality you feel absolutely rotten."

Gina Ford, 47, of Kingswood, is also through to the national finals. She works as an administrator for a car hire company, but was a professional cabaret dancer in London in her 20s.

"When I got too old for that I became a personal trainer for a while, and that's how I got involved with body building in the first place," said Gina, who spends an hour each morning and an hour each evening working out.

"One of my friends in the gym told me about the body building competition, and we decided to enter it – more for a laugh than anything else.

"The women's body building comes in two classes – physique or trained figures. I participate in the trained figures class, which is all about being toned and well shaped.

"The physique class is the one that everyone thinks of as women's body building – but to me that just looks like men in bikinis. I wouldn't want to be that big and muscular."

But Gina says that doesn't stop people raising an eyebrow at the idea of a woman wanting to body build.

"When I first told my parents that I was going to have a go at body building competitions, they were horrified," she recalled.

"My dad wouldn't come to them at all at first. But they eventually started to realise that it's not as they imagined. It's a sport really, and it takes a lot of work and dedication to become a winner in your chosen field."

Gina started training back in the early 1990s, but she says it is now coming out of a long period of being unfashionable.

"Body building was very popular in the 1980s and early 1990s, when Arnold Schwarzenegger was in his prime," she explained. "But then it became very unfashionable to look muscular in the late 1990s. It seems to be growing in popularity again now, and it's great to see young lads like Dan and Dave coming up through the ranks."

And there's even more hope for the future, with beginners like Daniel Hall already showing real body building promise after just a few of months of working out. The 33-year-old, of Mangotsfield, ironically enough, spends his days running a bodyshop – for cars.

Daniel may be a body building novice, but he has already won a place in the novice championships in November.

"You do feel a bit silly at first," he admitted. "It's not natural to get up on stage in your Speedos and pose to music. But you get used to doing it. At the end of the day it is all about who can pose the best. People think that body builders are all going to be big butch arrogant guys, but actually we're all quite quiet and friendly.

"I've found all the more experienced guys to be really supportive. There's a real community atmosphere among the body builders here at the gym. That's probably why we're all getting on so well. You definitely need that kind of enthusiasm and support around you."