Cheerleading is not all pom-poms and inane grins. Today's stars are top-class athletes who will do anything to win

Without instruction, they unfurl the rubber mats stacked against the far wall and roll them out across the wooden floor. A few girls stretch, arms clasped behind their backs, before joining the others in a circle on the mats. The squad has just returned to Glasgow from the British Open Cheerleading Championships in Nottingham, where they won first place in a number of divisions. But they're not happy with their performance. It's time for some soul-searching.

If you thought cheerleading existed only on the sun-kissed terraces of Californian high schools, welcome to Ibrox Community Complex, home of the highest-placed all-girl cheerleading squad in Europe, also currently ranked third in the world: Glasgow's Goldstar Galaxy. There are no pom-poms, cheesy grins or mini-skirts in sight, just aching thighs, impressive biceps and a resolute will to succeed.

Coach Claire McKay joins the circle of girls on the mats. "Okay, it was a tough weekend, we're all exhausted," she says, her voice hoarse. "So, what's on your mind? What have you learned?"

The girls look down, twist their ponytails and wipe away tears. They talk through the emotions they shared over the weekend competition, how they felt "crazy and nervy" before and during their performance. They mention mind-games and tactics used by other teams to shatter their focus and the weight of pressure they feel is on them. Since stunning their American rivals by taking the bronze medal in last year's International Cheerleading Worlds competition, the 24-strong squad is subject to ever-increasing expectations of success. "This is something you just have to face if you have ambition and want to succeed," says McKay. "Fear, nerves, anxiety, self-doubt – these are the only things that can hold you back, and you control these things. Don't let anything stand between you and what you want."

Cheerleading has suddenly grown up and is taking itself seriously. Squads no longer exist simply as support acts to all-male football or basketball teams, but are competitive athletes in their own right, their main purpose to compete for national and international titles. While pom-poms are still used for dancing, all star cheerleading – the most popular form of the sport – is a much more athletic and demanding affair. Routines of two and a half minutes by a group of up to 36 girls feature acrobatic tumbles and aerobic stunts, human pyramids and mid-air arabesques. It's frenetic, high-energy and faultlessly choreographed. As the Goldstar team prepares to defend its bronze medal in this year's Worlds competition in Orlando, Florida, members train for up to ten hours a week.

The circle fans out like a sunflower as more girls shift on to their stomachs and kick out their legs behind them. They all wear the same lightweight white trainers and a mixture of black shorts and leggings and Goldstar 'Go For It' T-shirts. Their ponytails, secured with red and gold sparkly ribbons, are the only concession to typical cheerleader glitz. "You need to remember that you control yourself – physically and emotionally. It's your body and your mind," McKay tells them.

"You have the power to do this. I mean, look where we are from." She casts her arms around the draughty hall and picks at the tatty edges of the worn mats. "Look at this place. We've got nothing to lose. If we can walk the streets around here then we've got nothing to fear."

The Ibrox Community Complex sits in the shadow of the red brick home of Rangers Football Club. The stadium dominates the area. Sandwiched between the Clyde and the M8 motorway, this patch of south Glasgow has been promised regeneration for years. Until recently the small sports centre was surrounded by crumbling and abandoned tenements, their windows guarded with sheets of aluminium and covered in graffiti. The tenements have just been demolished but the land beyond the complex's chain-link fence is still scattered with the remaining bricks and rubble.

The most quintessentially American activity, cheerleading is a massive industry in the US, ingrained in teen culture and the high-school curriculum. Many squads have their own dedicated gyms and lucrative sponsorship deals, while universities offer competitive cheerleading scholarships and tournaments are broadcast on national television. In Ibrox, the team members pack customers' shopping bags at the local supermarket to raise the necessary funds for travel to competitions and to pay for the hourly hire of their practice hall. A full day's bag-packing will raise around 1,000, but the squad needs to put in a lot of hours at the checkouts, as well as organising raffles and fundraising dances, to cover the cost of 24 flights to Florida.

Despite being only 17, Pamela Roland has been with Goldstar for ten years. "When we went to America last year we had no reputation to live up to because no one there really knows what life's like in Scotland. So when we came third in the world you could tell the American teams were shocked. They were like, 'What? A bunch of girls from Scotland?'" She is studying dance and musical theatre at college but says she would be "nowhere" without Goldstar.

Her teammates express similar sentiments. Lauren 'Lolly' MacKenzie, who is 18, laughs and says, "I would probably be morbidly obese if I didn't do cheer." She's joking, but at a time when teenagers face a hall of mirrors of body-image issues and excruciating self-consciousness, it's a point worth considering.

Cheerleading's popularity has exploded in recent years, thanks in part to the 2000 film Bring it On starring Kirsten Dunst, and the 'save the cheerleader, save the world' storyline in the NBC drama Heroes, which featured Hayden Panettiere in the role of the indestructible cheerleader Claire Bennet. The British Cheerleading Association represents over 700 clubs – 18,000 members – across the UK, a figure that is growing every month, while the International Cheer Union has 59 countries on its books, including China, Pakistan and Russia.

At the Cheerleading Worlds competition in Florida this weekend, Goldstar will perform in front of a near-hysterical crowd of thousands. The event, known as the Super Bowl of cheerleading, will be broadcast to households across the US by sports channel ESPN. The girls from Ibrox need to conquer their nerves. Cheerleading challenges them to push past limitations – mental as well as physical – and to defy expectations. The camaraderie of shared endeavour and accomplishment is one of its rewards.

Laura Jane 'LJ' Chalmers is the oldest member of the squad. At 24, she has been part of the club since it's formation, ten years ago. "It's hard for other people to understand what this means to us," she says. "We've been through so much together that I don't think the bonds between us could be broken now. We eat, sleep and breathe cheer. In a way it's like we are celebrities, in the sense that we've experienced something that makes us feel different from other people. This is our lives."

In the circle of mats the bond between the girls is clear. McKay addresses each member's anxieties in turn, and their worries are met with support and encouragement from their teammates. "Usually when we're performing I'm thinking, 'Look at me, I'm on fire,'" says Chalmers. "But this weekend I had doubts in the middle of the routine, and they totally tripped me up. We need to be strong of mind as a team and remember to keep focused."

The girls murmur agreement. "But I just can't hide my feelings," Jade Dalgleish sobs gently. "I wish I could push them down and move on, but when I get upset and stressed it all comes out."

The others reassure her. "Don't worry about it. Crying doesn't mean you are weak."

"Team spirit is central to the popularity of cheer," says McKay. "And there are not many opportunities for girls to experience this in the same way that football is such a big part of boys' lives. Teamwork teaches them about interdependence, about the pleasure and rewards of supporting each other. With cheer the girls physically support each other too. They throw each other in the air and have to be there to catch each other. This team spirit also encourages girls who lack confidence and wouldn't be comfortable performing alone."

McKay's evangelic coaching style and efforts to champion each member through their teenage years makes pastoral care a significant part of her role. Since starting Goldstar Galaxy, she never imagined the squad would become so successful. It's clear she lives and breathes cheerleading as much as her team. She is suffering from chronic laryngitis from hours spent shouting instructions at the girls over the frantic techno music they perform to. Before leading tonight's training session, she has spent the day answering texts and calls from team members and parents, booking flights to Florida for the Worlds competition, collecting visa-waiver forms, checking health insurance details for 24 girls and calling the costume suppliers to check their red-and-white Goldstar shorts and T-shirts are on schedule for delivery. She'll be up until 2am studying videos of the team's past performances. "For the first few years I worked pretty much seven days a week," she says. "Now it's more like six. As the business grows, it needs to succeed in different ways, and emotional counselling is a big part of my role as coach. I do worry about overburdening the girls. The success they have already achieved means there is now an expectation of even more success. Teenage girls doubt themselves, and our performances are intricate and complex. When they are nervous they shake, and that's when things go wrong."

Watching the squad rehearse, it's not difficult to see why the British Cheerleading Association is campaigning for cheer to be officially recognised as a sport. Training sessions are intense and physically demanding. The girls explode across the room, fizzing like fireworks into back-flips and high kicks, throwing each other into the air and tumbling across the mats. Their timing and spacing must be immaculate to impress the judges, and their complicated formations tightly choreographed and synchronised. Claire counts out the drill in the peculiar language of cheer – flip-tucks, tick-tocks, fan-kicks, viva-jumps. "Come on," she shouts. "Bigger, brighter, sharper, stronger. I want to see more desire. Sell it."

The girls follow her instructions. After an hour their faces are flushed and their breathing comes hard and deep from their chests. They use the bottom of their T-shirts to wipe the sweat from their faces but McKay's instructions are relentless: "Think, formation, spacing, timing, technique, showmanship, everything. Come on. Arch your back. Chin up. Put a bit of sass into it."

All star cheer's focus on acrobatics has a lot in common with gymnastics, but the strutting, show-off style is a crucial element. As the girls tumble across the floor they wiggle their shoulders, thrust their chests forward and hold their heads high, trying to remember to smile. It is still a performance and a spectator sport after all.

In the corridor outside the gym a couple of mothers wait to collect their daughters. They, too, have just returned from Nottingham and are planning to accompany the team to Florida. "Cheer keeps them fit and healthy and focused on something," says Roland's mum. "But the main thing is it keeps them off the streets. My daughter is 17 and I see other girls that age hanging around at night doing nothing or getting drunk and I'm glad to know she is here."

"They have to keep focused on their schoolwork too," says Debbie Gibson, whose daughter Aimee, at 14, is the youngest member of the squad. "Claire makes them sign a contract that they'll do their best at school and not let cheerleading get in the way of schoolwork or exams. Some of the girls have got Standard Grades coming up and she'll make them take their books with them to Florida and build time into their training schedule for studying."

Gibson has taken on a second job to finance the American trip. "I'd rather go to Florida with Goldstar than go on holiday with my husband," she says. The other mums laugh in agreement. "My oldest daughter used to do gymnastics and when I went to competitions with her it was all a bit stuffy. You'd stand around in silence and clap politely. At cheerleading competitions the parents dance and shout and sing along and cheer the girls on. Everyone really gets into it."

Back in the gym the mood is lighter. The girls laugh off their anxieties about their performance. It's taken over two hours to go around the circle, exorcising demons, releasing emotions and wiping away tears. Their time at the sports centre is up and the cleaners are waiting to get in. McKay breaks up the circle with a smile. "OK, next time remember to wear waterproof mascara," she tells them. They have a quick group hug, pull back and cheer, "Go Goldstar!"

Goldstar Galaxy competes at the International All Star Cheer Worlds competition (www.iasfworlds.org) in Florida this weekend. See www.goldstarcheerleaders.com.