In a tiny shop front near Tuggeranong, tucked between two super-sized mechanics, Hugo, 22, grabs hold of an overhead bar, lifting himself up off the ground. He hauls his legs forward so they touch the bar, lets them drop, then repeats the action over and over.
He is surrounded by a forest of flying legs as 15 or so other young people start to sweat. Over the next hour or so, the group will lift barbells, swing kettlebells and sprint holding 20-kilogram weights, all at a furious pace.
Their gym would not have looked out of place in the 1950s, with no mirrors on the walls, no treadmills, and definitely no steam rooms or saunas. In fact, the only pieces of modern sporting equipment are a couple of rowing machines against the wall.
Hugo will not vomit after this workout, but he often does. That is how he earned his nickname ''Spewgo''. For a while he would even bring his own bucket along when he showed up for competitions.
This is CrossFit Base, one of the first of eight CrossFit gyms that have opened in Canberra and Queanbeyan. A combination of gymnastics, sprinting and weightlifting, it is an American fitness program sweeping the capital. But there is controversy surrounding CrossFit. While Australians line up to get involved, some health and fitness professionals have concerns that the program could be dangerous.
Dr Kate Pumpa, an exercise physiologist from the University of Canberra, says while CrossFit offers plenty of positives it could become like a ''cult'', where participants' passion could become consuming. And Crossfit's mascots Pukie and Rhabdo betray a cavalier attitude towards the adverse effects of working out too much. The cartoon clowns refer to vomiting and the potentially fatal condition rhabdomyolysis, seemingly making light of the effects of over-exercise.
CrossFit is the brainchild of Greg Glassman, a former gymnast from California. He began developing his exercise program decades ago, focusing on short, varied, high-intensity workouts.
Glassman took a back-to-basics approach - running, rope climbing and weight lifting were the order of the day and, by most reports, he did not have much success initially. But then he launched Crossfit.com in 2001, and it took off.
The website is central to the CrossFit phenomenon. Each day, a new Work Out of the Day, or WOD is posted online and there is a message board for comparing performances, tips, and injuries.
It is not compulsory for all of the more than 3000 gyms worldwide to perform the CrossFit prescribed WOD, but for several months a year most of them do.
Since 2007, the annual CrossFit games has grown from a group of mates competing on a weekend to an international event, where the initial phase, the CrossFit Open, is held entirely online. Last year more than 25,000 people entered, all completing the same workouts at a certified gym and posting their results on the games website. There are then regional events held in-country, before finalists from around the world head to Carson, California, to compete for the title of ''Fittest on Earth''.
Competitors only find out what awaits them shortly before they are due to compete in the games finals. In previous years, ocean swims, beach runs, calisthenics, weight lifting and wall climbs have all been a part of the program.
Despite the brand's rhetoric about being suitable for everyone from housewives to ''terrorist hunters'', the CrossFitters at the Greenway gym are almost uniformly young, broad-shouldered and muscular and many are looking to push themselves to their physical limits. It is there that much of the criticism lies.
In an interview with The New York Times in 2005, Glassman warned about the dangers of CrossFit. ''It can kill you,'' he said. ''I've always been completely honest about that.''
And Pumpa says the program is ''notorious'' for participants over-exercising.
Some gyms have pictures of Pukie and Rhabdo up on their walls, and trainers often refer to them when dealing with the side effects of a big workout. Kylie Linbeck, owner and trainer at CrossFit Base, confirms that ''a visit from Pukie'' is a familiar term in their gym when someone loses their lunch.
Vomiting during or after a workout will often occur because intense exercise causes blood to leave the stomach but when the exercise stops it rushes back, causing a spasm.
Pumpa says vomiting should not be considered a normal part of exercising.
''It's not a good sign that you're working hard,'' she says. ''It decreases strength and conditioning and skill level, and could increase the risk of injury,'' Pumpa says.
But Lindbeck says that at CrossFit Base, at least, rhabdomyolysis is taken seriously. A condition where muscle fibres break down and their contents, myoglobin, enters the bloodstream, rhabdomyolysis can cause acute kidney failure.
Lindbeck says at CrossFit Base, workouts are scaled so participants can push themselves hard, but not too hard. In the four years she has been running CrossFit workouts in some form, she has had two cases of rhabdomyolysis, and both made full recoveries.
''We have to be aware of it, because it can happen and does happen,'' she says.
But Lindbeck does not necessarily fit the profile of a typical CrossFit trainer, or a typical fitness instructor of any kind for that matter. Along witZh her CrossFit accreditations, she has a Certificate III and IV qualifications in personal training, is certified by the Australian Weightlifting Federation to coach weightlifting, and is completing a bachelor of sports coaching and exercise science at the University of Canberra. But not everyone is as highly qualified.
Pumpa says the fast and furious nature of CrossFit workouts, and in particular the weightlifting component, meant that a high standard of coaching was required to avoid injury.
''The idea is to lift heavy, so correct lifting technique is so important,'' she says.
CrossFit.com says that its WODS are universally scalable. Weights can be reduced and movements can be modified. At CrossFit Base, new participants are eased into the program, and this may well be the case in many places. However the message boards on CrossFit.com are full of participants comparing injuries great and small.
In the past some gyms would even hand out Pukie the Clown T-shirts when someone vomited after a workout, but these days, thanks to a relatively new partnership with sportswear giant Reebok, CrossFit merchandise is subtly branded and looks much like any other workout gear.
It is a crossover into the mainstream that has not sat comfortably with some CrossFitters, who have expressed concern that the Reebok partnership reflects the commercialisation of a previously underground community. On various small online CrossFit communities, which have sprung up away from the CrossFit homepage, participants lashed out at Reebok's sponsorship of the 2011 CrossFit Games and their co-branded advertisements that proclaimed that ''the sport of fitness has arrived''.
''It was Reebok's attempt to introduce CrossFit to the masses, but CrossFit is not for the masses, it's not a f---ing pump class!'' Hewi, on The Brave site, wrote.
There are also fears that Reebok-branded gyms will squeeze out small, independently run outfits.
Lindbeck says that when she first heard of Reebok's involvement in CrossFit, she was disappointed. She met Glassman when she completed her CrossFit certification in 2008 and felt the sponsorship deal was a betrayal of some of the values he espoused back then.
''He was about community and not about being commercial and not about sponsorship, and now it's all coming about,'' she says.
But she said after speaking to Reebok representatives, she could see some advantages to the deal. She said they told her Reebok would help expand CrossFit's reach into areas where no gyms exist, but also help existing gyms grow, which may again threaten smaller operators.
''So it's a good and a bad thing,'' she says.
Others see Reebok's involvement as a sign of professionalism entering their ''sport''.
The 2011 Reebok CrossFit Games was broadcast on US sport cable television station ESPN with athletes kitted out in Reebok gear, a stark contrast from previous years where competitors were able to wear whatever they pleased.
No longer a niche underground movement, CrossFit is the latest in a long line of popular fitness trends - remember aerobics, Step Reebok, the thigh master, pole dancing for fitness, spin classes and Tae Bo?
But there seems to be a new intensity to what ordinary Australians are looking for in a work out.
Boot-camp-style programs have been around for a few years now; in parks and gardens in most big cities, commando-style trainers yelling at their sweaty, leggings-clad victims are a common sight.
Meanwhile, Tough Mudder, a touring adventure sport company owned by a former counter-terrorism agent for the British government, runs 16-kilometre to 19-kilometre extreme obstacle courses, which have involved fields of fire, electric shocks and giant pools of mud.
Tough Mudder sold out when it came to Australia this year, and they are planning to return to our shores in 2013.
If it all sounds a bit like joining the army, well, that is the idea. Indeed, CrossFit wears its connection to the military well and truly on its sleeves. CrossFit.com regularly publishes letters from US Marines thanking the program for helping them reach peak levels of fitness. CrossFit also names WODs after US soldiers who have died in Afghanistan and Iraq and participants post responses to the workout with tributes to the fallen.
''Wanted to stop and drop the weight so many times, but I knew JJ would never quit on us. R.I.P Brother,'' one read recently.
This year saw the first WOD named after a dead Australian soldier, and there are reports that ADFA cadets in Canberra have started their own CrossFit group.
University of Canberra psychologist Dr Vivienne Lewis says military-style exercise programs could be great for people who enjoy the camaraderie of working out in a team environment, and who get a buzz out of pushing themselves hard. Indeed, at Canberra's CrossFit Base, the atmosphere is overwhelmingly positive, with lots of encouragement and supervision. Participants seem to know each other well, and Lindbeck says it was that, along with constantly varied WODs, that kept people coming back.
But Lewis also says it is possible to become too consumed by any sport, and those very intense activities that emphasised strength or physique were among the most likely to attract people who may have a real problem.
Pumpa is willing to offer only cautious praise for the program.
''It's not a bad thing.'' She pauses. ''I'd like to know what the injury rate is and I'd like to know how long it's going to last.''