What is known is that tai chi, in any form, is beneficial to people. Scientific studies have long connected the sport's combination of controlled breathing, meditation and physical movements with health benefits such as improved heart condition, lowered blood pressure and relief from arthritis. The most recent study, by University of California Los Angeles, reports that tai chi effectively treats depression in the elderly because the exercise helps release endorphins.

But there we go again with the old-people bit. It's a stereotype tai chi may never shake, at least not until the art form gets the same type of exposure that the 2008 movie Ip Man did for wing chun. The last notable film to represent tai chi was 1993's Tai Chi Master, starring Jet Li. The small group of dedicated practitioners in the city, however, is proof that it's not just for the old.

On a warm Tuesday night at Kowloon Park, Gu - president of the Hong Kong Tai Ji Study Society (HKTSS, with 'tai ji' the pinyin spelling) - and her assistant, Leung Kin-hung, are teaching a class of about 30. It's a diverse group, including a local woman in her early 20s and a Japanese housewife in her 30s. At first glance, the group and their Chen-style form don't look much different from the slow, methodical movements often seen performed by the elderly in the park. at dawn.

Gu, a gaunt mainland native in her mid-30s, waves her arms in circular motions. With bent knees, she brings her right leg forward and, in one fluid motion, sweeps the leg towards the ground into a squat. Then, she goes back to a standing position, right leg slightly bent, palms open at chest level - a stance that screams 'I'm ready to strike'.

'That's the 'oblique stride and twisting step',' Leung says. 'There are 56 forms to the Chen-style tai chi, and this was one set.' Forgive the awkward English translation; the Chinese terms for the moves are actually poetic and sound like they could be titles for a Bruce Lee film.

Before I begin, Leung pulls me aside for stretching, which focuses on the pelvic area.

'It's the most important part of the body for tai chi,' says Leung, as he swirls his hips as if he's in a bad 1970s dance video. Leung, in his late 30s, started learning tai chi under Gu after experiencing constant back pain. He says his back doesn't hurt any more.

Others at HKTSS echo similar sentiments. Ritsuko Yanagita, a Japanese expat housewife, says the graceful, dance-like progression of meditative poses has helped ease aches all over her body, especially during 'that time of the month'. She finds the low-impact nature of the exercise ideal.

Dr Chan Kwok-ki, an expert in sports science and a Health Post advisory panel member, backs these statements, adding that tai chi's main benefits are enhancements to cardio-respiratory functions and muscle strength.

'Those are areas that many Hongkongers need [to] work on - regardless of age,' he says.

After stretching, I jump into the class trying to mimic Gu's movements. But I soon find that even the simplest movement requires a high level of balance - balance I do not have.

Seeing my struggle, Gu offers to take me back to the beginning. She guides me through the most fundamental moves, such as 'Buddha's warrior attendant pounds a mortar', which, despite sounding complicated, involves just shifting both arms from left to right, repeatedly.

Aside from sore knees, I didn't feel very different after the session. 'You're not going to see a difference immediately after the first session; tai chi works from the inside out,' Leung says.

Gu first learned tai chi at 14. After spending her teens and early 20s in London for school, she returned to Shenzhen, where she worked as a journalist. She says the stress of the job kept her sleepless many nights, until she picked up tai chi again. She's since become one of the top advocates of the sport, winning several wushu awards.

In 2003 she moved to Hong Kong, where her husband works as a schoolteacher. She felt the need to start HKTSS to promote Chen-style tai chi, which she believes to be the original form.

The Hong Kong Tai Chi Association's Ho, 53, doesn't really agree. 'The purest form of tai chi is the Yang and Ng style,' he says. 'Chen style has been promoted so heavily that we purists have given up trying to argue lately.'

Ho says Chen style is high on theatrics, is 'louder and harder', and contains Shaolin kung fu elements. 'It's a mishmash of many different types of martial arts,' he says. 'If you think of tai chi, in the smoothest form, it's Yang style.'

As a child, Ho learned kung fu from his father, a martial arts exponent specialising in hung kuen (a South Chinese art mostly associated with legendary folk hero Wong Fei-hung). At 14, he switched to tai chi because he felt it was more 'artful'. In the 1970s, when the Hong Kong government promoted tai chi with a citywide campaign, Ho was one of several providing demonstrations around the city.

'At the time, so many people wanted to learn, [but] we didn't have enough teachers,' he says.

He concedes that tai chi has fallen behind in the martial arts pecking order in the past couple of decades. 'It doesn't help that even the Hong Kong Tourism Board promotes it as a sport for the old,' he says. 'Still, the [Hong Kong Tai Chi Association] has a dedicated, diverse group of pupils who believe in the art.'

For the Tourism Board, which initially promoted tai chi as traditional kung fu, with dojos and sifus (masters) during the '70s, they decided to take a different approach in 1998, by making it more of a cultural sport.

'Tai chi, to [the Tourism Board], is a perfect promotional activity because it's got a distinct Chinese heritage and it can be simplified enough for anyone to pick up,' says William Ng Chiu-kit, 73. He and his wife, Pandora Wu, 64, are spokespeople for tai chi for the Tourism Board. They were approached by the board in 1998 to teach a thrice-weekly tai chi course outside the Hong Kong Museum of Art in Tsim Sha Tsui.

'The idea was this free programme for tourists to join, as a way to experience Hong Kong culture,' Ng says.

A tai chi instructor for decades, Ng says they were told to teach Yang style due to its slower nature, meaning it's easier to pick up. He says the classes are usually made up of young foreigners, but local senior citizens join in regularly, as well.

When asked about tai chi's reputation as an old person's sport, Ng is blunt with his answer: 'Who cares? Old people learn it, young people learn it; this is an art that is good for the body and soul.'