Tsang, the head coach of Venus Club, took up Thailand’s tough national sport for fitness at the age of 15 and first fought competitively, and won, at 18.

Muay Thai has boomed in popularity as a fitness regimen globally in recent years, but so has the number of tournaments for serious practitioners looking for a fight. And despite the risk of injury, a small number of Hong Kong women have broken the sex barrier by competing in the traditionally male combat sport.

READ MORE: JuJu Chan of new Crouching Tiger movie on why more Hong Kong women are turning to muay Thai for fitness

“I’ve liked men’s sports since I was very small,” says Tsang, who previously practised wing chun. “I got into muay Thai because I found it more exciting. The punches come lightning fast so you have to know quickly whether to fight back, block or move away. I find that fun.”

Within two years of her first win, Tsang was representing Hong Kong in international tournaments, scooping up a bronze and two silver medals. She was the Golden Belt female champion for three consecutive years from 2009 to 2011, in the 45kg, 48kg and 51kg weight classes.

Venus Club was opened last year as an offshoot of Ray’s Muaythai Gym, just around the corner. It caters primarily to a growing number of young women booking Thai boxing classes to stay trim.

READ MORE: The Facebook alternative: Hong Kong entrepreneur builds huge social media platform for martial arts fans, instructors and practitioners

Gym owner Ray Or says he opened Venus Club because his other facility was becoming too crowded, and almost 80 per cent of its members were young women. All four female trainers at Venus Club are his protégés, and Or says they are like daughters to him.

Tsang is the coach he is most proud of. When she turned up for her first class, Or didn’t see her as a future champion.

“She is so small, but she always wants to challenge the big girls,” he says. “When she started to fight she weighed just 43kg, and she always went up against girls who were 50kg to 55kg. They were much bigger than her, but she always won.

“I remember the first time we joined the IFMA [International Federation of Muaythai Amateur] tournament and there were more than 80 countries represented. She was then 45kg. From the first fight right to the final, she won them all by knockout. In the final fight she lost narrowly on points.”

The youngest coach at Venus Club is the deceptively shy Candy Wu Hoi-yan, 18. Wu started hanging around Or’s gym when she was 14, but showed so little interest he had to give her an ultimatum: train or leave.

“This girl is the youngest female champion fighter in Hong Kong,” he says. “I didn’t think she could be a fighter because she was just one of those girls who stay in the corner and she would never obey any commands. Even if you asked her to do a straight punch she would not do anything, just stare at you.”

READ MORE: Hong Kong muay Thai champions Gary Tang and Candy Wu like to fight fast

Wu, who Or says is the gym’s fiercest fighter, turned 18 last year with four champion belts. She has since joined the Hong Kong team and won a bronze medal. “For such a young girl it’s a good achievement,” he says.

Kwok Hoi-ling, 21, was equally unenthusiastic when she showed up six years ago, but is technically the most intelligent fighter of the four, Or says. Although he senses fear in Kwok when she is fighting, she has two champion belts in the 51kg class.

Yu Yau-pui, 23, is the least experienced coach but also a winner. Among her silverware, last year she was the 55kg champion in a tournament organised by the International Professional Combat Council.

Tsang says there were few women learning the sport 11 years ago when she took it up, but it has become more mainstream as an aid to weight loss and fitness. For those interested in fighting, there are inter-club or international competitions every month, all with women’s fights on the card. Venus Club coaches have contests lined up for the next three months.

WATCH: Venus Tsang in the WMC The One Muaythai Asia Female Championship

The main difference between the sexes, Tsang says, is that men strike with a stronger force, while female boxers, whose blows are less explosive, fight with more swiftness and speed.

“Women have lower muscle mass and strength, and a higher fat and water content, so will focus more on training the muscles,” she says. “Many people have the wrong impression that muscle training gives a person big muscles, but their muscles only become firmer and sturdier for more explosive hits.”

Purcell Tong Ka-yan knows only too well how tough it is fighting with men. She is the only female trainer at Warrior Muay Thai in Fortress Hill, where she coaches alongside half a dozen champions from Thailand.

Tong, 27, says she initially felt intimidated teaching alongside Thai fighters, but it has helped her enormously.

READ MORE: Martial arts craze gives Muay Thai a leg up in Hong Kong

“I was quite nervous because they all started when they were very young. They’re very professional,” she says, adding she often spars with them. “They like to toy with me. I can’t touch them.”

Tong has practised muay Thai for seven years and coached for 2½ years. It was a month spent training at a boxing camp in Thailand that persuaded her it was what she wanted to do.

“I was the only woman there, and eating and training together with the Thai guys, I started to understand what muay Thai is all about.”

She says her Thai teammates’ knowledge of technique is endless. “When you think you’ve learned a lot already, they’ve got more to teach. It made me a better trainer a lot faster.”

A common problem for women who want to fight, she says, is that they are not used to getting hit and so it often comes as a shock. They may also be scared of sparring with men. To overcome that fear, she suggests joining a women-only class so they can spar together.

Tong is now in training for an inter-club tournament being hosted by Warrior next month. Later in April, she will travel to Chiang Mai, northern Thailand, to get in the ring with a Thai fighter.

“I want to fight a Thai girl, Thai style. I think it’s a bit different from fighting a Hong Kong girl.”

She says she would like to see more women fighters at Warrior. “I want them to know more muay Thai so we can spar together and they can try to control their body movements and improve their skills.”