Nineteen-year-old Sayaka Matsuo lies on the tatami mat as a personal masseur works on her neck and shoulders to squeeze out the knots.

But this is no pamper package with relaxing music or detoxifying mist. Matsuo is warming up for a head-clashing bout of Japan's national sport -- sumo.

Strapping her "mawashi" -- loin cloth -- over her lycra bike shorts, she squats into position, her 60-kilogramme (132-pound) frame squaring off against a man more than two-and-a-half times her weight.

The huge size difference is no obstacle for Matsuo, whose determination and technique shuffle her massive opponent across and out of the ring.

"I started sumo as a hobby. I feel a lot of pressure from my dad and my goal is to win the women's Sumo World Championship one day," she tells AFP.

As the daughter of a former professional sumo-wrestler, whose ring name was Sadanohana, Matsuo had a leg up into a sport not usually associated with women, and started to wrestle at just five years old.

Now she is part of a small, but growing band of female grapplers who are turning the tables on one of Japan's oldest boys' clubs.


Shintoism


Opening up the sport to women is part of an effort to legitimise sumo as a possible future Olympic event, Tokyo University’s Sumo Club coach Toshiaki Hirahara said.

But Hirahara is also quick to point out that the top-level wrestling millions of Japanese watch on television needs to preserve its religious and spiritual origins.

"I think the fact that women cannot enter the sacred national dohyo (ring) is understandable as it is the realm of the gods," he said.

"But the amateur league has nothing to do with gods, so let girls and boys do it equally."

Sumo traces its origins back 2,000 years to a time when it was an integral part of the rituals of Japan's native Shintoism, an animistic religion.

But the sport's stock has fallen in recent years with claims of bout-fixing, illegal betting and bullying, including the death of a young apprentice wrestler in 2007.

It has also struggled to slough off claims that it is linked to the Yakuza, the country's home-grown mob.

The sport's popularity among the general public has suffered because of Japan's failure to produce champions -- all three of the present "yokozuna" (Grand Champions) are Mongolian, including record-breaking Hakuho, who, in January became the most successful wrestler ever after bagging his 33rd tournament title.

Establishing a parallel amateur sport, with proper weight divisions could be a good way to help boost sumo, says Hirahara.

It might also get around the negative associations sumo wrestlers can have among Japan's image-conscious women, who balk at the idea of eating the whopping 20,000 calories a day like Hakuho, who tips the scales at over 150 kilogrammes.

"I want to remain in the under 65kg weight category so I try to eat well-balanced food," Matsuo says, although she admits she has a weakness for "chankonabe", a traditional sumo stew of vegetables, meat and rice.

Fellow grappler Anna Fujita, 21, is also happy to stay on the lighter end of the sumo scale, and wrestles in the same under 65kg category.

"If I get bigger I'll fall into the heavyweight category and have to fight against girls weighing more than a hundred kilogrammes," she says.

And eating lots is too expensive anyway.

"I’m a student and have no money,” she says, adding she lives on a diet of Corn Flakes, rice and stir-fried vegetables.


Female strength


The proportion of female sumo wrestlers remains small -- there are almost 300 boys taking part in the sport for every girl in Japan's elementary schools, according to the Japan Sumo Federation.

Despite the yawning gap in numbers, female strength reigns supreme.

"Because the girls grow at a younger age, they are stronger than the boys," coach Hideto Tsushima of Nihon University says.

Fujita, who studies Taiwanese history by day, is testimony to the fact that, with a little training, female wrestlers can remain on top -- by night she throws men twice her size at Tokyo University Sumo Club.

So far, it's a passion practised in private, and she is yet to tell her parents.

"I think they’ll be surprised... I plan to tell them after I graduate, or maybe when I get married," she said.