OSAKA, Japan – For years, promoters of sumo wrestling have been pushing for the sport’s inclusion in the Olympic Games. To get there, the International Sumo Federation has gotten behind a form of the sport that would offend purists and surprise most everyone else: women’s sumo.

When the International Olympic Committee declared in 1994 that single-sex sports could no longer qualify as candidates for the Games, that was enough to turn the tradition of giant men slapping each other in the ring on its head. Since then, sumo has been coming into its own internationally as an equal-opportunity sport.

Such a radical change to Japan’s ancient national sport did not come easy, and the initial push came from outside the country. Among those who lobbied the IFS, as the sumo federation is commonly known, was Stephen Gadd, the general secretary of the European Sumo Union and president of the Netherlands Sumo Federation.

Men’s sumo started gaining a following internationally in the mid-1980s as part of Japan’s campaign to spread its culture internationally. More than a decade later, women’s sumo started gaining followers as the IFS, which oversees 87 member nations, started pushing for a women’s version of the sport.

"We held the very first women’s sumo tournament with the European championships in 1996," Gadd said. "After that, it really took off in Europe."

European women, especially those familiar with combat sports, felt no qualms about giving sumo a go, but Japanese women had more to contend with than just bigger Europeans. Their biggest hurdle came from a stigma that can be traced to the 18th century, when as entertainment for men, topless women sumo-wrestled blind men. Although this lewd variety faded away in the mid-20th century after being banned repeatedly, a ceremonial form has continued in regional festivals so far out on the fringe of society that it remains virtually unknown.

So when the Women’s Sumo Federation was set up in Japan in 1996, Japanese women were hardly clamoring to become involved, given the common belief that women just do not do sumo. After all, they had always been kept out of legitimate competition because of the sport’s cardinal rule: Women cannot touch or enter the sacred wrestling ring, the dohyo, lest they contaminate it with their "impurity."

Gadd said, "In the professional sumo world, women in sumo is as unthinkable as a rabbi sponsoring a pork farm."

But along with the rise of amateur sumo abroad, women’s sumo in Japan has been making strides.

"A growing number of women are involved, certainly in the hundreds," said Katrina Watts, the president of the Australian Sumo Federation and a stadium announcer for sumo events, including the world championships. "I’d say it’s a good sport for women because it’s a body-contact sport without being violent."

Nowadays, girls can even go to high school or college on a sumo scholarship. And there are women-only tournaments, like the All-Japan Women’s Sumo Championships, which took place this month in Osaka.

Forty top sumotori gathered for the 15th edition at the Ohama Park Sumo-jo. Shinsaku Takeuchi, the event’s organizer and head of the Women’s Sumo Federation, said that in recent years women had been getting better and tougher.

"Women’s sumo is becoming even more vicious than the men’s," he said.

Takeuchi explained that what set amateur sumo apart from professional was the inclusion of gender and weight classes and the removal of the religious ceremonies, which are still very much a part of men’s professional sumo. Amateur sumo has also been spared the recent scandals that have tainted professional sports in Japan, including a baseball betting scandal that laid bare the professional sport’s link with organized crime.

Originally performed as a Shinto ritual to entertain the gods so they would bestow a good harvest, the sport dates back more than 1,000 years. It is a trial of strength in which 48 techniques may be used to throw an opponent off balance so that he steps out of the ring or falls to the ground. A match begins with a head-on collision, followed by a wild fit of shoving, lifting, throwing, tripping, slapping, yanking or any combination thereof. It is often over in less than 10 seconds but can last a minute or more.

An 18-year-old high school senior, Yuka Ueta, was the strongest wrestler of the tournament. At 275 pounds, she plowed her way through five matches in the open weight class, dispatching each opponent within moments to earn her first gold medal in the senior group.

In August, competing among the world’s top sumo wrestlers, she won a bronze medal at the Sportaccord Combat Games in Beijing, her best showing yet. But at the world championships last weekend in Warsaw, she did not fare as well, placing fifth in the open weight class.

Ueta got into sumo at age 10 when she was encouraged to give it a try.

"Normal-size people can do any sports they like, but someone who is heavy doesn’t have many options," she said. "Sumo is perfect for this kind of woman. And if she has a complex about her body, that will change with sumo."

Another powerhouse, Sayumi Sasaki, took her fourth All-Japan gold medal in the 143-pound-and-over class. But at 21, she has decided to hang up her loincloth after the Warsaw games, where she was knocked out in the first round by the heavyweight winner, Anna Zhigalova of Russia.

"I want to quit while my record is still strong," Sasaki said.

The competition she has to face abroad might have factored into it.

Although Japanese women make up the greatest number of participants, Europeans tend to dominate, which was the case in Warsaw. Eastern Europeans won three of four divisions, and the only Japanese medalist of the tournament was lightweight Yukina Iwamoto, who took a silver medal, losing to Alina Boykova of Ukraine.

"Foreign players like the Russians and Ukrainians have more passion for sumo than we do and train harder," Sasaki said. "It’s too difficult to beat them."

Even Ueta said she was no match for them.

As for the battle to make it into the Olympics, Gadd, of the European Sumo Union, says the best chance is if Japan hosts the 2020 Games.

"Getting into the Olympics will give sumo the push it needs to become a major international sport," he said.

And now that the gender barrier is broken, one less obstacle stands in its way.