It was once the official in-house martial art of the KGB, a mandatory part of hand-to-hand combat training for Soviet special forces and the favourite childhood hobby of Vladimir Putin. Now, sambo is enjoying growing popularity well beyond the borders of Russia and the former USSR, where it was developed in the 1920s and 1930s, and its promoters are pushing for it be recognised as an Olympic sport.
Sambo, whose name is an acronym for the Russian words for "self-defence without weapons," is similar to Japanese judo but has a greater variety of moves such as leg locks and on-the-ground grappling techniques.
Most vivid is the hard-hitting version known as combat sambo, which allows punches, kicks and chokes and was officially a state secret in Soviet times available only to the military, police and KGB.
"It's closer to street fighting and any technique is permitted," Sergei Yeliseyev, president of the European Sambo Federation, told AFP on the sidelines of a recent sambo tournament in Moscow.
"We don't restrict the athlete. Do you want to use throws? Go ahead! Chokeholds? Please. If you have good striking techniques, go ahead and use them too," Yeliseyev said as a pair of fighters sparred behind him.
Onlookers sat on bleachers in a huge arena and occasionally shouted cheers of encouragement as fighters in blue and red uniforms circled each other warily, then grabbed their opponents to wrestle them to the mat.
The grunts of sweaty fighters and the whistles of referees echoed throughout the arena in southern Moscow as it hosted the Anatoly Kharlampiyev World Supercup, a tournament named after one of sambo's founders.
"I've been doing sambo since I was four years old, all my life, basically," said Vasily Karaulov, 19, a nimble lightweight from the southern Russian city of Armavir. "I don't really do anything else. I like to wrestle."
Men and women from over 20 countries including France, Nepal and Japan took part in the tournament, though it was dominated by fighters from Russia and former Soviet republics.
French sambo coach Guillaume Alberti said he started out in judo, but made the switch after he was introduced to sambo by a Russian immigrant and found that it offered "more interesting possibilities" than judo.
Sambo is growing in popularity in France, said Alberti, who flies to Moscow once a month to train with Russian sambo masters.
"In the past 10 years, there are more and more clubs," he said, referring to his native France.
Promoters of sambo say it received a major boost when Vladimir Putin became president of Russia in 2000 and revealed during one of his first interviews with foreign media that he had practiced sambo as a child.
Putin, a former KGB agent who served as president for eight years and is now Russia's powerful prime minister, started practicing sambo at age 14 before switching to judo. He eventually obtained a black belt in judo.
"Vladimir Putin is the public face of sambo. Today his authority has given a new impulse to the development of our sport," said Yeliseyev, the sambo federation chief.
Sambo traces its origins to the 1920s and 1930 when it was developed as the official fighting style of the Red Army and Soviet security services.
Its creators borrowed elements of traditional fighting styles from various republics of the Soviet Union - such as Georgia's chidaoba, Moldova's trinta and Uzbekistan's kurash - as well as other martial arts like judo.
Another factor that has led to increasing international interest in sambo, promoters say, is the popularity of mixed martial arts (MMA) tournaments in which fighters of different styles battle it out.
Practictioners of combat sambo have done well in such tournaments, notably the reigning heavyweight MMA champion, Fedor Emelianenko of Russia.
Yeliseyev said the number of national sambo federations around the world had grown from 40 a decade ago to 73 today, while the number of sambo clubs worldwide had doubled in that period.
Such numbers have led to optimism among sambo's promoters as they fight for the ultimate form of international recognition: the introduction of sambo as a sport in the Summer Olympics.
"Sambo could realistically become an Olympic sport by 2020," Yeliseyev said. "But this will require a great deal of work, and not just by Russia, but by other countries with an interest in sambo."