London - Brains and brawn, the 21st-century biathlon, the toughest and smartest - that's how people describe chess boxing.
It's a sport exactly as it sounds: four minutes of speed chess, two rounds of boxing, four more minutes of speed chess … and on it goes until someone gets knocked out in the ring, or checkmated on the board.
Chess boxing is a relatively new sport. The first London match was held in an East End working man's club in 2008.
London organiser Tim Woolgar says the sport is growing by the week. On Wednesday night, a bout was held in the Royal Albert Hall.
Not exactly "the" hall that sits 5,200 people and has seen performances by stars such as Jimi Hendrix, Frank Sinatra and Luciano Pavarotti, but pretty close.
The 141-year-old Royal Albert Hall's loading bay was transformed into a chess-boxing venue for 500 fans, replete with graffiti, a smoke machine, DJ, and, of course, a boxing ring.
It was a young, professional crowd who came after work to cheer, queue at the bar and chat. One wore a T-shirt that read: "Fighting is done in the ring, wars are waged on the board."
At a north London gym recently, Chris Levy, who had worked all day as a market researcher, still appeared energetic, skipping and shadow boxing. He topped that off with a few hours of chess on the computer.
Levy says the hardest thing about chess boxing is the transitions, especially going from boxing to chess.
"You've been in the ring trying to knock out your opponent, your adrenaline is going, your heart is pumping at 170 beats a minute, and then you have to sit down and really concentrate on a game of chess," Levy says.
Most of the competitors come to the sport with a background in chess. Levy is a former England county chess player. He says it's easier to train the body to jab and dodge than it is to teach the mind the intricacies of chess.
Neither Levy's chess experience, nor his physical training, paid off on Wednesday night, however, when he was beaten by Tim Benfeldt, a law student from Kiel, Germany. Win by checkmate.
The second match pitted banker versus banker: in one corner Sean Mooney from Goldman Sachs, and in the other Bryan Woon from Citibank. Mooney scored the victory after the marathon match was judged in his favour by a combination of chess and boxing points.
What chess boxing lacks in tradition, it makes up for in razzmatazz.
There's the pumping music, wafting smoke, and a voluptuous blonde prancing around the ring with the round number held aloft on a sign.
There's a big screen showing the chess moves, and a commentator who explains the match. Chess boxers wear headphones while they play to drown out the noise.
The bouts are streamed live on the internet, with organisers counting 10,000 online viewers.
Woolgar says chess boxing is "mushrooming" around the world, with the sport now being played in Asia, North and South America, Australia and New Zealand.
Squaring off against a grandmaster or professional fighter, most chess boxers would quickly crumble, but they don't seem to mind.
The combination of brawn and brains makes them the toughest, smartest, competitors in the world, they say.