By Jo Twist
BBC News Online technology reporter
Playing football computer games usually requires no more physical exertion than rapid thumb movement and the punching of fists in the air.
Two or more players can have a go
But a ball game developed by Dublin researchers forces players to sweat while facing rivals who are miles away.
Breakout for Two uses video conferencing over broadband to create a virtual "glass wall" players have to break down with a ball.
The aim to find out how people can bond via exertion, not just e-mail.
The prototype game is a mix of soccer, tennis and the hit video game Breakout, and has been developed by the Human Connectedness group at MIT's Media Lab Europe in Dublin.
State of arousal
"It is a game in which we have what we call an 'exertion interface', which is an interface which requires great physical exertion and makes you very tired," explained Dr Stefan Agamanolis, group leader.
"But it's perfect for sports over a distance, which is exactly what we wanted to have happen," he told BBC News Online.
Breakout was a hugely popular video game
It was designed, he said, to show how remote strangers can bond and feel more at ease with each other more rapidly when they have to exert themselves physically, rather than when relying on "traditional" electronic communication, like instant messaging or e-mail.
The researchers think online games could be adapted to incorporate life-sized video conferencing interfaces like this in sports clubs, or even arcades.
It also has the potential to act as a "getting to know you" team-building exercise for new employees around the world.
"When you get into that state of arousal, you are more likely to be able to bond socially with other people around you.
"We want you to work up a sweat and get your adrenaline moving because that's something that's unique to sports," Dr Agamanolis said.
The players share a "court", but remain in their own half, as in tennis.
Opponents see each other's giant, life-sized image projected onto a wall in front of them, which makes it seem as if players are looking at each other through a glass wall.
The system behind it is essentially video conferencing technology over a high-speed internet connection.
The "glass wall" is segmented into "virtual blocks". Players have to knock out the panels with their balls, and the first one to do so wins.
Information about the blocks is synchronised over the net connection so that when a block disappears on one side, it does so at the same time on his or her opponent's side.
Playing sports makes social bonding easier
The exhausting game is complete with the sound of breaking glass, and players can talk to - or berate - each other in real-time too.
It has already proved to be a big hit with 56 volunteers who tested the game, and the researchers who have worked on it.
None of the volunteers knew each other before the experiments.
But after 30 minutes' play, they reported that they bonded much faster and felt they were far more matey than those who played similar games not requiring any sweating.