Space station astronauts are expected to work out for about 14 hours per week. The best way to get a really good workout is to play at it - what kind of sports can an astronaut do?
Take a look at some of the recent efforts at sports in space:
In March, Japanese astronaut Takao Doi threw a small boomerang aboard the station to see if it would come back without gravity. (It apparently did, according to Japanese space agency officials.)
Last year, NASA astronaut Sunita Williams, a die-hard Boston Red Sox fan, ran the Boston Marathon from orbit in 4 hours, 24 minutes.
n 2006, European astronaut Christer Fugelsang, a former Swedish national Frisbee champion, kept a Frisbee aloft inside the station for 20 seconds - thanks to the lack of gravity - to break the previous world record of 16.72 seconds for a single toss.
And don't forget the golfing practice both outside the ISS and, of course, on the Moon during the Apollo 14 mission. We've got highlights!
(Alan Shephard practicing with a six iron)
As usual, writers have gone before us. Science fiction fans will recall the fast sports in the Freeside orbital resort from Neuromancer, the 1984 cyberpunk classic by William Gibson.
Higher you climb, the lower the gravity. Sports up there. There's velodrome ring here." He pointed.
"They race bicycles," Molly said. "Low grav, high-traction tires, get up over a hundred kilos an hour."
(Read more about the low-gravity velodrome)
Here's an earlier reference that might come in handy should mankind ever return to the Moon and stay long enough for recreation.
They're lovely! - titanalloy struts as light and strong as bird-bones, tension-compensated wrist-pinion and shoulder joints, natural action in the alula slots, and automatic flap action in stalling. The wing skeleton is dressed in styrene feather-foils, with individual quilling of scapulars and primaries. They almost fly themselves...
I perked up and felt sorry for all groundhogs, tied down by six times proper weight, who never, never, never could fly.
(Read more about Storer-Gulls wings)
Who ever thought about flying around in lunar caves? Robert Heinlein, in his 1957 novel The Menace From Earth.