Flight Engineer Suni Williams started her gruelling run on a treadmill at the same time as terrestrial runners in the Boston marathon, and completed the 26 miles 385 yards in four hours and 24 minutes.
However, since the ISS is moving at eight kilometres a second, the race distance was covered in a little over five seconds.
"I encourage kids to start making physical fitness part of their daily lives, " Williams said. "I think a big goal like a marathon will help get this message out there."
Williams is a keen marathon runner and finished last year's Houston marathon in three hours 29 minutes.
This time she was hampered by bungee cords that kept her on the treadmill, and helped by a laptop that showed the actual marathon in real time, as well as Russian flight engineer Oleg Kotov dangling an orange just out of reach.
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