A NASA astronaut will attempt to become the first person to run a marathonin space - tethered to a treadmill so she doesn't float away.

Suni Williams, 41, a US Navy commander on the international space station,decided to conduct attempt the run after qualifying for the Bostonmarathon when she broke the barrier of three hours 30 minutes by just threeseconds in the Houstonmarathon.

The Bostonmarathon starts at 10am on April 16 and Cdr Williams will do her best to starton time. This might not be possible, however, because her sleep schedule istied to the arrival of a Soyuz mission.

"She thought it would be cool if she gave it a try," said hersister, Dina Pandya, who will run the race the traditional way.

Cdr Williams said: "I considered it a huge honour to qualify, and Ididn't want my qualification to expire." without giving it a shot."