An American astronaut will run this year's Boston Marathon on board the International Space Station.
Sunita Williams will be tethered to a treadmill on board the ISS
Sunita Williams, 41, a US Navy commander, will be tied to a treadmill to combat the effect of weightlessness.
She qualified for a place by finishing last year's Houston Marathon in three hours 29 minutes and 57 seconds.
But she blasted off on board the Discovery space shuttle in December, prompting her decision to try to run the race in space on 16 April.
"I consider it a huge honour to qualify, and I didn't want my qualification to expire without giving it a shot," Ms Williams told the race organisers, the Boston Athletics Association (BAA).
She has already broken the record for the length of time in space by a woman, and is poised to break the US record for continuous time in space before she returns home in the summer.
In the past three years marathon organisers have worked to accommodate qualifiers who cannot take to the streets of Boston.
They have sent trophies, water bottles and finishing line tape to Iraq for troops stationed there and plan a similar shipment to Kosovo this year.
Ms Williams, though, is the first Boston marathon runner to attempt the course while orbiting 210 miles (338km) above the surface of the Earth.
"The Boston Marathon is the pinnacle of achievement for most runners," said BAA spokesman Jack Fleming, who said she would pioneer "a new frontier" with her run.
"For Suni to choose to run the 26.2 miles (42.2km) in space on Patriots Day is really a tribute to the thousands of marathoners who are running here on Earth."
Running in space will test Ms Williams' physical fitness in a variety of unusual ways.
Nasa has built a "vibration isolation system" to keep the space station steady as Ms Williams runs, but this places extra strain on the runner's hips and shoulders.
"That harness gets hard on her back and her shoulders or her hips," said the astronaut's sister, Dina Pandya.
"Her foot was going numb because the strap was on her hip so much."
And once Ms Williams finishes running she knows she will not have access to many of the home comforts available back on Earth.
"She mentioned the other day there's no hot bath," Ms Pandya said.