The famed Boston Marathon has an official entry from space - Indian American astronaut Sunita Williams - who will run the distance on a treadmill aboard the International Space Station, 338 kms above Earth.

This will be another first in space history for an astronaut.

Williams, who qualified for the Boston race by finishing the Houston Marathon last year in 3 hours, 29 minutes and 57 seconds, will run the race on a station treadmill, circling Earth at least twice in the process, running as fast about 13 km per hour but flying more than 8 km each second, NASA said.

Williams hopes her unique run in April will serve as an inspiration.

"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."

Sunita won't be the only one from her family in this unique adventure.

Her sister Dina Pandya and a fellow NASA astronaut, Karen Nyberg, will run the race in Boston.

Williams and Nyberg qualified for the Boston race by finishing among the top 100 females in the Houston Marathon.

Exercise is essential in NASA's efforts to counteract the effects of long-duration weightlessness on astronauts' health.

For months, Sunita has been training for the marathon while aboard the station. She runs at least four times a week, two longer runs and two shorter runs.

Station crews are required to exercise on the treadmill, a stationary bike and a resistive exercise machine to counter loss of bone density and muscle mass.

Due to the crew's sleep schedule, Sunita's run of the marathon on the station may not coincide exactly with the race on the ground, but mission control is working to match the events as closely as possible.