Williams, who has been on the space station since December as a member of the Expedition 14 crew, is an official entrant in the Boston race. She will run the marathon on a station treadmill, circling Earth at least twice during the process, NASA said in a release.
Williams said she is running the race to encourage kids to make physical fitness part of their daily lives. She and fellow astronaut Karen Nyberg qualified for the Boston race by finishing among the top 100 females in the Houston Marathon in January 2006.
Williams has been training for the marathon while aboard the station, running at least four times a week. NASA said space 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.