Sunita “Suni” Williams is a U.S. astronaut used to extreme challenges. She is a graduate of the U.S. Naval Academy, an experienced pilot who has flown more than 30 types of aircraft, an accomplished athlete, and she’s spent hundreds of days in space over several missions.

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So, she’s done it all, right? In 2007, there was one record just waiting to be broken. Who could run the first marathon in space? That’s right, on April 16, Suni ran the 42.2 km (26.2-mile) Boston Marathon on the International Space Station treadmill.

It’s vital that astronauts use their bones and muscles daily in reduced gravity and microgravity. Otherwise, their muscles lose strength and their bones become fragile. Most astronauts on the space station exercise about two hours a day to prevent muscle and bone loss. Suni’s marathon took a little more than four hours, which was a pretty amazing feat considering she was strapped to the treadmill with giant rubber bands so she wouldn’t float away!

While runners on Earth were making the race in windy 9° C (48° F) weather, Suni was in the climate-controlled space station orbiting the Earth at more than 27,000 kph (17,000 mph). In fact, Suni went around the Earth more than twice while her sister Dina Pandya and fellow astronaut Karen Nyberg were running the earthbound Boston Marathon.

Suni’s marathon wasn’t just a publicity stunt: Staying fit in space is not optional. Suni’s message to all of us is that staying active is important on Earth AND in space.

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