NASA requires its astronauts to exercise on space flights to fight off the debilitating effects of zero-gravity on the body's bone and muscle. But Sunita Williams, U.S. commander of the Expedition 33 crew at the International Space Station, took things to another level when she completed the first ever triathlon in space — running, biking, and even swimming to compete with Earth-based athletes 240 miles below in Southern California. A closer look at her stunning achievement:

What equipment did Williams use?
Since quarters are a bit cramped at the I.S.S., Williams used special exercise equipment to keep up with triathletes competing in the Nautica Malibu Triathlon in Southern California. For the half-mile "swimming" portion, Williams strapped into something called the Advanced Resistive Exercise Device (ARED), which uses weights to imitate water resistance while swimming through anti-gravity. For the 18-mile biking portion she used a stationary bike, and for the four-mile run she used a specially outfitted treadmill that strapped her in to keep her from floating off. (Watch a video below.)

How did she fare?
Pretty well. She completed the whole race with a respectable time of 1:48:33. "I'm happy to be done," said Williams as she crossed the finish line. "It wasn't easy and I'm sure everybody in California's very happy to be done too."

What kind of training did she do? 
Williams, an "avid athlete," says Clara Moskowitz at, began training on solid pavement before she launched off to the space station on July 14. Once in space, she kept up with her training, competing in the seven-mile Falmouth Road Race in Massachusetts on Aug. 12. The triathlon, however, "wasn't her first orbital athletic achievement," says Moskowitz. In 2007, she ran the Boston marathon on a space treadmill, finishing with a time of 4:23:10. 

Take a look:

Sources: CNN, Slate,