For space travelers, fitness is an absolute priority

This story is part of a series on human spaceflight in the United States.

The space – with its bulky combinations and microgravity – does not seem like a good place to play sports. Over the years, however, astronauts have found time to play.

More famous, astronaut Alan Shepard hid a folding golf club in his spacesuit when he arrived on the surface of the moon as commander of Apollo 14 in 1971. Shepard dropped two golf balls in the lunar dust, then moved away with his weapon of fortune 6- the iron.

More recently, astronauts have organized relay races as well as tennis and badminton matches on the International Space Station (ISS).

However, not everything is fun and the games in space. It is very important to keep astronauts fit and healthy in a microgravity environment. Do not forget that astronauts stay in space longer. In recent years, Scott Kelly and his Russian counterpart, Mikhail Kornienko, have spent almost a year (340 days) on the ISS.

Being in a weightless environment can weaken the muscles and weaken the bones. Weightlessness is also difficult for the heart because, with little gravity, the heart does not have to work as hard to pump blood to all parts of the body.

Some have compared being in space for long periods of time to stay in bed for months. The body weakens without moving and without regular exercise.

So, how can astronauts train and stay in shape in space? It's a tricky question, because almost every exercise – lifting weights, running, jumping – makes the body stronger because it fights against gravity.

I asked Sunita "Suni" (pronounced Sunny) Williams to give him answers. She has been an astronaut for 20 years and has spent more than 300 days in space. Williams also recorded more than 50 hours of spacewalks. She is training for a six – month mission to the ISS, which should begin next year.

Williams said it was useful to be in shape before flying off. An astronaut must have some physical form to be able to work in space. Outings in space, according to Williams, are particularly exhausting. Several hours of work outside the ISS can give the impression of "spending a whole day skiing".

Williams, 53, began to get in shape when she grew up in Needham, Massachusetts. She was a competitive swimmer who also hiked, ran across the country and played football. Williams is still running and has even brought his passion for running in space.

ISS astronauts (usually six) must train two hours a day. They spend about an hour exercising their legs and their heart by pedaling on a stationary bike and running on a treadmill.

The computerized treadmill is not the one you would see in a local gym. Astronauts must wear a special harness and belts to prevent them from floating out of the machine.

Williams used the treadmill to race at the Boston Marathon in 2007. She had qualified for the famous 26.2 mile event but was going to be in space during the actual run of the race. His sister contacted the race organizers and asked if Williams could run anyway. . . on the treadmill of the ISS.

The organizers of the race said they agreed. So Williams jumped on the treadmill at the start of the marathon and traveled the entire distance. She even had an official race number.

Astronauts "lift weights" to keep their upper body in shape. Of course, they do not lift weight because everything is weightless in space. Instead, they use a resistance exercise device in which the astronaut pulls, pumps and squats against the force of the vacuum.

Williams's advice to kids who think all this is fun?

First, "do not take your health for granted" and "stay in shape". Astronauts will need to be physically fit to support long space travels and work on Mars. "We will not send people to Mars to be couch potatoes," she said.

Williams encourages children to get used to thinking "out of the box". Everything in this world of weightlessness forces people to think in new and creative ways.

Like when NASA's engineers and astronauts continued to wonder: how to stay fit in space?

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