(CNN) -- Being in space is like being Superman every day, says Clay Anderson, a NASA astronaut from Omaha, Nebraska. At the international space station, where he spent five months last year, he flew to breakfast, work and the bathroom.
Shuttle Endeavour is delivering the advanced Resistive Exercise Device to the international space station.
But floating around in zero-G can have some serious consequences for the human body, NASA's experts have learned, including the weakening of bones. In fact, studies have shown that space travelers can lose 1 to 2 percent of their bone mass each month on average, according to NASA.
One way that astronauts have been fighting bone loss is through strength training. And they're getting some help with a new machine delivered this week by the shuttle Endeavour, which docked with the international space station on Sunday.
The advanced Resistive Exercise Device, aRED for short, functions like a weight machine in a gym on Earth, except it has no conventional weights. Instead, it has vacuum cylinders -- canisters with air that have had a vacuum applied -- that provide concentric workloads up to 600 pounds, NASA says.
The device works somewhat like a bicycle pump, only in reverse, said Mark Guilliams, a NASA trainer. For example, if you are squatting, the vacuum gets pulled out as you stand up, and when you squat back down, the vacuum pulls the bar back to the normal position.
Between the vacuum cans and the bar, there are small flywheels that spin in opposite directions, creating an artificial gravity when someone lifts the bar.
Astronauts can do upper and lower-body exercises, such as squats, dead lift, heel raises, bicep curls and bench press on the device, NASA said.
"In the movie, the 'Transformers,' it looks like one of those things that unfolds into some kind of big monster," Anderson said. "It's huge."
The existing exercise device on the space station has a mechanism that more closely resembles a rubber band. The farther you pull the rubber band, the more force you generate, Guilliams said. The limitations of this device made it somewhat boring, Anderson said.
The new device will allow astronauts do many more kinds of exercises than the old one. The tradeoff is its larger size, Anderson said. It will be in use almost constantly during the day, assuming astronauts work out about two hours a day each, he said.
The international space station also is equipped with a treadmill and a bicycle, Guilliams said.
So what's the difference between exercising on Earth and working out on the international space station?
"When you run outside on Earth, you've got 195 pounds smacking against the pavement every time you take a step," said Anderson, who weighs 195 pounds on Earth. "In zero gravity, you're trying to use bungees to hold you down."
The treadmill has clip harnesses to hold an astronaut down, such that the fewer clips used, the more force acts around the legs, making running more difficult, he said.
Using the previous exercise device on the space station wasn't so different from a cable machine in a weight room on Earth, he said.
"Instead of lifting a big piece of iron, you're basically pulling against a gear or a can," he said. "I think they were very similar in terms of feel."
Both before and after space travel, astronauts go through the same kinds of exercises familiar to athletes and others who exercise on Earth, Guilliams said -- aerobic activity such as running, and weight training. Astronauts training for a flight have scheduled exercise time two or three times a week for two hours each session, but in unscheduled time, they'll go for a run, he said.
But people who want to leave the planet must be in really great shape, right?
Guilliams says that's not the case -- as long as a person is healthy and has no cardiovascular problems, he or she can, in theory, can become a NASA astronaut, even if out of shape.
For Anderson, who played football in college and has been athletic for much of his life, space travel was "physically easy." Space walks did get fatiguing because they required him to use his forearms, hands and upper body, which don't get much exercise on Earth.
"On Earth, you tend to use your big muscle group, and in space you tend to use your smaller muscle group, especially on a space walk when you use your forearms and your hands almost exclusively," he said.
Anderson lost only 4 percent of his body mass in his 152 days off the planet, compared with the expected 12 to 16 percent, he said. He also exercised for two-and-a-half hours a day for 151 out of the 152 days, he said.
Returning to Earth on the shuttle Discovery last November, Anderson walked off the orbiter with a little assistance, and it only took him about 24 hours to walk and stand normally again.
He credits this speedy recovery to his frequent use of the exercise equipment on the space station.
Combating bone loss is one of the challenges that the space program has, especially given the goal of a mission to Mars.
An ongoing study is measuring how much astronauts who stay on board the international space station eat and exercise, Anderson said. The experiment will determine what kinds of dietary supplements astronauts should take in addition to the food they eat, and also the appropriate level and type of exercise they should get, he said.
"I think they're making some good strides in figuring out how to keep people healthy on a six- to nine-month trip to Mars," he said, although experts are still a long way away from figuring out the bone loss issue for a round-trip journey of about two years.
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