When space-age technology can't keep astronaut muscles from withering, there's only one thing left for NASA to do: upgrade.

The Advanced Resistance Exercise Device, or aRED, was installed two months ago inside the International Space Station. Smaller and more powerful than any earthly all-in-one gym set, aRED is expected to provide astronauts with much-needed muscle work.

"When we think about the space environment, you have to reset the baseline," said Scott Trappe, director of Ball State University's Human Performance Laboratory. "On Earth, it's hypertrophy: 'How big can I get my muscles?' In space, it's 'How can I protect what I have?'"

In the first-ever analysis of muscles from International Space Station astronauts, Trappe's team found that six months in near zero-gravity had produced a 15 percent loss in muscle volume and 25 percent loss in strength.

The findings, published last week in the Journal of Applied Physiology, are concerning on multiple levels.

Space station astronauts already follow a strict workout routine designed to prevent the loss of bone and muscle seen in the crew of the Mir and Skylab space expeditions.

If the consequences of those missions are any guide, astronauts may have a difficult time recovering their full strength, and some may never regain it. And six months is the minimum time needed for a manned mission to reach Mars.

However, the exercise of space station astronauts is limited to the machines they're given. Though a treadmill and stationary bicycle work fine, they're intended primarily for aerobic conditioning. Muscle strength is the responsibility of the Interim Resistance Exercise Device, or iRED — and, with a maximum resistance of just 300 pounds, it can't do the job.

"Astronauts are working out hard, but the loading characteristics aren't there," said Trappe. "They're losing more muscle mass than they should be."

Simply maintaining muscle mass in space, said Trappe, requires a high-weight, low-repetition workout. The aRED is the first piece of NASA exercise equipment to meet this need. Providing resistance in each exercise are two piston-driven vacuum cylinders that are a bit like oversize bicycle pumps. Resistance increases as a piston is pulled in or out, so weights are set by adjusting the length of a mechanical arm that attaches pistons to lift bar.

Attached to the pistons is a flywheel, explained NASA astronaut strength conditioning and rehabilitation specialist Jim Loehr. Pushing the pistons out sets the flywheels spinning. That rotation, combined with vacuum pressure, provides a counter force against direction reversal so that a leg press in space requires effort as the weight is returned to its starting position, just as it does on Earth.

"ARED was designed to provide a constant force throughout the range of motion," said Loehr, mimicking the physiological gold standard of free weight resistance. In contrast, the iRED was a 21st century version of a Bowflex machine, with unidirectional resistance provided by an ingenious arrangement of rubber bands that provide an "ascending force curve that doesn't match traditional free weights," and can lose strength over time.

For some exercises, like squats, a person needs to lift twice as much weight in space to get the same result as on Earth. So iRED's maximum weight of 300 pounds translates to just 150 pounds squatted on Earth. Maintaining leg strength becomes extremely difficult with that amount of weight. And it's the legs, accustomed to constantly supporting our bulks against Earth gravity, that weaken first in space. ARED's maximum load of 600 pounds means astronauts can squat the equivalent of 300 pounds on Earth, which should be enough to keep their legs in shape.

Another problem with a Bowflex-style apparatus, said Trappe, is safety. "They have all these rubber cords and things attached to it that could snap," he said, explaining that people fail to appreciate the extraordinary demands placed upon exercise machines in space.

In the fragile bubble of life that is a spacecraft, it's imperative that machines never fail. A loose screw or frayed wire, an injury to an exercising astronaut, could start a chain of events that dooms a mission.

And once safety is accounted for, there's science to worry about.

Instruments are so sensitive that the slightest vibration could throw off their readings, jeopardizing an experiment or even navigation.

Combine those demands with the need for full-body workout and a cramped environment, and it's very hard to make an effective machine, said Trappe, but aRED might be it. It can mimic everything from squats to bicep curls to bench presses, has its every vibration is dampened, and has undergone hundreds of thousands of trial repetitions without wearing down.

The first wave of ISS astronauts to use the aRED are training on it now, and their bodies will be evaluated upon return.

Asked whether astronauts could use chemicals to enhance their physiques, Trappe said the chances were slim: in addition to individual differences in pharmacological response, drugs may work differently in space than on Earth.

"There's no doping in space," he said.

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Image: International Space Station/Japan Aerospace Exploration Agency astronaut Koichi Wakata

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