updated 11/20/2005 3:14:39 AM ET 2005-11-20T08:14:39

Laurence Theil lounges around in bed, with attendants to massage her back and bring her breakfast on a tray.

But it isn't exactly a life of leisure: Theil has spent 50 straight days confined to bed for space research.

She is not allowed to stand or sit up, ever, and there's a 24-hour surveillance camera to make sure. She showers lying down and even jogs in bed, strapped in to a vertical treadmill that makes people feel they are racing up a wall.

"Running while you're on your back takes some getting used to," says the 36-year-old French nurse, one of 24 Europeans who volunteered to boldly go where few women have gone before — to bed for 60 days.

The joint study by the European Space Agency, the French space agency CNES, the Canadian Space Agency and NASA will fill in unknowns about how to protect women astronauts from the dramatic physical side effects of weightlessness.

Twelve women completed the study six months ago; the rest are now in bed at a hilltop research center overlooking the red tile roofs of Toulouse, in southwest France. Day and night, in comfy T-shirts and pajamas, they lounge on hospital beds tilted so their feet are 6 degrees higher than their heads — provoking a physical reaction akin to weightlessness.

In space, like in the off-kilter beds, fluids shift to the upper body, which can make the face swell, disrupt digestion and bring on vertigo.

In microgravity, the magic of floating makes up for it. "Human beings become halfway between a fish and a bird," said Roberto Vittori, a European Space Agency astronaut who visited the clinic to cheer volunteers on.

But floating also means being deprived of weight-bearing exercise. The lower body starts wasting away: People lose up to 3 percent of muscle mass a week in some parts of their legs at first, and bone mass in segments of their lower bodies drops about 2 percent in a month, said Dr. Peter Jost, project manager for the study.

Bed-rest studies are frequent in space study, and testing nutritional supplements and exercise routines is important to keep astronauts fit for longer missions. A manned trip to Mars, for example, would expose astronauts to weightlessness or reduced gravity for up to three years. When they land on the Red Planet, they have to be strong enough to work.

Few of the studies have focused on women, however, as 10 times as many men than women have been astronauts, Jost said. Today, nearly 21 percent of NASA's astronauts are women.

"We know there are subtle differences, but we don't know which, and to what extent," Jost said.

One question mark is the ideal level of exercise to protect women from bone loss, keeping in mind that strenuous workouts can modify women's complex hormonal systems and cause their periods to stop.

In the first group of bed-rest volunteers, all lost bone mass at first, but after six months they are back to normal, said Dr. Arnaud Beck, the coordinator in charge of medical ethics.

One surprise find: Past research from short-term missions suggested that women astronauts are more susceptible to dizziness after returning home. But that did not prove true during tests in Toulouse. One possibility is that the difference may fade or disappear during long-term missions.

Volunteers came from across Europe to spend 100 days at the center, more than half of it in bed. They are paid $17,500 to give constant blood samples, submit to electrocardiograms and take tests for bone density and muscle strength. Their urine — all of it — is stored and analyzed. The women also receive counseling and are meticulously cared for. Scientists will check up on them for three years.

Anne Bouchet, a 36-year-old translator, is used to putting her body to the test hiking in the French Alps. She signed up to test the opposite extreme — sloth.

"I thought it would be interesting to live confined for a long period, without moving at all," says Bouchet, who papered her walls with cheery marker drawings by her nieces. One shows a rocket blasting off, an inspirational touch. (Under the study's rules, The Associated Press was not allowed to speak face-to-face to the volunteers during a recent visit. They described their routines while chatting by telephone from down the hall.)

Bouchet is a member of the control group. Another group is testing protein supplements. Theil is among those on a high-power exercise regimen that includes the vertical treadmill. The contraption generates artificial gravity and sucks the soles of her feet to the tread — even though her toes are pointed to the ceiling and she is on her back.

Theil feels in good shape and says she even lost some flab on her legs. On Nov. 27, she will test them on solid ground.

She might be wobbly, if the first group is anything to go by. All of the women could walk, if unsteadily. The most stir-crazy among them wanted to run.

© 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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