Starting this month, fifty healthy men age 30 to 55 will be paid $5,000 each to spend 28 days in bed, just lolling around. They won't even be allowed up to go to the bathroom.
The unusual study, at Tufts-New England Medical Center in Boston, is designed to document just how debilitating bed rest is for muscles and bones - and to see whether resistance training with springs and pulleys, along with special protein supplements, can reverse this downward slide.
The implications are huge - and not just for the National Aeronautics and Space Administration, which is funding the study to find ways to protect astronauts' muscles and bones on long space flights, such as those planned to Mars. In past flights, astronauts have lost a third of their muscle strength and sustained the equivalent of four years of earthly bone loss after just one month in space.
Bed rest is the best earth-bound substitute for studying weightlessness. But the Tufts findings might be even more useful on Earth.
Many medical conditions, including high-risk pregnancies, congestive heart failure and some surgeries, send people to bed for prolonged periods. Some nursing home patients virtually live in bed. And some who suffer chronic fatigue or fibromyalgia mistakenly put themselves to bed for long periods.
Bluntly put, prolonged bed rest can be a medical disaster. That's why hospitals insist that patients get up, even after major surgery. Human bodies evolved in sync with the gravitational pull of the earth. Without that force to pull against, muscles and bones get weak with stunning rapidity as the rate of muscle protein synthesis drops.
"If you're healthy, you can tolerate a week without trouble, but after that, you start to see large losses of muscles and bone," says Dr. Ronenn Roubenoff, the leader of the study and an associate professor of medicine and nutrition at Tufts.
Among other things, bed rest triggers inflammatory cytokines, natural chemicals that tell muscles to export amino acids to the liver so the body can make the antibodies and white blood cells to fight disease. "We are built to sacrifice protein from muscle, in times of stress, to boost the immune system," says Roubenoff. "We're designed to get better relatively quickly or drop dead."
Cytokines are the reason people feel lousy when they get the flu, says Dr. Jeremy Walston, a geriatrician at Johns Hopkins Bayview Medical Center. "People feel malaise and weakness. That's due to the impact [of cytokines] on muscle."
Other problems: calcium can leach out of the bones, resulting in kidney stones, and it takes only a few days of bed rest to cause insulin resistance, which can lead to diabetes. Lung function deteriorates, too.
In the landmark Dallas Bed Rest and Training Study, researchers put five healthy college men to bed for three weeks in 1966 and measured their muscle loss and other factors. When allowed to get up and exercise again, the men recovered.
Thirty years later, the researchers tested the same men again. The results were stunning: The three weeks of bed rest the men experienced in their 20s "had a more profound effect on physical work capacity than did three decades of aging."
The good news is that a little judicious exercise in bed can minimize the dangers.
Dr. Christopher Cooper, an exercise physiologist at the University of California, Los Angeles, says his data show that even frail, geriatric patients can exercise in bed, which lowers the risk of incontinence. (This often occurs in people who get so weak from bed rest they can't get out of bed.)
You have to use common sense, of course. Don't exercise in bed if you have a fever. But you can try to sit up several times a day. Stay away from sugar - you're at risk of insulin resistance from lying around. Try high-protein supplements instead.
Judy Foreman is a lecturer at Harvard Medical School.