Bedridden for Mars

Study to examine ways to keep astronauts fit for long space journeys

Several dozen middle-aged men will spend almost a month flat on their backs so that astronauts of the future—perhaps those on a mission to Mars—will be able to remain physically fit.

The bedridden volunteers will be part of a four-year study by a group of Tufts scientists that will examine the relationship between resistance training and nutritional supplements on muscle strength. The project is part of a nationwide research initiative to reduce the health risks of long-term space travel. The subjects will be bed-bound because that is the earthly condition that most closely mimics the weightlessness of space.

ronnen roubenoff

Dr. Ronenn Roubenoff and a team of Tufts researchers are embarking on a study to help astronauts weather the inactivity of lengthy missions. © Kathleen Dooher

“With muscle, it’s use it or lose it,” said Dr. Ronenn Roubenoff, visiting scientist at the Nutrition, Exercise Physiology and Sarcopenia Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts and principal investigator on the study. Because astronauts, especially those on long-term space flights, don’t have gravity to contend with, they are at risk for muscle atrophy, a condition that can jeopardize their long-term health and the success of their mission.

“We’re trying to come up with ways to counter that, measures for the safety of the astronauts and their ability to carry out their mission,” said Roubenoff, who also holds appointments as associate professor at the Friedman School of Nutrition Science and Policy and at the School of Medicine.

Not only must the solutions be scientifically sound, but they have to be adaptable to the constraints aboard a spacecraft—namely, tight quarters and a strict daily schedule.

Fit for space
“Astronauts’ days are mapped out in five-minute increments,” Roubenoff said. “For every job, you need a timeline. The longest single piece is 90 minutes for exercise, which seems like a long time, but that also includes 15 minutes to set up and 15 minutes to take down the equipment.

“What we’re trying to do is figure out [exercise] sequences with the most impact for cardio, muscle, bone strength, possibly balance, within that hour,” he said.

While astronauts generally experience an initial decline in cardiovascular fitness during their initial time in space, that can usually be remedied through the use of treadmills with bungee cords or other aerobic exercises, Roubenoff said. “They can get back to baseline within a month. We know what to do.”

But muscle and bone loss present another problem. “There is only limited capacity for resistance training in space, so we have to figure out what to do to get the maximum benefits,” Roubenoff said. “They can’t lift weights.” Without gravity, even the most massive barbell could be hoisted with ease. “The only exercise where [earthbound] physics still applies is springs.” An appropriate device already exists in the form of the RED (Resistive Exercise Device), a machine that has been used on the space shuttle and the International Space Station and will be used by the subjects in the Tufts study.

Amino acid strength
What Roubenoff’s team, co-directed by Dr. Carmen Castaneda-Sceppa, another HNRCA scientist, will be doing is feeding subjects an amino acid supplement and examining what effect the supplement, in conjunction with exercise, has on muscle mass and strength. Amino acids are the building blocks of protein, which forms an integral part of muscle. The supplement will contain “essential” amino acids—those that cannot be made by the human body.

The Tufts project builds upon previous work done at the University of Texas Medical Branch at Galveston, which found that amino acid supplements can help lessen muscle atrophy in bedridden subjects.

“If you take healthy young guys and give them amino acids, it appears to increase the amount of amino acids that go into the muscle,” Roubenoff said. The Tufts study will concentrate on the timing of the nutritional supplements—whether consuming them just before exercising will increase the amount of amino acids absorbed by the muscles even further.

“Exercise gives the signal [to muscle] to accept the amino acids,” Roubenoff said. “If exercise ‘opens the gate,’ can you then ‘flood’ the muscle? Will feeding amino acids before exercising prevent substantial muscle wasting?”

The bed-rest subjects will be divided into three groups: a control group that will receive nutritional supplements but will not exercise, a group that will exercise but receive the supplements hours later and a group that will receive supplements just before exercising.

The subjects will be healthy men, ages 30 to 55, who will be on strict bed rest in a horizontal position at Tufts-New England Medical Center for 28 days. Cable television, books and computers will be available for entertainment. Afterward, the subjects will undergo 14 days of physical rehabilitation, or more if needed. Castaneda-Sceppa, an assistant professor at the Friedman School, will be running the study on a day-to-day basis.

While elderly or infirm people who endure enforced bed rest often develop dangerous side effects such as pressure ulcers (bed sores), blood clots or kidney stones, Roubenoff said the researchers don’t expect to see such problems with the volunteers. “These are healthy folks. These are not seriously ill people,” Roubenoff said. “Those [conditions] usually occur in people who can’t wiggle or turn.”

Rethinking exercise
Ideas about the medical effects of bed rest have changed considerably over the past century, Roubenoff said. “From about 1900 to 1940, the general medical feeling was that exercise was good,” he said. Then, from about 1940 to 1970, the medical establishment began to feel that exercise was harmful for people who were sick. This thinking came from observations of people with rheumatoid arthritis whose joint pain improved with bed rest in the days before effective pharmacological therapy.

“In the early ’70s, we began to see the downside of bed rest and began to move toward early mobilization,” Roubenoff said. “We’re slowly swinging back toward the idea of more physical activity, getting people up sooner.”

Because of physiological differences between men and women—including differences in body composition and menstrual nitrogen losses in women—a separate follow-up study will be needed for women if the men’s study proves fruitful.

The $2 million study is funded through the National Space Biomedical Research Institute, a consortium of universities and biomedical institutions that conducts research related to the health issues of long-term space travel. A 30-month Mars mission, with 12 to 18 months of travel time, is the most ambitious project under discussion, but a one-year space station stay and a 45-day mission to the moon have also been proposed by NASA.

“Each of those missions is different in levels of importance for medical impact,” Roubenoff said. So far, the longest space flights have been undertaken by the Russians, but there is only spotty scientific data available from those missions, he said.

Like much of the research conducted through the years for the space program, there will likely be benefits for those on Earth, too. Several ancillary studies using the bed-rest subjects are planned by other Tufts researchers, including a study on the impact of bed rest on calcium absorption and a study looking at the effect of amino acid supplements on immune system function.