Why Space Hates Our Bones (and what we can do about it)


Think it might be fun to live in space? Better ask your bones.

Earth’s space agencies have tackled some of the major obstacles to living in space, with pressurized spacesuits that offset the deadly vacuum and deflect incoming solar and cosmic rays. But in the absence of gravity, astronauts aboard the International Space Station are still losing up to 10 times more bone mass than most Earth-bound post-menopausal women. 

In an attempt to address this bone loss, University of Washington researchers found 22 volunteers for a study using bed rest as an analog of spaceflight. The current crop of volunteers are halfway through their commitment to remain in bed, in a six-degree, head-down tilt position for 84 days. The study subjects are still sane, and already, results are promising.

Photo courtesy of Peter Cavanagh, University of Washington

Surprisingly, it’s not necessarily students who are answering the call. Volunteers must be at least 22 years old, so the results apply to the age range of people most likely to be astronauts.

The head-down tilt mimics many of the physiological adaptations astronauts experience during spaceflight, such as bodily fluid shifts toward the head. The bed rest confinement mimics the complete “unloading” of the musculoskeletal system that astronauts feel as they float through space due to the lack of gravity, which accelerates bone loss.

Study leader Peter Cavanagh, a University of Washington professor of orthopaedics and sports medicine, said the volunteers have to be raised to a standing position at the end of their terms very slowly, “because they are very likely to faint” until the heart regains its ability to push blood to the brain. Sometimes, he said, volunteers feel pain in the bottoms of their feet when they finally put them down, and have trouble navigating corners while walking.

“They feel sort of generally weak,” Cavanagh said. “We put them through two weeks of rehab, and we buy them a membership at the health club for another month.”

In that respect, the study volunteers’ experience is similar to that of astronauts returning from long bouts in space. But for half the study subjects, there is a key difference — it’s in their stride.

Half of the study participants perform individually prescribed intermittent treadmill exercise similar to workouts by astronauts in space – but with one important difference: they are pulled towards the treadmill surface by a harness applying greater force than what the research team has previously measured during walking and running on the International Space Station treadmill.

The results from the first half of the study are “extremely promising,” Cavanagh said. Of the five study subjects so far who have been assigned to the exercise group, bone loss in four of them has been prevented in important skeletal regions by the treadmill exercise countermeasure, while the six non-exercising control subject participants all lost bone mass.

“We have found that we can, on average, prevent bone loss in an important region of the hip with this intervention,” Cavanagh said. “No bed rest study ever before has accomplished this.”

Cavanagh said the study results will impact bone health in space by improving exercise prescriptions for astronauts on future space missions. Here on Earth, the work could help scientists understand how individualized exercise programs affect age- and gender-related osteoporosis.

As for the volunteers, the study leaders encourage them to “achieve something special,” Cavanagh said. “Some tried to learn Spanish. We had others who were preparing for exams, and doing things they would have difficulty doing if they led their life with the typical distractions.”

Cavanagh said the study subjects are kept busy with tests during the week, but the weekends can be difficult. 

The volunteers make around $8 an hour, but they’re working 24 hours a day.

“One of my most satisfying moments,” Cavanagh said, “is handing them a $12,000 check at the end.”

Source: University of Washington and Peter Cavanagh

Added 3/24: See an interview with study participant Tabitha Garcia at author Anne Minard’s blog.

17 Replies to “Why Space Hates Our Bones (and what we can do about it)”

  1. Yeah, Conic, please go ahead post your “pretty easy” designs for artificial gravity.

  2. Whatever happened to the idea of rotating a spacecraft around its long axis (nose-to-tail) to generate centripetal force to mimic gravity’s effects? Once a spacecraft is rotating, it takes very little energy to maintain that rotation (angular velocity remains constant, and energy is only needed to change/accelarate it). This sort of solution to the problem was standard fare in Golden Age science fiction, but NASA for some reason doesn’t seem to want to try it out. Okay, why? There has to be a reason for not using it, so what is it?

  3. friends, what exactly about the Tacoma Narrows Bridge is relevant to rotating space station design? Or if the relevant point in that video was the construction difficulties in cable installation for a suspension bridge, what’s the connection to a (usually solid hull) circular station spinning? Possibly if you’re referring to the dumb-bell style station using tethers to connect everything, but before spin-up cable deployment is little more than a regular docking and undocking maneuver, with a tether attached between them before the two modules undock. Then just maneuver the two vehicles some distance apart to pull the tether taught, and spin-up. Not a garage-project by any means, but that I can see not much more difficult than assembly of something like Mir. With simpler interiors even, as equipment could be designed to operate using some level of ‘gravity’ instead of what zero-gee stations are forced to use.

  4. This setup could be applied to all stationary activities in space ie, treadmill exercise and sitting down when working on laptops, using the robotic arm etc.

    By having a chair with a couple of tie points per limb, each attached to spring pulley as in the photo, you would have at least some sort of force to work against.

  5. I don’t understand why the ISS isn’t equipped with a separate module that rotates. I could be a rehab habitat that they could at least use to determine when and how often the astronauts need some artificial gravity to maintain their bones.

  6. “# kvenlander Says:
    March 23rd, 2009 at 11:56 am

    Yeah, Conic, please go ahead post your “pretty easy” designs for artificial gravity.”

    Spin the spacecraft. PERIOD.

    Any questions? The engineering concerns here are similar to the technology needed to go fishing or rock climbing. Wow that is scary technical.

    We dont spin the space station because people dont stay there for very long, and because we want the micro gravity for our experiments. Any long duration space flights (one year and more) would spin the spacecraft around a center of mass on a tether with some other massive object, generally this would be a spent rocket stage (something not needed if the tether should break).

    Can I ask a personal question? Have you ever read a rocketry book? Make sure the answer is yes before you post about rocketry.

  7. An “artificial gravity” module would have to be mounted at the end of a fairly long rotating lever to create sufficient centrifugal force.

    if r = length of the lever (in metres)
    and if v = velocity of the “gravity module” along the circular motion path (in metres per second)


    (v^2/r)/9.8 == the “artificial gravity” you create, given as a fraction of Earth’s gravity.

    bearing in mind that the length of the circular path is approximately 2r*3.14 metres, one can work out how long the lever has to be and how fast (in rpm) the contraption needs to rotate in order to create a desired amount of mock gravity.

    one also needs to bear in mind that more than one rotation every 30 seconds will probably cause vertigo.

    I reckon this may answer a few questions.

  8. oops… I forgot: the contraption _does_ need constant acceleration, really, in order to create mock gravity.

  9. Try rebounding instead of treadmill. Be attached by a spring system where it will pull you back down to the rebounder and bounce back up.

  10. I am only a semi- Trekie and do not recall anyone ever explaining their system- it was almost taken for granted- much like the speed of light and inertia dampeners- which are not likely to happen in this universe.

    Perhaps it was created by the antimatter/matter drive using the dilithium crystals. Even when the ship was powered down they had gravity and their ships sure did not spin in circles, not even the shuttle craft. No there must be more to this story, I bet that they had figured out the secret to gravity and learned to use it to their benefit.

    OK- I know it is make believe, but it should give us all something to aspire too

    Perhaps in a few more years/thousand we will learn how to control gravity. Maybe we just need an ounce or two or dark matter.
    Or maybe it is just one of those laws of the universe that cannot be broken.
    Wait – if the ship was made out of a material dense enough then it would have its own gravity.
    Oh where are the scientists when we need them!

  11. Conic, why don’t you try being an aerospace engineer before you start posting about the difficulties in creating artificial gravity?

    Maybe you just need to explain yourself more cleary so that I can understand you, but I don’t think you know what you are talking about. Fishing and rock climbing? I just don’t see how you can make a comparison between that and aerospace engineering.

    Andrew Vienne was on the right track with his comments, but another huge issue is budget. There certainly are people working on this problem, but currently NASA is basically handed their orders by the President, and then they have to accomplish those goals with 1/2 the money they’d like. It means that cool stuff like this doesn’t move along as quickly as was possible during the Apollo days.

    Yeah, we have a lot of ideas that could potentially work. But it’s really hard to convince some to spend several million dollars to explore these ideas when all they want to do is go back to the moon. Not to mention the billions needed after you’ve picked a project to actually get it up and running.

    Source: I have degrees in aerospace engineering from Purdue University and am currently working on a specialty in bioastronautics.

  12. “Stupid question, but astronauts do drink their milk, right?”

    Yes, and other calcium-rich foods (or even supplements) But your body doesn’t use it for bone-building, just because it’s there. (though it must indeed be there)

    Like muscle-building, it happens in response to force and stress. Including the everyday kind on Earth that we don’t even think of as ‘exercise.’

    That’s why extended bedrest is a reasonable analog.. If you aren’t even putting the force of normal walking on your long bones…well, use it or lose it.

    So, it’s either spinning the ship in some manner, find better forms of exercise and resistance that will fake out whatever it is that senses the forces and cause bone building, or find some bio-chemical means of turning on that bone-building ‘switch’ directly, even in the absence of gravity. (which might be useful on bone-degenerative diseases down here,as well)

  13. Remember the space station in “2001, A Space Odyssey”? We must have a centrifugal equivalent of gravity on a circular revolving space station. Our body will automatically adjust to whatever new environment it is placed in. The revolutions per unit of body mass must be maintained at all times to prevent bone loss, not to mention proper body fluid and blood gas concentrations.

    In future space travel, to go to planets larger than Earth, centrifugal space stations will be mandatory to “acclimate” our body to the new environment. Our bone mass will have to increase to meet the new demands. Our bodily fluids (blood and gases) will have to be capable of functioning in an environment of larger planetary mass. There may be planets with life that we cannot visit due to our physical limitations.

    Future planetary medicine may find ways of adding modified body fluids and/or gases for larger planetary exploration.

    When we return from a lengthy visit to Mars, we must return in a centrifugal craft to incrementally re-mass our bone structure. If we do not, we will be forced to stay on Mars for the remainder of our lives.

    To build a Centrifugal space station:

    We should be adding enough propellant and additional controls to our separating shuttle rocket boosters, to propel them into an outer “storage orbit” for future station construction.

    The two solid tank boosters could easily be turned into the “spokes” of the station. The larger liquid tank boosters, could be attached as the outer “wheel”. The center or the “hub” of the space station wheel could easily be the “docking port” for the Shuttles. This would be more practical and cost effective than allowing the “spent” boosters to burn up, falling back to Earth.

    I ask you to look at the size of these shuttle booster rockets, then compare them to the size of an astronaut. There’s a lot of room for science and living facilities. After shuttle separation, how difficult would it be to modify and add enough additional fuel to propel these boosters into an outer Earth orbit?

    The whole station, en mass, would make a huge, livable, practical way for us to travel across our solar system. And this is using “today’s current technology” with no “bone loss”.

    I might add, we could tow the Hubble Space Telescope out to a storage orbit after NASA shuts it down. We could, at a later time, repair and modify it, and take it along with us to Mars and beyond.

    Star Trek can some day become more than a television show and movie. Let’s see what’s out there… Let’s build the first Enterprise interplanetary space craft. If we wait, it may be too late. Let’s not talk about it, let’s do it… How? Merge and integrate private and public participation with NASA. If we wait for Congressional funding, we’ll die of old age waiting. We went to the moon almost 40 years ago? We can change this…
    and it’s time…

    L. Dickman
    [email protected]

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