Will space colonisation cripple our astronauts?
We know that living in zero gravity is bad for your bones but what about the low gravity that Mars or Moon colonists will face? Scientists thought exercise would be enough to compensate but new research suggests that it's back to the drawing board. Richard Lovett reports.
Astronauts returning from long-term space travel are at enormous risk of fractured hips and crumbling spines because their bones weaken under zero gravity. Scientists are less clear how the bones of possible future colonists might fair under low gravity on Mars, with three-eighth’s Earth’s gravity, or the moon with one-sixth.
Weightless living removes the stresses that stimulate bones to maintain mass. But space researchers had hoped running on a treadmill might do the trick. That might not be enough as Peter Cavanagh, a professor of orthopaedics and sports medicine at the University of Washington, Seattle, reported at the International Calgary Running Symposium this month.
To put the idea to the test, Cavanagh installed a treadmill on the “vomit comet”. Like a roller coaster in the sky, these aeroplanes repeatedly jet high into the air then fall back, to simulate up to 30 seconds of low gravity comparable to being on the Moon.
During the fall, Cavanagh’s research subjects walked or ran on the treadmill. Sensors measured both the force of their footfalls and the accelerations experienced by their bones.
In some experiments the participants ran free under the simulated lunar gravity. In others they wore harnesses that pulled them down with enough force to simulate full Earthly body weight.
Running without the harness felt “great – like running on a cloud”, says Andrea Hanson, a senior scientist in the Exercise Physiology Countermeasures Lab at NASA’s Johnson Space Center, who was one of the test subjects.
But using the harness was much more difficult – and much harder than running on the ground. The harness loaded weight onto certain parts of the body rather than distributing it evenly like gravity does. To run, Hanson had to lean forward as though she was pulling a sled.
In the past exercise has been the dominant counter-measure
for NASA, but it just hasn’t worked.
That unpredictable change of gait is one of the reasons, she says, why it was important to get real experimental data, rather than relying on computer models.
The test results were disappointing for those hoping that running on a treadmill or taking excursions in heavy spacesuits would be enough for lunar residents to keep their bones healthy. The peak forces on the runners’ bones are only 50% of body weight, far lower than anything normally experienced on Earth.
The harness produced higher forces, Hanson adds, but still not enough at the running speed tested (about six minutes per kilometre).
James Pawelczyk, a physiologist and former space shuttle astronaut at Pennsylvania State University, adds that we still don’t understand exactly what bones need to remain strong – or how weak they will become after extended periods in low gravity.
In zero gravity, he says, “our best guess is that it’s something like a person who has a chronic spinal-cord injury and is confined to bed”. Those people ultimately lose half their lower-body bone density – devastating for an astronaut returning from a two to three-year space mission.
Cavanagh agrees. “It may be that exercise alone will not do it,” he says. “It may be that there will have to be therapeutic drugs. In the past exercise has been the dominant counter-measure for NASA, but it just hasn’t worked.”
The next step, says Cavanagh, is likely to be animal experiments on the International Space Station, in which scientists get to see what drugs can do to slow the rate of bone loss in space.