Bone and Muscle Loss
Possibly the most well known effect of weightlessness is the steady deterioration of muscles and bones. On Earth, the human body uses these organs for support and, in zero-g, they suddenly have a lot less to do.
Astronauts lose an average of 1 to 2 percent of their bone mass each month in space, causing NASA to consider bone loss one of the primary hazards of long-term spaceflight. As well, muscle mass can vanish at rates as high as 5 percent a week.
Making matters worse, calcium from bones leaches out into the bloodstream, where it creates increased risk for kidney stones – a potentially very painful event for an astronaut to endure. And those calcium-deficient bones become very brittle and liable to break, weakening astronauts on long missions. When they touch down back on Earth, some space travelers have to be carried away in stretchers.
These numbers are only averages and the actual effects vary greatly. Some astronauts have lost as much as 20 percent of their bone mass in six months. Others get off quite lucky. Cosmonaut Valery Polyakov – the current record holder for time in space – was able to walk from his capsule to a nearby chair after returning to Earth following 438 days in space. An American astronaut said that Polyakov looked “big and strong” like “he could wrestle a bear.”
Once back on Earth, bones and muscles return to their former strength. Research suggests that a day of recovery in Earth’s gravity is needed for each day in space. Doctors are also working to combat the weakening, in some cases through hormone therapy. Such treatments may also be able to help people on Earth who suffer from degenerative bone diseases such as osteoporosis.
So far, the most effective way that astronauts can work to maintain their pre-spaceflight strength while in space involves diligent exercise. Astronauts aboard the International Space Station currently strap themselves into a special treadmill designed to minimize vibrations that could affect the sensitive microgravity experiments on the ISS. The machine is called the Combined Operational Load Bearing External Resistance Treadmill, or COLBERT, after comedian Stephen Colbert, who had members of his audience write in votes to NASA during a naming contest.
Images: 1) Astronaut Ken Bowersox, jogs on a treadmill in the Zvezda service module aboard the International Space Station. The suit was designed to measure stress on lower extremity bones and muscles during everyday activities. NASA. 2) Astronaut Michael Fincke is carried to a medical tent shortly after landing back on Earth in 2009. Though Fincke spent six months in space, he may have been strong enough to stand and getting carried in this way might just be a precautionary measure. NASA