WASHINGTON, Oct. 25 -- Astronauts on long space missions experience a weakening of the muscles supporting the spine, and they don't return to normal even after several weeks back on Earth, U.S. researchers said Tuesday.
The study, funded by the U.S. space agency NASA and published in the research journal Spine, provided new insights into the elevated rates of back pain and spinal disc disease associated with prolonged spaceflight.
Back pain is common during prolonged missions, with more than half of crew members reporting spinal pain. Astronauts are also at increased risk of spinal disc herniation in the months after returning from spaceflight -- about four times higher than in matched controls.
Back issues in astronauts are accompanied by a roughly five-centimeter increase in body height, thought to result from spinal unloading and other body changes related to microgravity.
In the new study, six astronauts from NASA were analyzed before and after spending four to seven months in microgravity on the International Space Station.
Each astronaut had magnetic resonance imaging (MRI) scans of their spines before their mission, immediately after their return to Earth and again one to two months later.
The MRI scans indicated the spinal muscles during the astronauts' time in space shrunk by an average of 19 percent. A month or two later, only about two-thirds of the reduction had recovered.
In contrast, there was no consistent change in the height of the spinal intervertebral discs.
"These findings run counter to the current scientific thinking about the effects of microgravity on disc swelling," first author Douglas Chang, associate professor at the University of California San Diego, said in a statement.
"Further studies will be needed to clarify the effects on disc height, and determine whether they contribute to the increase in body height during space missions, and to the increased risk of herniated discs. However, it's information like this that could provide helpful information needed to support longer space missions, such as a manned mission to Mars."
Chang said these findings suggest possible ways to reduce the spinal effects of spaceflight.
For instance, core-strengthening exercises, like those recommended for patients with back pain on Earth, might be a useful addition to the astronaut exercise training program.
Yoga might be another promising approach, especially for addressing spinal stiffness and reduced mobility, Chang added.
