Living in space can take its toll on an astronaut’s back, causing the muscles within the spine to weaken over time, a new study confirms. In microgravity, these muscles are prone to atrophy, and that causes the bones in the spine to stiffen and straighten out. Such body changes could explain why so many astronauts suffer from back pain after taking trips to lower-Earth orbit. And fixing this problem may be crucial if NASA wants to send humans to Mars someday.

Fixing this problem may be crucial if NASA wants to send humans to Mars

Up until now, researchers thought that astronauts’ back pain was caused by fluids swelling up in the spinal discs — cartilage joints that cushion the bones of the spine. But after conducting MRIs and other tests of six NASA astronauts, scientists at the University of San Diego found that the discs didn’t change their shape that much while in space. Instead, the paraspinal muscles, which connect the bones of the spine together and control their movement, shrunk by about 19 percent in size, according to NASA-sanctioned research detailed today in the journal Spine.

The findings may mean it’s time for astronauts to make some changes to their daily routines in space to stay healthy. Currently, astronauts exercise for about two hours each day to strengthen their muscles and bones. These systems can weaken in space, since they aren’t working against any gravity. Study author Alan Hargens says core strengthening exercises and neck exercises may be needed to keep the back healthy as well.

"We think that the neck is a part of the spine that is particularly susceptible to this loss of gravity," Hargens, a professor of orthopaedic surgery at UC San Diego, tells The Verge. "So there need to be better exercises for the astronaut’s necks. Right now they don’t have anything as far as we know."

JAXA astronaut Koichi Wakata exercising on the space station treadmill. (NASA)

Normally, there is a natural curve in a person’s spine, but in space there is no gravity pulling down on those bones, so they naturally straighten out. And as the surrounding muscles weaken, the bones may stiffen even more, causing the vertebrae to stack on top of each other and erase that natural curvature. That could explain why around two-thirds of people who spend multiple months in space suffer from back pain of some sort, and astronauts have a four times higher risk of herniated discs when they get back to Earth. (Astronauts suffer from a host of other health problems in space, too.)

These back issues also seem to coincide with a lengthening of the spine

These back issues also seem to coincide with a lengthening of the spine. Astronauts usually come back to Earth about two inches taller than before they left. "If all of that curvature is gone, then we think that explains why the astronauts grow," says Hargens. "And with a lot of muscle atrophy around the spine, that makes the spine susceptible to injury when the astronauts come back to Earth."

Today’s study shows all these problems may be due to considerable weakening of the spinal muscles. MRIs and stress tests on six NASA astronauts showed that paraspinal muscles shrunk by about 19 percent in size after spaceflight, and the cross-sectional area of the muscles — key for muscle strength — shrank from 86 percent to 72 percent after spaceflight. Two months after flight, the cross-sectional areas only recovered by about two-thirds.

"It makes sense. With muscle, if you don’t use it you lose it," Dorit Donoviel, deputy chief scientist at the National Space Biomedical Research Institute, who was not involved with the study, tells The Verge. "If you don’t need to stabilize your spine against gravity, it would make sense those muscles would atrophy with time."

Yoga may help with core strength

Given these findings, Hargens and his team are working on recommendations for NASA on the best exercises and devices to mitigate these effects. Yoga, for instance, may help with core strength, Hargens says, and neck devices that simulate gravity could also help, since that’s the area where astronauts experience the most herniated discs. Additionally, astronauts may be lifting too many weights during their workouts in space, Hargens says, which may be hurting the spine even more.

It’s important to determine the proper exercise regimen for astronauts, especially since NASA wants to send humans to the surface of Mars someday. Trips to the Red Planet could take upward of six months to complete, and astronauts will need to be in the best health possible when they arrive. "They have to be ready to do all sorts of things, even possibly quickly evacuate from a space vehicle if they have a crash landing," says Hargen. "We really don’t want the astronauts injured halfway to Mars."