How Does Spending Time in Space Affect the Human Body?

Two little-known side effects of space travel involve changes to the spine and back muscles of astronauts who spend extended periods of time in microgravity conditions. Researchers have determined that in space, an astronaut’s spinal curvature flattens and the torso lengthens, actually causing him or her to "grow" taller by as much as 2 inches (5 cm). And while this is only a temporary change, another side effect of spending significant time in microgravity is more serious. Body scans have shown that the muscle mass supporting an astronaut’s spine can atrophy, making it four times more likely that he or she will suffer from spinal disc herniation.

Back pain in space:

• The study, reported in a 2016 issue of the journal Spine, found that muscle tone decreased by an average of 19 percent. Back on Earth, only two-thirds of muscle mass returned.
• Astronauts don’t use the muscles in their lower backs in space because they aren't bending over or using their lower backs to move, as they would do on Earth.
• About 70 percent of astronauts report spine discomfort after only a few days in space. Half experience back pain when they get back on terra firma.