A six-month stay on the International Space Station can be a pain in the back for astronauts. While they may gain up to 2 inches in height temporarily, that effect is accompanied by a weakening of the muscles supporting the spine, according to a new study.
In 1994, astronaut Mark Lee had his height measured by fellow astronaut Jerry Linenger as part of a study on back pain. Astronauts have been reporting back pain since the late 1980s when space missions grew longer. Their flight medical data show that more than half of US astronauts have reported back pain, especially their lower backs. Up to 28% indicated that it was moderate to severe pain, sometimes lasting the duration of their mission. Things don’t improve when they return to Earth’s gravity. In the first year after their mission, astronauts have a 4.3 times higher risk of a herniated disc. It’s sort of an ongoing problem that has been a significant one
with cause for concern,” said Dr. Douglas Chang, first author of the new study and associate professor of orthopedic surgery and chief of physical medicine and rehabilitation service at University of California San Diego Health. “So this study is the first to take it from just an epidemiological description and look at the possible mechanisms for what is going on with the astronauts’ backs. Much attention has been focused on intervertebral discs, the spongy shock absorbers that sit between our vertebrae, as the culprit for astronauts’ back issues. But the new study runs counter to that thinking. In this research, funded by NASA, Chang’s team observed little to no changes in the discs, height, or swelling.
Chang said that what they observed in six astronauts who spent four to seven months on the ISS was a tremendous degeneration and atrophying of the supporting musculature in the lumbar (lower) spine. These muscles are the ones that help us stay upright, walk and move our upper extremities in an environment like Earth while protecting discs and ligaments from strain or injury.
In microgravity, the torso lengthens, most likely due to spinal unloading, in which the spinal curvature flattens. Astronauts also aren’t using the muscle tone in their lower backs because they aren’t bending over or using their lower backs to move, like on Earth, Chang said. This is where the pain and stiffening occur, much like if the astronauts were in a body cast for six months.