Astronauts returning to Earth may have deformed back muscles, sometimes up to four years after their mission.
Astronauts who spend several months aboard a space station experience back muscle deformities after returning to Earth, according to a new study. Some compositional changes are even still present up to four years after long-duration spaceflight, according to research by Katelyn Burkhart (Massachusetts Institute of Technology) and colleagues. They write, “Spaceflight-induced changes in lower back morphology may contribute to back pain commonly reported in astronauts.”
Reduction in muscle size
To reach this conclusion, the researchers analyzed the muscles around the spine of 17 astronauts who had carried out missions on the International Space Station. Their average stay in space was six months.
Results: The examinations revealed a reduction in the size of the muscles of the back. For individual muscles, size decreased by 4.6 to 8.8%. The scans also showed a significant increase in the amount of fatty tissue present in the paravertebral muscles. As a result, the astronauts’ muscle density, which is inversely related to fat content, decreased by 5.9-8.8%.
Two to four years after the astronaut’s return
For most muscles, the composition returned to normal after one year. However, for two muscles, the fat content remained higher than the pre-flight values, even two to four years after the astronaut’s return from space. These muscles, which connect the spine to the pelvis, are located next to the spine. By comparison, the paravertebral muscles behind the spine returned to normal size and density.
Changes in size and muscle composition varied from person to person. For some muscles, changes in size were at least partly related to the amount and type of exercise the astronauts performed in weightlessness: resistance exercise or cycling. In-flight exercise did not appear to affect changes in muscle density.
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