Long-duration space missions may shrink spinal muscles: Study
Astronauts who spend several months on the International Space Station (ISS) are likely to have significant reductions in the size and density of spinal muscles after returning to Earth, according to a study.
Some changes in muscle composition are still present up to four years after long-duration spaceflight, said researchers from the Massachusetts Institute of Technology (MIT) in the US.
As NASA plans for future missions to Mars and beyond, these results can be used to guide future countermeasures to mitigate declines in trunk muscle morphology and associated functional deficits, they said.
"Spaceflight-induced changes in paraspinal muscle morphology may contribute to back pain commonly reported in astronauts," said Katelyn Burkhart from MIT.
For individual muscles, muscle size decreased by 4.6 to 8.8 per cent. In follow-up scans performed one year later, size returned at least to normal for all muscles.
The scans also showed significant increases in the amount of fatty tissue present in the paraspinal muscles. Accordingly, the astronauts' muscle density, which is inversely related to fat content, decreased by 5.9 to 8.8 per cent.
These muscles, which connect the spinal column to the pelvis, are located alongside the spinal column. By comparison, paraspinal muscles located behind the spinal column regained normal size and density.
Changes in muscle size and composition varied between individuals. For some muscles, changes in size were at least partly related to the amount and type of exercise the astronauts performed while in zero gravity: either resistance exercise or cycling.
In-flight exercise did not seem to affect changes in muscle density, researchers said.
The results show that muscle size returns to normal upon Earth recovery, but that some changes in muscle composition -- particularly increased fatty infiltration -- may persist for at least a few years.