Story highlights Astronauts can temporarily gain 2 inches in height but suffer muscle loss and back pain More countermeasures involving exercise may help mitigate pain and muscle loss CNN  —  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. 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 in 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. …