Astronauts gain a couple of inches in height during long-term space flight, but lose vital muscle mass, according some of the most detailed observations yet of how the body is altered by living in low gravity.

Growing taller might sound like an attractive bonus of space travel - the physical equivalent of gaining a million extra Twitter followers. In reality, changes to the spine during space flight are often accompanied by severe back pain and injuries that could blight a future long distance space mission to Mars, Nasa scientists said.

The latest study, in which six Nasa astronauts were given MRI scans before and after lengthy stints in space, suggest that back problems could be linked to the wasting of tiny muscles that surround the spine.

Gains in height are mostly explained by the spine straightening out when no longer compressed by the body’s weight, the scientists said, and any height gained is rapidly reversed on return to Earth.

The findings may paint a bleak picture of future colonisers of Mars sitting around moaning about incapacitating back pain rather than conquering new frontiers on the planet. The upside, the scientists said, is that a tailored exercise regime could help offset the problems. However, their suggested workout might not fit with astronauts’ traditionally macho image.

“If you could do yoga in space that might really help the astronauts,” said Alan Hargens, professor of orthopaedic surgery at the University of California, San Diego. “We need to reproduce the normal daily loading activity on the spine in space.”



The crew members participating in the study, published on Tuesday in the journal Spine, were scanned before and after spending four to seven months on the International Space Station.

On average, the cross-sectional area of muscles running along the spine decreased by 19% from pre-flight to immediate post-flight scans. A month or two later, only about two-thirds of the reduction had recovered. The paraspinal muscles connect to the vertebrae and direct the motion of individual bones, helping to support the spine and prevent misalignment.

The findings show how quickly the spinal muscles atrophy when they are no longer being relied on to constantly stabilise and support the body as the astronaut floats weightlessly in space.

Previously, scientists had attributed back problems to the swelling of the spinal discs when the back was not compressed by the body’s own weight, but the MRI images showed no evidence of this.

“These findings run counter to the current scientific thinking about the effects of microgravity on disc swelling,” said Douglas Chang, associate professor of orthopaedic surgery and first author of the study. “Further studies will be needed to clarify the effects on disc height, and determine whether they contribute to the increase in body height during space missions, and to the increased risk of herniated discs.”

Back problems are a common affliction for astronauts, with around 70% suffering from discomfort during their first few days in space, half experiencing severe spine pain on return and slipped discs being four times more likely than for the rest of the population.

“In some astronauts back pain is quite severe and lasts the whole mission. In others it’s just for a few days,” said Hargens, adding that two out of the six astronauts studied had been injured by the onboard exercise stations, showing that better workout regimes were needed.

Prof Lewis Dartnell, an astrobiologist at the University of Westminster who was not involved in the work, said the findings highlight the major biological hurdles that still need to be overcome for a manned Mars mission to be a realistic ambition. “The Moon is like a long weekend’s holiday. You’re fine to take photos of your footprints and plant some flags,” he said. “When you get to Mars there’s a serious chance you might fall off the ladder when you climb out of the spacecraft. It might be much more serious than a bit of a gripe and a joke. If you break your hip on Mars, you’re basically dead.”