What does spending more than a year in space do to the human body?
The record for a single trip into space currently stands at 371 days, but prolonged periods in orbit alters astronaut's body's in some surprising ways, changing their muscles, brains and even their gut bacteria.
With a few handshakes, a brief photoshoot and a wave, Nasa astronaut Frank Rubio bid farewell to the American-football-field-sized collection of modules and solar panels that had been his home for 371 days. His departure from the International Space Station (ISS) and return to Earth marked the end of the longest single spaceflight by an American to date.
His time in orbit – which surpassed the previous US record of 355 consecutive days – was extended in March 2023 after the spacecraft he and his crewmates had been due to fly home in developed a coolant leak. The extra months in space allowed Rubio to clock up a total of 5,963 orbits around the Earth, travelling 157.4 million miles (253.3 million km). Even so, he was still around two months short of the record for the longest ever spaceflight by a human – Russian cosmonaut Valeri Polyakov spent 437 days onboard the Mir Space Station in the mid 1990s.
With a huge grin on his face, Rubio was carried from the Soyuz MS-23 spacecraft after it bumped safely back to Earth in a cloud of dust near the town of Zhezkazgan in the Kazakhstan Steppe. Spending so much time in the low gravity environment of the ISS had taken a toll on his body, so he had to be lifted out of the capsule by the recovery teams.
His extended trip in space, however, will have provided valuable insights into how humans can cope with long-duration spaceflight and how best to counteract the problems it can present. He is the first astronaut to participate in a study examining how exercising with limited gym equipment can affect the human body.
It is information that will prove vital as humans set their sights on sending crews on missions to explore deeper into the Solar System. A return journey to Mars, for example, is expected to take around 1,100 days (just over three years) under current plans. The spacecraft they will travel in will be far smaller than the ISS, meaning smaller lightweight exercise devices will be needed.
But problems keeping fit aside, just what does spaceflight do to the human body?
Muscles and bones
Without the constant tug of gravity on our limbs, muscle and bone mass quickly begins to diminish in space. The most affected are those muscles that help to maintain our posture in our back, neck, calves and quadriceps – in microgravity they no longer have to work nearly as hard and begin to atrophy. After just two weeks muscle mass can fall by as much as 20% and on longer missions of three-to-six months it can fall by 30%.
Similarly, because astronauts are not putting their skeletons through as much mechanical strain as they do when subject to Earth's gravity, their bones also start to demineralise and lose strength. Astronauts can lose 1-2% of their bone mass every month they spend in space and up to 10% over a six-month period (on Earth, older men and women lose bone mass at a rate of 0.5%-1% every year). This can increase their risk of suffering fractures and increase the amount of time it takes to heal. It can take up to four years for their bone mass to return to normal after returning to Earth.
To combat this, astronauts undertake 2.5 hours a day of exercise and intense training while in orbit on the ISS. This includes a series of squats, deadlifts, rows and bench presses using a resistive exercise device installed in the ISS's "gym", alongside regular bouts tethered to a treadmill and on an exercise bike. They also take diet supplements to help keep their bones as healthy as possible.
A recent study, however, highlighted that even this exercise regime was not enough to prevent losses in muscle function and size. It recommended testing whether higher loads in resistance exercises and high intensity interval training might help to counteract this muscle loss.
The lack of gravity pulling down on their bodies can also mean that astronauts find they grow a little taller during their stay on the ISS as their spines elongate slightly. This can lead to issues such as back pain while in space and slipped disks once back on Earth. During a briefing onboard the ISS ahead of his return to Earth, Rubio himself said his spine was growing and said it might help him to avoid a common neck injury that astronauts can suffer when their spacecraft hit the ground if they try to crane out of their seats to see what is happening.
"I think my spine has extended just enough that I'm kind of wedged into my seat liner, so I shouldn't move much at all," he said.
Bbc.com
