Spending time in space and having an unrivalled view of planet Earth is an experience many of us dream of. However, the human body evolved to function in the gravity of Earth. So time in the weightlessness of space can take years to fully recover from.
Astronauts Suni Williams and Butch Wilmore are back on Earth after their eight-day mission aboard the International Space Station (ISS) unexpectedly became a nine-month enforced stay. Now, their recovery begins.
“Space is by far the most extreme environment that humans have ever encountered and we’ve just not evolved to handle the extreme conditions,” Prof Damian Bailey, who studies human physiology, at the University of South Wales, says.
Entering space changes the human body – and initially that feels awesome. “It feels like a holiday,” astronaut Tim Peake, who went to the ISS in 2015, says. “Your heart is having an easy time. Your muscles and bones are having an easy time. You’re floating around the space station in this wonderful zero-gravity environment.”
But when it comes to muscle, it is a case of use it or lose it. Even the simple act of standing still uses muscles throughout the body to hold you upright. And that is not happening in the microgravity on board the ISS. Muscle strength takes on a different meaning when everything is practically weightless.
The heart and your blood vessels also have an easier time as they no longer have to pump blood against gravity – and they start to weaken. And the bones become weaker and more brittle. There should be a balance between the cells breaking down old bone and those making new. But that balance is disrupted without the feedback and resistance of working against gravity. “Every month, about 1% of their bone and muscles are going to wither away – it’s accelerated ageing,” Prof Bailey says.
All of this is why astronauts go up to space in tip-top physical condition. Then, their daily routine involves two hours of exercise – a combination of treadmill, cycling machine and weights – to maintain as much muscle and bone health as possible. And now, Suni and Butch will start an intense exercise training programme to regain their lost function.
But that is just muscle and bone – space changes the whole body. Even the types of good bacteria living in us – the microbiome – are altered.
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