NASA astronauts Suni Williams and Butch Wilmore returne to Earth after an unexpected nine-month stay aboard the International Space Station.
Credit : X-@MosheDe_
For most of us, floating through space and gazing down at Earth sounds like a dream.
But for astronauts like Suni Williams and Butch Wilmore, who recently returned from an unexpected nine-month stay aboard the International Space Station (ISS), the experience also comes with serious physical consequences.
“Space is by far the most extreme environment humans have ever faced,” says Prof Damian Bailey, a physiology expert at the University of South Wales. “We simply haven’t evolved to cope with it.”
The effects of zero gravity on the human body
Weightlessness may feel exhilarating at first – like an extended holiday, according to British astronaut Tim Peake – but the lack of gravity causes the body to quickly lose strength and resilience.
In space, there’s no need to stand upright or support your own weight, and this triggers a rapid loss of muscle mass. As Prof Bailey puts it: “It’s a simple case of use it or lose it.”
The impact of space on muscles, bones and heart health
While floating inside the ISS might look effortless, your body is quietly deteriorating. Without gravity, even your heart and blood vessels no longer have to pump against the pull of Earth, so they weaken over time. The same happens to bones, which become brittle and lose density because they are no longer under constant load.
Astronauts in space lose around 1 per cent of their muscle and bone mass every month, leading experts to liken it to ‘accelerated ageing.’ By the time they return home, astronauts often require assistance to stand and walk, as seen when Williams and Wilmore were helped out of their capsule and onto stretchers.
That’s why astronauts go into space in peak physical condition and stick to a strict exercise routine while aboard the ISS – including two hours a day of treadmill running, cycling, and weight training.
Still, as Dr Helen Sharman, the first Briton in space, explains, recovery is no quick fix. “It can take months to regain muscle mass and years for bones to rebuild – and even then, some changes to the bone structure may be permanent.”
More than just muscles: How space alters the entire body
The effects of microgravity don’t stop at muscles and bones. Spaceflight reshapes the body in surprising ways, from shifting fluids upwards – giving astronauts the classic ‘puffy face’ look – to altering their gut microbiome.
Perhaps more concerning is the pressure this causes inside the skull, leading to changes in the optic nerve and retina, and contributing to the mysterious ‘spaceflight-associated neuro-ocular syndrome.’ In some cases, astronauts experience blurred vision or long-term eye damage.
Balance is another issue. Microgravity distorts the vestibular system, the inner-ear structure responsible for spatial orientation. Without the concept of up or down, astronauts often feel disorientated both in space and once they’re back on solid ground.
“Those first two or three days back on Earth can be punishing,” Peake admits. “You feel dizzy, weak, and unsteady as your body tries to re-adapt.”
For Williams and Wilmore, the road to full recovery has just begun – but their story is a reminder that life in space is far from effortless.
