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Astronauts Suni Williams and Butch Wilmore recently returned to Earth after spending nine months aboard the International Space Station, far longer than their planned eight-day mission. Their experience gives researchers a deeper look at how space affects the human body.
"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.
Microgravity in space causes muscle and bone loss at a rapid pace. Even standing still on Earth uses muscles, but in space, that effort disappears. Without resistance from gravity, astronauts lose about 1% of bone and muscle mass each month. Despite strict two-hour daily exercise routines using treadmills, cycling machines, and weights, muscle strength drops. Recovery on Earth takes months for muscles and years for bones—and rebuilt bone may never fully return to normal.
Fluid in the body also shifts upwards, affecting vision and brain pressure. Some astronauts develop “spaceflight-associated neuro-ocular syndrome,” which can blur vision and cause lasting eye damage. Balance also suffers, as the body’s sense of direction becomes confused in weightlessness. Returning astronauts often feel dizzy and weak and need support just to walk.
Even the microbiome—the community of good bacteria inside the body—undergoes changes. These physical shifts explain why only the fittest are chosen for space missions, and why recovery is long and intense. This story, covered by BBC Inside Science, shows how space continues to test the limits of the human body.
