Astronauts Suni Williams and Butch Wilmore have finally returned to Earth after an unexpected nine-month stay in space. But how has this extended mission affected their bodies?

For many, the idea of space travel is thrilling—floating weightlessly and viewing Earth from above. However, the human body is built for Earth’s gravity. Adapting to weightlessness is challenging, and returning to normal after months in space is an even longer process.

Originally scheduled for just eight days aboard the International Space Station (ISS), Williams and Wilmore ended up staying nearly 270 days due to an unexpected delay. Now, they face a demanding rehabilitation process to regain their physical strength and overall health.

The Physical Toll of Microgravity

Spending months in space changes the body significantly. At first, the experience may feel easy—there’s no need to support body weight, and moving around requires minimal effort.

“It almost feels like a vacation,” says astronaut Tim Peake, who spent time on the ISS in 2015. “Your heart doesn’t have to work as hard, and your muscles and bones get a break.”

However, this lack of resistance leads to deterioration over time. Scientists often use prolonged bed rest studies on Earth to simulate how microgravity weakens the body.

Muscle and Bone Loss in Space

Without gravity, muscles and bones deteriorate quickly. Standing, walking, and even maintaining posture require effort on Earth, but in space, those demands disappear.

“Each month in space, astronauts lose about 1% of their bone and muscle mass,” explains Prof. Damian Bailey, an expert in human physiology at the University of South Wales. “This rapid decline mimics an accelerated aging process.”

The cardiovascular system also weakens. With no gravity pulling blood downward, circulation changes, and the heart does not need to pump as forcefully. This can cause dizziness and difficulty standing once astronauts return.

To combat these effects, astronauts exercise rigorously during their missions, spending about two hours daily on treadmills, stationary bikes, and resistance machines. However, exercise can only slow down—not prevent—the decline.

Upon landing, Williams and Wilmore had to be assisted out of their capsule, highlighting the toll of their extended stay. Their rehabilitation will take months, with muscle recovery happening first. However, bone density loss may take years to fully reverse—if it ever does.

The Impact on the Body Beyond Muscles and Bones

Microgravity doesn’t just affect muscles and bones—it alters nearly every system in the body. Even gut bacteria, known as the microbiome, change in space. Fluid shifts also play a major role in the changes astronauts experience.

On Earth, gravity pulls bodily fluids downward, but in space, fluids move toward the head and chest. This shift causes facial puffiness and pressure buildup, which can impact vision. Some astronauts develop “spaceflight-associated neuro-ocular syndrome,” leading to blurry vision and, in some cases, permanent eye damage.

The vestibular system, which controls balance, is also affected. Without gravity to orient the body, astronauts feel disoriented. Returning to Earth can be overwhelming as the body relearns how to balance.

Tim Peake recalls, “That first phase of regaining balance, stopping dizziness, and walking normally takes two or three days. Those first days back on Earth can be incredibly difficult.”

The Long Road to Recovery

Astronauts spend months training to prepare for space, but their hardest challenge often comes after returning home. Their bodies must readjust to gravity, a process that takes weeks or even months.

For Williams and Wilmore, their rehabilitation program will involve physiotherapy, cardiovascular conditioning, and strength training to rebuild muscle and bone density. Doctors will monitor their vision and overall health to understand the long-term effects of their prolonged stay in space.

As space agencies plan for even longer missions—including potential trips to Mars—understanding the impact of microgravity is critical. Future astronauts will need advanced countermeasures to minimize these effects and improve recovery times.