Spending time in space is a dream come true for many, offering an unparalleled view of Earth from orbit. However, while the experience of floating in microgravity and observing our planet from above may seem magical, the human body is not adapted for the harsh environment of space. In fact, time spent in space can result in significant physical changes, some of which may take years to fully recover from once back on Earth.
Two astronauts, Suni Williams and Butch Wilmore, are currently undergoing recovery after an unexpected nine-month mission aboard the International Space Station (ISS). Originally planned for only eight days, their mission was extended, and now they are facing the long road to regaining their physical health after such an extended stay in space.
The impact of extended time in microgravity on the human body is profound, particularly in relation to muscles, bones, and other bodily systems that rely on the pull of Earth’s gravity.
Muscle weakness: Use it or lose it
When on Earth, even standing still requires muscle activity to hold the body upright against gravity. However, in the microgravity environment of space, these muscles are not required to perform this function. As a result, muscle strength diminishes rapidly in space, with astronauts experiencing a noticeable loss in mass and function after only a few months.
Astronauts on the ISS are required to exercise for at least two hours each day to counteract the effects of muscle loss. This includes using a treadmill, a cycling machine, and weight training. Despite these efforts, muscle atrophy is inevitable in the absence of gravity. This phenomenon is similar to the effects of prolonged bed rest, where muscles weaken due to disuse.
The impact on bones: Accelerated ageing
The bones also undergo significant changes when in space. Under normal conditions on Earth, the body maintains a balance between breaking down old bone cells and forming new ones. However, in microgravity, the process is disrupted. Without the mechanical stress placed on bones by gravity, astronauts experience a reduction in bone mass, making bones weaker and more brittle.
Professor Damian Bailey, an expert in human physiology at the University of South Wales, explains that astronauts lose about 1% of their bone and muscle mass every month in space. This accelerated ageing process becomes evident when astronauts return to Earth. Their bones are more fragile, and they often require assistance when exiting their spacecraft. Recovery can take months, and in some cases, bone mass may take years to fully regenerate. However, even once recovered, astronauts may never fully regain the original strength and density of their bones.
Cardiovascular changes: The heart’s easy ride
One area where astronauts initially benefit from space travel is the cardiovascular system. In microgravity, the heart has less work to do because it no longer needs to pump blood against the force of gravity. As a result, astronauts often experience a reduction in heart size and strength, a phenomenon that can make the heart less efficient.
However, upon returning to Earth, the heart must quickly adapt to gravity once again, which can cause issues. Blood pressure regulation can become more challenging, and astronauts may experience dizziness or lightheadedness as the body re-adjusts to the Earth’s gravitational pull.
Fluid shifts and swelling
Another noticeable effect of microgravity is the redistribution of fluids in the body. On Earth, gravity pulls fluids downwards towards the lower half of the body. In space, however, fluids float upwards, causing the upper body, including the face, to appear swollen. This change is often one of the first things astronauts notice when they reach orbit.
The shift in fluids can also have more serious consequences. Swelling in the brain can occur, leading to changes in the eyes, including alterations to the optic nerve, retina, and even the shape of the eye itself. This can cause blurred vision and, in some cases, irreversible damage. The condition known as “spaceflight-associated neuro-ocular syndrome” can result from these changes, highlighting just one of the many risks associated with extended space travel.
Balance and coordination: A dizzying experience
The vestibular system, responsible for our sense of balance and orientation, is also affected by the absence of gravity. In space, there is no “up” or “down,” and astronauts must rely on other cues to determine their position. This can make astronauts feel disoriented and dizzy, both while in space and upon their return to Earth.
Tim Peake, who spent six months aboard the ISS, has shared his experience of regaining balance after returning to Earth. “That initial phase of stopping feeling dizzy, of regaining your balance and having strength to walk around normally, that’s just two or three days,” he says. However, even after a short period, the readjustment can be taxing, and the first few days back on Earth can feel “punishing.”
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The recovery process
After an extended mission, astronauts like Williams and Wilmore will undergo a rigorous recovery programme, focusing on rebuilding muscle strength, bone density, and cardiovascular fitness. The recovery process is challenging and can take months or even years, depending on the duration of the mission and the individual astronaut’s physical condition prior to launch.
While muscle mass may take a few months to rebuild, bone mass recovery is a more prolonged process. Some aspects of the bone’s structure may never return to normal, even after years of rehabilitation.
Conclusion
Space is a remarkable environment that offers a unique perspective of our planet, but it also has a significant impact on the human body. For astronauts, the journey to space and back is not just a physical adventure, but a challenge for the body’s adaptability. With careful preparation, exercise, and a long recovery process, astronauts can eventually regain their strength and health. But the effects of space travel on the body serve as a reminder that even the most extraordinary environments come with their own set of risks and challenges.
