Spending time in space and witnessing the breathtaking view of Earth is an experience many dream of. However, the human body has evolved to function under Earth’s gravity, making prolonged weightlessness a significant challenge. Returning to normal after such an experience can take years.
Two astronauts recently returned to Earth after what was supposed to be an eight-day mission turned into a nine-month stay aboard the International Space Station (ISS). Now, their bodies must go through a period of recovery.
Space presents an extreme environment for humans. Entering microgravity initially feels effortless. The heart, muscles, and bones do not work as hard, and astronauts experience a sensation similar to a vacation. Floating in a zero-gravity environment may seem easy, but it has long-term consequences on the body.
Muscle deterioration is one of the first effects. Even standing on Earth requires numerous muscles to engage, but in space, this effort is unnecessary. Without resistance, muscles weaken over time. The cardiovascular system also takes a hit as the heart and blood vessels do not have to work against gravity, leading to reduced strength.
Bone loss is another major concern. Normally, bones constantly regenerate through a balance of breakdown and rebuilding. However, in space, this process is disrupted. The absence of gravity causes bones to weaken and become brittle at an accelerated rate. Astronauts lose about 1% of their bone and muscle mass each month, leading to what is often described as accelerated aging.
The effects become evident upon return to Earth. Astronauts frequently require assistance exiting the capsule, as their bodies have lost strength. To counteract these effects, astronauts undergo rigorous physical training before, during, and after their missions. While in space, they engage in two hours of daily exercise, including treadmill running, cycling, and weight training. This routine helps mitigate muscle and bone loss but does not entirely prevent it.
Recovery after returning to Earth is a slow process. Muscle mass can take months to rebuild, while bone density recovery can take years. Even after regaining strength, the structure of the rebuilt bone may differ from its original form, and some changes may never fully reverse.
Beyond muscles and bones, space also affects the body’s microbiome, the collection of beneficial bacteria living inside humans. Additionally, bodily fluids shift without gravity, causing fluid to accumulate in the chest and face. This results in puffiness and, more concerningly, pressure changes that can affect the brain and eyes. Vision issues can arise, with changes occurring in the optic nerve, retina, and overall eye shape. In some cases, these alterations can lead to permanent vision impairment.
Microgravity also disrupts the vestibular system, responsible for balance and spatial awareness. In space, without a clear sense of up or down, astronauts may feel disoriented. This disorientation continues upon returning to Earth, where reacclimating to gravity can be difficult. Many experience dizziness and balance issues for several days.
Recovery is a complex process requiring intense rehabilitation. The first few days back on Earth can be particularly challenging, as astronauts struggle to regain their equilibrium and basic mobility. Over time, with training and support, they gradually return to normal function. However, certain physiological changes from prolonged space travel may remain indefinitely, highlighting the profound impact space has on the human body.
