As Group Captain Shubhanshu Shukla prepares to return to Earth after his mission aboard the International Space Station (ISS), attention turns to the profound effects of microgravity on the human body. Spaceflight, even for short durations, presents unique physiological and psychological challenges that require careful preparation, adaptation, and recovery.
In microgravity, the absence of Earth's gravitational pull disrupts the normal distribution of fluids in the body. On Earth, gravity helps keep fluids in the lower extremities, but in space, these fluids shift upwards, leading to facial puffiness, nasal congestion, and increased pressure in the head and eyes.
This redistribution can cause vision problems and pressure changes in the brain. The heart, no longer working against gravity, may weaken over time, and astronauts often experience a reduction in blood volume and impaired cardiac function. Upon return, this can lead to orthostatic intolerance—difficulty standing up without feeling faint.
A well-documented consequence of microgravity is the loss of bone density and muscle atrophy. Without gravity providing resistance, weight-bearing muscles and bones weaken rapidly. Astronauts can lose 1–1.5% of bone mineral density per month, especially in the hips, spine, and legs, resembling accelerated osteoporosis.
Muscle mass also decreases unless countered with daily exercise using resistance bands and specialized equipment. These effects are more pronounced during long missions, but even short stays require post-mission physiotherapy and monitoring to regain strength and balance.
The vestibular system, which governs balance and spatial orientation, is heavily reliant on gravity. In microgravity, astronauts often experience disorientation, dizziness, and motion sickness (known as space adaptation syndrome), especially during the initial days in orbit. The cerebellum must adjust to a new way of coordinating movement, making even simple tasks challenging until adaptation occurs.
On the ISS, astronauts witness up to 16 sunrises and sunsets every 24 hours due to the station's rapid orbit. This disrupts the circadian rhythm, the body’s internal clock that regulates sleep, hormone production, and metabolism. Without a consistent light-dark cycle, astronauts rely on strict schedules and artificial lighting to maintain regular sleep patterns, but sleep disturbances and fatigue are common.
Microgravity can suppress immune function and induce physiological changes that mimic accelerated aging, such as reduced bone density, muscle loss, and cardiovascular deconditioning. These effects are generally reversible, but recovery can take weeks to months, depending on mission duration and individual health.
Living in confined quarters, isolated from family and familiar surroundings, astronauts face psychological stressors such as monotony, sensory deprivation, and anxiety. Mental health support and psychological training are essential to build resilience and adaptability. Practices like yoga and meditation, integrated into India’s astronaut training, have been shown to enhance immunity, cognitive function, and emotional stability, helping astronauts cope with the high-stress environment of space.
After returning to Earth, astronauts undergo a period of quarantine and medical monitoring. Recovery protocols include physiotherapy, cardiovascular and bone health assessments, vision tests, and mental health support. Each astronaut’s recovery plan is personalised, and while some adjust quickly, others may take longer to fully regain normal function.
Microgravity profoundly impacts nearly every system in the human body—cardiovascular, musculoskeletal, vestibular, immune, and psychological. While many effects are reversible, they underscore the importance of rigorous preparation, in-flight countermeasures (like exercise and structured routines), and comprehensive post-mission rehabilitation to ensure astronauts like Group Captain Shubhanshu Shukla return healthy and ready for life back on Earth.