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The NASA Human Research Program has monitored the impacts of space travel on the human body since the agency’s early days. Its research shows that the microgravity environment can permanently alter bone density, muscle mass, and vision, but many of these changes are reversible once astronauts return to Earth.

University of South Wales professor Damian Bailey explained to the BBC, “Space is the most extreme environment humans have ever faced, and our bodies simply aren’t evolved for it.” Prior to launch, astronauts undergo rigorous medical training and conditioning to ensure they’re physically ready to handle the stresses of flight and to respond swiftly to any health issues that arise. Routine assessments of blood, body weight, strength, urine, vision, and more track how their bodies adapt.

After splash‑down, the Astronaut Strength, Conditioning and Rehabilitation (ASCR) team customizes a reconditioning plan tailored to each crew member’s needs. For most, a 45‑day program is sufficient, but long‑duration missions may require extended rehabilitation, and in some cases full recovery can take years.

What does the rehabilitation program look like for astronauts?

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During missions aboard the International Space Station, astronauts avoid alcohol, bread, and carbonated drinks to protect bone health and reduce fluid shifts. Despite these restrictions, they still log two hours of daily exercise on a cycle ergometer, treadmill, and resistance training equipment to counteract the loss of gravity‑based loading.

Once back on Earth, the medical team reintroduces astronauts to gravity in a staged manner. The first phase focuses on restoring balance, gait, and lower‑limb strength. As astronaut Tim Peake noted in a BBC interview, “The initial days of regaining steadiness and the ability to walk normally can be surprisingly tough.”

The second phase ramps up cardiovascular conditioning with cycling, rowing, and elliptical training, while targeted strength work expands muscle endurance. Throughout the process, mental health support—mindfulness practices and stress‑management coaching—helps crews navigate the psychological transition from isolation in space to everyday life on Earth.