What are some physical effects of space travel on the human body?

Space travel affects the body in many ways. Without gravity, muscles and bones lose strength because they aren’t used as much. Astronauts can also experience fluid shifts, where body fluids move toward the head, making faces puffy and legs thinner. Vision may change because of pressure inside the skull. The immune system can become weaker, and radiation exposure can slightly increase health risks. To fight these effects, astronauts exercise two hours a day and eat balanced meals. After returning to Earth, they go through rehabilitation to rebuild strength and adjust to gravity again.