Now that astronaut Sunita Williams is back on terra firma and is going through a process of physical rehabilitation, space travel — which now includes orbital flights with private civilians — presents an extraordinary challenge to the human body. While floating in microgravity may seem effortless, the absence of gravitational forces affects nearly every physiological system. That’s why the body takes time to restore its normal functions after adapting to weightlessness. How to counter muscle atrophy and bone loss On Earth, muscles constantly work against gravity, whether we are standing, walking, or simply maintaining posture. In space, the lack of gravitational resistance leads to muscle atrophy, particularly in the legs, back, and core. That’s why astronauts need endurance and motor control upon return. In space, bone density decreases at a rate of 1-2% per month, making astronauts vulnerable to fractures upon their return. Story continues below this ad Progressive weight-bearing exercises: Treadmill walking, running, and resistance training are key to rebuilding muscle mass and strength. Calcium and vitamin D supplementation: These are essential for bone …