Learn how astronauts can lose bone density and how muscles can weaken. As we continue to explore space, NASA is looking into how to prevent this as well.
Sign up for our email newsletter for the latest science news Crewed space travel isn't just an engineering feat. It's a test of the endurance and resilience of the human body. In microgravity, astronauts' bodies undergo dramatic changes: muscles weaken, bones lose density, fluids shift, and vision can be affected. Beyond that, deep space exposes them to radiation, which can damage DNA and increase long-term health risks. As space agencies and private companies plan for missions to the Moon, Mars, and beyond, understanding exactly how space travel impacts the human body is key. That's why researchers are continuously developing exercise regimens, protective technologies, and medical countermeasures informed by countless studies. But still, space remains an unforgiving frontier — one that continues to push the limits of human biology with every mission. Microgravity's Toll on the Body Gravity is a silent force shaping the human body. On Earth, it strengthens muscles, maintains bone density, and regulates fluid distribution. In microgravity, however, that balance is lost. Without the need to support body weight, muscles begin to weaken — especially in the legs, back, and core. Bones suffer, too. NASA research shows that astronauts typically lose 1 percent to 1.5 percent of their bone density per month, increasing the risk of fractures and osteoporosis. To combat these effects, astronauts on the International Space Station (ISS) follow a strict exercise routine, spending about two hours a day on resistance-based workouts using specialized equipment. Some are even prescribed bone-strengthening medications, such as bisphosphonates, to help slow deterioration. While these measures help, they don't completely prevent bone loss, making long-duration missions a challenge for human physiology. Read More: The International Space Station May be Too Clean - But These Microbes Could Help Fluid Shifts and Vision Changes Microgravity doesn't just weaken muscles and bones.…