The skeletal muscle system is the largest organ system of the human body. The body has fifferent responese to the weights it lifts under earth's gravity. This is a quality known as plasticity.
Your Immune System Suffers
Many parts of the cordiovascular system , including the heart, ar influeneced by gravity. On earth, for example, the veins in our legs work against gravity to get blood back to the heart.
The effects of gravitiy and pressure are needed to maintain our bones. They make the new material they need or get rid of any material that isn't needed.
The immune system suffers, which protects the body against disease, is also affected. There are a number of reasons this happens: radiation, microgravitiy. These herms can alter their immune system respones, which may increase the chance of infections amoung the crew.