This suggests that the concentration of RBCs should increase. However, this does not happen. Thus, the concentration of RBCs must be somehow decreasing. As the concentration of fluid decreases, the kidney reduces the production of erythroprotein which in turn surpresses RBC formation. Thus the concentration of RBCs is maintained in the blood preventing any extremities.
Human muscles adapt to new situations.
When we need our muscles, we can activate them almost immediately. When astronauts return to earth, these muscles can still cause problems. Thus, in microgravity, tension is reduced on muscles that support the body against gravity, resulting in a loss of muscle mass and an accompanying loss of muscle strength. The main problem to be faced is that exposure to microgravity causes a reduction in the endurance capacity of skeletal muscle. A reduction in bone marrow also results due to the absence of gravitational force.