Bone M and Gravity?

bone density will fall. osteoblasts and osteoclasts (bone-forming and bone degrading cell, respectively) respond to piezoelectric signals generated when the bone is stressed in different directions. that's why constant stresses on bones can cause them to grow in a different manner. without gravity, your muscles -- while able to move your bones -- are provided no resistance by gravity and no stresses are made on the bones. its the same kinda problem with bed-ridden people who don't move around much (in addition to muscle atrophy).