Osteobiology, strain, and microgravity. Part II: studies at the tissue level.

Loading microgravity, and/or defective mechanical strain-forces have important effects on bone cells and bone quality and quantity. The complex mechanisms induced by strain and microgravity on bone cells have been reviewed in Part I of this paper. In Part II, we have considered the data on the alterations induced by unloading and microgravity on the skeleton and the mechanisms that are involved at the tissue level in animals and humans.