Bone is the hardest material in the body, except for the non-living enamel of the Teeth. It is made up of complex crystalline calcium (with magnesium) salts, which gives it the necessary hardness. In addition, this hard material is interspersed with strong fibrous strands in a living matrix, which gives resilience and some elasticity to the hard, but otherwise brittle calcium component. It is important to understand that bone is a living tissue and, as such, has cells (osteocytes) which maintain its functional integrity. It also has a rich blood supply and bleeds like any other tissue when injured. Living bone responds to a great extent to the stresses habitually imposed upon it, so long as raw materials (calcium, vitamins etc) are available in the diet and the individual is otherwise in good physical health. Bones are designed in the body in direct relation to their use. It is common to classify bones according to their shapes, i.e. long, short, flat or irregular, but with little reference to use.

As a lever. The bones of the upper and lower limbs pull and push, with the help of muscles. As a calcium store. 97% of the body's calcium is stored in bone. Here it is easily available and turns over fast. In pregnancy the demands of the fetus for calcium require a suitable diet and after menopause hormonal control of calcium levels may be impaired: calcium leaches out leaving brittle osteoporotic bones.

It is often said that girls should not start point work in classical ballet before about 12 years of age because their bones would be too weak and liable to bend in growth. Work leads to increase in bone strength; lack of work leads to withdrawal of calcium from the bone, with consequent loss of strength. Thus a fit dancer can subject bones to stresses and strains in the course of activity, which could lead to fractures (breaks) in an unfit individual.

Osteoporosis Osteosarcoma Osteoarthritis Adenocarcinoma