Bones: Strong and Elastic

It is important for the bones of the body to be both strong and elastic. If they are strong but brittle, there is a greater chance that some impact will cause a fracture. It is a problem with aging that the bones may become more brittle, so there are tests of the health of bones and some medications that help prevent embrittlement.

Materials can be tested to determine their elastic properties. The bulk modulus of a material may be tested by determining the amount of compression that occurs for a given applied pressure. By putting tension on a material and measuring the amount of stretch, the Young's modulus can be determined. Neither of these is simply done clinically.

Measurement of the bone mineral densities can be clinically done and can indicate the kind of embrittlement that might lead to fractures. There are also acoustical approaches to measuring the modulus of elasticity of bones. The resonant frequency of the ulna bone in the arm multiplied by the length of the ulna has been used to correlate with frequency of fractures. For a vibrating string, the resonant frequency is proportional to the inverse of the length, so resonant frequency times length would be a constant determined by the physical properties of the string.