DOSE-RESPONSE RELATIONSHIP BETWEEN PHYSICAL LOADING AND MECHANICAL COMPETENCE OF BONE

A dose-response relationship between mechanical loading and bone can b e inferred by the fact that bone response is proportional to the appli ed load in cell and organ culture and in animal models where a known l oad at a given magnitude and frequency is applied, Proportional respon ses have been observed in second messengers, growth factors, bone matr ix, and bone strength, In the human model, however, the determination of a dose-response relationship is hindered by the lack of appropriate technology to directly evaluate the mechanical load and the skeletal competence, In vitro loading of bone does not duplicate the in vivo ph ysiologic conditions, in particular the neuromuscular responses to the loads applied to the skeleton, While animal studies aid in determinin g the mechanisms of bone response to mechanical loading and dietary in teractions, they do not obviate the need for human clinical trials to evaluate the effects of physical activity on both skeletal competence and fall prevention, The literature reviewed shows that physical activ ity increases the competence of the skeleton to resist fracture by the maintenance and improvement of bone mineral density (BMD) and neuromu scular competency, thus reducing skeletal fragility, predisposition to falls, and fall impact.