Cross Sectional Studies of Exercise and Bone Density

The association between mechanical stress and bone mass was first recorded by Galileo in 1683 who noted the relationship between body weight and bone size; but it was not until 1892 that Julius Wolff, a German anatomist realised that changes in the mechanical stresses applied to a bone influenced bone strength. Immobility or prolonged bed rest rapidly leads to hypercalcuria, negative calcium balance, and bone loss. However in paralysed individuals, weightbearing without muscle activity—for example, assisted standing—does not decrease the urinary calcium losses or affect the bone mass. From these findings, it would seem the duration and force of the muscle activity on bone are important in maintaining bone mass. The aim of this paper is to review the evidence for exercise preventing and treating osteoporosis, with the protective effects against fracture also considered.