The Effect of Aging on Skeletal Mechanoresponsiveness: Animal Studies

Growth and remodeling of skeletal tissue in response to its mechanical environment is a well established phenomenon. Relatively little is known regarding the interaction of aging and skeletal responses to mechanical loading, although several early studies have contributed to the “conventional wisdom” that old bones are relatively unresponsive. Development of non-pharmacological therapies for treatment of skeletal pathologies requires better understanding of such interactions, especially if aimed at maintaining or restoring bone mass in the elderly. The use of intrinsic (e.g., running) and extrinsic (e.g., tibial compression) loading models provide means to study age effects in animal studies. We identified 15 studies that address age effects explicitly, although only nine of these include a truly old group (e.g., 18–24 months old for mice). Though the outcomes of the studies have not been uniform, two general themes have emerged. First, bones from old animals are mechano-responsive provided they are presented with an appropriate stimulus. Second, it is unclear if bones from old animals are less responsive than from younger animals, as there is evidence for and against this view. Therefore, we advocate a re-examination of the conventional wisdom, and offer a few guidelines for designing studies to address the questions regarding aging and bone mechano-responsiveness.