Considerable research on osteoporosis has recently focused on the prevention of bone loss in the later years. Researchers and clinicians are now able to accurately measure the effects of therapies and preventive strategies on the skeleton. It has been suggested that regular physical activity will be one of the valuable strategies in maintaining bone density and preventing osteoporosis. This paper will review the quantitative techniques available for bone density assessment and provide an overview of the recent cross-sectional and longitudinal studies related to the potential benefits of physical activity on the aging skeleton.