Does exercise during growth prevent fractures in later life?

Regular weight-bearing exercise, especially during the pre- or early peripubertal years, leads to substantial benefits in bone mass and skeletal structure, enhancing bone strength at loaded sites. However, few fragility fractures occur in young adulthood, and only if the exercise-induced skeletal benefits are retained into older age, a time when the incidence of fragility fractures rises exponentially, would these changes be of biological significance for fracture reduction. The limited data available indicate that exercise benefits in areal bone mineral density are eroded in the long term. In contrast, several studies suggest that exercise-induced structural changes may be retained even following the cessation of exercise. These structural changes may be more important to overall bone strength than bone mass or density alone. In addition, residual benefits in nonskeletal factors, such as improved muscle strength, coordination and balance, may also reduce fracture risk. However, it is uncertain what actually happens to the fracture risk of individuals who retire from exercise and reduce their level of activity to that of the average individual. Recent retrospective observational and case-control studies suggest that there could be a reduced fracture risk in former athletes. However, since these studies are cross-sectional, no inferences could be drawn as regards causality. Selection bias at baseline would actually produce the same results. Furthermore, the biological explanation for the reduced fracture incidence is not clear although several explanations have been proposed, including: residual benefits to bone structural properties, muscle strength, coordination and balance. Each of these traits could be maintained in former athletes after their active career, and may help to reduce the number of fractures later in life. Therefore, based on the current evidence, we recommend a physically active lifestyle during growth as a possible preventive strategy against fragility fractures in old age.