The skeleton in a long-term perspective--are exercise induced benefits eroded by time?

About 30-50% of women, and 15-30% of men will suffer a fracture related to osteoporosis in their lifetime 1. Prevention of fractures is important because fractures are associated with increased morbidity, mortality and impose a financial burden on the community 2,3. During the last few years, several studies have shown that drugs reduce the fracture risk by about 50% in women with osteoporosis, a bone mineral density (BMD) 2.5 standard deviations (SD) below the young normal mean, the definition of osteoporosis advocated by the World Health Organisation 4,5. This risk reduction is only confined to the most vulnerable high risk group, whereas most fractures are derived from the much larger population of individuals at more modest risk, individuals with osteopenia (BMD between-1 to-2.5 SD below the young normal mean) 5. These subjects should not be given drugs because drug trials have not shown a fracture reduction in this group. Lifelong treatment of all women and men from the age of 50 years, irrespective of their BMD, can not be recommended because this approach is not evidence based, it is not feasible, or cost effective 6. Thus, the public health burden of fractures cannot be solved with drugs. Instead, community-based interventions are needed that are safe, widely accessible, inexpensive to implement and that do reduce the number of individuals with fractures. Exercise has the first three features and so could be an attractive approach to reducing the burden of fractures. But, what evidence exists that exercise does reduce the number of fractures? Most individuals who are subjected to exercise during adolescence reduce their exercise level in the middle aged period, the period in life when work and family increase the demands of the individual. If exercise has a preventive effect of fragility fractures, exercise induced skeletal benefits must not be eroded by time. The purpose of this review is to critically examine the evidence that exercise induced benefits of the skeleton are retained into old age and if there exists an association with exercise during growth and young years and reduced risk to sustain fragility fractures. In the following sections, all presented differences are significant unless otherwise stated but for brevity these are presented without confidence intervals or p-values. Exercise seems to increase bone mass, with the most obvious benefits to the skeleton reached during growth 7-12. Also, bone size and skeletal architecture, both independently providing bone strength, may be affected …