Regulation of bone mass by mechanical loading: Microarchitecture and genetics

For decades, the processes that couple bone architecture and mass to function have been investigated and characterized. It is well known, and now well accepted, that increases in exercise and loading of bone are associated with increased bone mass, and that disuse induces osteopenia. However, the mechanisms by which disuse leads to bone loss remain poorly understood, even in the 21st century. Clearly, the skeleton is able to perceive and respond to some general input(s) generated, or lost, as a consequence of mechanical unloading of bone that are distinct from habitual activity, so called functional adaptation. It is the focus of this paper to evaluate the evidence underlying roles for genetics, osteocytes, and interstitial fluid flow in mediating disuse osteopenia.Larry J. Suva, Dana Gaddy, Daniel S. Perrien, Ruth L. Thomas and David M. Findla

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Targeted exercise against osteoporosis: A systematic review and meta-analysis for optimising bone strength throughout life

Background Exercise is widely recommended to reduce osteoporosis, falls and related fragility fractures, but its effect on whole bone strength has remained inconclusive. The primary purpose of this systematic review and meta-analysis was to evaluate the effects of long-term supervised exercise (≥6 months) on estimates of lower-extremity bone strength from childhood to older age. Methods We searched four databases (PubMed, Sport Discus, Physical Education Index, and Embase) up to October 2009 and included 10 randomised controlled trials (RCTs) that assessed the effects of exercise training on whole bone strength. We analysed the results by age groups (childhood, adolescence, and young and older adulthood) and compared the changes to habitually active or sedentary controls. To calculate standardized mean differences (SMD; effect size), we used the follow-up values of bone strength measures adjusted for baseline bone values. An inverse variance-weighted random-effects model was used to pool the results across studies. Results Our quality analysis revealed that exercise regimens were heterogeneous; some trials were short in duration and small in sample size, and the weekly training doses varied considerably between trials. We found a small and significant exercise effect among pre- and early pubertal boys [SMD, effect size, 0.17 (95% CI, 0.02-0.32)], but not among pubertal girls [-0.01 (-0.18 to 0.17)], adolescent boys [0.10 (-0.75 to 0.95)], adolescent girls [0.21 (-0.53 to 0.97)], premenopausal women [0.00 (-0.43 to 0.44)] or postmenopausal women [0.00 (-0.15 to 0.15)]. Evidence based on per-protocol analyses of individual trials in children and adolescents indicated that programmes incorporating regular weight-bearing exercise can result in 1% to8% improvements in bone strength at the loaded skeletal sites. In premenopausal women with high exercise compliance, improvements ranging from 0.5% to 2.5% have been reported. Conclusions The findings from our meta-analysis of RCTs indicate that exercise can significantly enhance bone strength at loaded sites in children but not in adults. Since few RCTs were conducted to investigate exercise effects on bone strength, there is still a need for further well-designed, long-term RCTs with adequate sample sizes to quantify the effects of exercise on whole bone strength and its structural determinants throughout life.BioMed Central Open acces