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. 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. 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. 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.

Loading modality is a strong external determinant of structure and concomitant strength of the femoral neck. Particularly effective seem to be loadings, which arise from high impacts or impacts from atypical loading directions. Introduction: Physical loading plays an important role, not only in the process of bone modeling and remodeling, but also in shaping a mechanically appropriate bone structure. This study aimed at testing the hypothesis that the type of loading partly determines the femoral neck structure. Materials and Methods: A total of 255 premenopausal female athletes representing volleyball, hurdling, squash-playing, soccer, speed skating, step aerobics, weight-lifting, orienteering, cross-country skiing, cycling, and swimming and their 30 nonathletic counterparts were measured with DXA. Besides the conventional areal BMD (aBMD) of the femoral neck, the hip structure analysis (HSA) was used to estimate the cross-sectional area (CSA), subperiosteal width (W), and section modulus (Z, an index of bone strength) at the narrowest section of the femoral neck. Also, training history, muscle strength, and calcium intake were assessed. The above-mentioned sports were classified according to the type of loading they apparently produce at the hip region; that is, high-impact loading (volleyball, hurdling), odd-impact loading (squash-playing, soccer, speed-skating, step aerobics), high-magnitude loading (weightlifting), low-impact loading (orienteering, cross-country skiing), and nonimpact loading (swimming, cycling). Results: High-impact and odd-impact loading sports were associated with the highest age-, weight-, and height-adjusted aBMD (23% and 29% higher values compared to nonathletic referents), CSA (22% and 27%), and Z (22% and 26%). In contrast, repetitive, nonimpact loading sports were not associated with any clear benefit in any bone value compared with the referents. The W at the narrowest femoral neck section was similar in all groups. Body height and weight accounted virtually for one-half of the variation in Z, whereas the type of loading predicted 13% of the total variation of this variable—clearly more than the 2% attributable to isometric leg extension strength. Both high-impact and odd-impact loading modalities were associated with a large benefit in Z, corresponding to >1 SD in the reference group, whereas repetitive, low-impact loading showed a benefit that was only one-half of that. Surprisingly, high-magnitude loading (weightlifting) was not associated with a statistically significant increase in Z. Conclusion: We conclude that mechanical loading and its modality are strong external determinants of structure and concomitant strength of the femoral neck. Particularly effective seem to be loadings, which arise from high impacts or impacts from atypical loading directions.