A one-year exercise intervention program in pre-pubertal girls does not influence hip structure

<p>Abstract</p> <p>Background</p> <p>We have previously reported that a one-year school-based exercise intervention program influences the accrual of bone mineral in pre-pubertal girls. This report aims to evaluate if also hip structure is affected, as geometry independent of bone mineral influences fracture risk.</p> <p>Methods</p> <p>Fifty-three girls aged 7 – 9 years were included in a curriculum-based exercise intervention program comprising 40 minutes of general physical activity per school day (200 minutes/week). Fifty healthy age-matched girls who participated in the general Swedish physical education curriculum (60 minutes/week) served as controls. The hip was scanned by dual X-ray absorptiometry (DXA) and the hip structural analysis (HSA) software was applied to evaluate bone mineral content (BMC), areal bone mineral density (aBMD), periosteal and endosteal diameter, cortical thickness, cross-sectional moment of inertia (CSMI), section modulus (Z) and cross-sectional area (CSA) of the femoral neck (FN). Annual changes were compared. Group comparisons were done by independent student's <it>t</it>-test between means and analyses of covariance (ANCOVA). Pearson's correlation test was used to evaluate associations between activity level and annual changes in FN. All children remained at Tanner stage 1 throughout the study.</p> <p>Results</p> <p>No between-group differences were found during the 12 months study period for changes in the FN variables. The total duration of exercise during the year was not correlated with the changes in the FN traits.</p> <p>Conclusion</p> <p>Evaluated by the DXA technique and the HSA software, a general one-year school-based exercise program for 7–9-year-old pre-pubertal girls seems not to influence the structure of the hip.</p

The influence of muscular action on bone strength via exercise

Mechanical stimuli influence bone strength, with internal muscular forces thought to be the greatest stressors of bone. Consequently, the effects of exercise in improving and maintaining bone strength have been explored in a number of interventional studies. These studies demonstrate a positive effect of high-impact activities (i.e. where large muscle forces are produced) on bone strength, with benefits being most pronounced in interventions in early pubertal children. However, current studies have not investigated the forces acting on bones and subsequent deformation, preventing the development of optimised and targeted exercise interventions. Similarly, the effects of number and frequency of exercise repetitions and training sessions on bone accrual are unexplored. There are conflicting results as to gender effects on bone response to exercise, and the effects of age and starting age on the osteogenic effects of exercise are not well known. It also appears that exercise interventions are most effective in physically inactive people or counteracting conditions of disuse such as bed rest. Bone strength is only one component of fracture risk, and it may be that exercise resulting in improvements in, e.g., muscle force/power and/or balance is more effective than those whose effects are solely osteogenic. In summary, exercise is likely to be an effective tool in maintaining bone strength but current interventions are far from optimal. © Springer Science+Business Media 2013

Analysing cortical bone cross-sectional geometry by peripheral QCT: Comparison with bone histomorphometry

A distinct advantage of peripheral quantitative computed tomography (pQCT) is its ability to assess bone strength by measuring cross-sectional geometry and density of cortical bone. For accurate determination of cortical bone cross-sectional area (CoA), it is important to select the appropriate analysis mode and thresholds. No study has assessed which analysis protocol best represents tibial bone geometry—as determined by histomorphometry. We measured bone geometry from 16 human cadaver tibiae (mean age 74 [SD 6] yr) with pQCT (XCT 2000) at the 25% site, measured proximally from the distal tibia plafond. We conducted histomorphometry at the same site as the criterion standard. Scans were analyzed using modes and thresholds recommended by the manufacturer (Norland Stratec Medizintechnic GmbH, Pforzheim, Germany). We also investigated agreement of two additional thresholds (calculated by half-maximum height and inflection point methods) to define the endosteal border of cortical bone. Compared to the criterion, the smallest error (−1.0%, p = 0.002) in total cross-sectional area (ToA) was obtained using Contour mode 3 with an outer threshold of 169 mg/cm3. The smallest error (0.1%, NS) in CoA was obtained with Separation mode 4 (outer threshold 200 mg/cm3, inner threshold 670 mg/cm3). CoA was overestimated by 5–7% (p < 0.001) from the criterion when an inner threshold of 480 mg/cm3 was used in combination with any of the recommended outer thresholds. pQCT measurements of bone geometry in vitro vary to some extent between modes and thresholds selected. The effect of variation in bone geometry measurements on the predictive ability of bone strength indices derived from CoA needs to be assessed