Training, detraining and bone : effect of exercise on bone mass and structure with special reference to maintenance of the exercise-induced bone gain

The objectives of this thesis were to investigate the effects of long-term mechanical loading on mass, size and mechanical strength of bone in male and female racquet sports players and to evaluate the maintenance of exercise-induced bone gain in these players during the following years of reduced training

Neighborhood Built Environment Measures and Association with Physical Activity and Sedentary Time in 9–14-Year-Old Children in Saskatoon, Canada

This study assessed whether perceptual and researcher-rated measures of neighborhood-built environments (BEs) predict device-based multiple activity-related outcomes, specifically: moderate-to-vigorous physical activity (MVPA), light physical activity (LPA), and sedentary time (ST), in children. Eight hundred and sixteen children aged 9–14 years from Saskatoon, Canada, were surveyed on their perceptions of BE, and their PA outcomes were objectively monitored for one week at three different time frames over a one-year period, September 2014 to August 2015. The researcher-rated BE measures were collected by trained researchers using multiple BE audit tools: neighborhood active living potential (NALP) and Irvine Minnesota inventory (IMI), 2009–2010. A multilevel modeling approach was taken to understand BE influences of children’s PA outcomes. Children’s perceived availability of parks and sidewalks predicted a higher accumulation of MVPA and a lower accumulation of ST. Children’s report of the absence of neighborhood social disorder (e.g., threats from scary dogs/people) predicted a higher LPA, while reported concern about crime predicted a lower MVPA. Researcher-rated neighborhood activity friendliness predicted a lower ST, however, researcher-rated safety from crime predicted a higher ST. Perceived BE characteristic were stronger predictors of children’s PA outcomes compared to researcher-rated BE factors

Bone strength and its determinants in pre- and early pubertal boys and girls

Higher fracture rates in women than men may be related to a sex difference in bone strength that is thought to emerge during growth. However, sexual dimorphism in bone strength and the determinants of bone strength in boys and girls are not well understood. Thus, our objectives were to (1) compare tibial bone strength and its components (geometry and density) between pre- and early pubertal boys and girls and (2) identify the contribution of muscle cross-sectional area and other modulating factors to bone outcomes. We used pQCT to assess the distal tibia (8%) and tibial midshaft (50%) in 424 Asian and Caucasian pre- and early pubertal boys and girls. Our primary outcomes were bone strength index (BSI, mg2/mm4) at the distal tibia and strength strain index (SSI, mm3) at the midshaft.We also assessed components of bone strength including bone geometry [total (ToA) and cortical (CoA) cross-sectional areas, mm2] and total (ToD, mg/cm3) and cortical (CoD, mg/cm3) density.We used ANCOVA to compare bone outcomes between boys and girls in each maturity group (PRE or EARLY pubertal by Tanner stage) and multiple regression to evaluate the contribution of muscle cross-sectional area (MCSA,mm2 by pQCT), maturity, ethnicity, physical activity, dietary calcium, and vertical jump height to bone outcomes. After adjusting for tibial length and MCSA, bone strength indices were 6–15% (P < 0.05) greater in PRE and EARLYboys compared with PRE and EARLY girls. The sex difference in bone strength was due largely to greater bone areas (4–6%) in boys. At the distal tibia ToD was significantly greater in PRE boys (6%, P < 0.001) compared with PRE girls and at the midshaft CoD was slightly greater in both PRE and EARLY girls (1%, P = 0.01). After adjusting for tibial length, MCSAwas the primary explanatory variable of tibial bone geometry and strength in both sexes accounting for 10–16% of the variance. The influence of maturity, ethnicity, physical activity, and dietary calcium on pQCT bone outcomes was small and was both site- and sex-specific. Sexual dimorphism in tibial bone strength is evident in prepuberty. Our results are consistent with a functional model of bone development in which bone adapts its geometry and strength to withstand challenges from muscle forces during growt

Accuracy and precision of internal displacement and strain measurements in long human bones using HR-pQCT and digital volume correlation

Digital volume correlation (DVC) is a technique for measuring 3D, internal displacements and strains in loaded structures. One application of DVC is the study of internal bone mechanics and the validation of subject-specific finite element (FE) models. While micro-computed tomography (µCT) is a common choice for DVC studies of small samples of bone, long human bones such as the tibia may exceed the spatial limitations of conventional µCT. High resolution peripheral quantitative CT (HR-pQCT) scanners, with their large bore and open-ended design, may be a viable option for long-bone DVC. However, HR-pQCT is afflicted by stitching artefacts, caused by the stacking of scan blocks to form the large scan volume, resulting in erroneous steps in DVC displacements and bands of increased strain error. This study proposed a modified HR-pQCT scanning protocol and stitching methodology to mitigate the effects of stitching artefacts on DVC measurements of displacement and strain. With the application of the proposed scanning/stitching methodology, displacements greater than 11.7µm (0.29 voxels) and strains greater than 1633µε could be repeatedly measured by DVC. These results show that HR-pQCT combined with DVC is suitable for measuring internal bone displacements in long human bones with sub-voxel precision and strains greater than 1633µε.</p

The Effects of Elk Velvet Antler Dietary Supplementation on Physical Growth and Bone Development in Growing Rats

Elk velvet antler (EVA) has been used in traditional Oriental medicine for centuries to promote general health; however, little evidence for its effect on bone development is available. We investigated the effects of lifelong exposure of Wistar rats to a diet containing 10% EVA on physical growth and bone development. Measurements included weekly body weights, blood chemistry and kidney and testis/ovary indices (sacrificed at 5, 9, or 16 weeks of age), and bone traits of the femur bones by peripheral quantitative computed tomography (pQCT). Mean body weights were higher in the EVA group at 4–8 weeks in males and at 5 weeks of age in females. The kidney indices were greater in EVA dietary supplemented male rats at 5 and 16 weeks of age, in females at 16 weeks of age, and testis/ovary indices at 5 weeks of age. The femoral length was increased in both males and females at 5 weeks, and several pQCT-measured parameters had increased in EVA males and females. The activity of alkaline phosphatase (ALP) increased in EVA group while the content of calcium and phosphorus did not differ among groups. Our results seem to support a role for dietary supplementation of EVA on growth and bone development in this model

Examining bone surfaces across puberty: A 20-month pQCT trial

This follow-up study assessed sex differences in cortical bone growth at the tibial midshaft across puberty. In both sexes, periosteal apposition dominated over endosteal resorption. Boys had a greater magnitude of change at both surfaces, and thus, a greater increase in bone size across puberty. Relative increase in cortical bone area was similar between sexes

Prevention of osteoporosis and bone fragility: a pediatric concern

The importance of optimal bone growth in childhood and adolescence has been recognized as one of the key strategies in osteoporotic fracture prevention. Low birth size, poor childhood growth, and low peak bone mass at the cessation of growth have been linked to the later risk of osteoporosis and hip fracture. Formerly, the focus was merely on maximizing bone mineral accrual because a high peak bone mineral mass may prevent attainment of a critical "fracture threshold" associated with age-related bone loss and osteoporosis. More recently, the focus has shifted away from bone mineral accrual-as measured by dual-energy X-ray absorptiometry (DXA)-toward the optimization of bone strength. This is partly because of the advances in bone imaging that have enabled estimation of bone strength beyond bone mass. In this review, we briefly describe long-bone growth and structural development and our abilities to assess bone properties by medical imaging tools. In addition, we summarize the evidence of factors contributing to skeletal growth, bone fragility, and the development of strong, healthy bones