: Sex differences in bone strength and fracture risk are well documented. However, we know little about bone strength accrual during growth and adaptations in bone microstructure, density, and geometry that accompany gains in bone strength. Thus, our objectives were to (1) describe growth related adaptations in bone microarchitecture, geometry, density, and strength at the distal tibia and radius in boys and girls; and (2) compare differences in adaptations in bone microarchitecture, geometry, density, and strength between boys and girls. We used HR-pQCT at the distal tibia (8% site) and radius (7% site) in 184 boys and 209 girls (9 to 20 years old at baseline). We aligned boys and girls on a common maturational landmark (age at peak height velocity [APHV]) and fit a mixed effects model to these longitudinal data. Importantly, boys showed 28% to 63% greater estimated bone strength across 12 years of longitudinal growth. Boys showed 28% to 80% more porous cortices compared with girls at both sites across all biological ages, except at the radius at 9 years post-APHV. However, cortical density was similar between boys and girls at all ages at both sites, except at 9 years post-APHV at the tibia when girls’ values were 2% greater than boys’. Boys showed 13% to 48% greater cortical and total bone area across growth. Load-to-strength ratio was 26% to 27% lower in boys at all ages, indicating lower risk of distal forearm fracture compared with girls. Contrary to previous HR-pQCT studies that did not align boys and girls at the same biological age, we did not observe sex differences in Ct.BMD. Boys’ superior bone size and strength compared with girls may confer them a protective advantage. However, boys’ consistently more porous cortices may contribute to their higher fracture incidence during adolescence. Large prospective studies using HR-pQCT that target boys and girls who have sustained a fracture are needed to verify this. © 2016 American Society for Bone and Mineral Research.

Summary: Objective: Investigate associations of TV viewing time and accelerometry‐derived sedentary time with inflammatory and endothelial function biomarkers in children.Methods: Cross‐sectional analysis of 164 7–10‐year‐old children. TV viewing time was assessed by parental proxy report and total and patterns of sedentary time accumulation (e.g. prolonged bouts) were assessed by accelerometry. C‐reactive protein (CRP), homeostasis model assessment of insulin resistance, interleukin‐2, ‐6, ‐8, ‐10, tumour necrosis factor alpha, adiponectin, resistin, brain‐derived neurotrophic factor, soluble intercellular and vascular adhesion molecule 1, plasminogen activator inhibitor 1 and soluble E‐selectin were assessed. Generalised linear models assessed the associations of TV viewing and sedentary time with biomarkers, adjusting for sex, waist circumference, moderate‐ to vigorous‐intensity physical activity and diet density.Results: Each additional h week⁻¹ of TV viewing was associated with 4.4% (95% CI: 2.1, 6.7) greater CRP and 0.6% (0.2, 1.0) greater sVCAM‐1 in the fully adjusted model. The association between frequency and duration of 5–10 min bouts of sedentary time and CRP was positive after adjustment for sex and waist circumference but attenuated after adjustment for diet density.Conclusions: This study suggests that TV viewing was unfavourably associated with several markers of inflammation and endothelial dysfunction. The detrimental association between 5 and 10 min bouts of sedentary time and CRP approached significance, suggesting that further research with a stronger study design (longitudinal and/or experimental) is needed to better understand how the accumulation of sedentary time early in life may influence short and longer term health.

Objectives Bone loss remains a primary health concern for astronauts, despite in-flight exercise. We examined changes in bone microarchitecture, density and strength before and after long-duration spaceflight in relation to biochemical markers of bone turnover and exercise. Methods Seventeen astronauts had their distal tibiae and radii imaged before and after space missions to the International Space Station using high-resolution peripheral quantitative CT. We estimated bone strength using finite element analysis and acquired blood and urine biochemical markers of bone turnover before, during and after spaceflight. Pre-flight exercise history and in-flight exercise logs were obtained. Mixed effects models examined changes in bone and biochemical variables and their relationship with mission duration and exercise. Results At the distal tibia, median cumulative losses after spaceflight were −2.9% to −4.3% for bone strength and total volumetric bone mineral density (vBMD) and −0.8% to −2.6% for trabecular vBMD, bone volume fraction, thickness and cortical vBMD. Mission duration (range 3.5–7 months) significantly predicted bone loss and crewmembers with higher concentrations of biomarkers of bone turnover before spaceflight experienced greater losses in tibia bone strength and density. Lower body resistance training volume (repetitions per week) increased 3–6 times in-flight compared with pre-spaceflight. Increases in training volume predicted preservation of tibia bone strength and trabecular vBMD and thickness. Conclusions Findings highlight the fundamental relationship between mission duration and bone loss. Pre-flight markers of bone turnover and exercise history may identify crewmembers at greatest risk of bone loss due to unloading and may focus preventative measures.

Early childhood is a critical period for the development of active living behaviours; however, very little is known about the physical activity levels of preschoolers from Canada. The objectives of this study were to (i) examine physical activity in a sample of Ontario preschoolers by using high-frequency accelerometry to determine activity and step counts; (ii) assess the relationship between step counts and physical activity; (iii) examine the influence of epoch length or sampling interval on physical activity; and (iv) compare measured physical activity to existing recommendations. Thirty 3- to 5-year-old children wore accelerometers to monitor habitual physical activity in 3-s epochs over a 7-day period. Preschoolers engaged in an average of 220 min of daily physical activity, 75 min of which were spent in moderate-to-vigorous physical activity (MVPA), and they accumulated 7529 ± 1539 steps·day(-1). Preschoolers who engaged in more MVPA also took more steps on a daily basis (r = 0.81, p < 0.001). Compared with a 3-s epoch, sampling intervals of 15, 30, and 60 s resulted in an average of 2.9, 9.0, and 16.7 missed minutes of MVPA per day, respectively. All 30 preschoolers met the National Association for Sport and Physical Education recommendation of at least 120 min of total physical activity per day for preschool-age children. Our data highlight important methodological considerations when measuring physical activity in preschoolers and the need for preschool-specific physical activity guidelines for Canadian children.