Gender-specific effects of physical activity on children's academic performance: The Active Smarter Kids cluster randomized controlled trial.

Active learning combines academic content with physical activity (PA) to increase child PA and academic performance, but the impact of active learning is mixed. It may be that this is a moderated relationship in which active learning is beneficial for only some children. This paper examine the impact of baseline academic performance and gender as moderators for the effects of active learning on children's academic performance. In the ASK-study, 1129 fifth-graders from 57 Norwegian elementary schools were randomized by school to intervention or control in a physical activity intervention between November 2014 and June 2015. Academic performance in numeracy, reading, and English was measured and a composite score was calculated. Children were split into low, middle and high academic performing tertiles. 3-way-interactions for group (intervention, control)∗gender (boys, girls)∗academic performance (tertiles) were investigated using mixed model regression. There was a significant, 3-way-interaction (p=0.044). Both boys (ES=0.11) and girls (ES=0.18) in the low performing tertile had a similar beneficial trend. In contrast, middle (ES=0.03) and high performing boys (ES=0.09) responded with small beneficial trends, while middle (ES=-0.11) and high performing girls (ES=-0.06) responded with negative trends. ASK was associated with a significant increase in academic performance for low performing children. It is likely that active learning benefited children most in need of adapted education but it may have a null or negative effect for those girls who are already performing well in the sedentary classroom. Differences in gendered responses are discussed as a possible explanation for these results. TRIAL REGISTRATION: Clinicaltrials.gov registry, trial registration number: NCT02132494.

Reference data for jumping mechanography in Canadian children, adolescents and young adults.

OBJECTIVES: To provide age- and sex-specific reference data for mechanography-derived parameters of muscle function in Canadian children and youth using the single two-legged jump (S2LJ) with hands-on-waist. METHODS: Our sample included 2017 observations from 715 participants (9-21 years; 338 girls). Participants performed three S2LJ with hands-on-waist on a force platform (Leonardo Mechanograph, Novotec). Outcomes were maximum peak power (Pmax), Pmax/mass, peak force/body weight (Fmax/BW), force efficiency, maximum jump height (Hmax), and velocity (Vmax). We used the LMS method to construct age- and sex-specific percentile curves and mixed effects models to examine sex and ethnic differences. RESULTS: With the exception of Efficiency, mechanography outcomes were greater in girls (4-40%, p<0.05) than boys at age 9. Boys' advantage in mechanography parameters emerged in adolescence (age 11-13 years; 3-65%, p<0.05) and persisted into young adulthood, except for Fmax/BW which was not greater in boys until age 17 (4-10%, p<0.05). Mechanography outcomes were 3-9% (p<0.05) greater in Asian compared with white participants. CONCLUSIONS: We provide the first reference data for the S2LJ using the hands-on-waist protocol in children, youth and young adults. These data support previous findings using freely moving arms and can be used when evaluating muscle function in pediatric studies.

Deficits in distal radius bone strength, density and microstructure are associated with forearm fractures in girls: an HR-pQCT study.

UNLABELLED: Forearm fractures are common during growth. We studied bone strength in youth with a recent forearm fracture. In girls, suboptimal bone strength was associated with fractures. In boys, poor balance and physical inactivity may lead to fractures. Prospective studies will confirm these relationships and identify targets for prevention strategies. INTRODUCTION: The etiology of pediatric forearm fractures is unclear. Thus, we examined distal radius bone strength, microstructure, and density in children and adolescents with a recent low- or moderate-energy forearm fracture and those without forearm fractures. METHODS: We assessed the non-dominant (controls) and non-fractured (cases) distal radius (7% site) using high-resolution peripheral quantitative computed tomography (HR-pQCT) (Scanco Medical AG) in 270 participants (girls: cases n = 47, controls n = 61 and boys: cases n = 88, controls n = 74) aged 8-16 years. We assessed standard anthropometry, maturity, body composition (dual energy X-ray absorptiometry (DXA), Hologic QDR 4500 W) physical activity, and balance. We fit sex-specific logistic regression models for each bone outcome adjusting for maturity, ethnicity, height, and percent body fat. RESULTS: In girls, impaired bone strength (failure load, ultimate stress) and a high load-to-strength ratio were associated with low-energy fractures (odds ratios (OR) 2.8-4.3). Low total bone mineral density (Tt.BMD), bone volume ratio, trabecular thickness, and cortical BMD and thickness were also associated with low-energy fractures (ORs 2.0-7.0). In boys, low Tt.BMD, but not bone strength, was associated with low-energy fractures (OR = 1.8). Boys with low-energy fractures had poor balance and higher percent body fat compared with controls (p < 0.05). Boys with fractures (both types) were less active than controls (p < 0.05). CONCLUSIONS: Forearm fracture etiology appears to be sex-specific. In girls, deficits in bone strength are associated with fractures. In boys, a combination of poor balance, excess body fat, and low physical activity may lead to fractures. Prospective studies are needed to confirm these relationships and clarify targets for prevention strategies.

Does frequency of resistance training affect tibial cortical bone density in older women? A randomized controlled trial.

SUMMARY: This randomized controlled trial evaluated the effect of resistance training frequency (0, 1, and 2 times/week) on cortical volumetric bone mineral density (vBMD) at the tibia in older women. There was no mean difference in change in tibial cortical vBMD in older women who engaged in resistance training (RT) one or two times/week compared with the control group over 12 months after adjusting for baseline values. INTRODUCTION: National guidelines recommend RT two to three times/week to optimize bone health. Our objective was to determine the effect of a 12-month intervention of three different RT frequencies on tibial volumetric cortical density (CovBMD) in healthy older women. METHODS: We randomized participants to the following groups: (1) 2×/week balance and tone group (i.e., no resistance beyond body weight, BT), (2) 1×/week RT (RT1), and (3) 2×/week RT (RT2). Treatment allocation was concealed, and measurement team and the bone data analyst were blinded to group allocation. We used peripheral quantitative computed tomography to acquire one 2.3-mm scan at the 50 % tibia, and the primary outcome was CovBMD. Data were collected at baseline, 6 and 12 months, and we used linear mixed modeling to assess the effect at 12 months. RESULTS: We assessed 147 participants; 100 women provided data at all three points. Baseline unadjusted mean (SD) tibial CovBMD (in milligrams per cubic centimeter) at the 50 % site was 1,077.4 (43.0) (BT), 1,087.8 (42.0) (RT1), and 1,058.7 (60.4) (RT2). At 12 months, there were no statistically significant differences (-0.45 to -0.17 %) between BT and RT groups for mean difference in change in tibial CovBMD for exercise interventions (BT, RT1, RT2) after adjusting for baseline tibial CovBMD. CONCLUSION: We note no mean difference in change in tibial CovBMD in older women who engaged in RT one or two times/week compared with the control group over 12 months. It is unknown if RT of 3× or 4×/week would be enough to promote a statistically significant difference in change of bone density.

The challenge of low physical activity during the school day: at recess, lunch and in physical education.

PURPOSE: To describe physical activity (PA) intensity across a school day and assess the percentage of girls and boys achieving recommended guidelines. METHODS: The authors measured PA via accelerometry in 380 children (8-11 years) and examined data representing (1) the whole school day, (2) regular class time, (3) recess, (4) lunch and (5) scheduled physical education (PE). Activity was categorised as sedentary (SED), light physical activity (LPA) or moderate to vigorous physical activity (MVPA) using age-specific thresholds. They examined sex differences across PA intensities during each time period and compliance with recommended guidelines. RESULTS: Girls accumulated less MVPA and more SED than boys throughout the school day (MVPA -10.6 min; SED +13.9 min) recess (MVPA -1.6 min; SED +1.7 min) and lunch (MVPA -3.1 min; SED +2.9 min). Girls accumulated less MVPA (-6.2 min), less LPA (-2.5 min) and more SED (+9.4 min) than boys during regular class time. Fewer girls than boys achieved PA guidelines during school (90.9% vs 96.2%), recess (15.7% vs 34.1%) and lunch (16.7% vs 37.4%). During PE, only 1.8% of girls and 2.9% of boys achieved the PA guidelines. Girls and boys accumulated similar amounts of MVPA, LPA and SED. CONCLUSION: The MVPA deficit in girls was due to their sedentary behaviour as opposed to LPA. Physical activity strategies that target girls are essential to overcome this deficit. Only a very small percentage of children met physical activity guidelines during PE. There is a great need for additional training and emphasis on PA during PE. In addition schools should complement PE with PA models that increase PA opportunities across the school day.

Anterior-posterior bending strength at the tibial shaft increases with physical activity in boys: evidence for non-uniform geometric adaptation.

UNLABELLED: We investigated bone structural adaptations to a 16-month school-based physical activity intervention in 202 young boys using a novel analytical method for peripheral quantitative computed tomography scans of the tibial mid-shaft. Our intervention effectively increased bone bending strength in the anterior-posterior plane as estimated with the maximum second moment of area (I(max)). INTRODUCTION: We previously reported positive effects of a physical activity intervention on peripheral quantitative computed tomography (pQCT)-derived bone strength at the tibial mid-shaft in young boys. The present study further explored structural adaptations to the intervention using a novel method for pQCT analysis. METHODS: Participants were 202 boys (aged 9-11 years) from 10 schools randomly assigned to control (CON, 63 boys) and intervention (INT, 139 boys) groups. INT boys participated in 60 min/week of classroom physical activity, including a bone-loading program. We used ImageJ to process pQCT images of the tibial mid-shaft and determine the second moments of area (I(max), I(min)) and cortical area (CoA) and thickness (CTh) by quadrant (anterior, medial, lateral, posterior). We defined quadrants according to pixel coordinates about the centroid. We used mixed linear models to compare change in bone outcomes between groups. RESULTS: The INT boys had a 3% greater gain in I(max) than the CON boys (p = 0.04) and tended to have a greater gain in I(min) ( approximately 2%, NS). Associated with the greater gain in I(max) was a slightly greater (NS) gain (1-1.4%) in CoA and CTh in the anterior, medial, and posterior (but not lateral) quadrants. CONCLUSION: Our results suggest regional variation in bone adaptation consistent with patterns of bone formation induced by anterior-posterior bending loads.

Cortical and trabecular bone in the femoral neck both contribute to proximal femur failure load prediction.

UNLABELLED: We examined the contributions of femoral neck cortical and trabecular bone to proximal femur failure load. We found that trabecular bone mineral density explained a significant proportion of variance in failure load after accounting for total bone size and cortical bone mineral content or cortical area. INTRODUCTION: The relative contribution of femoral neck trabecular and cortical bone to proximal femur failure load is unclear. OBJECTIVES: Our primary objective was to determine whether trabecular bone mineral density (TbBMD) contributes to proximal femur failure load after accounting for total bone size and cortical bone content. Our secondary objective was to describe regional differences in the relationship among cortical bone, trabecular bone, and failure load within a cross-section of the femoral neck. MATERIALS AND METHODS: We imaged 36 human cadaveric proximal femora using quantitative computed tomography (QCT). We report total bone area (ToA), cortical area (CoA), cortical bone mineral content (CoBMC), and TbBMD measured in the femoral neck cross-section and eight 45 degrees regions. The femora were loaded to failure. RESULTS AND OBSERVATIONS: Trabecular bone mineral density explained a significant proportion of variance in failure load after accounting for ToA and then either CoBMC or CoA respectively. CoBMC contributed significantly to failure load in all regions of the femoral neck except the posterior region. TbBMD contributed significantly to failure load in all regions of the femoral neck except the inferoanterior, superoposterior, and the posterior regions. CONCLUSION: Both cortical and trabecular bone make significant contributions to failure load in ex vivo measures of bone strength.

Prevention in the first place: schools a setting for action on physical inactivity.

Promoting physical activity has become a priority because of its role in preventing childhood obesity and chronic disease. Ecological approaches that recognise the interaction between individuals and the settings in which they spend their time are currently at the forefront of public health action. Schools have been identified as a key setting for health promotion. An overview of the literature addressed the promotion of physical activity in schools and showed that school-based strategies (elementary or high school) that utilised classroom-based education only did not increase physical activity levels; one notable exception was screen time interventions. Although evidence is sparse, active school models and environmental strategies (interventions that change policy and practice) appear to promote physical activity in elementary schools effectively. There is also strong evidence to support multicomponent models in high schools, particularly models that incorporate a family and community component. An emerging trend is to involve youth in the development and implementation of interventions. In the context of childhood obesity and sedentary lifestyles, modest increases in physical activity levels in school-based trials are important. School initiatives must be supported and reinforced in other community settings. Health professionals play a key role as champions in the community, based on their influence and credibility. Health professionals can lend support to school-based efforts by asking about and emphasising the importance of physical activity with patients, encouraging family-based activities, supporting local schools to adopt an "active school" approach and advocating for support to sustain evidence-based and promising physical activity models within schools.

Does a novel school-based physical activity model benefit femoral neck bone strength in pre- and early pubertal children?

UNLABELLED: The effects of physical activity on bone strength acquisition during growth are not well understood. In our cluster randomized trial, we found that participation in a novel school-based physical activity program enhanced bone strength acquisition and bone mass accrual by 2-5% at the femoral neck in girls; however, these benefits depended on teacher compliance with intervention delivery. Our intervention also enhanced bone mass accrual by 2-4% at the lumbar spine and total body in boys. INTRODUCTION: We investigated the effects of a novel school-based physical activity program on femoral neck (FN) bone strength and mass in children aged 9-11 yrs. METHODS: We used hip structure analysis to compare 16-month changes in FN bone strength, geometry and bone mineral content (BMC) between 293 children who participated in Action Schools! BC (AS! BC) and 117 controls. We assessed proximal femur (PF), lumbar spine (LS) and total body (TB) BMC using DXA. We compared change in bone outcomes between groups using linear regression accounting for the random school effect and select covariates. RESULTS: Change in FN strength (section modulus, Z), cross-sectional area (CSA), subperiosteal width and BMC was similar between control and intervention boys, but intervention boys had greater gains in BMC at the LS (+2.7%, p = 0.05) and TB (+1.7%, p = 0.03) than controls. For girls, change in FN-Z tended to be greater (+3.5%, p = 0.1) for intervention girls than controls. The difference in change increased to 5.4% (p = 0.05) in a per-protocol analysis that included girls whose teachers reported 80% compliance. CONCLUSION: AS! BC benefits bone strength and mass in school-aged children; however, our findings highlight the importance of accounting for teacher compliance in classroom-based physical activity interventions.

Muscle power is related to tibial bone strength in older women.

UNLABELLED: We enrolled 65 to 75 year-old community-dwelling women and measured muscle power, strength, physical activity using accelerometry and tibial bone strength using peripheral quantitative computed tomography (pQCT). Muscle power contributed 6.6% of the variance in the bone strength-strain index and 8.9% in the section modulus after accounting for age, height, weight, and physical activity; moderate to vigorous physical activity was related to muscle power in the lower extremity. INTRODUCTION: Muscle power is associated with DXA measurements of bone mass, but it is not known whether muscle power is associated with bone strength. There are no reports of investigations that have tested the effect of muscle power on bone compartments using advanced imaging. METHODS: We enrolled 74 community-dwelling women aged 65-75 years. We measured muscle power and strength of leg extension using Keiser air-pressure resistance equipment. All participants wore a waist-mounted Actigraph accelerometer to record physical activity. We used peripheral quantitative computed tomography (pQCT) to measure tibial mid-shaft (50% of the site) bone strength (strength-strain index, section modulus). We used Pearson correlations and multi-level linear regression to investigate the associations between muscle and bone. RESULTS: Muscle power contributed 6.6% (p = 0.007) of the variance in the bone strength-strain index and 8.9% (p = 0.001) the variance in the section modulus in older women after accounting for age, height, weight, and physical activity. Moderate to vigorous physical activity was significantly related to muscle power in the lower extremity (r = 0.260; p = 0.041). CONCLUSION: Muscle power significantly contributed to the variance in estimated bone strength. Whether power training will prove to be a more effective stimulus for bone strength than conventional strength training will require further studies.

Strength indices from pQCT imaging predict up to 85% of variance in bone failure properties at tibial epiphysis and diaphysis.

Our primary objective was to validate the Bone Strength Index for compression (BSIC) by determining the amount of variance in failure load and stiffness that was explained by BSIC and bone properties at two distal sites in human cadaveric tibiae when tested in axial compression. Our secondary objective was to assess the variance in failure moment and flexural rigidity that was explained by bone properties, geometry and strength indices in the tibial diaphysis when tested in 4-point bending. Twenty cadaver tibiae pairs from 5 female and 5 male donors (mean age 74 yrs, SD 6 yrs) were measured at the distal epiphysis (4 and 10% sites of the tibial length from the distal end) and diaphysis (50 and 66% sites) by peripheral Quantitative Computed Tomography (pQCT; XCT 2000, Stratec). After imaging, we conducted axial compression tests on the distal tibia and 4-point bending tests on the diaphysis. Total bone mineral content and BSIC (product of total area and squared density of the cross-section) at the 4% site predicted 75% and 85% of the variance in the failure load and 52% and 57% in stiffness, respectively. At the diaphyseal sites 80% or more of the variance in failure moment and/or flexural rigidity was predicted by total and cortical area and content, geometry and strength indices corresponding to the axes of bending.

Characterising cortical density in the mid-tibia: intra-individual variation in adolescent girls and boys.

BACKGROUND: Inter-individual differences in cortical bone volumetric density (CoD), such as those related to sex, are a product of differences in remodelling rates. While cortical bone is often treated as a uniform tissue, remodelling rates also vary within individual bones. This level of adaptation has largely been overlooked in analyses of peripheral quantitative computed tomography (pQCT) images. Further, such variation in CoD has never been assessed in growing bones. We hypothesised that CoD varied significantly within the same cross-section of the mid-tibia of adolescents. We further hypothesised that due to the profound impact of oestrogen on remodelling, this variation would be different between sexes. METHODS: Subjects were 183 adolescents (99 girls and 84 boys) in grade 6 and 7 with a mean age of 12.1 years. We used age at peak height velocity to adjust for maturational differences between sexes. Image data from a mid-tibia pQCT scan of each subject were assessed regionally within eight sectors distributed about the cortex and aligned by the anterior tibial crest. We used a repeated measures general linear model to assess intra-individual variation in CoD while controlling for differences in ethnicity, maturity, height, weight, physical activity level and total cross-sectional bone area (ToA). RESULTS: Sector based variation in CoD was significant (p<0.001), with the anterior cortex having lower density than the posterior cortex. The largest percentage difference (anterior vs posteromedial sectors) was 12.2%. A significant sector*sex interaction (p = 0.018) was detected; however, its impact was relatively small with girls having 1.1-3.6% denser bones than boys depending on the sector (2.7% average difference). CONCLUSIONS: The magnitude of the variation in CoD across sectors within individuals of both sex was far greater than the mean differences between the sexes. This finding indicates that the microstructural variation within the mid-tibia is detectable by pQCT and its magnitude suggests an important level of adaptation to loading.

An active school model to promote physical activity in elementary schools: action schools! BC.

OBJECTIVE: To assess the impact of an active school model on children's physical activity (PA). DESIGN: 16-month cluster randomised controlled trial. SETTING: 10 elementary schools in Greater Vancouver, BC. PARTICIPANTS: 515 children aged 9-11 years. INTERVENTION: Action Schools! BC (AS! BC) is an active school model that provided schools with training and resources to increase children's PA. Schools implemented AS! BC with support from either external liaisons (liaison schools, LS; four schools) or internal champions (champion schools, CS; three schools). Outcomes were compared with usual practice (UP) schools (three schools). MAIN OUTCOME MEASUREMENTS: PA was measured four times during the study using pedometers (step count, steps/day). RESULTS: Boys in the LS group took 1175 more steps per day, on average, than boys in the UP group (95% CI: 97 to 2253). Boys in the CS group also tended to have a higher step count than boys in the UP group (+804 steps/day; 95% CI: -341 to 1949). There was no difference in girls' step counts across groups. CONCLUSIONS: The positive effect of the AS! BC model on boys' PA is important in light of the current global trend of decreased PA.

Hand dominance and bone response after a distal radial fracture: a peripheral QCT study.

There are no reports on bone geometry or volumetric bone density adaptations in those who have sustained a distal radial fracture. We used peripheral quantitative computed tomography (pQCT) and dual-energy X-ray absorptiometry (DXA) to quantify bone and muscle response to immobilization. We measured side-side differences in women aged > or =50 yr who had previously sustained a wrist fracture (4.0+/-3.5 mean yr since fracture). We used pQCT and DXA to measure bone in 31 women (mean age 72.4+/-9.7 yr) at the 4% and 30% sites of bilateral radii; measured grip strength and functional outcome. Initially, we compared the fractured side to intact side and did not control for hand dominance. We observed greater total area (ToA) at the distal (4%) radius on the fractured side without a significant increase in density. At the midshaft (30% site), we observed significantly less ToA and cortical bone on the fracture side. Grip strength was also significantly less on the fractured side (p<0.01). We assessed dominant side fractures and nondominant fractures separately. We observed a greater discrepancy between limbs with a nondominant side fracture, even after accounting for dominance. This cross-sectional study suggests that the bone response to a nondominant fracture may differ from a dominant fracture.

Does parental support influence children's active school travel?

Today's 'backseat generation' of children is more often driven to school. Active school travel (AST) can contribute up to 30% of recommended daily physical activity. Although governed by a complex set of factors, parents are considered 'gatekeepers' of children's travel mode decisions. Therefore, we investigate the relationship between parental support and children's AST. Data were from Active Streets, Active People-Junior (British Columbia, Canada). Children self-reported travel mode to/from school for 1 week (10 trips). We assessed parental perceived neighborhood traffic and crime safety (Neighborhood Environmental Walkability Scale-Youth) and frequency of parental support for AST (0-5 ×/week). We investigated the association between daily AST behaviour and parental support using logistic regression (controlling for age, sex, distance to school and perceived neighborhood safety). In our sample (n = 179, 11.0 ± 1.0 years, 59% girls), 57% reported daily AST and 63% of parents provided daily support. Bivariate analyses showed AST behaviour was significantly associated with parental support frequency and parents' perceived safety. In adjusted analysis, daily parental support remained significantly associated with daily AST (OR 9.0, 95% CI 4.2, 19.7). The relationship between parental support and AST was independent of noted correlates of AST. Thus, interventions that focus solely on changes to the built environment may not be enough to encourage AST. Therefore, interventions that aim to increase AST should involve parents and children in the planning process.

Bone geometric response to chronic disuse following stroke: a pQCT study.

OBJECTIVES: The objectives of this study were to 1) assess volumetric bone geometry and density at the distal radius of individuals with chronic stroke and 2) assess whether bone strength is associated with measures of muscle strength and impairment. MATERIAL AND METHODS: Cross-sectional study of bone and muscle parameters in 15 community-dwelling people living with the residual effects of a stroke (between 1 and 9 years post-incident stroke). RESULTS: The 4% site of the distal radius had significantly lower bone mineral content and density on the paretic side (p<0.006). There was a significant difference in pQCT measures of bone cortical density (p<0.03), area (p<0.05) and bone strength [Stress-Strain Index; SSI] (p<0.01) (lower on the paretic side) at the 30%. We found significant correlations between composite muscle strength score of the upper extremities and pQCT-generated bone strength. CONCLUSIONS: This cross-sectional study highlights lower bone strength on the paretic limb and an adaptive response to disuse.

Older adults' quality of life - Exploring the role of the built environment and social cohesion in community-dwelling seniors on low income.

The built environment and social cohesion are increasingly recognized as being associated with older adults' quality of life (QoL). However, limited research in this area still exists and the relationship has remained unexplored in the area of Metro Vancouver, Canada. This study examined the association between the built environment and social cohesion with QoL of 160 community-dwelling older adults (aged ≥ 65 years) on low income from Metro Vancouver. Cross-sectional data acquired from the Walk the Talk (WTT) study were used. Health-related QoL (HRQoL) and capability wellbeing were assessed using the EQ-5D-5L and the ICECAP-O, respectively. Measures of the environment comprised the NEWS-A (perceived built environment measure), the Street Smart Walk Score (objective built environment measure), and the SC-5PT (a measure of social cohesion). The primary analysis consists of Tobit regression models to explore the associations between environmental features and HRQoL as well as capability wellbeing. Key findings indicate that after adjusting for covariates, older adults' capability wellbeing was associated with street connectivity and social cohesion, while no statistically significant associations were found between environmental factors and HRQoL. Our results should be considered as hypothesis-generating and need confirmation in a larger longitudinal study.

"Bounce at the Bell": a novel program of short bouts of exercise improves proximal femur bone mass in early pubertal children.

OBJECTIVES: To examine the effects of a simple and inexpensive physical activity intervention on change in bone mass and structure in school aged children. METHODS: Fifty one children (n = 23 boys and 28 girls; mean age 10.1 years) participated in "Bounce at the Bell" which consisted of 10 counter-movement jumps 3x per day (total approximately 3 min/day). Controls were 71 matched children who followed usual school practice. We assessed dietary calcium, physical activity, physical performance, and anthropometry in September and after 8 months of intervention (June). We measured bone mineral content (BMC) and bone area at the lumbar spine, total body, and proximal femur. Proximal femur scans were also analysed for bone geometry and structural strength using the hip structural analysis program. Lean and fat mass (g) were also calculated. RESULTS: Groups were similar at baseline and did not differ in weight, height, total body, lumbar spine, proximal femur, or femoral neck BMC. Control children had a greater increase in adjusted total body BMC (1.4%). Intervention children gained significantly more BMC at the total proximal femur (2%) and the intertrochanteric region (27%). Change in bone structural parameters did not differ between groups. CONCLUSIONS: This novel, easily implemented exercise program, took only a few minutes each day and enhanced bone mass at the weight bearing proximal femur in early pubertal children. A large, randomised study of boys and girls should be undertaken powered to test the effectiveness of Bounce at the Bell in children at different stages of maturity, and in boys and girls independently.

Calcium accretion in girls and boys during puberty: a longitudinal analysis.

The primary purpose of this study was to estimate the magnitude and variability of peak calcium accretion rates in the skeletons of healthy white adolescents. Total-body bone mineral content (BMC) was measured annually on six occasions by dual-energy X-ray absorptiometry (DXA; Hologic 2000, array mode), a BMC velocity curve was generated for each child by a cubic spline fit, and peak accretion rates were determined. Anthropometric measures were collected every 6 months and a 24-h dietary recall was recorded two to three times per year. Of the 113 boys and 115 girls initially enrolled in the study, 60 boys and 53 girls who had peak height velocity (PHV) and peak BMC velocity values were used in this longitudinal analysis. When the individual BMC velocity curves were aligned on the age of peak bone mineral velocity, the resulting mean peak bone mineral accrual rate was 407 g/year for boys (SD, 92 g/year; range, 226-651 g/year) and 322 g/year for girls (SD, 66 g/year; range, 194-520 g/year). Using 32.2% as the fraction of calcium in bone mineral, as determined by neutron activation analysis (Ellis et al., J Bone Miner Res 1996;11:843-848), these corresponded to peak calcium accretion rates of 359 mg/day for boys (81 mg/day; 199-574 mg/day) and 284 mg/day for girls (58 mg/day; 171-459 mg/day). These longitudinal results are 27-34% higher than our previous cross-sectional analysis in which we reported mean values of 282 mg/day for boys and 212 mg/day for girls (Martin et al., Am J Clin Nutr 1997;66:611-615). Mean age of peak calcium accretion was 14.0 years for the boys (1.0 years; 12.0-15.9 years), and 12.5 years for the girls (0.9 years; 10.5-14.6 years). Dietary calcium intake, determined as the mean of all assessments up to the age of peak accretion was 1140 mg/day (SD, 392 mg/day) for boys and 1113 mg/day (SD, 378 mg/day) for girls. We estimate that 26% of adult calcium is laid down during the 2 adolescent years of peak skeletal growth. This period of rapid growth requires high accretion rates of calcium, achieved in part by increased retention efficiency of dietary calcium.