Susanna Stenevi-Lundgren

Exercise, bone mass and bone size in prepubertal boys: one-year data from the pediatric osteoporosis prevention study.

This non‐randomized prospective controlled study evaluates a daily school‐based exercise intervention program of 40 min/school day for 1 year in a population‐based cohort of 81 boys aged 7–9 years. Controls were 57 age‐matched boys assigned to the general school curriculum of 60 min/week. Bone mineral content (BMC; g) and areal bone mineral density (aBMD; g/cm2) were measured with dual X‐ray absorptiometry (DXA) of the total body, the third lumbar vertebra (L3) and the femoral neck (FN). Bone width for L3 and FN was calculated from the lumbar spine and hip scan. No differences between the groups were found at baseline in age, anthropometrics or bone parameters. The mean annual gain in L3 BMC was 5.9 percentage points higher (P<0.001), L3 aBMD a mean 2.1 percentage points higher (P=0.01) and L3 width a mean 2.3 percentage points higher (P=0.001) in the cases than in the controls. When all individuals were included in one cohort, the total duration of exercise including both school‐based and spare‐time training correlated with L3 BMC (r=0.26, P=0.003), L3 aBMD (r=0.18, P=0.04) and L3 width (r=0.24, P=0.006). The study suggests that exercise in pre‐pubertal boys influences the accrual of bone mineral and bone width and that a 1‐year school‐based exercise program confers skeletal benefits, at least in the lumbar spine.

Muscle determinants of bone mass, geometry and strength in prepubertal girls

PURPOSE The aim of this study was to compare the relative contribution of peak muscle force (isokinetic peak torque) with surrogate estimates of muscle force, including leg lean tissue mass (LTM) and vertical jump height (VJH), on bone mass, geometry and strength in healthy prepubertal girls (n = 103). METHODS Total leg and FN BMC and leg LTM were measured by DXA; the hip strength analysis program was used to assess FN diameter, cross-sectional area (CSA) and section modulus (Z). Isokinetic peak torque of the knee extensors and flexors (60 degrees .s) were used as direct measures of peak muscle force. VJH was measured as an estimate of neuromuscular function. Total leg length or femoral length was used as a surrogate measure of moment arm length. RESULTS All estimates of muscle function, except VJH, were positively associated with leg BMC (r = 0.72 - 0.90) and FN BMC, geometry and strength (r = 0.35-0.65) (all, P < 0.001). Multiple linear regression analyses revealed that leg LTM and isokinetic peak torque were independently and equally predictive of leg BMC and FN BMC, bone geometry and strength, explaining 8 to 28% of the variance in each of the bone traits after accounting for moment arm length. When isokinetic peak torque was corrected for both leg LTM and moment arm length, it remained an independent predictor of BMC, CSA and Z, but only accounted for an additional 2 to 5% of the variance. CONCLUSION These data suggest that DXA-derived leg LTM can be used as a reasonable surrogate for isokinetic peak muscle forces when assessing bone strength in relation to muscular function in healthy pre-pubertal girls.

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

BackgroundWe 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.MethodsFifty-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 students t-test between means and analyses of covariance (ANCOVA). Pearsons 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.ResultsNo 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.ConclusionEvaluated 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.

A school-curriculum-based exercise intervention program for two years in pre-pubertal girls does not influence hip structure

BackgroundIt is known that physical activity during growth has a positive influence on bone mineral accrual, and is thus possibly one strategy to prevent osteoporosis. However, as bone geometry, independent of areal bone mineral density (aBMD), influences fracture risk, this study aimed to evaluate whether hip structure in pre-pubertal girls is also affected by a two-year exercise intervention program.MethodsForty-two girls aged 7–9 years in a school-curriculum-based exercise intervention program comprising 40 minutes of general physical activity per school day (200 minutes per week) were compared with 43 age-matched girls who participated in the general Swedish physical education curriculum comprising a mean of 60 minutes per week. The hip was scanned by dual energy X-ray absorptiometry (DXA) and the hip structural analysis (HSA) software was applied to evaluate bone mineral content (BMC, g), areal bone mineral density (aBMD, g/cm2), periosteal diameter, cross-sectional area (CSA, cm2), section modulus (Z, cm3) and cross-sectional moment of inertia (CSMI, cm4) of the femoral neck (FN). Annual changes were compared. Subjective duration of physical activity was estimated by questionnaire and objective level of everyday physical activity at follow-up by means of accelerometers worn for four consecutive days. All children remained at Tanner stage 1 throughout the study. Group comparisons were made by independent students t-test between means and analyses of covariance (ANCOVA).ResultsAt baseline, the two groups did not differ with regard to age, anthropometrics or bone parameters. No between-group differences were observed for annual changes in the FN variables measured.ConclusionA two-year school-based moderately intense general exercise program for 7–9-year-old pre-pubertal girls does not influence structural changes in the FN.

Influence of a 3-year exercise intervention program on fracture risk, bone mass, and bone size in prepubertal children.

Published prospective pediatric exercise intervention studies are short term and use skeletal traits as surrogate endpoints for fractures, whereas other reports infer exercise to be associated with more trauma and fractures. This prospective, controlled exercise intervention study therefore followed both skeletal traits and fracture risk for 36 months. Fractures were registered in children aged 7 to 9 years; there were 446 boys and 362 girls in the intervention group (2129 person‐years) and 807 boys and 780 girls in the control group (4430 person‐years). The intervention included school physical education of 40 minutes per day for 3 years. The control children achieved the Swedish standard of 60 minutes per week. In a subsample of 76 boys and 48 girls in the intervention group and 55 boys and 44 girls in the control group, bone mineral content (BMC, g) and bone width (cm) were followed in the lumbar spine and hip by dual‐energy X‐ray absorptiometry (DXA). The rate ratio (RR) for fractures was 1.08 (0.71, 1.62) [mean (95% confidence interval)]. In the DXA‐measured children, there were no group differences at baseline in age, anthropometrics, or bone traits. The mean annual gain in the intervention group in lumbar spine BMC was 0.9 SD higher in girls and 0.8 SD higher in boys (both p < .001) and in third lumbar vertebra width 0.4 SD higher in girls and 0.3 SD higher in boys (both p < .05) than in control children. It is concluded that a moderately intense 3‐year exercise program in 7‐ to 9‐year‐old children increases bone mass and possibly also bone size without increasing fracture risk.

A School-Based Exercise Intervention Program Increases Muscle Strength in Prepubertal Boys

This prospective controlled intervention study over 12 months evaluated the effect of exercise on muscular function, physical ability, and body composition in pre-pubertal boys. Sixty-eight boys aged 6–8 years, involved in a general school-based exercise program of 40 min per school day (200 min/week), were compared with 46 age-matched boys who participated in the general Swedish physical education curriculum of mean 60 min/week. Baseline and annual changes of body composition were measured by dual energy X-ray absorptiometry (DXA), stature, and body mass by standard equipments, isokinetic peak torque (PT) of the knee extensors, and flexors at 60 and 180 deg/sec by computerized dynamometer (Biodex) and vertical jump height (VJH) by a computerized electronic mat. The annual gain in stature and body mass was similar between the groups whereas the increase in total body and regional lean mass (P < .001) and fat mass (P < .001) was greater in the exercise group. The one-year gain in body mass-adjusted knee extensor and flexor PT at 180 deg/sec was significantly greater in the intervention group compared with the control group (P < .01, adjusted for age at baseline and P < .001, adjusted for age and muscle strength at baseline, resp.). There was no group difference in VJH. In conclusion, the increase in school-based physical education from 60 to 200 minutes per week enhances the development of lean body mass and muscle strength in pre-pubertal boys.

Bone mineral accrual and gain in skeletal width in pre-pubertal school children is independent of the mode of school transportation - one-year data from the prospective observational pediatric osteoporosis prevention (POP) study.

BackgroundWalking and cycling to school could be an important regular source of physical activity in growing children. The aim of this 12 months prospective observational study was thus to evaluate the effect of self-transportation to school on bone mineral accrual and gain in bone width in pre-pubertal children, both traits independently contributing to bone strength.MethodsNinety-seven girls and 133 boys aged 7–9 years were recruited as a part of the Malmö Pediatric Osteoporosis Prevention (POP) Study in order to evaluate the influence of self-selected school transportation for the accrual of bone mineral and bone width. Children who walked or cycled to school were compared with children who went by bus or car. Bone mineral content (BMC) was measured by dual energy X-ray absorptiometry (DXA) in the lumbar spine (L2–L4), third lumbar vertebra (L3) and hip, and bone width was calculated at L3 and femoral neck (FN). Changes during the first 12 months were compared between the groups. Subjective duration of physical activity was estimated by a questionnaire and objective level of everyday physical activity at follow-up by accelerometers worn for four consecutive days. All children remained in Tanner stage 1 throughout the study. Comparisons were made by independent students t-tests between means, ANCOVA and Fishers exact tests.ResultsThere were no differences in baseline or annual changes in BMC or bone width when the transportation groups were compared. No differences were detected in objectively measured daily level of physical activity by accelerometer. All children reached above 60 minutes of moderate to intense daily physical activity per day, the international recommended level of daily physical activity according to the United Kingdom Expert Consensus Group.ConclusionThe everyday physical activity in these pre-pubertal children seems to be so high that the school transportation contributes little to their total level of physical activity. As a result, the choice of school transportation seems not to influence the accrual of bone mineral or gain in bone size during a 12-month follow-up period.