A 3-year physical activity intervention program increases the gain in bone mineral and bone width in prepubertal girls but not boys: the prospective copenhagen school child interventions study (CoSCIS).

The aim of this study was to evaluate the effect of increasing the amount of time spent in physical education classes on bone mineral accrual and gain in bone size in prepubertal Danish children. A total of 135 boys and 108 girls, aged 6-8 years, were included in a school-based curriculum intervention program where the usual time spent in physical education classes was doubled to four classes (180 min) per week. The control group comprised age-matched children (62 boys and 76 girls) recruited from a separate community who completed the usual Danish school curriculum of physical activity (90 min/week). Dual-energy X-ray absorptiometry was used to evaluate bone mineral content (BMC; g), bone mineral density (g/cm(2)), and bone width at the calcaneus and distal forearm before and after 3 years of intervention. Anthropometrics and Tanner stages were evaluated on the same occasions. General physical activity was measured with an accelerometer worn for 4 days. In girls, the intervention group had a 12.5% increase (P = 0.04) in distal forearm BMC and a 13.2% increase (P = 0.005) in distal forearm scanned area compared with girls in the control group. No differences were found between the intervention and control groups in boys. Increasing the frequency of physical education classes for prepubertal children is associated with a higher accrual of bone mineral and higher gain in bone size after 3 years in girls but not in boys.

Peripheral bone mineral density and different intensities of physical activity in children 6-8 years old: the Copenhagen School Child Intervention study.

This study aimed to evaluate the association between objectively measured habitual physical activity and calcaneal and forearm bone mineral density (BMD, g/cm(2)), one mechanically more loaded and one less loaded skeletal region, in children aged 6-8 years. BMD was measured in 297 boys and 265 girls by peripheral dual-energy X-ray absorptiometry in the forearm and calcaneus. An accelerometer registered the level of physical activity during 4 days (2 weekdays and the weekend). Weight, height, and skinfold thickness were measured. In order to establish thresholds (count . min(-1)) for bone-stimulating physical activity, we evaluated different definitions of vigorous physical activity. The boys had 3.2% higher distal forearm bone mineral content (BMC, P < 0.001) and 4.5% higher distal forearm BMD (P < 0.001) than the girls. They also carried out 9.7% more daily physical activity and spent 14.6-19.0% more time in vigorous physical activity (all P < 0.05) compared to the girls. In contrast, the girls had 3.8% higher calcaneal BMC (P < 0.01) and 2.5% higher calcaneal BMD (P < 0.05) than the boys. Both calcaneal and forearm BMD were significantly related to total time of daily physical activity as well as with intense physical activity above all the chosen cut-off points (all P < 0.05). The beta value for mean count . min(-1) physical activity was significantly lower than that for all the chosen cut-off points of vigorous activity both for calcaneal and distal forearm BMD. This study suggests that both habitual daily physical activity and amount of vigorous physical activity in children aged 6-8 years are associated with appendicular BMD.

Sex differences in bone size and bone mineral density exist before puberty. The Copenhagen School Child Intervention Study (CoSCIS).

BACKGROUND: The aim of this study was to provide normative data of bone mineral density (BMD; g/cm(2)) of the forearm and the calcaneus, evaluated by peripheral dual X ray absorbtiometry (DXA), in children aged 6 to 7 years of age and to evaluate the association with anthropometrics and sex. MATERIAL AND METHODS: 368 boys and 326 girls with a mean age of 6.7 +/- 0.4 years participated. BMD was measured by DXA in the forearms and the os calcanei, with average values presented in this report. Measurements of weight, height, skinfolds, the width of distal radius and ulna, and the femur condyles were collected and body composition estimated from skinfolds measurements. RESULTS: There was no difference in calcaneus BMD when comparing boys and girls, whereas the boys had 4.5% (0.013 g/cm(2)) higher forearm BMD than the girls (P < 0.001). Calcaneal BMD (mean 0.318 g/cm(2)) was 11% higher than forearm BMD (mean 0.283 g/cm(2)). Linear relationship was found between calcaneus BMD and weight (partial r = 0.50), Fat free mass (FFM) (partial r = 0.50), Fat mass (FM) (partial r = 0.45), % body fat (partial r = 0.29) and knee width (partial r = 0.46), all P < 0.000 respectively. Adjusted for weight the relationship between calcaneus BMD and FFM, FM, %body fat and knee width disappeared. There were significant relationships between the forearm BMD and weight (partial r = 0.37), FFM (partial r = 0.39), FM (partial r = 0.28), %body fat (partial r = 0.14) and wrist width (partial r = 0.24), all P < 0.000 respectively. Adjusted for body weight, the relationship remained between forearm BMD and FFM (r = 0.10), FM (R = -0.10) and % body fat (r = -0.12), all P < 0.000 respectively. Children measured in the spring had 3.5% (P < 0.01) higher calcaneus BMD than children measured in the winter. CONCLUSION: Seven year old boys have higher BMD in the forearm but not in the calcaneus in comparison with girls of a similar age. Body weight is the best predictor of calcaneus BMD, accounting for 25% of the variance whereas body weight and FFM are the best predictors of forearm BMD, each accounting for 17% of the variance, respectively.

Maximum oxygen uptake and objectively measured physical activity in Danish children 6-7 years of age: the Copenhagen school child intervention study.

OBJECTIVES: To provide normative data on maximum oxygen uptake (Vo(2)max) and physical activity in children 6-7 years of age and analyse the association between these variables. METHODS: Vo(2)max was measured in 366 boys (mean (SD) 6.8 (0.4) years of age) and 332 girls (6.7 (0.4) years of age) from preschool classes in two suburban communities in Copenhagen, during a progressive treadmill exercise. Habitual physical activity was measured with accelerometers. RESULTS: Boys had higher Vo(2)max both in absolute values (1.19 (0.18) v 1.06 (0.16) litres/min (+11%), p<0.001) and relative to body weight (48.5 (6.0) v 44.8 (5.6) ml/kg/min (+8%); p<0.001) than girls. The difference in Vo(2)max between boys and girls decreased to +2% when expressed relative to lean body mass (LBM). Absolute Vo(2)max was related to LBM, body mass, and stature (all p<0.001). Boys were more physically active than girls (mean counts +9.4%, p<0.001), and even when boys and girls with the same Vo(2)max were compared, boys were more active. The difference in physical activity between the sexes was higher when sustained activity of higher intensity was compared. CONCLUSIONS: Vo(2)max is higher in boys than girls (+11%), even when related to body mass (+8%) and LBM (+2%). Most of the difference in Vo(2)max relative to body mass was explained by the larger percentage body fat in girls. When boys and girls with the same Vo(2)max were compared, boys engaged in more minutes of exercise of at least moderate intensity.