title: Peripheral bone mineral density and different intensities of physical activity in children 6-8 years old: the Copenhagen School Child Intervention study.
abstract: 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.
authors.affiliation: Institute of Exercise and Sport Sciences, University of Copenhagen, Nørre Allé 51, DK-2200 Copenhagen N, Denmark. hhasselstrom@ifi.ku.dk
authors.forename: H
authors.initials: H
authors.lastname: Hasselstrøm
authors.forename: K M
authors.initials: KM
authors.lastname: Karlsson
authors.forename: S E
authors.initials: SE
authors.lastname: Hansen
authors.forename: V
authors.initials: V
authors.lastname: Grønfeldt
authors.forename: K
authors.initials: K
authors.lastname: Froberg
authors.forename: L B
authors.initials: LB
authors.lastname: Andersen
mesh_terms: D015502:Absorptiometry, Photon; D015519:Bone Density / Q000502:physiology*; D002111:Calcaneus / Q000502:physiology*; D002648:Child; D003430:Cross-Sectional Studies; D003718:Denmark; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D011884:Radius / Q000502:physiology*; D012727:Sex Characteristics; D014457:Ulna / Q000502:physiology*