title: Effect of a general school-based physical activity intervention on bone mineral content and density: a cluster-randomized controlled trial.
abstract: BACKGROUND
  Specific physical loading leads to enhanced bone development during childhood. A general physical activity program mimicking a real-life situation was successful at increasing general physical health in children. Yet, it is not clear whether it can equally increase bone mineral mass. We performed a cluster-randomized controlled trial in children of both gender and different pubertal stages to determine whether a school-based physical activity (PA) program during one school-year influences bone mineral content (BMC) and density (BMD), irrespective of gender.
  
  
  METHODS
  Twenty-eight 1st and 5th grade (6-7 and 11-12 year-old) classes were cluster randomized to an intervention (INT, 16 classes, n=297) and control (CON; 12 classes, n=205) group. The intervention consisted of a multi-component PA intervention including daily physical education with at least 10 min of jumping or strength training exercises of various intensities. Measurements included anthropometry, and BMC and BMD of total body, femoral neck, total hip and lumbar spine using dual-energy X-ray absorptiometry (DXA). PA was assessed by accelerometers and Tanner stages by questionnaires. Analyses were performed by a regression model adjusted for gender, baseline height and weight, baseline PA, post-intervention pubertal stage, baseline BMC, and cluster.
  
  
  RESULTS
  275 (72%) of 380 children who initially agreed to have DXA measurements had also post-intervention DXA and PA data. Mean age of prepubertal and pubertal children at baseline was 8.7±2.1 and 11.1±0.6 years, respectively. Compared to CON, children in INT showed statistically significant increases in BMC of total body, femoral neck, and lumbar spine by 5.5%, 5.4% and 4.7% (all p<0.05), respectively, and BMD of total body and lumbar spine by 8.4% and 7.3% (both p<0.01), respectively. There was no gender *group, but a pubertal stage *group interaction consistently favoring prepubertal children.
  
  
  CONCLUSIONS
  A general school-based PA intervention can increase bone health in elementary school children of both genders, particularly before puberty.
authors.affiliation: Institute of Exercise and Health Science, University of Basel, 4052 Basel, Switzerland. ursina.meyer@unibas.ch
authors.forename: Ursina
authors.initials: U
authors.lastname: Meyer
authors.forename: Michael
authors.initials: M
authors.lastname: Romann
authors.forename: Lukas
authors.initials: L
authors.lastname: Zahner
authors.forename: Christian
authors.initials: C
authors.lastname: Schindler
authors.forename: Jardena J
authors.initials: JJ
authors.lastname: Puder
authors.forename: Marius
authors.initials: M
authors.lastname: Kraenzlin
authors.forename: Rene
authors.initials: R
authors.lastname: Rizzoli
authors.forename: Susi
authors.initials: S
authors.lastname: Kriemler
mesh_terms: D015519:Bone Density; D002648:Child; D016000:Cluster Analysis; D015444:Exercise; D006801:Humans; D012574:Schools