title: An increase in school-based physical education increases muscle strength in children.
abstract: OBJECTIVE
  Children and adolescents are encouraged to maintain a habitually active lifestyle because of the known health benefits associated with regular physical activity, but there are some reports that a high level of activity may be associated with increased fracture risk. This prospective controlled exercise intervention study in prepubertal children evaluated if a school-based exercise intervention could enhance growth-related gains in muscle strength and muscular function without affecting fracture risk.
  
  
  METHODS
  Fractures were registered in 417 girls and 500 boys age 7-9 yr in the intervention and in 836 age-matched girls and 872 boys. The intervention included 40 min·d of school physical education for 2 yr, whereas the controls achieved 60 min·wk. In a subsample consisting of 49 girls and 80 boys in the intervention and 50 girls and 53 boys in the control group, body composition was measured by dual-energy x-ray absorptiometry, muscle strength by isokinetic peak torque (PT) of the knee extensors, and flexors at 60 and 180°·s by a computerized dynamometer and neuromuscular performance by vertical jump height.
  
  
  RESULTS
  The rate ratio (95% confidence interval) for children in the intervention group to sustain a fracture was 1.07 (0.66-1.68). The annual gain in knee extensor PT at 180°·s was significantly higher for both girls (P < 0.001) and boys (P < 0.01) in the intervention compared with the control group. Boys in the intervention group also had a greater annual gain in knee flexion PT at 180°·s (P < 0.001), and girls had a greater gain in vertical jump height (P < 0.05).
  
  
  CONCLUSIONS
  An increase in school-based physical education from 60 to 200 min·wk enhanced muscle strength in prepubertal children without affecting fracture risk.
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Department of Clinical Sciences, Lund University, Lund, Sweden. bjarne.lofgren@med.lu.se
authors.forename: Bjarne
authors.initials: B
authors.lastname: Löfgren
authors.forename: Robin M
authors.initials: RM
authors.lastname: Daly
authors.forename: Jan-Åke
authors.initials: JÅ
authors.lastname: Nilsson
authors.forename: Magnus
authors.initials: M
authors.lastname: Dencker
authors.forename: Magnus K
authors.initials: MK
authors.lastname: Karlsson
mesh_terms: D001823:Body Composition / Q000502:physiology; D002648:Child; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology*; D015438:Health Behavior; D006801:Humans; D008019:Life Style; D008297:Male; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000502:physiology; D010806:Physical Education and Training; D010809:Physical Fitness / Q000502:physiology*; D011446:Prospective Studies