title: A 5-year exercise program in children improves muscle strength without affecting fracture risk.
abstract: OBJECTIVE
  High level of physical activity (PA) is associated with great muscle strength and high fracture risk. This prospective controlled population-based study evaluated how a pediatric PA intervention program influenced muscle strength and fracture risk.
  
  
  METHODS
  We carried out a school-based exercise intervention program with 200 min of PA per week for 5 years in 335 girls and 408 boys aged 6-9 years at study start. An age-matched control cohort including 756 girls and 782 boys continued with 60 min of PA per week. We registered fractures during the study period and calculated rate ratio. In a sub-sample, including 74 girls and 107 boys in the intervention and 51 girls and 54 boys in the control group, we measured knee flexion and extension strength by a computerized dynamometer and leg composition by dual energy X-ray absorptiometry. Group comparisons were adjusted for differences in age, baseline value for the measured parameter and changes in height.
  
  
  RESULTS
  Children in the intervention group had a rate ratio to sustain a fracture of 1.03 (0.78, 1.36) (mean and 95 % confidence interval) (p = 0.79). The annual gain in flexion peak torque muscle strength was greater in both girls (at 60°/s) [1.1 Nm (0.5, 1.8), p < 0.01] and boys (at 180°/s) [0.7 Nm (0.1, 1.2), p < 0.05] in the intervention than in the control group, while leg composition was similar.
  
  
  CONCLUSIONS
  Increased PA during a 5-year period, starting in the pre-pubertal period, improves the gain in muscle strength without affecting the fracture risk.
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Departments of Orthopedics and Clinical Sciences, Skåne University Hospital, 205 02, Malmö, Sweden. jesper.fritz@med.lu.se.
authors.forename: Jesper
authors.initials: J
authors.lastname: Fritz
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Departments of Orthopedics and Clinical Sciences, Skåne University Hospital, 205 02, Malmö, Sweden.
authors.forename: Marcus E
authors.initials: ME
authors.lastname: Cöster
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Departments of Orthopedics and Clinical Sciences, Skåne University Hospital, 205 02, Malmö, Sweden.
authors.forename: Susanna
authors.initials: S
authors.lastname: Stenevi-Lundgren
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Departments of Orthopedics and Clinical Sciences, Skåne University Hospital, 205 02, Malmö, Sweden.
authors.forename: Jan-Åke
authors.initials: JÅ
authors.lastname: Nilsson
authors.affiliation: Departments of Clinical Physiology and Clinical Sciences, Lund University, Skåne University Hospital, 205 02, Malmö, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Dencker
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Departments of Orthopedics and Clinical Sciences, Skåne University Hospital, 205 02, Malmö, Sweden.
authors.forename: Björn E
authors.initials: BE
authors.lastname: Rosengren
authors.affiliation: Clinical and Molecular Osteoporosis Research Unit, Departments of Orthopedics and Clinical Sciences, Skåne University Hospital, 205 02, Malmö, Sweden.
authors.forename: Magnus K
authors.initials: MK
authors.lastname: Karlsson
mesh_terms: D002648:Child; D015444:Exercise; D005081:Exercise Therapy / Q000009:adverse effects*; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology* / Q000517:prevention & control; D006801:Humans; D008297:Male; D053580:Muscle Strength; D010806:Physical Education and Training / Q000706:statistics & numerical data
keywords: Body composition; Fracture risk; Isokinetic peak torque; Muscle strength; Physical activity; School-based intervention