title: Children with low muscle strength are at an increased risk of fracture with exposure to exercise.
abstract: OBJECTIVE
  To use objective measures of physical fitness and muscle function to assess the interplay between exercise, muscle and fractures during childhood.
  
  
  METHODS
  A cross-sectional analysis was performed using The Young Hearts Project, a population-based cohort recruited from Northern Ireland. Grip strength was assessed with a hand-held dynamometer. Aerobic fitness was assessed using the 20-metre endurance shuttle run. The outcome of interest was reported fractures. Data were also collected on other potential confounders.
  
  
  RESULTS
  There were 787 boys (49.5%) and 803 girls aged 13.9±1.5 years. 414 (26.0%) children reported a fracture at anytime since birth. There was a positive association between higher aerobic fitness and reported fracture (OR 1.23, 95%CI 1.05 to 1.45, P=0.012) greatest in those with lowest grip strength (OR 2.10, 95%CI 1.23 to 3.31, P=0.005). Conversely, in those with highest grip strength, no association was seen between aerobic fitness and reported fractures.
  
  
  CONCLUSIONS
  In children, higher levels of aerobic fitness are associated with an increased risk of fractures, with the greatest risk seen in those with low muscle strength. Our results suggest that there is the potential for exercise protocols that aim to strengthen forearm musculature to reduce upper limb fractures in adolescents.
authors.affiliation: Academic Rheumatology, Musculoskeletal Research Unit, University of Bristol, Avon Orthopaedic Centre, Southmead Hospital, Bristol BS105NB, UK. emma.clark@bristol.ac.uk
authors.forename: E M
authors.initials: EM
authors.lastname: Clark
authors.forename: J H
authors.initials: JH
authors.lastname: Tobias
authors.forename: L
authors.initials: L
authors.lastname: Murray
authors.forename: C
authors.initials: C
authors.lastname: Boreham
mesh_terms: D000293:Adolescent; D002648:Child; D015331:Cohort Studies; D015897:Comorbidity / Q000639:trends; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology* / Q000503:physiopathology; D006801:Humans; D008297:Male; D018908:Muscle Weakness / Q000453:epidemiology* / Q000503:physiopathology; D010809:Physical Fitness / Q000502:physiology*