title: Bone architecture and strength in the growing skeleton: the role of sedentary time.
abstract: OBJECTIVE
  Today's youths spend close to 60% of their waking hours in sedentary activities; however, we know little about the potentially deleterious effects of sedentary time on bone health during this key period of growth and development. Thus, our objective was to determine whether sedentary time is associated with bone architecture, mineral density, and strength in children, adolescents, and young adults.
  
  
  METHODS
  We used high-resolution peripheral quantitative computed tomography (Scanco Medical) to measure bone architecture (trabecular and cortical microstructure and bone macrostructure) and cortical and total bone mineral density (BMD) at the distal tibia (8% site) in 154 males and 174 females (9-20 yr) who were participants in the University of British Columbia Healthy Bones III study. We applied finite element analysis to high-resolution peripheral quantitative computed tomography scans to estimate bone strength. We assessed self-reported screen time in all participants using a questionnaire and sedentary time (volume and patterns) in a subsample of participants with valid accelerometry data (89 males and 117 females; ActiGraph GT1M). We fit sex-specific univariate multivariable regression models, controlling for muscle cross-sectional area, limb length, maturity, ethnicity, dietary calcium, and physical activity.
  
  
  RESULTS
  We did not observe independent effect of screen time on bone architecture, BMD, or strength in either sex (P > 0.05). Likewise, when adjusted for muscle cross-sectional area, limb length, maturity, ethnicity, dietary calcium, and physical activity, accelerometry-derived volume of sedentary time and breaks in bouts of sedentary time were not a determinant of bone architecture, BMD, or strength in either sex (P > 0.05).
  
  
  CONCLUSIONS
  Further study is warranted to determine whether the lack of association between sedentary time and bone architecture, BMD, and strength at the distal tibia is also present at other skeletal sites.
authors.affiliation: 1Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia, CANADA; 2Child and Family Research Institute, Vancouver, British Columbia, CANADA; 3Centre for Hip Health and Mobility, Vancouver Coastal Health Research Institute, Vancouver, British Columbia, CANADA; and 4Department of Family Practice, University of British Columbia, Vancouver, British Columbia, CANADA.
authors.forename: Leigh
authors.initials: L
authors.lastname: Gabel
authors.forename: Heather A
authors.initials: HA
authors.lastname: McKay
authors.forename: Lindsay
authors.initials: L
authors.lastname: Nettlefold
authors.forename: Douglas
authors.initials: D
authors.lastname: Race
authors.forename: Heather M
authors.initials: HM
authors.lastname: Macdonald
mesh_terms: D015502:Absorptiometry, Photon; D061725:Accelerometry; D000293:Adolescent; D000886:Anthropometry; D015519:Bone Density; D001846:Bone Development; D001842:Bone and Bones / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D002136:Calcium, Dietary; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D057185:Sedentary Behavior; D013977:Tibia / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D002136:Calcium, Dietary