title: Peak lean tissue mass accrual precedes changes in bone strength indices at the proximal femur during the pubertal growth spurt.
abstract: OBJECTIVE
  We examined the timing of the age and the magnitude of peak lean tissue mass accrual (PLTV) relative to the age and magnitude of two variables of bone strength [peak cross sectional area velocity (PCSAV), and peak section modulus velocity, (PZV)] at the proximal femur in males and females during the adolescent growth spurt. We hypothesized that the age of PLTV would precede the ages of PCSAV and PZV and that there is a positive relationship between the magnitude of PLTV and both PCSAV and PZV in both genders.
  
  
  METHODS
  41 males and 42 females aged 8-18 years were selected from the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-2005). Participants' total body lean tissue mass was assessed annually for 6 consecutive years using DXA. Narrow neck and femoral shaft cross sectional areas (CSA) and section modulus (Z) were determined using the hip structural analysis (HSA) program. Participants were aligned by maturational age (years from peak height velocity). Lean tissue mass, CSA, and Z were converted into whole year velocities and the maturational age of peak tissue velocities was determined using a cubic spline curve fitting procedure. A 2 x 3 (gender x tissue) factorial MANOVA with repeated measures was used to test for differences between age of PLTV and the ages of PCSAV and PZV between genders. Multiple regression analyses were used to examine the relationship between PLTV and both PCSAV and PZV.
  
  
  RESULTS
  There were no sex differences in the ages at which tissue peaks occurred when aligned by maturational age. There were significant differences between the age of PLTV and both PCSAV and PZV at the narrow neck (p=0.001) and femoral shaft (p=0.03), where the age of PLTV preceded both PCSAV and PZV when pooled by gender. PLTV was a significant predictor of the magnitude of both PCSAV and PZV at all sites (p<0.05).
  
  
  CONCLUSIONS
  These findings support the hypothesis that the age of PLTV precedes the age of PCSA and PZV at the proximal femur. Results support the theory that muscle development is an important factor in affecting bone strength.
authors.affiliation: University of Saskatchewan, Saskatoon, SK, Canada. stefan.jackowski@usask.ca
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Jackowski
authors.forename: Robert A
authors.initials: RA
authors.lastname: Faulkner
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Farthing
authors.forename: Saija A
authors.initials: SA
authors.lastname: Kontulainen
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Beck
authors.forename: Adam D G
authors.initials: AD
authors.lastname: Baxter-Jones
mesh_terms: D000293:Adolescent; D000886:Anthropometry; D001696:Biomechanical Phenomena; D001823:Body Composition; D015519:Bone Density / Q000502:physiology*; D002648:Child; D005260:Female; D005269:Femur / Q000254:growth & development / Q000502:physiology*; D006801:Humans; D008297:Male; D011627:Puberty / Q000502:physiology*; D012727:Sex Characteristics