title: Site-specific advantages in skeletal geometry and strength at the proximal femur and forearm in young female gymnasts.
abstract: OBJECTIVE
  We evaluated site-specific skeletal adaptation to loading during growth, comparing radius (RAD) and femoral neck (FN) DXA scans in young female gymnasts (GYM) and non-gymnasts (NON).
  
  
  METHODS
  Subjects from an ongoing longitudinal study (8-26yr old) underwent annual DXA scans (proximal femur, forearm, total body) and anthropometry, completing maturity and physical activity questionnaires. This cross-sectional analysis used the most recent data meeting the following criteria: gynecological age ≤2.5yr post-menarche; and GYM annual mean gymnastic exposure ≥5.0h/wk in the prior year. Bone geometric and strength indices were derived from scans for 173 subjects (8-17yr old) via hip structural analysis (femoral narrow neck, NN) and similar radius formulae (1/3 and Ultradistal (UD)). Maturity was coded as M1 (Tanner I breast), M2 (pre-menarche, ≥Tanner II breast) or M3 (post-menarche). ANOVA and chi square compared descriptive data. Two factor ANCOVA adjusted for age, height, total body non-bone lean mass and percent body fat; significance was tested for main effects and interactions between gymnastic exposure and maturity.
  
  
  RESULTS
  At the distal radius, GYM means were significantly greater than NON means for all variables (p<0.05). At the proximal femur, GYM exhibited narrower periosteal and endosteal dimensions, but greater indices of cortical thickness, BMC, aBMD and section modulus, with lower buckling ratio (p<0.05). However, significant interactions between maturity and loading were detected for the following: 1) FN bone mineral content (BMC) and NN buckling ratio (GYM BMC advantages only in M1 and M3; for BMC and buckling ratio, M1 advantages were greatest); 2) 1/3 radius BMC, width, endosteal diameter, cortical cross-sectional area, and section modulus (GYM advantages primarily post-menarche); and 3) UD radius BMC and axial compressive strength (GYM advantages were larger with greater maturity, greatest post-menarche).
  
  
  CONCLUSIONS
  Maturity-specific comparisons suggested site-specific skeletal adaptation to loading during growth, with greater advantages at the radius versus the proximal femur. At the radius, GYM advantages included greater bone width, cortical cross-sectional area and cortical thickness; in contrast, at the femoral neck, GYM bone tissue cross-sectional area and cortical thickness were greater, but bone width was narrower than in NON. Future longitudinal analyses will evaluate putative maturity-specific differences.
authors.affiliation: Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, NY 13210, USA. dowthwaj@upstate.edu
authors.forename: Jodi N
authors.initials: JN
authors.lastname: Dowthwaite
authors.forename: Paula F
authors.initials: PF
authors.lastname: Rosenbaum
authors.forename: Tamara A
authors.initials: TA
authors.lastname: Scerpella
mesh_terms: D000293:Adolescent; D000328:Adult; D001827:Body Height / Q000502:physiology; D015519:Bone Density / Q000502:physiology; D002648:Child; D015331:Cohort Studies; D005260:Female; D005269:Femur / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D005542:Forearm / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D006173:Gymnastics; D006801:Humans; D008954:Models, Biological; D009928:Organ Specificity; D011859:Radiography; D011884:Radius / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D012044:Regression Analysis; D012741:Sexual Maturation / Q000502:physiology; D055815:Young Adult