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Confounders in the association between exercise and femur bone in postmenopausal women

Beck, TJ and Kohlmeier, LA and Petit, MA and Wu, G and Leboff, MS and Cauley, JA and Nicholas, S and Chen, Z (2011) Confounders in the association between exercise and femur bone in postmenopausal women. Medicine and Science in Sports and Exercise, 43 (1). 80 - 89. ISSN 0195-9131

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Abstract

Introduction: Abundant animal and human evidence demonstrates that loading stimuli generate positive adaptive changes in bone, but effects of activity on bone mineral density (BMD) are often modest and frequently equivocal. Hypothesis: Physical activity effects on the femur would be better reflected in measurements of geometry than BMD. Study Design: Cross-sectional cohort study. Methods: We used data from 6032 women of mixed ethnicity aged 50-79 yr who had dual-energy X-ray absorptiometry (DXA) scans of the total body and hip from the Women's Health Initiative observational study. Subjects were distributed in three ways: self-report categories included 1) tertiles of MET and 2) reported minutes per week walking for exercise. A third, more objective, category was based on tertile of lean body mass fraction (LMF) from DXA scans. Femur outcomes included conventional femoral neck and total hip BMD, bone mineral content and region area, and geometry measurements using the Hip Structure Analysis software. Outcomes were compared between activity groups using models adjusted for common confounders. Results: Adjusted bone measurements showed similar activity effects with all three grouping variables, but these were greater and more significant when evaluated by LMF tertile. Women in the highest LMF tertile had the widest femurs. Differences in section modulus between highest and lowest tertile of LMF were 50%-80% greater than the association with bone mineral content and two to three times that on BMD. Conclusions: More active women in the Women's Health Initiative observational study had geometrically stronger femurs, although effects are underestimated, not apparent, or sometimes negative when using BMD as an outcome. Clinical Relevance: Exercise improves the strength of the femur largely by adding bone to the outer cortical surface; this improves resistance to bending, but because of the way DXA measurements are made, this may paradoxically reduce BMD. © 2010 by the American College of Sports Medicine.


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Details

Item Type: Article
Status: Published
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Beck, TJ
Kohlmeier, LA
Petit, MA
Wu, G
Leboff, MS
Cauley, JAJCauley@edc.pitt.eduJCAULEY
Nicholas, S
Chen, Z
Date: 1 January 2011
Date Type: Publication
Journal or Publication Title: Medicine and Science in Sports and Exercise
Volume: 43
Number: 1
Page Range: 80 - 89
DOI or Unique Handle: 10.1249/mss.0b013e3181e57bab
Schools and Programs: Graduate School of Public Health > Epidemiology
Refereed: Yes
ISSN: 0195-9131
Date Deposited: 03 Apr 2015 00:35
Last Modified: 02 Feb 2019 15:55
URI: http://d-scholarship.pitt.edu/id/eprint/24249

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