title: Bone mineral density across a range of physical activity volumes: NHANES 2007-2010.
abstract: BACKGROUND
  The association between aerobic physical activity volume and bone mineral density (BMD) is not completely understood. The purpose of this study was to clarify the association between BMD and aerobic activity across a broad range of activity volumes, particularly volumes between those recommended in the 2008 Physical Activity Guidelines for Americans and those of trained endurance athletes.
  
  
  METHODS
  Data from the 2007-2010 National Health and Nutrition Examination Survey were used to quantify the association between reported physical activity and BMD at the lumbar spine and proximal femur across the entire range of activity volumes reported by US adults. Participants were categorized into multiples of the minimum guideline-recommended volume based on reported moderate- and vigorous-intensity leisure activity. Lumbar and proximal femur BMD were assessed with dual-energy x-ray absorptiometry.
  
  
  RESULTS
  Among women, multivariable-adjusted linear regression analyses revealed no significant differences in lumbar BMD across activity categories, whereas proximal femur BMD was significantly higher among those who exceeded the guidelines by 2-4 times than those who reported no activity. Among men, multivariable-adjusted BMD at both sites neared its highest values among those who exceeded the guidelines by at least 4 times and was not progressively higher with additional activity. Logistic regression estimating the odds of low BMD generally echoed the linear regression results.
  
  
  CONCLUSIONS
  The association between physical activity volume and BMD is complex. Among women, exceeding guidelines by 2-4 times may be important for maximizing BMD at the proximal femur, whereas among men, exceeding guidelines by ≥4 times may be beneficial for lumbar and proximal femur BMD.
authors.affiliation: 1Division of Epidemiology, Human Genetics, and Environmental Sciences, University of Texas School of Public Health, Austin, TX; 2Division of Geriatric Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO; 3Center for Clinical and Translational Sciences, University of Texas Health Science Center, Houston, TX; and 4Department of Kinesiology and Health Education, University of Texas at Austin, Austin, TX.
authors.forename: Geoffrey P
authors.initials: GP
authors.lastname: Whitfield
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Kohrt
authors.forename: Kelley K
authors.initials: KK
authors.lastname: Pettee Gabriel
authors.forename: Mohammad H
authors.initials: MH
authors.lastname: Rahbar
authors.forename: Harold W
authors.initials: HW
authors.lastname: Kohl
mesh_terms: D000328:Adult; D000368:Aged; D015519:Bone Density; D005260:Female; D005269:Femur / Q000378:metabolism; D006801:Humans; D008159:Lumbar Vertebrae / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009749:Nutrition Surveys; D055815:Young Adult