title: Differential effects of exercise on tibial shaft marrow density in young female athletes.
abstract: BACKGROUND
  Increased mechanical loading can promote the preferential differentiation of bone marrow mesenchymal stem cells to osteoblastogenesis, but it is not known whether long-term bone strength-enhancing exercise in humans can reduce marrow adiposity.
  
  
  OBJECTIVE
  Our objective was to examine whether bone marrow density (MaD), as an estimate of marrow adiposity 1) differs between young female athletes with contrasting loading histories and bone strengths and 2) is an independent predictor of bone strength at the weight-bearing tibia.
  
  
  METHODS
  Mid-tibial MaD, cortical area (CoA), total area, medullary area, strength strain index (SSI), and cortical volumetric bone mineral density (vBMD) (total, endocortical, midcortical, and pericortical) was assessed using peripheral quantitative computed tomography in 179 female athletes involved in both impact and nonimpact loading sports and 41 controls aged 17-40 years.
  
  
  RESULTS
  As we have previously reported CoA, total area, and SSI were 16% to 24% greater in the impact group compared with the controls (all P < .001) and 12% to 18% greater than in the nonimpact group (all P < .001). The impact group also had 0.5% higher MaD than the nonimpact and control groups (both P < .05). Regression analysis further showed that midtibial MaD was significantly associated with SSI, CoA, endocortical vBMD, and pericortical vBMD (P < .05) in all women combined, after adjusting for age, bone length, loading groups, medullary area, muscle cross-sectional area, and percent fat.
  
  
  CONCLUSIONS
  In young female athletes, tibial bone MaD was associated with loading history and was an independent predictor of tibial bone strength. These findings suggest that an exercise-induced increase in bone strength may be mediated via reduced bone marrow adiposity and consequently increased osteoblastogenesis.
authors.affiliation: Centre for Physical Activity and Nutrition Research, School of Exercise and Nutrition Sciences, Deakin University, Melbourne, VIC 3125, Australia. timo.rantalainen@jyu.fi
authors.forename: Timo
authors.initials: T
authors.lastname: Rantalainen
authors.forename: Riku
authors.initials: R
authors.lastname: Nikander
authors.forename: Ari
authors.initials: A
authors.lastname: Heinonen
authors.forename: Tomas
authors.initials: T
authors.lastname: Cervinka
authors.forename: Harri
authors.initials: H
authors.lastname: Sievänen
authors.forename: Robin M
authors.initials: RM
authors.lastname: Daly
mesh_terms: D052438:Adipocytes, White / Q000166:cytology* / Q000000981:diagnostic imaging; D050154:Adiposity; D000293:Adolescent; D041923:Adolescent Development; D000328:Adult; D056352:Athletes; D015519:Bone Density; D001853:Bone Marrow / Q000737:chemistry* / Q000000981:diagnostic imaging / Q000254:growth & development; D001854:Bone Marrow Cells / Q000166:cytology* / Q000000981:diagnostic imaging; D055598:Chemical Phenomena; D018483:Diaphyses / Q000737:chemistry / Q000166:cytology* / Q000000981:diagnostic imaging / Q000254:growth & development; D015444:Exercise; D005260:Female; D006801:Humans; D010006:Osteoblasts / Q000166:cytology; D010012:Osteogenesis; D013977:Tibia / Q000737:chemistry / Q000166:cytology* / Q000000981:diagnostic imaging / Q000254:growth & development; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing; D055815:Young Adult