title: Type IIB human skeletal muscle fibers positively correlate with bone mineral density irrespective to age.
abstract: BACKGROUND
  Age-associated decrease in type IIA/B human skeletal muscle fibers was detected in human biopsies in our previous study. The relationship between change in muscle fiber typing and bone mineral density (BMD) is, however, unknown either cross-sectionally or longitudinally. We therefore conducted a cross-sectional study to investigate their correlation using human muscle biopsies.
  
  
  METHODS
  Forty human subjects aged (53.4 ± 20.2) years were recruited. Histomorphometric parameters of their muscle biopsies were measured by ATPase staining and image analysis, including average area percentage, fiber number percentage, mean fiber area, and area percentage of connective tissues. Hip and spine BMD was measured by dual-energy X-ray absorptiometry. Partial correlation with adjusting age was performed.
  
  
  RESULTS
  Type IIB muscle fiber was found positively correlated with hip BMD irrespective to age and demonstrated significantly stronger relationship with BMD among all fiber types, in terms of its cross-sectional area (r = 0.380, P = 0.029) and size (r = 0.389, P = 0.025). Type IIA muscle fibers associated with hip BMD in mean fiber area only (r = 0.420, P = 0.015).
  
  
  CONCLUSIONS
  Type IIB muscle fiber may play an important role in maintaining bone quality. This may also be a relatively more sensitive fiber type of sarcopenia and osteoporosis. These findings further consolidate the muscle-bone relationship.
authors.affiliation: Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
authors.forename: Wing-Hoi
authors.initials: WH
authors.lastname: Cheung
authors.forename: Wing-Sze
authors.initials: WS
authors.lastname: Lee
authors.forename: Ling
authors.initials: L
authors.lastname: Qin
authors.forename: Ning
authors.initials: N
authors.lastname: Tang
authors.forename: Vivian Wing-Yin
authors.initials: VW
authors.lastname: Hung
authors.forename: Kwok-Sui
authors.initials: KS
authors.lastname: Leung
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density / Q000502:physiology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology* / Q000378:metabolism*; D011446:Prospective Studies; D055815:Young Adult