title: Matters of fiber size and myonuclear domain: Does size matter more than age?
abstract: BACKGROUND
  The relationship between fiber size and myonuclear content is poorly understood.
  
  
  METHODS
  Biopsy cross-sections from young and old trained and untrained healthy individuals were analyzed for fiber area and myonuclei, and 2 fiber-size-dependent cluster analyses were performed.
  
  
  RESULTS
  When comparing fibers of similar size, no effect of training or age was found for myonuclear domain. There was a linear relationship between fiber area and myonuclei per fiber (r = 0.99; P < 0.001) and a non-linear relationship between fiber area and domain (r = 0.97-0.99; P < 0.0001), with a markedly smaller domain in fibers <3,000 µm(2). A higher proportion of type II fibers <3,000 µm(2) was observed in the old subjects.
  
  
  CONCLUSIONS
  These findings suggest that age-related reductions in myonuclear domain size could be explained by the greater proportion of small fibers. The data also highlight the usefulness of determining fiber-size-based clusters for gaining mechanistic insight into the relationship between skeletal muscle fiber size and myonuclear content.
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Karlsen
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Couppé
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Jesper L
authors.initials: JL
authors.lastname: Andersen
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Ulla R
authors.initials: UR
authors.lastname: Mikkelsen
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Rie H
authors.initials: RH
authors.lastname: Nielsen
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: S Peter
authors.initials: SP
authors.lastname: Magnusson
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
authors.affiliation: Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Building 8, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark.|Department of Biomedical Sciences, Centre for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Abigail L
authors.initials: AL
authors.lastname: Mackey
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D000704:Analysis of Variance; D001706:Biopsy; D002467:Cell Nucleus / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000502:physiology*; D055815:Young Adult
keywords: aging muscle; cluster analysis; myonuclear domain; sarcopenia; small fibers