Quantification and characterization of grouped type I myofibers in human aging

Neil A. Kelly, Kelley G. Hammond, Michael J. Stec, C. Scott Bickel, Samuel T. Windham, S. Craig Tuggle, Marcas M. Bamman

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


Introduction: Myofiber type grouping is a histological hallmark of age-related motor unit remodeling. Despite the accepted concept that denervation–reinnervation events lead to myofiber type grouping, the completeness of those conversions remains unknown. Methods: Type I myofiber grouping was assessed in vastus lateralis biopsies from Young (26 ± 4 years; n = 27) and Older (66 ± 4 years; n = 91) adults. Grouped and ungrouped type I myofibers were evaluated for phenotypic differences. Results: Higher type I grouping in Older versus Young was driven by more myofibers per group (i.e., larger group size) (P < 0.05). In Older only, grouped type I myofibers displayed larger cross-sectional area, more myonuclei, lower capillary supply, and more sarco(endo)plasmic reticulum calcium ATPase I (SERCA I) expression (P < 0.05) than ungrouped type I myofibers. Discussion: Grouped type I myofibers retain type II characteristics suggesting that conversion during denervation–reinnervation events is either progressive or incomplete. Muscle Nerve 57: E52–E59, 2018.

Original languageEnglish (US)
Pages (from-to)E52-E59
JournalMuscle and Nerve
Issue number1
StatePublished - Jan 2018
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physiology
  • Clinical Neurology
  • Cellular and Molecular Neuroscience
  • Physiology (medical)


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