title: Changes in myonuclear domain size do not precede muscle hypertrophy during prolonged resistance-type exercise training.
abstract: OBJECTIVE
  Muscle fibre hypertrophy is accompanied by an increase in myonuclear number, an increase in myonuclear domain size or both. It has been suggested that increases in myonuclear domain size precede myonuclear accretion and subsequent muscle fibre hypertrophy during prolonged exercise training. In this study, we assessed the changes in muscle fibre size, myonuclear and satellite cell content throughout 12 weeks of resistance-type exercise training in young men.
  
  
  METHODS
  Twenty-two young men (23 ± 1 year) were assigned to a progressive, 12-weeks resistance-type exercise training programme (3 sessions per week). Muscle biopsies from the vastus lateralis muscle were taken before and after 2, 4, 8 and 12 weeks of exercise training. Muscle fibre size, myonuclear content, myonuclear domain size and satellite cell content were assessed by immunohistochemistry.
  
  
  RESULTS
  Type I and type II muscle fibre size increased gradually throughout the 12 weeks of training (type I: 18 ± 5%, type II: 41 ± 6%, P < 0.01). Myonuclear content increased significantly over time in both the type I (P < 0.01) and type II (P < 0.001) muscle fibres. No changes in type I and type II myonuclear domain size were observed at any time point throughout the intervention. Satellite cell content increased significantly over time in both type I and type II muscle fibres (P < 0.001).
  
  
  CONCLUSIONS
  Increases in myonuclear domain size do not appear to drive myonuclear accretion and muscle fibre hypertrophy during prolonged resistance-type exercise training in vivo in humans.
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, the Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Snijders
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, the Netherlands.
authors.forename: J S J
authors.initials: JS
authors.lastname: Smeets
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, the Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: van Kranenburg
authors.affiliation: DSM Biotechnology Center, Applied Biochemistry Department, Delft, the Netherlands.
authors.forename: A K
authors.initials: AK
authors.lastname: Kies
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, the Netherlands.
authors.forename: L J C
authors.initials: LJ
authors.lastname: van Loon
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, the Netherlands.
authors.forename: L B
authors.initials: LB
authors.lastname: Verdijk
mesh_terms: D049108:Cell Enlargement; D053145:Cell Nucleus Size; D006801:Humans; D006984:Hypertrophy; D007150:Immunohistochemistry; D008297:Male; D018485:Muscle Fibers, Skeletal; D055070:Resistance Training; D032496:Satellite Cells, Skeletal Muscle; D055815:Young Adult
keywords: ceiling theory; hypertrophy; myonuclei; satellite cell