title: Protein Supplementation Augments Muscle Fiber Hypertrophy but Does Not Modulate Satellite Cell Content During Prolonged Resistance-Type Exercise Training in Frail Elderly.
abstract: OBJECTIVE
  Protein supplementation increases gains in lean body mass following prolonged resistance-type exercise training in frail older adults. We assessed whether the greater increase in lean body mass can be attributed to muscle fiber type specific hypertrophy with concomitant changes in satellite cell (SC) content.
  
  
  METHODS
  A total of 34 frail elderly individuals (77 ± 1 years, n = 12 male adults) participated in this randomized, double-blind, placebo-controlled trial with 2 arms in parallel.
  
  
  METHODS
  Participants performed 24 weeks of progressive resistance-type exercise training (2 sessions per week) during which they were supplemented twice-daily with milk protein (2 × 15 g) or a placebo.
  
  
  METHODS
  Muscle biopsies were taken at baseline, and after 12 and 24 weeks of intervention, to determine type I and type II muscle fiber specific cross-sectional area (CSA), SC content, and myocellular characteristics.
  
  
  RESULTS
  In the placebo group, a trend for a 20% ± 11% increase in muscle fiber CSA was observed in type II fibers only (P = .051), with no increase in type I muscle fiber CSA. In the protein group, type I and II muscle fiber CSA increased by 23% ± 7% and 34% ± 10% following 6 months of training, respectively (P < .01). Myonuclear domain size increased over time in both groups and fiber types (P < .001), with no significant differences between groups (P > .05). No changes in myonuclear content and SC contents were observed over time in either group (both P > .05). Regression analysis showed that changes in myonuclear content and domain size are predictive of muscle fiber hypertrophy.
  
  
  CONCLUSIONS
  Protein supplementation augments muscle fiber hypertrophy following prolonged resistance-type exercise training in frail older people, without changes in myonuclear and SC content.
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Center(+), Maastricht, The Netherlands.
authors.forename: Marlou L
authors.initials: ML
authors.lastname: Dirks
authors.affiliation: Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands; Top Institute Food and Nutrition (TIFN), Wageningen, The Netherlands.
authors.forename: Michael
authors.initials: M
authors.lastname: Tieland
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Center(+), Maastricht, The Netherlands; Top Institute Food and Nutrition (TIFN), Wageningen, The Netherlands.
authors.forename: Lex B
authors.initials: LB
authors.lastname: Verdijk
authors.affiliation: Department of Neuroscience, School of Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: Mario
authors.initials: M
authors.lastname: Losen
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Center(+), Maastricht, The Netherlands.
authors.forename: Rachel
authors.initials: R
authors.lastname: Nilwik
authors.affiliation: Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
authors.forename: Marco
authors.initials: M
authors.lastname: Mensink
authors.affiliation: Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands; Top Institute Food and Nutrition (TIFN), Wageningen, The Netherlands.
authors.forename: Lisette C P G M
authors.initials: LCPGM
authors.lastname: de Groot
authors.affiliation: NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Center(+), Maastricht, The Netherlands; Top Institute Food and Nutrition (TIFN), Wageningen, The Netherlands. Electronic address: L.vanLoon@maastrichtuniversity.nl.
authors.forename: Luc J C
authors.initials: LJC
authors.lastname: van Loon
mesh_terms: D000368:Aged; D049108:Cell Enlargement; D053145:Cell Nucleus Size; D004044:Dietary Proteins / Q000008:administration & dosage*; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D006984:Hypertrophy; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000473:pathology*; D055070:Resistance Training / Q000379:methods*
chemical_list: D004044:Dietary Proteins
keywords: Sarcopenia; amino acids; resistance exercise; skeletal muscle