title: The impact of ageing, physical activity, and pre-frailty on skeletal muscle phenotype, mitochondrial content, and intramyocellular lipids in men.
abstract: BACKGROUND
  The exact impact of ageing on skeletal muscle phenotype and mitochondrial and lipid content remains controversial, probably because physical activity, which greatly influences muscle physiology, is rarely accounted for. The present study was therefore designed to investigate the effects of ageing, physical activity, and pre-frailty on skeletal muscle phenotype, and mitochondrial and intramyocellular lipid content in men.
  
  
  METHODS
  Recreationally active young adult (20-30 yo; YA); active (ACT) and sedentary (SED) middle-age (50-65 yo; MA-ACT and MA-SED); and older (65 + yo; 65 + ACT and 65 + SED) and pre-frail older (65 + PF) men were recruited. Muscle biopsies from the vastus lateralis were collected to assess, on muscle cross sections, muscle phenotype (using myosin heavy chain isoforms immunolabelling), the fibre type-specific content of mitochondria (by quantifying the succinate dehydrogenase stain intensity), and the fibre type-specific lipid content (by quantifying the Oil Red O stain intensity).
  
  
  RESULTS
  Only 65 + SED and 65 + PF displayed significantly lower overall and type IIa fibre sizes vs. YA. 65 + SED displayed a lower type IIa fibre proportion vs. YA. MA-SED and 65 + SED displayed a higher hybrid type IIa/IIx fibre proportion vs. YA. Sedentary and pre-frail, but not active, men displayed lower mitochondrial content irrespective of fibre type vs. YA. 65 + SED, but not 65 + ACT, displayed a higher lipid content in type I fibres vs. YA. Finally, mitochondrial content, but not lipid content, was positively correlated with indices of muscle function, functional capacity, and insulin sensitivity across all subjects.
  
  
  CONCLUSIONS
  Taken altogether, our results indicate that ageing in sedentary men is associated with (i) complex changes in muscle phenotype preferentially affecting type IIa fibres; (ii) a decline in mitochondrial content affecting all fibre types; and (iii) an increase in lipid content in type I fibres. They also indicate that physical activity partially protects from the effects of ageing on muscle phenotype, mitochondrial content, and lipid accumulation. No skeletal specific muscle phenotype of pre-frailty was observed.
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.
authors.forename: Félix
authors.initials: F
authors.lastname: St-Jean-Pelletier
authors.affiliation: Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.|Département de Biologie, Faculté des Sciences, UQAM, Quebec, Canada.
authors.forename: Charlotte H
authors.initials: CH
authors.lastname: Pion
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Leduc-Gaudet
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Sgarioto
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.
authors.forename: Igor
authors.initials: I
authors.lastname: Zovilé
authors.affiliation: Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.|Département de Biologie, Faculté des Sciences, UQAM, Quebec, Canada.|Département de Neurosciences, Faculté de Médecine, Université de Montréal, Québec, Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Barbat-Artigas
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.
authors.forename: Olivier
authors.initials: O
authors.lastname: Reynaud
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.
authors.forename: Feras
authors.initials: F
authors.lastname: Alkaterji
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.
authors.forename: François C
authors.initials: FC
authors.lastname: Lemieux
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.
authors.forename: Alexis
authors.initials: A
authors.lastname: Grenon
authors.affiliation: Département de Médecine, UdeM, et Centre de Recherche du Centre Hospitalier de l'UdeM, Quebec, Canada.
authors.forename: Pierrette
authors.initials: P
authors.lastname: Gaudreau
authors.affiliation: Department of Kinesiology and Division of Critical Care Medicine, McGill University, Quebec, Canada.|McGill University Health Centre-Research Institute, Quebec, Canada.
authors.forename: Russell T
authors.initials: RT
authors.lastname: Hepple
authors.affiliation: McGill University Health Centre-Research Institute, Quebec, Canada.|Division of Geriatric Medicine, McGill University, Quebec, Canada.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Chevalier
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Belanger
authors.affiliation: McGill University Health Centre-Research Institute, Quebec, Canada.|Division of Geriatric Medicine, McGill University, Quebec, Canada.
authors.forename: José A
authors.initials: JA
authors.lastname: Morais
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.|Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal, Quebec, Canada.
authors.forename: Mylène
authors.initials: M
authors.lastname: Aubertin-Leheudre
authors.affiliation: Département de Sciences de l'activité Physique, Faculté des Sciences, UQAM, Quebec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Québec, Canada.|Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal, Quebec, Canada.
authors.forename: Gilles
authors.initials: G
authors.lastname: Gouspillou
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D001786:Blood Glucose / Q000032:analysis; D001823:Body Composition; D015444:Exercise; D000073496:Frailty; D018737:Hand Strength; D006801:Humans; D007328:Insulin / Q000097:blood; D050356:Lipid Metabolism; D008055:Lipids / Q000032:analysis; D008297:Male; D008875:Middle Aged; D008931:Mitochondria, Muscle / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000737:chemistry / Q000378:metabolism*; D010641:Phenotype; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D007328:Insulin; D008055:Lipids
keywords: Atrophy; Exercise; Human muscle ageing; Lipid content; Mitochondria; Sarcopenia