title: Muscle mass and muscle function over the adult life span: a cross-sectional study in Flemish adults.
abstract: BACKGROUND
  Aging is accompanied with a progressive deterioration of skeletal muscle mass (SMM) and muscle function, also termed sarcopenia.
  
  
  METHODS
  The aim was to describe SMM (based on bioelectrical impedance) and muscle function of the leg extensors over the adult age span in 819 men and 578 women, aged 18-78 years. The distribution of skeletal muscle index (SMI; SMM/height(2)) groups was described and muscle force-velocity characteristics were examined between SMI-groups over the adult life span. Subjects were divided into age categories and SMI groups to compare their muscle strength characteristics. Isometric and isokinetic strength, ballistic movement speed and muscular endurance of the knee extensors were evaluated on a Biodex dynamometer.
  
  
  RESULTS
  Age by gender interaction effects were found significant (P<0.01) for all strength tests. In general, the overall drop in slow and faster knee extension strength was larger than the isometric component, with women showing larger losses by the age of 60-70 years compared to men. Regression analysis revealed significant (P<0.01) age-related reductions, with the largest explained variance for the muscular endurance parameter (24%). No age by SMI-group interaction effect was observed for muscle function, but main effects of age and SMI were significant (P<0.01).
  
  
  CONCLUSIONS
  The age-related decline in muscle function was stronger in women. Furthermore, a low SMI results in a weaker muscle function compared to a normal SMI in each age-category, pointing out that its relationship with physical disability should therefore be further examined over the adult life-span.
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Kinesiology, Physical Activity, KU Leuven, Tervuursevest 101, 3001 Leuven, Belgium.
authors.forename: Ruben
authors.initials: R
authors.lastname: Charlier
authors.affiliation: Faculty of Physical Education and Physiotherapy, Department of Human Biometrics and Biomechanics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Evelien
authors.initials: E
authors.lastname: Mertens
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Kinesiology, Physical Activity, KU Leuven, Tervuursevest 101, 3001 Leuven, Belgium.
authors.forename: Johan
authors.initials: J
authors.lastname: Lefevre
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Kinesiology, Physical Activity, KU Leuven, Tervuursevest 101, 3001 Leuven, Belgium. Electronic address: martine.thomis@faber.kuleuven.be.
authors.forename: Martine
authors.initials: M
authors.lastname: Thomis
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001530:Belgium; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007717:Knee / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D055948:Sarcopenia / Q000175:diagnosis / Q000208:ethnology / Q000503:physiopathology*; D044465:White People
keywords: Adult life span; Aging; Muscle function; Sarcopenia; Skeletal muscle index; Skeletal muscle mass