title: The role of genetics and environment in lifting force and isometric trunk extensor endurance.
abstract: OBJECTIVE
  Our understanding of what different back performance tests are measuring is limited. The purpose of this study was to investigate the relative contributions of genetics and unique and common environmental factors for 3 tests of back muscle performance in a classic twin analysis.
  
  
  METHODS
  The subjects were a population-based sample of 122 monozygotic and 131 dizygotic male twin pairs aged 35 to 69 years (mean=49.9, SD=7.7).
  
  
  METHODS
  Variance component analysis was applied to estimate genetic and environmental influences on isokinetic and psychophysical lifting and isometric trunk extensor endurance test performance. The Cholesky decomposition genetic factor model was used to estimate genetic and environmental correlations of these variables. Path analysis was applied to study determinants of isokinetic and psychophysical lifting and isometric trunk extensor endurance test performance.
  
  
  RESULTS
  Genetic effects accounted for 60%, 33%, and 5% of the total variance of isokinetic and psychophysical lifting forces and isometric trunk extensor endurance, respectively, and unique environmental factors accounted for 35%, 49%, and 61% of the variance.
  
  
  CONCLUSIONS
  Genetics had a dominant role in isokinetic lifting and unique environmental factors in isometric trunk extensor endurance. The relatively high role of genetics in lifting force suggests the potential to increase and sustain changes in back muscle force in the general population may be particularly challenging.
authors.affiliation: Department of Physiology, University of Kuopio, PO Box 1627, 70211 Kuopio, Finland. annina.ropponen@uku.fi
authors.forename: Annina
authors.initials: A
authors.lastname: Ropponen
authors.forename: Esko
authors.initials: E
authors.lastname: Levälahti
authors.forename: Tapio
authors.initials: T
authors.lastname: Videman
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Michele C
authors.initials: MC
authors.lastname: Battié
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D001415:Back / Q000502:physiology; D004777:Environment; D015444:Exercise; D005387:Finland; D006304:Health Status; D006801:Humans; D007537:Isometric Contraction / Q000235:genetics*; D007899:Leisure Activities; D017770:Lifting; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic