title: Genetic analysis of physical activity in twins.
abstract: BACKGROUND
  The reduced contribution of physical activity (PA) to daily energy expenditure contributes to the increased prevalence of obesity. A genetic control of activity-induced energy expenditure (AEE) may contribute to a genetic susceptibility to obesity.
  
  
  OBJECTIVE
  Our aim was to investigate the relative contribution of genetic and environmental factors to the variation and covariation in AEE and PA.
  
  
  METHODS
  Twelve monozygotic and 8 same-sex dizygotic (including 2 same-sex sibling pairs; age differences: 2 and 2.5 y) twin pairs aged between 18 and 39 y participated. AEE was measured in a respiration chamber for 24 h and with doubly labeled water in daily life for 2 wk. PA was recorded simultaneously with a triaxial accelerometer. Structural equation modeling was used to separate and quantify the observed variance into sex-adjusted additive genetic and common and unique environmental contributions.
  
  
  RESULTS
  In the respiration chamber, common and unique environmental factors explained the variance in AEE and PA, and no genetic contribution was found. In daily life, genetic factors explained 72% of the variance in AEE and 78% of the variance in PA. Unique environmental factors explained the remaining variance. The same additive genetic factors explained 67% of the covariance in AEE and PA in daily life.
  
  
  CONCLUSIONS
  In the present exploratory study that used gold standard measurements for AEE and PA but a limited sample size, genetic influence explained a large part of the variation in AEE and PA in daily life, whereas both AEE and PA were influenced by environment only within the confined area of the respiration chamber.
authors.affiliation: Department of Human Biology, Maastricht University, Maastricht, Netherlands. a.joosen@hb.unimaas.nl
authors.forename: Annemiek M C P
authors.initials: AM
authors.lastname: Joosen
authors.forename: Marij
authors.initials: M
authors.lastname: Gielen
authors.forename: Robert
authors.initials: R
authors.lastname: Vlietinck
authors.forename: Klaas R
authors.initials: KR
authors.lastname: Westerterp
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D000886:Anthropometry; D001481:Basal Metabolism / Q000235:genetics / Q000502:physiology; D001823:Body Composition / Q000502:physiology; D001834:Body Water / Q000378:metabolism; D003903:Deuterium; D004734:Energy Metabolism / Q000235:genetics* / Q000502:physiology; D004777:Environment; D015444:Exercise / Q000502:physiology*; D005260:Female; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D008297:Male; D009765:Obesity / Q000209:etiology / Q000235:genetics*; D010101:Oxygen Consumption; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D003903:Deuterium