title: A twin study on the heritability of walking ability among older women.
abstract: BACKGROUND
  This study examined the role of genetic and environmental factors explaining individual differences in women's walking ability in old age.
  
  
  METHODS
  A maximal walking speed test over 10 meters and a 6-minute walking endurance test were done under standard conditions among 92 monozygotic and 105 dizygotic pairs of twin sisters reared together, aged 63-75 years.
  
  
  RESULTS
  The mean maximum walking speed was 1.73 +/- 0.32 m/s and the mean distance covered in the 6-minute walking test was 525.6 +/- 77.3 m. Multivariate genetic modeling showed that a minor part of the variances in walking speed (16%, 95% confidence interval [CI]: 0%-54%) and endurance (20%, 95% CI: 0%-56%) were accounted for by genetic influences, and that the genetic influences were common to both traits. The corresponding proportions for common environmental factors were 37% (95% CI: 4%-58%) and 26% (95% CI: 0%-52%), and for individual environmental factors 46% (95% CI: 35%-59%) and 54% (95% CI 42%-68%), respectively. The environmental effects were partially common to both traits.
  
  
  CONCLUSIONS
  Among relatively healthy older women, a modest portion of the variances of walking speed and endurance were accounted for by genetic factors, whereas shared and individual environmental factors explained most of the variance in both traits.
authors.affiliation: MSc, University of Jyväskylä, Department of Health Sciences, P.O. Box 35 (Viveca), Jyväskylä, 40014 Finland. alfredo.ortega@sport.jyu.fi
authors.forename: Alfredo
authors.initials: A
authors.lastname: Ortega-Alonso
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Urho M
authors.initials: UM
authors.lastname: Kujala
authors.forename: Sarianna
authors.initials: S
authors.lastname: Sipilä
authors.forename: Timo
authors.initials: T
authors.lastname: Törmäkangas
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Markku
authors.initials: M
authors.lastname: Koskenvuo
authors.forename: Taina
authors.initials: T
authors.lastname: Rantanen
mesh_terms: D000368:Aged; D004777:Environment; D005260:Female; D006801:Humans; D008875:Middle Aged; D010807:Physical Endurance / Q000235:genetics*; D016138:Walking