A twin study on the heritability of walking ability among older women.

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.