title: Lap time variation and executive function in older adults: the Baltimore Longitudinal Study of Aging.
abstract: BACKGROUND
  poor cognitive and motor performance predicts neurological dysfunction. Variable performance may be a subclinical indicator of emerging neurological problems.
  
  
  OBJECTIVE
  examine the cross-sectional association between a clinically accessible measure of variable walking and executive function.
  
  
  METHODS
  older adults aged 60 or older from the Baltimore Longitudinal Study of Aging (n = 811) with data on the 400-m walk test and cognition. Based on ten 40-m laps, we calculated mean lap time (MLT) and variation in time across ten 40-m laps (lap time variation, LTV). Executive function tests assessed attention and short-term memory (digit span forward and backward), psychomotor speed [Trail Making Test (TMT) part A] and multicomponent tasks requiring cognitive flexibility [TMT part B, part B-A (Delta TMT) and digit symbol substitution test (DSST)]. Multivariate linear regression analysis examined the cross-sectional association between LTV and executive function, adjusted for MLT, age, sex and education, as well as the LTV × MLT interaction.
  
  
  RESULTS
  the LTV was univariately associated with all executive function tests except digit span (P < 0.001); after adjustment, the association with TMT part A remained (standardised β = 0.142, P = 0.002). There was an interaction between MLT and LTV; among fast walkers, greater LTV was associated with a greater Delta TMT (β for LTV × MLT = -1.121, P = 0.016) after adjustment.
  
  
  CONCLUSIONS
  at any walking speed, greater LTV is associated with psychomotor slowing. Among persons with faster walking speed, variation is associated with worse performance on a complex measure of cognitive flexibility. A simple measure of variability in walking time is independently associated with psychomotor slowing.
authors.affiliation: National Institute on Aging, NIH-Translational Gerontology Branch, Baltimore, MD, USA.
authors.forename: Qu
authors.initials: Q
authors.lastname: Tian
authors.affiliation: National Institute on Aging, NIH-Translational Gerontology Branch, Baltimore, MD, USA.
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Simonsick
authors.affiliation: National Institute on Aging (NIA), NIH, Baltimore, MD, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Resnick
authors.affiliation: National Institute on Aging, NIH-Translational Gerontology Branch, Baltimore, MD, USA.
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Shardell
authors.affiliation: National Institute on Aging, NIH-Translational Gerontology Branch, Baltimore, MD, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: Ferrucci
authors.affiliation: National Institute on Aging, NIH-Translational Gerontology Branch, Baltimore, MD, USA.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Studenski
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000523:psychology*; D015142:Baltimore; D056344:Executive Function; D005080:Exercise Test; D005260:Female; D015577:Geriatric Assessment; D006304:Health Status; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D015999:Multivariate Analysis; D009483:Neuropsychological Tests; D011237:Predictive Value of Tests; D013997:Time Factors; D016138:Walking
keywords: cognitive flexibility; lap time variation; older people; psychomotor speed