title: Is gait variability reliable in older adults and Parkinson's disease? Towards an optimal testing protocol.
abstract: BACKGROUND
  Despite the widespread use of gait variability in research and clinical studies, testing protocols designed to optimise its reliability have not been established. This study evaluates the impact of testing protocol and pathology on the reliability of gait variability.
  
  
  OBJECTIVE
  To (i) estimate the reliability of gait variability during continuous and intermittent walking protocols in older adults and people with Parkinson's disease (PD), (ii) determine optimal number of steps for acceptable levels of reliability of gait variability and (iii) provide sample size estimates for use in clinical trials.
  
  
  METHODS
  Gait variability was measured twice, one week apart, in 27 older adults and 25 PD participants. Participants walked at their preferred pace during: (i) a continuous 2 min walk and (ii) 3 intermittent walks over a 12 m walkway. Gait variability was calculated as the within-person standard deviation for step velocity, length and width, and step, stance and swing duration.
  
  
  RESULTS
  Reliability of gait variability ranged from poor to excellent (intra class correlations .041-.860; relative limits of agreement 34-89%). Gait variability was more reliable during continuous walks. Control and PD participants demonstrated similar reliability. Increasing the number of steps improved reliability, with most improvement seen across the first 30 steps.
  
  
  CONCLUSIONS
  In this study, we identified testing protocols that improve the reliability of measuring gait variability. We recommend using a continuous walking protocol and to collect no fewer than 30 steps. Early PD does not appear to impact negatively on the reliability of gait variability.
authors.affiliation: Institute for Ageing and Health, Clinical Ageing Research Unit, Newcastle University, NE4 5PL, United Kingdom. brook.galna@ncl.ac.uk
authors.forename: Brook
authors.initials: B
authors.lastname: Galna
authors.forename: Sue
authors.initials: S
authors.lastname: Lord
authors.forename: Lynn
authors.initials: L
authors.lastname: Rochester
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005260:Female; D005684:Gait; D020233:Gait Disorders, Neurologic / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D015577:Geriatric Assessment / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D015203:Reproducibility of Results