title: Reliability of System Identification Techniques to Assess Standing Balance in Healthy Elderly.
abstract: OBJECTIVE
  System identification techniques have the potential to assess the contribution of the underlying systems involved in standing balance by applying well-known disturbances. We investigated the reliability of standing balance parameters obtained with multivariate closed loop system identification techniques.
  
  
  METHODS
  In twelve healthy elderly balance tests were performed twice a day during three days. Body sway was measured during two minutes of standing with eyes closed and the Balance test Room (BalRoom) was used to apply four disturbances simultaneously: two sensory disturbances, to the proprioceptive and the visual system, and two mechanical disturbances applied at the leg and trunk segment. Using system identification techniques, sensitivity functions of the sensory disturbances and the neuromuscular controller were estimated. Based on the generalizability theory (G theory), systematic errors and sources of variability were assessed using linear mixed models and reliability was assessed by computing indexes of dependability (ID), standard error of measurement (SEM) and minimal detectable change (MDC).
  
  
  RESULTS
  A systematic error was found between the first and second trial in the sensitivity functions. No systematic error was found in the neuromuscular controller and body sway. The reliability of 15 of 25 parameters and body sway were moderate to excellent when the results of two trials on three days were averaged. To reach an excellent reliability on one day in 7 out of 25 parameters, it was predicted that at least seven trials must be averaged.
  
  
  CONCLUSIONS
  This study shows that system identification techniques are a promising method to assess the underlying systems involved in standing balance in elderly. However, most of the parameters do not appear to be reliable unless a large number of trials are collected across multiple days. To reach an excellent reliability in one third of the parameters, a training session for participants is needed and at least seven trials of two minutes must be performed on one day.
authors.affiliation: Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, the Netherlands.|Department of Biomechanical Engineering, Delft University of Technology, Delft, the Netherlands.
authors.forename: Jantsje H
authors.initials: JH
authors.lastname: Pasma
authors.affiliation: Department of Biomechanical Engineering, Institute for Biomedical Technology and Technical Medicine (MIRA), University of Twente, Enschede, the Netherlands.
authors.forename: Denise
authors.initials: D
authors.lastname: Engelhart
authors.affiliation: Department of Medicine and Aged Care, Royal Melbourne Hospital, University of Melbourne, Melbourne, Australia.|Department of Human Movement Sciences, MOVE Research Institute Amsterdam, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
authors.forename: Andrea B
authors.initials: AB
authors.lastname: Maier
authors.affiliation: Department of Mechanical Automation and Mechatronics, University of Twente, Enschede, the Netherlands.
authors.forename: Ronald G K M
authors.initials: RG
authors.lastname: Aarts
authors.affiliation: Center for Human Drug Research, Leiden, the Netherlands.
authors.forename: Joop M A
authors.initials: JM
authors.lastname: van Gerven
authors.affiliation: Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: J Hans
authors.initials: JH
authors.lastname: Arendzen
authors.affiliation: Department of Biomechanical Engineering, Delft University of Technology, Delft, the Netherlands.|Department of Biomechanical Engineering, Institute for Biomedical Technology and Technical Medicine (MIRA), University of Twente, Enschede, the Netherlands.
authors.forename: Alfred C
authors.initials: AC
authors.lastname: Schouten
authors.affiliation: Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Carel G M
authors.initials: CG
authors.lastname: Meskers
authors.affiliation: Department of Biomechanical Engineering, Delft University of Technology, Delft, the Netherlands.|Department of Biomechanical Engineering, Institute for Biomedical Technology and Technical Medicine (MIRA), University of Twente, Enschede, the Netherlands.
authors.forename: Herman
authors.initials: H
authors.lastname: van der Kooij
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans; D004856:Postural Balance; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity