title: Reliability of traditional and fractal dimension measures of quiet stance center of pressure in young, healthy people.
abstract: OBJECTIVE
  To assess reliability of traditional and fractal dimension measures of quiet stance center of pressure (COP).
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  Thirty young healthy men (n=20) and women (n=10) (mean age, 23 y).
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  COP was recorded for 3 trials across 4 conditions: eyes open and eyes closed standing on firm and foam surfaces. Traditional COP variables--peak sway velocity and range of sway, both in the anteroposterior (AP) and mediolateral (ML) directions, and total excursion area, and fractal dimension of the COP in the AP and ML directions--were calculated. Reliability statistics were calculated.
  
  
  RESULTS
  Range of sway (AP) was the most reliable traditional variable (intraclass correlation coefficient model 2,1 [ICC(2,1)] range -.28 to .72.). Peak sway velocity (AP) had poorest reliability (ICC(2,1) range, .05-.29). Only 1 of the traditional variables had excellent reliability; total excursion area (firm, eyes closed) (ICC(2,1)=.95). All bar 1 fractal dimension measures had excellent ICCs. Relative technical error of measurement ranged from 4% to 7% for the fractal dimension measures. Coefficients of variation were also very good, ranging from 1.8% to 6.7%.
  
  
  CONCLUSIONS
  Fractal dimension measures were more reliable than traditional measures of COP. Although traditional measures are used extensively to assess COP, their reliability is questionable. Fractal dimension measures show promise to reliably quantify COP and warrant further investigation.
authors.affiliation: School of Biomedical and Sports Science, Edith Cowan University, Joondalup, Western Australia, Australia. tdoyle@nd.edu.au
authors.forename: Tim L
authors.initials: TL
authors.lastname: Doyle
authors.forename: Robert U
authors.initials: RU
authors.lastname: Newton
authors.forename: Angus F
authors.initials: AF
authors.lastname: Burnett
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005260:Female; D017709:Fractals; D006801:Humans; D008297:Male; D008954:Models, Biological; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011312:Pressure; D011434:Proprioception / Q000502:physiology; D015203:Reproducibility of Results