title: A comparative study on approximate entropy measure and poincaré plot indexes of minimum foot clearance variability in the elderly during walking.
abstract: BACKGROUND
  Trip-related falls which is a major problem in the elderly population, might be linked to declines in the balance control function due to ageing. Minimum foot clearance (MFC) which provides a more sensitive measure of the motor function of the locomotor system, has been identified as a potential gait parameter associated with trip-related falls in older population. This paper proposes nonlinear indexes (approximate entropy (ApEn) and Poincaré plot indexes) of MFC variability and investigates the relationship of MFC with derived indexes of elderly gait patterns. The main aim is to find MFC variability indexes that well correlate with balance impairments.
  
  
  METHODS
  MFC data during treadmill walking for 14 healthy elderly and 10 elderly participants with balance problems and a history of falls (falls risk) were analysed using a PEAK-2D motion analysis system. ApEn and Poincaré plot indexes of all MFC data sets were calculated and compared.
  
  
  RESULTS
  Significant relationships of mean MFC with Poincaré plot indexes (SD1, SD2) and ApEn (r = 0.70, p < 0.05; r = 0.86, p < 0.01; r = 0.74, p < 0.05) were found in the falls-risk elderly group. On the other hand, such relationships were absent in the healthy elderly group. In contrast, the ApEn values of MFC data series were significantly (p < 0.05) correlated with Poincaré plot indexes of MFC in the healthy elderly group, whereas correlations were absent in the falls-risk group. The ApEn values in the falls-risk group (mean ApEn = 0.18 +/- 0.03) was significantly (p < 0.05) higher than that in the healthy group (mean ApEn = 0.13 +/- 0.13). The higher ApEn values in the falls-risk group might indicate increased irregularities and randomness in their gait patterns and an indication of loss of gait control mechanism. ApEn values of randomly shuffled MFC data of falls risk subjects did not show any significant relationship with mean MFC.
  
  
  CONCLUSIONS
  Results have implication for quantifying gait dynamics in normal and pathological conditions, thus could be useful for the early diagnosis of at-risk gait. Further research should provide important information on whether falls prevention intervention can improve the gait performance of falls risk elderly by monitoring the change in MFC variability indexes.
authors.affiliation: Department of Electrical & Electronic Engineering, The Universityof Melbourne, VIC 3010, Australia. a.khandoker@ee.unimelb.edu.au
authors.forename: Ahsan H
authors.initials: AH
authors.lastname: Khandoker
authors.forename: Marimuthu
authors.initials: M
authors.lastname: Palaniswami
authors.forename: Rezaul K
authors.initials: RK
authors.lastname: Begg
mesh_terms: D000369:Aged, 80 and over; D000465:Algorithms; D003627:Data Interpretation, Statistical; D005260:Female; D005528:Foot / Q000502:physiology*; D005684:Gait / Q000502:physiology*; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016138:Walking / Q000502:physiology*