title: Study of age-related changes in postural control during quiet standing through linear discriminant analysis.
abstract: BACKGROUND
  The human body adopts a number of strategies to maintain an upright position. The analysis of the human balance allows for the understanding and identification of such strategies. The displacement of the centre of pressure (COP) is a measure that has been successfully employed in studies regarding the postural control. Most of these investigations are related to the analysis of individuals suffering from neuromuscular disorders. Recent studies have shown that the elderly population is growing very fast in many countries all over the world, and therefore, researches that try to understand changes in this group are required. In this context, this study proposes the analysis of the postural control, measured by the displacement of the COP, in groups of young and elderly adults.
  
  
  METHODS
  In total 59 subjects participated of this study. They were divided into seven groups according to their age. The displacement of the COP was collected for each subject standing on a force plate. Two experimental conditions, of 30 seconds each, were investigated: opened eyes and closed eyes. Traditional and recent digital signal processing tools were employed for feature computation from the displacement of the COP. Statistical analyses were carried out in order to identify significant differences between the features computed from the distinct groups that could allow for their discrimination.
  
  
  RESULTS
  Our results showed that Linear Discrimination Analysis (LDA), which is one of the most popular feature extraction and classifier design techniques, could be successfully employed as a linear transformation, based on the linear combination of standard features for COP analysis, capable of estimating a unique feature, so-called LDA-value, from which it was possible to discriminate the investigated groups and show a high correlation between this feature and age.
  
  
  CONCLUSIONS
  These results show that the analysis of features computed from the displacement of the COP are of great importance in studies trying to understand the ageing process. In particular, the LDA-value showed to be an adequate feature for assessment of changes in the postural control which can be related to functional changes that occur over the ageing.
authors.affiliation: Biomedical Engineering Laboratory, Faculty of Electrical Engineering, Federal University of Uberlândia, Campus Santa Mônica, Bloco 1E, Av, João Naves de Avila, 2121, Uberlândia, Minas Gerais, 38,408-100, Brazil. glcavalheiro@yahoo.com.br
authors.forename: Guilherme L
authors.initials: GL
authors.lastname: Cavalheiro
authors.forename: Maria Fernanda S
authors.initials: MF
authors.lastname: Almeida
authors.forename: Adriano A
authors.initials: AA
authors.lastname: Pereira
authors.forename: Adriano O
authors.initials: AO
authors.lastname: Andrade
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001698:Biomedical Engineering; D016002:Discriminant Analysis; D006801:Humans; D008875:Middle Aged; D009068:Movement; D004856:Postural Balance; D011187:Posture; D011312:Pressure; D012815:Signal Processing, Computer-Assisted