title: A gait abnormality measure based on root mean square of trunk acceleration.
abstract: BACKGROUND
  Root mean square (RMS) of trunk acceleration is seen frequently in gait analysis research. However, many studies have reported that the RMS value was related to walking speed. Therefore, the relationship between the RMS value and walking speed should be considered when the RMS value is used to assess gait abnormality. We hypothesized that the RMS values in three sensing axes exhibit common proportions for healthy people if they walk at their own preferred speed and that the RMS proportions in abnormal gait deviate from the common proportions. In this study, we proposed the RMS ratio (RMSR) as a gait abnormality measure and verified its ability to discriminate abnormal gait.
  
  
  METHODS
  Forty-seven healthy male subjects (24-49 years) were recruited to examine the relationship between walking speed and the RMSR. To verify its ability to discriminate abnormal gait, twenty age-matched male hemiplegic patients (30-48 years) participated as typical subjects with gait abnormality. A tri-axial accelerometer was attached to their lower back, and they walked along a corridor at their own preferred speed. We defined the RMSR as the ratio between RMS in each direction and the RMS vector magnitude.
  
  
  RESULTS
  In the healthy subjects, the RMS in all directions related to preferred walking speed. In contrast, RMSR in the mediolateral (ML) direction did not correlate with preferred walking speed (rs = -0.10, p = 0.54) and represented the similar value among the healthy subjects. Moreover, the RMSR in the ML direction for the hemiplegic patients was significantly higher than that for the healthy subjects (p < 0.01).
  
  
  CONCLUSIONS
  These results suggest that the RMSR in the ML direction exhibits a common value when healthy subjects walk at their own preferred speed, even if their preferred walking speed were different. For subjects with gait abnormality, the RMSR in the ML direction deviates from the common value of healthy subjects. The RMSR in the ML direction may potentially be a quantitative measure of gait abnormality.
authors.affiliation: Faculty of Biomedical Engineering, Osaka Electro-Communication University, 18-8 Hatsucho, Neyagawa, Osaka 572-8530, Japan. m-sekine@isc.osakac.ac.jp.
authors.forename: Masaki
authors.initials: M
authors.lastname: Sekine
authors.forename: Toshiyo
authors.initials: T
authors.lastname: Tamura
authors.forename: Masaki
authors.initials: M
authors.lastname: Yoshida
authors.forename: Yuki
authors.initials: Y
authors.lastname: Suda
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kimura
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Miyoshi
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Kijima
authors.forename: Yuji
authors.initials: Y
authors.lastname: Higashi
authors.forename: Toshiro
authors.initials: T
authors.lastname: Fujimoto
mesh_terms: D000054:Acceleration; D000328:Adult; D001696:Biomechanical Phenomena; D005684:Gait / Q000502:physiology*; D020233:Gait Disorders, Neurologic / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D004856:Postural Balance; D060726:Torso; D016138:Walking; D055815:Young Adult