title: A Validated Smartphone-Based Assessment of Gait and Gait Variability in Parkinson's Disease.
abstract: BACKGROUND
  A well-established connection exists between increased gait variability and greater fall likelihood in Parkinson's disease (PD); however, a portable, validated means of quantifying gait variability (and testing the efficacy of any intervention) remains lacking. Furthermore, although rhythmic auditory cueing continues to receive attention as a promising gait therapy for PD, its widespread delivery remains bottlenecked. The present paper describes a smartphone-based mobile application ("SmartMOVE") to address both needs.
  
  
  METHODS
  The accuracy of smartphone-based gait analysis (utilizing the smartphone's built-in tri-axial accelerometer and gyroscope to calculate successive step times and step lengths) was validated against two heel contact-based measurement devices: heel-mounted footswitch sensors (to capture step times) and an instrumented pressure sensor mat (to capture step lengths). 12 PD patients and 12 age-matched healthy controls walked along a 26-m path during self-paced and metronome-cued conditions, with all three devices recording simultaneously.
  
  
  RESULTS
  Four outcome measures of gait and gait variability were calculated. Mixed-factorial analysis of variance revealed several instances in which between-group differences (e.g., increased gait variability in PD patients relative to healthy controls) yielded medium-to-large effect sizes (eta-squared values), and cueing-mediated changes (e.g., decreased gait variability when PD patients walked with auditory cues) yielded small-to-medium effect sizes-while at the same time, device-related measurement error yielded small-to-negligible effect sizes.
  
  
  CONCLUSIONS
  These findings highlight specific opportunities for smartphone-based gait analysis to serve as an alternative to conventional gait analysis methods (e.g., footswitch systems or sensor-embedded walkways), particularly when those methods are cost-prohibitive, cumbersome, or inconvenient.
authors.affiliation: School of Computing, National University of Singapore, Computing 1, 13 Computing Drive, Singapore, 117417, Singapore.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Ellis
authors.affiliation: Department of Rehabilitation Medicine, Singapore General Hospital, Outram Rd, Singapore, 169608, Singapore.
authors.forename: Yee Sien
authors.initials: YS
authors.lastname: Ng
authors.affiliation: NUS Graduate School for Integrative Sciences and Engineering, 28 Medical Drive, Singapore, 117456, Singapore.
authors.forename: Shenggao
authors.initials: S
authors.lastname: Zhu
authors.affiliation: Department of Rehabilitation Medicine, Singapore General Hospital, Outram Rd, Singapore, 169608, Singapore.
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Tan
authors.affiliation: School of Computing, National University of Singapore, Computing 1, 13 Computing Drive, Singapore, 117417, Singapore.
authors.forename: Boyd
authors.initials: B
authors.lastname: Anderson
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Palmer 127, Boston, MA, 02215, United States of America.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Schlaug
authors.affiliation: School of Computing, National University of Singapore, Computing 1, 13 Computing Drive, Singapore, 117417, Singapore; NUS Graduate School for Integrative Sciences and Engineering, 28 Medical Drive, Singapore, 117456, Singapore.
authors.forename: Ye
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000058:Accidental Falls / Q000706:statistics & numerical data; D000161:Acoustic Stimulation; D000368:Aged; D005260:Female; D005684:Gait / Q000502:physiology*; D020233:Gait Disorders, Neurologic / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D063731:Mobile Applications; D010300:Parkinson Disease / Q000150:complications / Q000503:physiopathology*; D011597:Psychomotor Performance / Q000502:physiology*; D000068997:Smartphone / Q000295:instrumentation