title: Balance and Gait Represent Independent Domains of Mobility in Parkinson Disease.
abstract: The Instrumented Stand and Walk (ISAW) test, which includes 30 seconds of stance, step initiation, gait, and turning, results in many objective balance and gait metrics from body-worn inertial sensors. However, it is not clear which metrics provide independent information about mobility.
  
  
  
  It was hypothesized that balance and gait represent several independent domains of mobility and that not all domains would be abnormal in individuals with Parkinson disease (PD) or would change with levodopa therapy.
  
  
  
  This was a cross-sectional study.
  
  
  
  A factor analysis approach was used to identify independent measures of mobility extracted from the ISAW in 100 participants with PD and 21 control participants. First, a covariance analysis showed that postural sway measures were independent of gait measures. Then, the factor analysis revealed 6 independent factors (mobility domains: sway area, sway frequency, arm swing asymmetry, trunk motion during gait, gait speed, and cadence) that accounted for 87% of the variance of performance across participants.
  
  
  
  Sway area, gait speed, and trunk motion differed between the PD group in the off-levodopa state and the control group, but sway frequency (but not sway area) differed between the PD group in the off-levodopa state and the control group. Four of the 6 factors changed significantly with levodopa (off to on): sway area, sway frequency, trunk motion during gait, and cadence. When participants were on levodopa, the sway area increased compared with off levodopa, becoming more abnormal, whereas the other 3 significant metrics moved toward, but did not reach, the healthy control values.
  
  
  
  Exploratory factor analysis was limited to the PD population.
  
  
  
  The different sensitivity various balance and gait domains to PD and to levodopa also support neural control of at least 6 independent mobility domains, each of which warrants clinical assessment for impairments in mobility.
authors.affiliation: F.B. Horak, PT, PhD, Veterans Affairs Portland Health Care System (VAPORHCS), Portland, Oregon; Department of Neurology, Oregon Health & Science University, Portland, Oregon.
authors.forename: Fay B
authors.initials: FB
authors.lastname: Horak
authors.affiliation: M. Mancini, PhD, Department of Neurology, Oregon Health & Science University, 3181 SW Sam Jackson Rd, Portland, OR 97239 (USA). mancinim@ohsu.edu.
authors.forename: Martina
authors.initials: M
authors.lastname: Mancini
authors.affiliation: P. Carlson-Kuhta, PhD, Department of Neurology, Oregon Health & Science University.
authors.forename: Patricia
authors.initials: P
authors.lastname: Carlson-Kuhta
authors.affiliation: J.G. Nutt, MD, Department of Neurology, Oregon Health & Science University.
authors.forename: John G
authors.initials: JG
authors.lastname: Nutt
authors.affiliation: A. Salarian, PhD, Department of Neurology, Oregon Health & Science University.
authors.forename: Arash
authors.initials: A
authors.lastname: Salarian
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000627:therapeutic use*; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005163:Factor Analysis, Statistical; D005260:Female; D020233:Gait Disorders, Neurologic / Q000503:physiopathology*; D006801:Humans; D007980:Levodopa / Q000627:therapeutic use*; D008297:Male; D051346:Mobility Limitation; D010300:Parkinson Disease / Q000188:drug therapy* / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa