title: Nonlinear analysis of ambulatory activity patterns in community-dwelling older adults.
abstract: BACKGROUND
  The natural ambulatory activity patterns of older adults are not well understood. User-worn monitors illuminate patterns of ambulatory activity and generate data suitable for analysis using measures derived from nonlinear dynamics.
  
  
  METHODS
  Ambulatory activity data were collected continuously from 157 community-dwelling older adults for 2 weeks. Participants were separated post hoc into groups based on the mean number of steps per day: highly active (steps > or = 10,000), moderately active (5,000 < or = steps < 10,000 steps), and inactive (steps <5,000 steps). Detrended fluctuation analysis (DFA), entropy rate (ER), and approximate entropy (ApEn) were used to examine the complexity of daily time series composed of 1-minute step count values. Coefficient of variation was used to examine time series variability. Between-group differences for each parameter were evaluated using analysis of variance.
  
  
  RESULTS
  All groups displayed patterns of fluctuating step count values containing complex temporal structure. DFA, ER, and ApEn parameter values increased monotonically and significantly with increasing activity level (p < .001). The variability of step count fluctuations did not differ among groups.
  
  
  CONCLUSIONS
  Highly active participants had more complex patterns of ambulatory activity than less active participants. The results supported the idea that, in addition to the volume of activity produced by an individual, patterns of ambulatory activity contain unique information that shows promise for offering insights into walking behavior associated with healthy aging.
authors.affiliation: Department of Physical Therapy, University of New England, 716 Stevens Avenue, Portland, ME 04103, USA. jcavanaugh@une.edu
authors.forename: James T
authors.initials: JT
authors.lastname: Cavanaugh
authors.forename: Naomi
authors.initials: N
authors.lastname: Kochi
authors.forename: Nicholas
authors.initials: N
authors.lastname: Stergiou
mesh_terms: D000203:Activities of Daily Living; D000368:Aged / Q000502:physiology*; D000369:Aged, 80 and over; D019277:Entropy; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D016138:Walking / Q000502:physiology*