title: Movement variability in stroke patients and controls performing two upper limb functional tasks: a new assessment methodology.
abstract: BACKGROUND
  In the evaluation of upper limb impairment post stroke there remains a gap between detailed kinematic analyses with expensive motion capturing systems and common clinical assessment tests. In particular, although many clinical tests evaluate the performance of functional tasks, metrics to characterise upper limb kinematics are generally not applicable to such tasks and very limited in scope. This paper reports on a novel, user-friendly methodology that allows for the assessment of both signal magnitude and timing variability in upper limb movement trajectories during functional task performance. In order to demonstrate the technique, we report on a study in which the variability in timing and signal magnitude of data collected during the performance of two functional tasks is compared between a group of subjects with stroke and a group of individually matched control subjects.
  
  
  METHODS
  We employ dynamic time warping for curve registration to quantify two aspects of movement variability: 1) variability of the timing of the accelerometer signals' characteristics and 2) variability of the signals' magnitude. Six stroke patients and six matched controls performed several trials of a unilateral ('drinking') and a bilateral ('moving a plate') functional task on two different days, approximately 1 month apart. Group differences for the two variability metrics were investigated on both days.
  
  
  RESULTS
  For 'drinking from a glass' significant group differences were obtained on both days for the timing variability of the acceleration signals' characteristics (p = 0.002 and p = 0.008 for test and retest, respectively); all stroke patients showed increased signal timing variability as compared to their corresponding control subject. 'Moving a plate' provided less distinct group differences.
  
  
  CONCLUSIONS
  This initial application establishes that movement variability metrics, as determined by our methodology, appear different in stroke patients as compared to matched controls during unilateral task performance ('drinking'). Use of a user-friendly, inexpensive accelerometer makes this methodology feasible for routine clinical evaluations. We are encouraged to perform larger studies to further investigate the metrics' usefulness when quantifying levels of impairment.
authors.affiliation: Centre for Rehabilitation and Human Performance Research, University of Salford, Greater Manchester, UK. s.thies@salford.ac.uk
authors.forename: Sibylle B
authors.initials: SB
authors.lastname: Thies
authors.forename: Phil A
authors.initials: PA
authors.lastname: Tresadern
authors.forename: Laurence P
authors.initials: LP
authors.lastname: Kenney
authors.forename: Joel
authors.initials: J
authors.lastname: Smith
authors.forename: David
authors.initials: D
authors.lastname: Howard
authors.forename: John Y
authors.initials: JY
authors.lastname: Goulermas
authors.forename: Christine
authors.initials: C
authors.lastname: Smith
authors.forename: Julie
authors.initials: J
authors.lastname: Rigby
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance; D020521:Stroke / Q000503:physiopathology*; D013997:Time Factors; D034941:Upper Extremity / Q000502:physiology*