title: Stroke affects the coordination and stabilization of head, thorax and pelvis during voluntary horizontal head motions performed in walking.
abstract: OBJECTIVE
  This study was conducted to investigate and compare the coordination and stabilization of axial segments during walking with and without horizontal voluntary head turns, in healthy (n=5) and hemiparetic (n=10) subjects.
  
  
  METHODS
  Subjects were instructed to turn the head as fast and as soon as possible in the direction indicated by an illuminated arrow signal (right, left or none) that was triggered at initial contact of the right (healthy) or paretic (hemiparetic) foot. Head, thorax, and pelvis motions were obtained from a 9-segment model using retro-reflective markers and a Vicon-512 system with 6 high-resolution cameras. Coordination of axial segments in the horizontal plane was characterized using cyclographs and cross-correlation analyses. Stabilization of the segments was quantified using root mean square (RMS) values of the segment's normalized acceleration profile.
  
  
  RESULTS
  The healthy subjects showed a direction-dependent modulation of axial segment coordination, with head turns toward and away from the stance limb favoring and hindering, respectively, the contra-rotational pattern of the thorax with respect to the pelvis during locomotion. Meanwhile, pelvis motions remained unaltered. This direction-specific modulation pattern was disrupted in the hemiparetic subjects, both in the spatial and temporal domains. Moreover, larger RMS values for head and thorax segments were observed in the hemiparetic groups, both with and without the superimposition of voluntary head motions.
  
  
  CONCLUSIONS
  The findings suggest that: (1) head rotations during walking modify axial segment coordination in a direction-specific manner, (2) the pelvic rotations associated with locomotion remained unaffected by head rotations and (3) stroke alters this coordination behavior, which may contribute to balance dysfunctions during locomotion.
authors.affiliation: School of Physical and Occupational Therapy, McGill University, 3654 Promenade Sir-William-Osler, Montreal, Que., Canada H3G 1Y5. anouk.lamontagne@mcgill.ca
authors.forename: Anouk
authors.initials: A
authors.lastname: Lamontagne
authors.forename: Sophie J
authors.initials: SJ
authors.lastname: De Serres
authors.forename: Joyce
authors.initials: J
authors.lastname: Fung
authors.forename: Nicole
authors.initials: N
authors.lastname: Paquet
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D007839:Functional Laterality; D006257:Head / Q000503:physiopathology*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D010291:Paresis / Q000503:physiopathology; D010388:Pelvis / Q000503:physiopathology*; D004856:Postural Balance; D011597:Psychomotor Performance / Q000502:physiology*; D012399:Rotation; D020521:Stroke / Q000503:physiopathology*; D013909:Thorax / Q000503:physiopathology*; D016138:Walking / Q000502:physiology*