cqvip:Objective: This study was conducted to investigate and compare the coordinatio n 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 t he 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 usi ng retro-reflective markers and a Vicon-512 system with 6 high-resolution cam eras. Coordination of axial segments in the horizontal plane was characterized u sing cyclographs and cross-correlat- ion analyses. Stabilization of the segments was quantified using root mean squ are (RMS) values of the segment’s normalized acceleration profile. Results: The healthy subjects showed a direction-dependent modulation of axial segment coor dination, with head turns toward and away from the stance limb favoring and hind ering, respectively, the contrarotational 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 witho ut the superimposition of voluntary head motions. Conclusions:The findings sugge st that: (1) head rotations during walking modify axial segment coordination in a direction-specific manner, (2) the pelvic rotations associated with locomotio n remained unaffected by head rotations and (3) stroke alters this coordination behavior, which may contribute to balance dysfunctions during locomotion.
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