Sagittal plane head stabilization during level walking and ambulation on stairs.

BACKGROUND AND PURPOSE Head stabilization in space provides a stable reference frame for visual and vestibular systems during locomotor tasks. The purpose of the present study was to examine upper body movement patterns used to maintain head stability in response to the increased challenge of stair ambulation. METHOD A repeated-measures study design was used and the order of conditions was randomized for each subject. Eight healthy, non-disabled, young adults walked 10 metres on a level surface, ascended and descended four steps. Head, neck and trunk angular positions in space were obtained for three trials of each condition. Significant differences in mean head, neck and trunk angular orientation in space and segment excursions were determined. Cross-correlation analyses between head and neck, neck and trunk, and head and trunk determined movement patterns used for maintaining head stability. The chi-square test examined the homogeneity of movement pattern distributions for each segment pair across conditions. RESULTS Head in space flexion orientation and angular excursions were greater during stair ascent and greater still during stair descent as compared to level walking. This indicates a progressively significant increase in the challenge to head stability. Neck flexion orientation in space and angular excursion were greater during stair descent as compared to level walking. Movement patterns between segment pairs demonstrated phase leads and lags between segments when threats to head stability were minimal. With increased challenge to head stability, segments moved synchronously in opposite directions to maintain balance. With further challenges to head stability, segments moved synchronously in the same direction to maintain body segment alignment. CONCLUSIONS Head stabilization was significantly challenged when ascending stairs and is further challenged while descending stairs. Movement patterns reflected changes associated with challenges to head stability. Increased head excursion during stair ambulation may reflect the need to orient vision for foot placement. Results suggest that individuals with visual or vestibular deficits may be at risk for falls during stair ambulation.