Taylor, D., Ngan-Hing, L., Shepard, N., Ashburn, A. and Burgneay, J.
Visually guided step turns: the effect of age on the movement pattern and muscle activation pattern
At ISPGR 2007 2007, Vermont.
14 - 18 Jul 2007.
7 pp, .
Full text not available from this repository.
Visually guided step turning occurs frequently
during daily life yet we have limited knowledge about how turning
actions are controlled. Studies of healthy young adults indicated
a clear temporal relationship between eye, head, trunk and
foot movements during visually guided turning tasks (Hollands
et al 2004).We were interested in whether similar relationships
occurred in older adults.We were also interested to determine if
there was a temporal relationship between lower limb muscle
activity and onset of eye or head movement. This study is part
of a multi-site initiative to explore the mechanisms underlying
instability in older adults and people following stroke. The general
hypothesis is that visually guided eye, head and body orientations
are a top-down event resulting in stable visual and head
orientation prior to full body orientation. Specific hypotheses
for this study were; a) the latency to onset of eye movement would
increase in older adults; b) a similar temporal order of movement
will remain in older adults compared to younger adults; c) preparatory muscle activity would be similar in the turning
task as it is during a forward stepping task.
Methods: Ten healthy volunteers between the ages of 20 and 85
years performed visually guided step turns to locations at 30 or
60 degrees of sub-tended arc movement. Electro-oculography
was used to measure onset of eye movement, a Qualysis motion
analysis system was used to collect 3-D movement data and a
Bortec telemetered electromyography system was used to collect
muscle activation data from lower limb muscles.
Results: Preliminary data indicates that the latency of onset of
eye movement is increased in older adults compared to younger
adults (t = -5.9; p<0.001). The temporal order of eye, head, foot
movement also differed in the older adult group in that there
was no consistent temporal order of eye and head movement (W
= 0.02; p = 0.56) compared to the younger group (W = 0.61; p
<0.001). The older adults appeared to move their head and eyes
at about the same time. Preparatory muscle activity occurred in
only 38% of the trials in young adults turning at self-selected
speeds, lower than that expected in a gait initiation movement.
This low level of preparatory activity may be related to the different
postural requirements of gait initiation and step turning
in the young adult population. Analysis of the muscle activation
data is ongoing.
Conclusions: These findings indicate that the strategy used in
visually guided step turning tasks may differ in young and older
adults. It was unexpected to find that the older adults tended to
move the eyes and head at about the same time as this strategy
is unlikely to allow a stable visual platform on which to assist
postural control during turning tasks. Further data collection
and analysis is required to verify these findings.
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