Visually guided step turns: the effect of age on the movement pattern and muscle activation pattern

Taylor, D., Ngan-Hing, L., Shepard, N., Ashburn, A., Burnett, M. and Burgneay, J. (2007) Visually guided step turns: the effect of age on the movement pattern and muscle activation pattern. ISPGR 2007 2007, Vermont, USA. 13 - 17 Jul 2007. p.33 .

Abstract

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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Contributors

Author: M. Burnett

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