Eye and body movement strategies during turning tasks in older adults at risk of falls
Objective: The aim of this study was to investigate eye and whole body movement strategies during a step turning task in older adults at risk of falls compared to healthy older adults. Specifically, this experiment investigates the sequence and latency of eye, head, trunk and foot movements; centre of pressure and anticipatory muscle activity while preparing for and initiating a turn from a static starting position. It is hoped that increasing the understanding of these complex movements will help with the development of rehabilitation strategies aimed at preventing falls during turning movements. Study Design: Laboratory based, experimental, repeated measures design. Participants: Twenty two participants volunteered for the study. Participants were allocated to either a healthy older adult (HOA) group (mean age 74 ± 7.6 years) or falls risk older adult (FROA) group (mean age 76 ± 7.8 years) based on a cut-off score of two on the Falls Risk Assessment Tool (FRAT). Main Measures: Three-dimensional motion analysis of head, trunk, pelvis and foot movement was used to determine onset and latency of body segmental movement. Onset of eye movement was determined by the use of electrooculography (EOG), while a force plate measured the onset of centre of pressure (COP). Muscle activity was determined using electromyography (EMG). Stepping strategies (ipsilateral or contralateral) were determined visually by reviewing data off-line. Results: An ipsilateral strategy was the most frequently used strategy when turning in both directions. Both older adult groups demonstrated an increased use of the contralateral strategy when turning to the right compared to the turning to the left (t(438) = -2.32, p < .05). FROAs were more likely to adopt the contralateral strategy (t(438) = -3.58, p < .05). While there was no difference in the order of onset of movement when turning right (COP, eye, head, trunk, pelvis and foot), there were differences in order of onset when turning to left. FROAs demonstrated a significant increase in onset latency when compared to HOAs when turning to the left, though no differences were found when turning to the right. Compared to gait initiation studies, stereotypical anticipatory muscle activity was infrequently observed (<50% of trials). Conclusions: Older adults at risk of falls were about three times as likely to use a contralateral strategy compared to healthy older adults. While this may suggest more flexibility in the turning programme, it may also contribute to an increase in falls risk. Findings from the current study suggest that older adults may move more en-bloc compared to previous studies of young adults. Falls risk in older adults may contribute to differences in the onset order and latency of segmental movement, and may have some relationship to the direction of turn and preference of turning strategy. While tibialis anterior and gastrocnemius have been observed to activate consistently in the anticipatory period of gait initiation studies, a clear pattern of activity could not be established during step turning.