The effect of optic flow on standing balance in young and older people with low and high fall risk
Sturnieks DL[1, 2], Tan BCY , Lord SR[1, 3]
- Falls, Balance and Injury Research Centre, Neuroscience Research
Australia, Sydney, Australia
- School of Medical Sciences, University of New South Wales, Sydney
- School of Public Health and Community Medicine, University of New South
Wales, Sydney Australia
Optic flow stimuli can destabilise posture, and especially so in older individuals with increased visual field dependence (VFD). This may lead to an increased incidence of elderly falls. This study aimed to investigate the differing effects of optic flow stimuli on postural stability between: 1) older and younger adults, 2) low-falls-risk and high-falls-risk older adults.
Seventy-six participants were recruited and grouped into ‘young’ (20-40 years, n=25), and ‘old’(≥65 years, n=51). The latter group was stratified into ‘old-LFR’ (low fall risk, n=27) and ‘old-HFR’ (high fall risk, n=24). All participants stood on a force platform in a dark room. Four types of optic flow stimuli were presented on a large screen as moving white dots: radial expansion and contraction, circular (roll vection) anti-clockwise and clockwise. Parameters of postural sway were calculated from participants’ centre of pressure (COP) taken from force platform recordings, specifically: change in COP position in the anteroposterior (AP) and mediolateral (ML) axes, path length travelled by COP in AP and ML axes, and total path length. Repeated measures analyses of variance were used to determine if optic flow stimuli influenced postural sway, and if this effect was different between three participant groups.
Optic flow stimuli led to significant increases in path length variables with notable instability in the anteroposterior directions predominantly. Path length analyses revealed larger optic flow-induced increases in sway in older compared with younger participants, most prominently in the old-HFR group. COP position did not show significant changes with optic flow nor across participant groups. These results suggest that optic flow plays a more significant role in reducing postural stability in older than younger adults, particularly so in older individuals with higher fall risk.