Advanced age brings a greater reliance on visual feedback to maintain balance during walking

Abstract

We implemented a virtual reality system to quantify differences in the use of visual feedback to maintain balance during walking between healthy young (n=12, mean age: 24 years) and healthy old (n=11, 71 years) adults. Subjects walked on a treadmill while watching a speed-matched, virtual hallway with and without mediolateral visual perturbations. A motion capture system tracked center of mass (CoM) motion and foot kinematics. Spectral analysis, detrended fluctuation analysis, and local divergence exponents quantified old and young adults' dynamic response to visual perturbations. Old and young adults walked normally with comparable CoM spectral characteristics, lateral step placement temporal persistence, and local divergence exponents. Perturbed visual flow induced significantly larger changes in mediolateral CoM motion in old vs. young adults. Moreover, visual perturbations disrupted the control of lateral step placement and compromised local dynamic stability more significantly in old than young adults. Advanced age induces a greater reliance on visual feedback to maintain balance during waking, an effect that may compensate for degradations in somatosensation. Our findings are relevant to the early diagnosis of sensory-induced balance impairments and also point to the potential use of virtual reality to evaluate sensory rehabilitation and balance training programs for old adults.

Keywords: Elderly; Optical flow; Sensorimotor; Stability; Virtual reality.

Copyright © 2015 Elsevier B.V. All rights reserved.

Figures

Fig. 1

We implemented a virtual reality system to perturb visual flow during treadmill walking and quantified the effects on sacrum motion (a surrogate for the center of mass) and step placement dynamics. We used heel marker data to construct time series of alternating left and right step widths.

Fig. 2

Relation between ML sacrum motion and lateral step placement during normal (black line) and visually perturbed (blue line) waking for representative old and young subjects. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Group average spectral characteristics of the ML sacrum position in old and young adults. Gray dashed lines indicate the visual perturbation frequencies. Single asterisks (*) indicate significant difference between normal and visually perturbed walking, and double asterisks (**) indicate significant difference between old and young adults (p < .05).

Fig. 4

Detrended fluctuation analysis results. (A) Step width time series over 90 consecutive steps extracted from the 300 analyzed during normal (black line) and visually perturbed (blue line) walking for representative old and young subjects. Normal and visually perturbed conditions are offset vertically only for clarity, and do not represent differences in mean step width. (B) Mean (standard error) 1st and 2nd order scaling exponents of the relation between the root mean square (RMS) residual of step width and number of steps. We interpreted these scaling exponents as follows: α = 0.5 indicates uncorrelated white noise; α < 0.5 indicates that deviations in one direction are likely to be followed by deviations in the opposite direction (i.e., anti-persistent); and α > 0.5 indicates that deviations in one direction are likely to be followed by deviations in the same direction (i.e., persistent). Single asterisks (*) indicate significant difference between normal and visually perturbed walking, and double asterisks (**) indicate significant difference between old and young adults (p < .05). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Local dynamic stability results. (A) Mean (standard error) divergence curves (Dingwell, 2006) for old and young adults during normal (black line) and visually perturbed (blue line) walking. (B) Mean (standard error) maximum short-term and long-term divergence exponents, where larger positive values are indicative of greater local dynamic instability. Single asterisks (*) indicate significant difference between normal and visually perturbed walking, and double asterisks (**) indicate significant difference between old and young adults (p < .05). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)