Gait variability in healthy old adults is more affected by a visual perturbation than by a cognitive or narrow step placement demand

Abstract

Gait variability measures have been linked to fall risk in older adults. However, challenging walking tasks may be required to elucidate increases in variability that arise from subtle age-related changes in cognitive processing and sensorimotor function. Hence, the study objective was to investigate the effects of visual perturbations, increased cognitive load, and narrowed step width on gait variability in healthy old and young adults. Eleven old (OA, 71.2±4.2 years) and twelve young (YA, 23.6±3.9 years) adults walked on a treadmill while watching a speed-matched virtual hallway. Subjects walked: (1) normally, (2) with mediolateral visual perturbations, (3) while performing a cognitive task (serial seven subtractions), and (4) with narrowed step width. We computed the mean and variability of step width (SW and SWV, respectively) and length (SL, SLV) over one 3-min trial per condition. Walking normally, old and young adults exhibited similar SWV and SLV. Visual perturbations significantly increased gait variability in old adults (by more than 100% for both SWV and SLV), but not young adults. The cognitive task and walking with narrowed step width did not show any effect on SWV or SLV in either group. The dramatic increase in step width variability when old adults were subjected to mediolateral visual perturbations was likely due to increased reliance on visual feedback for assessing whole-body position. Further work is needed to ascertain whether these findings may reflect sub-clinical balance deficits that could contribute to the increased fall risk seen with advancing age.

Keywords: Aging; Dual task; Dynamic balance; Optical flow; Virtual reality.

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

Figures

Figure 1

Experimental setup. 1a. Subject walks on a split-belt treadmill surrounded by a semicircular projection screen. A rear-projected virtual hallway moved at the same speed as the treadmill. Old adults wore a harness during testing that was adjusted to prevent falls but still allow free movement around the treadmill surface. 1b. During the visual perturbation trial, we added a mediolateral perturbation consisting of a sum of sinusoids to the virtual hallway motion. 1c. Step width and step length were calculated from heel kinematic data for both left-right and right-left steps.

Figure 2

The distribution of step width and step length values about the mean of two representative subjects plotted for each walking trial. Each gray dot represents the step width and step length for a single step, measured from heel markers. Scatter along the x-axis and y-axis represents variability in SW and SL, respectively. The scatter of SW and SL values is fairly tight for both subjects in all but the visual perturbation trial. Note the wide range of step placements for the old adult in the visual condition.

Figure 3

Summary step placement results for all subjects. Group mean ± standard deviation are represented. An asterisk (*) denotes a significant within-group difference between a challenging condition and normal walking (p

Figure 4

Young adults performed all trials at 100% and 80% of their preferred overground walking speed. Walking slower elicited shorter steps (p's