Walking forward while counting backward: Increased variability in temporal but not spatial gait variables for elderly slow walkers

BACKGROUND AND AIM: The literature typically reports that elderly persons decrease walking speed and increase gait variability during dual task as compared to single task walking [1,2]. However, changes in gait variability might be different for slow as compared to fast walkers. Furthermore, a change in walking speed during dual tasking is a potential confounder when evaluating gait variability measures that are related to walking speed [3]. The aim of this study was to investigate how gait variability changes from single to dual task gait in elderly slow versus fast walkers, while controlling for differences in gait speed. METHODS: 162 healthy elderly persons, mean age 78.6 ± 4.7 years, walked over an electronic gait mat (GaiRite) at 3 instructed speeds (slow, preferred, fast) and at preferred speed while counting backward from 50. Dependent measures were walking speed and variability in Step Length (SD), Step Width (SD), Step Time (CV), and Single Support Time (CV). RESULTS: Consistent with earlier studies, elderly persons walked slower when counting backward (mean gait speeds: 0.97 m/s versus 0.81 m/s) and showed increased variability in both spatial and temporal measures compared to single task walking at preferred speed (p's1.1 m/s) the slowest group demonstrated larger temporal variability (CV Step Time and CV Single Support Time) compared to the faster walkers during dual task walking. This was not the case for the spatial measures SD Step Length and SD Step Width. CONCLUSIONS: Gait speed has been suggested to have predictive value and is considered by some as the 6th vital sign. Together with temporal and spatial gait variables, gait speed can provide valuable information of gait in older persons. Our results confirm previous studies finding that dual task challenges gait control in older persons. The finding that increased variability shown by slow walkers in temporal but not spatial variables may draw attention to congruent factors that challenge elderly while walking. We speculate that temporal variables are sacrificed at the expense of control of spatial variables for slow walkers at challenging gait conditions. Thus, temporal gait variability measures can capture other aspects than spatial variability measures.