Decrease in gait variability while counting backward: a marker of “magnet effect”?

Abstract

Counting backward (CB) and walking are both rhythmic tasks. An improvement of CB performance has been reported while walking, and has been interpreted as a "magnet effect" which is the tendency of biological oscillators to attract each other. The objective of this study was to compare the coefficient of variation (CoV) of stride time (ST) and the number of enumerated figures while single- and dual-tasking between older adults who increased and decreased their CoV of ST while CB. The number of enumerated figures and the CoV of ST under single-task (i.e., CB while sitting or walking alone) and dual-task (i.e., CB while walking) were measured among 100 community-dwelling older subjects (mean, 69.8 ± 0.07 years). Subjects were separated into two groups according to the dual-task-related changes in CoV of ST (i.e., either above or below the mean value of CoV of ST under single-task). Seventeen participants decreased their CoV of ST while CB compared to usual walking (2.6 ± 1.6% vs. 2.0 ± 1.3%, P < 0.001), while 83 increased their CoV of ST (1.7 ± 0.6% vs 3.4 ± 2.3%, P < 0.001). The subjects who decreased their CoV of ST had a tendency to enumerate more figures while walking compared to sitting (20.9 ± 6.3 vs 19.4 ± 4.7, P = 0.046) unlike those who increased their CoV of ST (20.3 ± 5.0 vs 21.8 ± 6.0 while sitting, P = 0.001). We found that most of subjects had worse gait and CB performance while dual-tasking. Conversely, a limited number of subjects improved significantly their gait performance and simultaneously had a tendency to improve their CB performance while walking compared to sitting. This behavior was observed only among subjects with the highest gait variability and could be interpreted as an implicit strategy based on the "magnet effect".

Gait Is Associated with Cognitive Flexibility: A Dual-Tasking Study in Healthy Older People

“…Lower standard deviations in particular in variability-associated parameters under DT than under ST conditions may indicate some rhythmicity, cueing and “magnet” effects induced by the secondary task. These effects have been described previously (Ebersbach et al, 1995; Beauchet et al, 2010). Note that differences of absolute parameter values between groups are not provided in this figure.…”

Dual task-related gait changes in patients with mild cognitive impairment

“…To our knowledge, the SS task has never previously been employed in DT paradigms applied to MCI patients. The only enhancing effect (on both motor and cognitive tasks) previously found during dual tasking was observed when using CB by ones in elderly subjects with higher gait variability (Beauchet et al, 2010). However, CB by ones is a rhythmic and almost automatic task, and the enhanced gait performance in the study mentioned might be explained by a positive interaction with gait in subjects lacking rhythmicity.…”

Observing prioritization effects on cognition and gait: The effect of increased cognitive load on cognitively healthy older adults’ dual-task performance

“…1). DTBs for the cognitive task have previously been explained as possibly due to the synchronicity of concurrent tasks [23] or to healthy participants having sufficient postural reserve to allocate resources to the cognitive task when there is no significant risk of falling [11]. This finding of DTB is an encouraging sign that healthy older adults can allocate attention when they have to complete complex tasks.…”