Abstract
Human arm swing looks and feels highly automated, yet it is increasingly apparent that higher centres, including the cortex, are involved in many aspects of locomotor control. The addition of a cognitive task increases arm swing asymmetry during walking, but the characteristics and mechanism of this asymmetry are unclear. We hypothesized that this effect is lateralized and a Stroop word-colour naming task—primarily involving left hemisphere structures—would reduce right arm swing only. We recorded gait in 83 healthy subjects aged 18–80 walking normally on a treadmill and while performing a congruent and incongruent Stroop task. The primary measure of arm swing asymmetry—an index based on both three-dimensional wrist trajectories in which positive values indicate proportionally smaller movements on the right—increased significantly under dual-task conditions in those aged 40–59 and further still in the over-60s, driven by reduced right arm flexion. Right arm swing attenuation appears to be the norm in humans performing a locomotor-cognitive dual-task, confirming a prominent role of the brain in locomotor behaviour. Women under 60 are surprisingly resistant to this effect, revealing unexpected gender differences atop the hierarchical chain of locomotor control.
Highlights
At all walking speeds, arm swing in human gait is driven at least partially by muscle activity [1,2,3]
The large majority of studies investigating arm swing symmetry examined the effect of walking conditions or disease states on an absolute arm swing symmetry index (ASI) calculated from a range of base parameters including sagittal shoulder angles or wrist trajectories, with most indices a variation on this calculation, in which L is the parameter of interest on the left and R that on the right: ABS ASI = L − R × 100, max(L, R)
Our cohort broadly replicates findings relating to the effect of the Stroop and other cognitive dual-tasks on lower body kinematics [17,21,38], with healthy older subjects exhibiting a marked increase in step length variability and decreased foot clearance under increased cognitive load
Summary
Arm swing in human gait is driven at least partially by muscle activity [1,2,3]. Pattern generator (CPG) networks are implicated in arm swing generation and maintenance [3,4,5], recent 2 evidence supports a motor cortex contribution via the corticospinal tract [6]. Dual-task experiments, in which healthy participants walk while engaged in a secondary, cognitive task, have been observed to result in changes in the degree of arm swing amplitude relative to that of the contralateral arm—and the symmetry of the two movements [7,8,9,10].
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