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.

PresentationsText spelling out one of four colours (red, green, yellow and blue) presented at pseudorandom intervals using Powerpoint 2010 (Microsoft Corp., Redmond, WA, USA). The duration of each stimulus was between 600 and 1400ms. To avoid potential entrainment of temporal gait parameters and to encourage constant attention, stimulus duration was adjusted so that no more than two sequential stimuli had a duration within 200ms of that of the previous stimulus, although mean stimulus frequency was maintained at 1Hz over the trial.FINAL_DATAFinal data in xls. format. Please see readme for usage.final_for_dryad.xls