Abstract
Treadmill experiments suggest that left-dominant arm swing is common in healthy walking adults and is modulated by cognitive dual-tasking. Little is known about arm swing asymmetry in overground walking. We report directional (dASI) and non-directional arm swing symmetry indices (ndASI) from 334 adults (mean age 68.6 ± 5.9 y) walking overground at comfortable (NW) and fast (FW) speeds and while completing a serial subtraction task (DT). dASI and ndASI were calculated from sagittal shoulder range of motion data generated by inertial measurement units affixed to the wrist. Most (91%) participants were right-handed. Group mean arm swing amplitude was significantly larger on the left in all walking conditions. During NW, ndASI was 39.5 ± 21.8, with a dASI of 21.9 ± 39.5. Distribution of dASI was bimodal with an approximately 2:1 ratio of left:right-dominant arm swing. There were no differences in ndASI between conditions but dASI was smaller during DT compared to FW (15.2 vs 24.6; p = 0.009). Handedness was unrelated to ndASI, dASI or the change in ASI metrics under DT. Left-dominant arm swing is the norm in healthy human walking irrespective of walking condition or handedness. As disease markers, ndASI and dASI may have different and complementary roles.
Highlights
Rhythmic swinging of the arms is a universal feature of human bipedal gait that appears to have a minor[1,2,3,4] or negligible[5] role in reducing the metabolic cost of walking and is likely subject to a mix of cortical[6,7] and lower-level[1,8,9,10] neural control
Kuhtz-Buschbeck et al observed treadmill walking in eight right-handed and eight left-handed individuals and reported left-dominant arm swing in both groups[16], concluding that asymmetry is not related to handedness
Arm swing asymmetry has been identified as a potential prodromal biomarker for falls and PD11–13
Summary
Rhythmic swinging of the arms is a universal feature of human bipedal gait that appears to have a minor[1,2,3,4] or negligible[5] role in reducing the metabolic cost of walking and is likely subject to a mix of cortical[6,7] and lower-level[1,8,9,10] neural control. Why arm movements should be greater on the left is unclear, but a logical candidate mechanism would be a discrepant degree of automatism of the neural apparatus controlling arm swing habituated through arm preference for voluntary tasks, i.e. handedness. If this is the case, the ubiquity of left-dominant arm swing may reflect the prevalence of right-handedness in our species. Mirelman et al observed a dramatic increase in ndASI during serial subtraction in older adults[24], Plate et al noted no effect of counting backwards on dASI and ndASI in their cohort of healthy adults while reporting a significant increase in both forms of ASI during a Stroop dual-task. A characterisation of the effect of serial subtraction, widely-utilised in clinical practice and research, on both dASI and ndASI in target cohorts walking overground is lacking
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