Slow walking synergies reveal a functional role for arm swing asymmetry in healthy adults: a principal component analysis with relation to mechanical work

Abstract

<jats:title>Abstract</jats:title><jats:sec><jats:title>Introduction</jats:title><jats:p>The purpose of this study was to reveal a functional role for arm-swing asymmetry during gait in healthy adults. The primary aim was to identify differences in propulsive and collision work between sides at either end of the double-support phase of slow-walking (W<jats:sub>DS</jats:sub>). The secondary aim was to identify differences between sides in propulsive and collision work done at either end of the single-support phase (W<jats:sub>SS</jats:sub>) and the effect of arm-swing asymmetry on this difference. It was hypothesized that differences between sides would be evident during the double-support phase and that these differences would be coherent with differences in single-support control symmetry. It was also hypothesized that left-side dominant arm-swing would reduce the collision work done on the dominant lower-limb side.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>A secondary analysis of slow-walking trials of 25 healthy, uninjured adults was undertaken where a principal component analysis of kinematic data was carried out to generate the movement synergies (PM<jats:sub>k</jats:sub>). Independent variables included the tightness of neuromuscular control (N<jats:sub>k</jats:sub>) which was formulated from the first PM<jats:sub>k</jats:sub> and arm-swing asymmetry which was quantified using the directional Arm-swing asymmetry index (dASI). Dependent variables included the difference between double-support collision and propulsive work (W<jats:sub>DS</jats:sub>) and a ratio consisting of the difference between single-support collision and propulsive work of both sides (W<jats:sub>SS</jats:sub>). A linear mixed-effects model was utilized for aim 1 while a multiple linear regression analysis was undertaken for aim 2.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Healthy adult gait was accompanied by a left-side dominant arm-swing on average as seen elsewhere. For aim 1, N<jats:sub>k</jats:sub> demonstrated a significant negative effect on W<jats:sub>DS</jats:sub> while sidedness had a direct negative effect and indirect positive effect through N<jats:sub>k</jats:sub> on W<jats:sub>DS</jats:sub>. The most notable finding was the effect of a crossover interaction between dASI and N<jats:sub>k</jats:sub> which demonstrated a highly significant positive effect on W<jats:sub>ss</jats:sub>. All main-effects in aim 2 were in the hypothesized direction but were insignificant.</jats:p></jats:sec><jats:sec><jats:title>Interpretation</jats:title><jats:p>The aim 1 hypothesis was supported while the aim 2 hypothesis was not supported. N<jats:sub>k</jats:sub> exhibited opposing signs between ipsilateral and contralateral WBAM regulation, revealing a differential control strategy while the effect of sidedness on W<jats:sub>DS</jats:sub> was evident. The findings from aim 2 describe a relationship between arm-swing asymmetry and the magnitude of lower-limb mechanical work asymmetry that is cohesive with the sidedness effect found in aim 1. Individuals with left-side dominant arm-swing had an increased collision work indicative of a lateralised preference for WBAM regulation. Evidence was therefore put forward that arm-swing asymmetry during gait is related to footedness. Future studies should look to formally confirm this finding. Implications for further research into dynamic balance control mechanisms are also discussed.</jats:p></jats:sec><jats:sec><jats:title>Highlights</jats:title><jats:list list-type="bullet"><jats:list-item><jats:p>Left-side dominant arm-swing was found to be related to the degree of lower-limb mechanical work asymmetry.</jats:p></jats:list-item><jats:list-item><jats:p>The relationship between arm-swing asymmetry and lower-limb mechanical work symmetry was explained by a moderating effect of neuromuscular control.</jats:p></jats:list-item><jats:list-item><jats:p>A differential control on single-and double-support phases was demonstrated by the neuromuscular system, supporting previous studies and this control may be heavily influenced by sidedness.</jats:p></jats:list-item></jats:list></jats:sec>

Identifying differences in gait adaptability across various speeds using movement synergy analysis

“…Combining this insight with that of the aforementioned observations made by [ 7 ], we propose that asymmetry in limb control between the dominant and non-dominant sides was relevant in differentiating healthy adults in terms of gait adaptability in this study. The moderating effect of movement synergies on coupled asymmetries between the upper- and lower-limbs has been found in recent research and may have significant influence on gait performance and risk for injury [ 56 ]. The influence of these inherent asymmetries on gait stability has not been investigated in the research thus far.…”

Untitled

“…Combining this insight with that of the aforementioned observations made by [7], we propose that asymmetry in limb control between the dominant and non-dominant sides was relevant in differentiating healthy adults in terms of gait adaptability in this study. The moderating effect of movement synergies on coupled asymmetries between the upper-and lower-limbs has been found in recent research and may have significant influence on gait performance and risk for injury [56]. The influence of these inherent asymmetries on gait stability has not been investigated in the research thus far.…”