Modifiability and laterality of walking stability in unimpaired adults
Date
2022
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Introduction: In our previous studies of children with cerebral palsy, a population characterized by poor balance and high fall risk, we observed that the children with cerebral palsy did not walk in a manner that was protective against a forward loss of balance (i.e. a proactive strategy) despite exhibiting an impaired response to anterior perturbations (i.e. a reactive response) compared to children with typical development. We also observed an unexpected asymmetry such that the “dominant limb” had more lateral stability in typically developing children. This dissertation aimed to address two previously unexplored relationships to walking stability without the confounding influence of neurological impairment: proactive stability modifications and between-limb laterality across balance domains in unimpaired adults. ☐ Methods: For our first aim, 11 unimpaired adult participants, including six females and five males, completed a study of large anterior and posterior perturbations at multiple walking speeds, and a novel focus on pre-perturbation steps to investigate how stability could be modified proactively under threats to stability. We used the Margin of Stability (MoS), a spatial measure of stability that accounts for the position and velocity of the whole-body center of mass relative to the base of support, as an indicator of the state of stability should a perturbation occur. For our second aim, 30 unimpaired adult participants, including 15 females and 15 males, completed a study consisting of stability- and mobility-demanding tasks to investigate how between-limb asymmetries in lateral stability during walking were related to between-limb asymmetries across tasks in different balance domains. We used the Inter-Limb Asymmetry (ILA) index to quantify the between-limb asymmetry, which measures the between-limb difference and scales that value to the participant’s height. ☐ Results: Aim 1—With the threat of posterior perturbations, there was an increase in posterior stability at foot strike (p < 0.001, mean difference (standard error) 1.70 (0.26) %BH). With the threat of anterior perturbations, there was more anterior instability at mid-swing during stance on the dominant limb compared to no perturbations (p = 0.005, 0.63 (0.15) %BH). Proactive modifications to stability were accompanied by shortened step lengths (p < 0.005, 1.7 to 2.2 (0.4) cm) and increased step rates (p < 0.004, 0.05 to 0.06 (0.01) steps⸱s-1). Specific to walking at the slow speed and with the threat of posterior perturbations, there was also less time spent in double support (p = 0.042, 0.99 (0.34) %gait cycle). ☐ Aim 2—There were no significant correlations between the ILA for minimum lateral MoS during walking and the respective ILA values for each task (Pearson r < 0.327, p > 0.119). Stepping with the non-preferred limb changed the task mechanics. When initiating gait with the non-preferred limb, the mediolateral displacement of the center of pressure during the anticipatory postural adjustment phase was significantly greater (p = 0.04, d = 0.43, mean difference (SE) 0.47 (1.09) cm). At foot strike when stepping with the non-preferred limb after simulated trips, participants had a larger anterior distance (p = 0.04, d = 0.40, 2.07 (5.12) cm) between the center of mass and the anterior edge of the base of support, with the center of mass posterior to the edge of the base of support. At foot strike when stepping with the non-preferred limb after simulated slips, participants had a larger posterior distance (p = 0.04, d = 0.45, 4.07 (9.14) cm) and a smaller lateral distance (p = 0.01, d = 0.65, 2.55 (3.90) cm) between the center of mass and the posterior edge of the base of support, with the center of mass anterior and medial to the edge of the base of support. ☐ Discussion: Beneficial modifications to posterior MoS at foot strike are indeed possible in an unimpaired population within a given walking speed. These proactive modifications to stability were implemented despite the capacity for unimpaired participants to rely on their ability to recover from perturbations. Consequently, anteroposterior stability may be a feasible target for fall-prevention interventions by targeting decreased step lengths or increased step rates while maintaining the same walking speed. ☐ Lower-extremity laterality may be specific to movement tasks or balance domains rather than a representation of systemic lower-extremity impedance/predictive control. Participants did exhibit strong tendencies towards limb preferences within tasks, but commonly used self-reported limb dominance did not seem to predict those preferences. Participants also showed between-limb differences when performing stepping tasks with the non-preferred limb. ☐ Conclusions: This work provides a framework with which to interpret walking stability and asymmetries in additional populations with and without impairments. Unperturbed walking stability is a modifiable risk factor of falls during walking. Lower-extremity laterality may be present but was not correlated across balance domains or explained by self-reported limb dominance. Future studies should not assume between-limb symmetry in stability or assume that self-reported limb dominance is a meaningful predictor of task preference or performance.
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Keywords
Asymmetry, Balance, Biomechanics, Gait, Laterality, Stability