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A novel system for introducing precisely-controlled, unanticipated gait perturbations for the study of stumble recovery

dc.contributor.authorKing, Shane T.
dc.contributor.authorEveld, Maura E.
dc.contributor.authorMartinez, Andres
dc.contributor.authorZelik, Karl E.
dc.contributor.authorGoldfarb, Michael
dc.identifier.citationKing ST, Eveld ME, Martínez A, Zelik KE, Goldfarb M. A novel system for introducing precisely-controlled, unanticipated gait perturbations for the study of stumble recovery. J Neuroeng Rehabil. 2019;16(1):69. Published 2019 Jun 10. doi:10.1186/s12984-019-0527-7en_US
dc.description.abstractBackgroundThe experimental study of stumble recovery is essential to better understanding the reflexive mechanisms that help prevent falls as well as the deficiencies in fall-prone populations. This study would benefit from a system that can introduce perturbations that: 1) are realistic (e.g., obstacle disrupting the foot in swing phase), 2) are unanticipated by subjects, 3) are controllable in their timing, and 4) allow for kinematic and kinetic evaluation.MethodsA stumble perturbation system was designed that consists of an obstacle delivery apparatus that releases an obstacle onto a force-instrumented treadmill and a predictive targeting algorithm which controls the timing of the perturbation to the foot during swing phase. Seven healthy subjects were recruited to take part in an experimental protocol for system validation, which consisted of two sub-experiments. First, a perception experiment determined whether subjects could perceive the obstacle as it slid onto the treadmill belt. Second, a perturbation experiment assessed the timing accuracy of perturbations relative to a target percent swing input by the experimenter. Data from this experiment were then used to demonstrate that joint kinematics and kinetics could be computed before and after the perturbation.ResultsOut of 168 perception trials (24 per subject), not a single obstacle was perceived entering the treadmill by the subjects. Out of 196 perturbation trials, 190 trials successfully induced a stumble event, with a mean targeting accuracy, relative to the desired percent swing, of 25 ms (6.2% of swing phase). Joint kinematic and kinetic results were then computed for three common stumble recovery strategies and shown to be qualitatively consistent with results from prior stumble studies conducted overground.ConclusionsThe stumble perturbation system successfully introduced realistic obstacle perturbations that were unanticipated by subjects. The targeting accuracy substantially reduced mistrials (i.e., trials that did not elicit a stumble) compared to previous studies. This accuracy enables stumble recovery to be studied more systematically as a function of when the perturbation occurs during swing phase. Lastly, joint kinematic and kinetic estimates allow for a comprehensive analysis of stumble recovery biomechanics.en_US
dc.description.sponsorshipFunding for this work was provided by the National Institutes of Health under grant no. R01HD088959.en_US
dc.publisherJournal of Neuroengineering and Rehabiliationen_US
dc.rightsOpen Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.
dc.subjectStumble Apparatusen_US
dc.subjectJoint Kinematicsen_US
dc.subjectJoint Kineticsen_US
dc.titleA novel system for introducing precisely-controlled, unanticipated gait perturbations for the study of stumble recoveryen_US

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