22 research outputs found

    Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking

    Get PDF
    <div><p>Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for <i>216</i> gait trials across <i>26</i> subjects (speeds from <i>0.75–2.63 m/s</i>) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R<sup>2</sup> of <i>75%</i> to <i>81%</i> in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of <i>13%</i> to <i>30%</i>. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.</p> </div

    The knee quasi-stiffness in the weight acceptance phase of the gait.

    No full text
    <p>The experimental values are shown by circles, and the predictions of the general-form model by diamonds with average error of <i>(14%)</i>, and the stature-based models by squares with average error of <i>(9%)</i> for the optimal gait speed.</p

    Details on Subjects and Experimental Trials used for Regression Fits.

    No full text
    <p>: Body weight (kg), and : Body height (m),</p><p> and : Minimum and maximum gait speed (m/s).</p><p> and : Minimum and maximum quasi-stiffness in flexion stage (Nm/rad).</p><p> and : Minimum and maximum quasi-stiffness in extension stage (Nm/rad).</p><p> and : Minimum quasi-stiffness in weight-acceptance phase (Nm/rad).</p><p> and : Minimum and maximum knee excursion in weight-acceptance phase (deg).</p><p>: Average of the linear fit on moment-angle curve in flexion stage.</p><p>: Average of the linear fit on moment-angle curve in extension stage.</p><p>: Froude number.</p>‡<p>: Data collected at Human PoWeR Lab, NC State University <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059993#pone.0059993-Farris1" target="_blank">[24]</a>.</p>†<p>: Data collected at Biomechanics Lab, East Carolina University <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059993#pone.0059993-Hortobgyi1" target="_blank">[29]</a>.</p

    General-Form Models to Predict the Quasi-Stiffness of the Knee Joint in Stance for Normal Walking.

    No full text
    <p>General-Form Models to Predict the Quasi-Stiffness of the Knee Joint in Stance for Normal Walking.</p

    Hip quasi-stiffness for subject 11, as an example, in extension (black) and flexion (gray) stages plotted against the gait speed.

    No full text
    <p>The circles indicate the experimental values and the diamonds indicate the predictions of the general-form models listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081841#pone-0081841-t002" target="_blank">Table 2</a>.</p

    Knee moment vs. angle curve for a representative subject walking at .

    No full text
    <p>Letters a-f on the graph correspond to the poses shown during a typical walking cycle (top, schematic timing is adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059993#pone.0059993-Rose1" target="_blank">[60]</a>). Quasi-stiffness is calculated based on the slope of the best line fit to the moment-angle curve of a<i>–</i>b for the flexion stage (), and b<i>–</i>d for the extension stage () of the weight acceptance phase (a<i>–</i>d). The average of these two quasi-stiffness values is defined as the quasi-stiffness of the weight acceptance phase ().</p

    Details on Subjects and Experimental Trials used for Regression Fits.

    No full text
    <p>: Body weight (kg), and : Body height (m).</p><p> and : Minimum and maximum gait speed (m/s).</p><p> and : Minimum and maximum quasi-stiffness in dorsi-flexion phase (Nm/rad).</p><p> and : Minimum and maximum quasi-stiffness in dual flexion phase (Nm/rad).</p><p> and : Minimum and maximum quasi-stiffness in plantar-flexion phase (Nm/rad).</p><p> and : Minimum and maximum propulsion energy (J).</p><p>, , and : Average of the linear fit on moment-angle curve in dorsi-flexion, dual-flexion, and plantar-flexion phases.</p>‡<p>Data collected at Human PoWeR Lab, NC State University <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059935#pone.0059935-Farris1" target="_blank">[28]</a>.</p>†<p>Data collected at Biomechanics Lab, East Carolina University <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059935#pone.0059935-Hortobgyi1" target="_blank">[43]</a>.</p><p>•Data collected at Laboratory of Biomedical Technologies at Politecnico Di Milano.</p

    Ankle quasi-stiffnesses (<i>N.m/rad</i>) in dorsi-flexion (top-left), dual-flexion (top-right), and plantar-flexion (bottom-left) phases, and propulsive work (<i>J</i>) in stance (bottom-tight) plotted against gait speed for subject 10 as an example.

    No full text
    <p>The circles indicate the experimental value and the diamonds are the predictions of the general-form models of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059935#pone-0059935-t002" target="_blank">Table 2</a>.</p

    Details on Subjects and Experimental Trials used for Regression Fits.

    No full text
    <p>: Body weight (kg), and : Body height (m),</p><p> and : Minimum and maximum gait speed (m/s)</p><p> and : Minimum and maximum hip quasi-stiffness in extension stage (Nm/rad)</p><p> and : Minimum and maximum hip quasi-stiffness in flexion stage (Nm/rad)</p><p> and : Minimum and maximum hip excursion in extension stage (deg)</p><p> and : Minimum and maximum hip excursion in flexion stage (deg)</p><p>: Average of the linear fit on moment-angle curve in extension stage</p><p>: Average of the linear fit on moment-angle curve in flexion stage</p><p>‡Data collected at Human PoWeR Lab, NC State University <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081841#pone.0081841-Farris1" target="_blank">[16]</a></p><p>†Data collected at Biomechanics Lab, East Carolina University <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081841#pone.0081841-Hortobgyi1" target="_blank">[55]</a></p><p>•Data collected at Laboratory of Biomedical Technologies at Politecnico Di Milano.</p

    Stature-Based Models to Predict the Quasi-Stiffness of the Knee Joint in Stance for Normal Walking at Optimal Gait Speed.

    No full text
    <p>Stature-Based Models to Predict the Quasi-Stiffness of the Knee Joint in Stance for Normal Walking at Optimal Gait Speed.</p
    corecore