The effect of walking speed on local dynamic stability is sensitive to calculation methods.

J. Stenum, S.M. Bruijn, B.R. Jensen

    Research output: Contribution to JournalArticleAcademicpeer-review

    Abstract

    Local dynamic stability has been assessed by the short-term local divergence exponent (λ<inf>S</inf>), which quantifies the average rate of logarithmic divergence of infinitesimally close trajectories in state space. Both increased and decreased local dynamic stability at faster walking speeds have been reported. This might pertain to methodological differences in calculating λ<inf>S</inf>. Therefore, the aim was to test if different calculation methods would induce different effects of walking speed on local dynamic stability. Ten young healthy participants walked on a treadmill at five speeds (60%, 80%, 100%, 120% and 140% of preferred walking speed) for 3min each, while upper body accelerations in three directions were sampled. From these time-series, λ<inf>S</inf> was calculated by three different methods using: (a) a fixed time interval and expressed as logarithmic divergence per stride-time (λ<inf>S-a</inf>), (b) a fixed number of strides and expressed as logarithmic divergence per time (λ<inf>S-b</inf>) and (c) a fixed number of strides and expressed as logarithmic divergence per stride-time (λ<inf>S-c</inf>). Mean preferred walking speed was 1.16±0.09m/s. There was only a minor effect of walking speed on λ<inf>S-a</inf>. λ<inf>S-b</inf> increased with increasing walking speed indicating decreased local dynamic stability at faster walking speeds, whereas λ<inf>S-c</inf> decreased with increasing walking speed indicating increased local dynamic stability at faster walking speeds. Thus, the effect of walking speed on calculated local dynamic stability was significantly different between methods used to calculate local dynamic stability. Therefore, inferences and comparisons of studies employing λ<inf>S</inf> should be made with careful consideration of the calculation method.
    Original languageEnglish
    Article number15
    Pages (from-to)3776-3779
    JournalJournal of Biomechanics
    Volume2014
    Issue number47
    DOIs
    Publication statusPublished - 2014

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