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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Jian Jin (Vrije Universiteit Amsterdam)

Abstract:
Falling is a major threat to health of the growing population of older adults. Identification of individuals at high risk of falling is increasingly important. Currently employed stability measures to assess gait stability (1) appear limited in predicting falls in older adults and (2) reduce stability to an average over the gait cycle. Inspired by recent findings of time-dependent changes of local stability within a stride cycle [1], we present a new phase-dependent stability measure. This measure is closely related to the often-employed local divergence exponent, also referred to as the maximum Lyapunov exponent. Our measure entails linearizing the system in a rotating hypersurface orthogonal to the gait cycle trajectory, and estimating the local divergence rates. The corresponding metric, i.e. the maximum of this local divergence rate over the gait cycle, can serve as predictor of gait robustness. We validated this using a mathematical 2D model of a compass biped walker [2], which has two configuration parameters, namely slope and mass ratio. For a given set of different configurations of the walker, a stable period-one gait was identified. For comparison we also determined the conventional maximum Lyapunov exponent [3]. To assess robustness, we computed the maximum floor variation the biped walker model may handle by increasing the size of a single step up/down until falls occurred. The new stability measure turned out to be highly correlated with gait robustness, with much better correlation than the maximum Lyapunov exponent. It may provide additional value in predicting falls in older adults from real human walking data. References 1. Ihlen, E. A. F., Goihl, T., Wik, P. B., Sletvold, O., Helbostad, J., & Vereijken, B. (2012). Phase-dependent changes in local dynamic stability of human gait. Journal of Biomechanics, 45(13), 2208–2214. 2. Bruijn, S. M., Bregman, D. J. J., Meijer, O. G., Beek, P. J., & van Dieën, J. H. (2012). Maximum Lyapunov exponents as predictors of global gait stability: A modelling approach. Medical Engineering and Physics, 34(4), 428–436. 3. Norris, J. A., Marsh, A. P., Granata, K. P., & Ross, S. D. (2008). Revisiting the stability of 2D passive biped walking: Local behavior. Physica D: Nonlinear Phenomena, 237(23), 3038–3045.