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Cameron T. Gibbons, Polemnia G. Amazeen and Aaron D. Likens

dynamics, but consists of continuous movement of the legs. The traditional measure of SD of leg position would indicate large variability because the leg constantly changes position around a mean resting state. By contrast, a nonlinear measure of variability, such as the largest Lyapunov exponent (λ 1

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Michael Buchecker, Stefan Wegenkittl, Thomas Stöggl and Erich Müller

. Rosenstein , M.T. , Collins , J.J. , & De Luca , C.J. ( 1993 ). A practical method for calculating largest Lyapunov exponents from small data sets . Physica D: Nonlinear Phenomena, 65 , 117 – 134 . doi:10.1016/0167-2789(93)90009-P 10.1016/0167-2789(93)90009-P Ruhe , A. , Fejer , R. , & Walker

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Cameron T. Gibbons, Polemnia G. Amazeen and Aaron D. Likens

placement affects postural sway. The first purpose is to investigate whether self-selection will improve postural stability, as observed in two sway measures, distance traveled and the largest Lyapunov exponent (λ 1 ). Distance traveled (or path length) is commonly used in the posture literature (e.g.,  Day

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Stefan Madansingh and Stacey L. Gorniak

We investigated the movement strategies of young, healthy participants (7 men/7 women) during the movement of a fragile object using nonlinear analysis. The kinematic variables of position, velocity, and acceleration were quantified using largest Lyapunov exponent (LyE) and approximate entropy (ApEn) analysis to identify the structure of their movement variability and movement predictability, respectively. Subjects performed a total of 15 discrete trials of an upper extremity movement task without crushing the object at each fragility condition, using each hand (left/right). We tested four fragility conditions hypothesizing that an increase in fragility would result in higher movement predictability and decreased temporal variability. Comparisons between the structure of movement variability and movement predictability were based on fragility condition, handedness, and kinematic measures. In this specific population, object fragility and participant handedness did not significantly impact the structure of movement variability (LyE) in the primary direction of movement (Z direction), although some effects were observed in the anterior/posterior directions. ApEn values were minimized across conditions, showing increased movement predictability, and is suggested for the analysis of discrete kinematic movements. In healthy populations, the results of this study suggest minimal effects on task performance and movement predictability as a result of object fragility.

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Fatemeh Azadinia, Ismail Ebrahimi-Takamjani, Mojtaba Kamyab, Morteza Asgari and Mohamad Parnianpour

largest Lyapunov exponents from small data sets . Physica D: Nonlinear Phenomena, 65 ( 1–2 ), 117 – 134 . doi: 10.1016/0167-2789(93)90009-P Ruhe , A. , Fejer , R. , & Walker , B. ( 2011a ). Center of pressure excursion as a measure of balance performance in patients with non-specific low back

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David I. Anderson

provide into typical and pathological development. He has popularized the use of a range of measures of nonlinear dynamics, including the largest Lyapunov exponent, approximate entropy, and the correlation dimension, to complement traditional measures of variability in motor control by providing