Abstract:
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The time course of the center of pressure (CoP) during human quiet stance, corresponding to body sway, is a stochastic process, influenced by a variety of features of the underlying neuro-musculo-skeletal system. Sway patterns have been characterized in an empirical way by a number of indices, such as mean sway velocity, rather than by directly estimating an underlying probability density function. Here, we describe a statistical approach with the aim of estimating "universal" indices, namely parameters that are independent of individual body characteristics; under the assumption that they might reflect underlying neural control during quiet stance. Such universal indices are identified by analyzing intra- and inter-subject variability of various indices. We found that universal indices characterize mainly slow aspects of sway, such as scaling exponents of low frequency power-law behavior; while individual-specific indices can be associated with fast oscillatory components of sway. These results support a mechanistic hypothesis claiming that the slow and the fast components of sway are associated, respectively, with neural control and biomechanics.
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