Loss of Lag Response Curvilinearity of Gait Poincare Plot Indices in Neurodegenerative Disorders

It is reported in the literature that the temporal structure of gait variability in healthy subjects exhibits deterministic processes where not only each stride is correlated with the neighbouring strides (i.e. short-range correlations), but at least on a statistical basis, with tens and hundreds of preceding and following strides (i.e. long-range correlations). Thus, an analysis hinging on a conventional gait Poincare plot with lag one which implicitly assumes that the current stride is influenced by the immediately preceding stride will likely underestimate the role of the autocovariance function of stride intervals. This implies that a series of lagged gait Poincare plots can potentially provide more information by reflecting short-range correlations of gait variability through the behaviour of Poincare indices in health as well as disease. Hence, in this study in the context of short-term variability, we assessed a curvilinear relation between lag (1 - 6) and Poincare indices in normal subjects and patients with neurodegenerative disorders. We found that while normal subjects exhibited this curvilinearity, the patients with neurodegenerative disorders showed its loss.