Nonlinear dynamical structure of sway path during standing in patients with multiple sclerosis and in healthy controls is affected by changes in sensory input and cognitive load

Although several studies have applied traditional linear measures to evaluate postural control of patients with multiple sclerosis (MS), little is known about the nonlinear dynamics of this patient group. In this study, recurrence quantification analysis (RQA), a well documented nonlinear method, was used to compare the nonlinear dynamical structure of postural sway in two groups consisting of MS patients (. n=. 23) and healthy matched controls (. n=. 23). The study focuses on three levels of postural difficulty consisting of (1) standing on a rigid surface (force platform) with eyes open, (2) standing on a rigid surface with eyes closed, and (3) standing on a foam surface with eyes closed. The two levels of cognitive difficulty measured, consisted of a single postural task and a dual postural-cognitive task. It was observed that as the postural conditions became more difficult, the center of pressure (COP) time series of both groups became less regular as recorded in lower recurrence rate, less complex in deterministic structure as reflected in lower RQA entropy, and less nonstationary as reflected in the recording of lower Trend. Moreover, as cognitive conditions became more difficult, COP time series became less regular (lower Rec in the anteroposterior direction and lower Det in both directions), less complex in deterministic structure (lower RQA Ent in the anteroposterior direction), and less nonstationary (lower trend in the anteroposterior direction). The analytical results of the research show that there is a similar dynamical structure for both the MS patients and the control group; however, the nonlinear behavior of both groups was different under various experimental conditions. © 2013 Elsevier Ireland Ltd

Comparison of the lower limb inter-segmental coordination during walking between healthy controls and people with multiple sclerosis with and without fall history

Background: This research aims to compare lower limb inter-segmental coordination, a higher order property of the human movement system, during walking between healthy controls and people with multiple sclerosis (PwMS) with and without fall history. Methods: Fifty PwMS (25 patients with fall history and 25 patients without fall history) and 25 healthy controls participated in the present study. Three-dimensional coordinate data of the lower limbs were collected during treadmill walking at a preferred walking speed. The phasing relationship and its variability between lower limb segments were evaluated using the mean absolute relative phase (MARP) and deviation phase (DP) during the stance and swing phases of gait. Results: Compared to healthy controls, both groups of PwMS demonstrated significantly greater shank-thigh MARP values during the stance phase (p < 0.001). In addition, MARP values of foot-shank coordination were significantly smaller in both groups of PwMS than the healthy controls during both the stance and swing phases (p < 0.001). For the DP of shank-thigh coordination, our analysis revealed greater values in both MS fallers and non-fallers compared to healthy controls during the stance (p < 0.001) and swing phases (p < 0.001, p = 0.004, respectively). Moreover, MS fallers demonstrated greater DP values than non-fallers in swing phase (p = 0.02). For the DP of foot-shank coordination, MS fallers showed greater values compared to non-fallers and healthy controls during the stance (p = 0.009, p = 0.001, respectively) and swing phases (p = 0.01, p = 0.006, respectively). Conclusion: Our results suggest that in addition to traditional gait parameters, examining and also facilitating lower limb inter-segmental coordination should be considered in future studies aimed at improving gait performance and reducing risk of falling in PwMS. © 2020 Elsevier B.V