Dataset Information

Postural stability in human running with step-down perturbations: an experimental and numerical study.

ABSTRACT: Postural stability is one of the most crucial elements in bipedal locomotion. Bipeds are dynamically unstable and need to maintain their trunk upright against the rotations induced by the ground reaction forces (GRFs), especially when running. Gait studies report that the GRF vectors focus around a virtual point above the centre of mass (VP_A), while the trunk moves forward in pitch axis during the stance phase of human running. However, a recent simulation study suggests that a virtual point below the centre of mass (VP_B) might be present in human running, because a VP_A yields backward trunk rotation during the stance phase. In this work, we perform a gait analysis to investigate the existence and location of the VP in human running at 5 m s^-1, and support our findings numerically using the spring-loaded inverted pendulum model with a trunk. We extend our analysis to include perturbations in terrain height (visible and camouflaged), and investigate the response of the VP mechanism to step-down perturbations both experimentally and numerically. Our experimental results show that the human running gait displays a VP_B of ?-30 cm and a forward trunk motion during the stance phase. The camouflaged step-down perturbations affect the location of the VP_B. Our simulation results suggest that the VP_B is able to encounter the step-down perturbations and bring the system back to its initial equilibrium state.

SUBMITTER: Drama O

PROVIDER: S-EPMC7735328 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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Postural stability in human running with step-down perturbations: an experimental and numerical study.

Drama Özge Ö Vielemeyer Johanna J Badri-Spröwitz Alexander A Müller Roy R

Royal Society open science 20201118 11

Postural stability is one of the most crucial elements in bipedal locomotion. Bipeds are dynamically unstable and need to maintain their trunk upright against the rotations induced by the ground reaction forces (GRFs), especially when running. Gait studies report that the GRF vectors focus around a virtual point above the centre of mass (VP<sub>A</sub>), while the trunk moves forward in pitch axis during the stance phase of human running. However, a recent simulation study suggests that a virtua ...[more]

PMID: 33391782

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Project description:Introduction: Freezing of gait (FOG) is a powerful determinant of falls in Parkinson's disease (PD). Automatic postural reactions serve as a protective strategy to prevent falling after perturbations. However, differences in automatic postural reactions between patients with and without FOG in response to perturbation are at present unclear. Therefore, the present study aimed to compare the response patterns and neuromuscular control between PD patients with and without FOG and healthy controls (HCs) after postural perturbations. Methods: 28 PD patients (15 FOG+, 13 FOG-) and 22 HCs were included. Participants stood on a moveable platform while random perturbations were imposed. The first anterior platform translation was retained for analysis. Center of pressure (CoP) and center of mass (CoM) trajectories and trunk, knee and ankle angles were compared between the three groups using the Statistical Parametric Mapping technique, allowing to capture changes in time. In addition, muscle activation of lower leg muscles was measured using EMG. Results: At baseline, FOG+ stood with more trunk flexion than HCs (p = 0.005), a result not found in FOG-. Following a perturbation, FOG+ reacted with increased trunk extension (p = 0.004) in comparison to HCs, a pattern not observed in FOG-. The CoM showed greater backward displacement in FOG- and FOG+ (p = 0.008, p = 0.027). Both FOG+ and FOG- showed increased co-activation of agonist and antagonist muscles compared to HCs (p = 0.010), with no differences between FOG+ and FOG-. Conclusions: Automatic postural reactions after a sudden perturbation are similar between PD subgroups with and without FOG but different from HCs. Reactive postural control, largely regulated by brain stem centers, seems to be modulated by different mechanisms than those governing freezing of gait. Greater differences in initial stance position, enhanced by joint stiffening, could however underlie maladaptive postural responses and increase susceptibility for balance loss in FOG+ compared to FOG-.

Dataset Information

Postural stability in human running with step-down perturbations: an experimental and numerical study.

Publications

Postural stability in human running with step-down perturbations: an experimental and numerical study.

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