Balance recovery in the double support during perturbed walking

Research output: Contribution to conferencePosterAcademic

Abstract

I. INTRODUCTION
Exoskeleton walking increases the relative time spent in the double support phase (DSP). It is therefore crucial to control balance when both feet are on the ground. Healthy humans have excellent balance capabilities to avoid falling. The centre of pressure (CoP) describes the control of the centre of mass (CoM) movement [1]. The range of possible CoP locations in the DSP is determined by the foot placement at the end of the preceding single support phase. This study focuses on the CoP modulation during the DSP in the control of the CoM state.
II. METHODS
CoP trajectories in response to pelvis perturbations were extracted from an existing data set by Vlutters et al [2]. Anteroposterior and mediolateral perturbations with magnitudes up to 16% of the body weight were given at the moment of toe off. Parameterized CoP trajectories were generated with a spline function based on the experimental CoP trajectories, examples are shown in figure 1. Parameterization was done as a function of 1) the duration of the DSP, 2) the amplitude of the CoP, and 3) percentage of the amplitude reached halfway the DSP (= midpoint). The parameters were varied within a range equal to the standard deviation around the mean value obtained from the experimental data. The generated trajectories were used in model simulations of the CoM during the first DSP following the perturbation. A simple inverted pendulum model, relating the horizontal distance between the CoP and CoM to CoM acceleration, was used to assess the effectiveness of the CoP modulation in counteracting perturbation induced CoM velocity changes [3].
III. RESULTS
The model outcome corresponds with the experimental data, figure 1. All the three CoP parameters are linearly related to the change in CoM velocity over the DSP, in both the experimental and modelled data. Changes of the midpoint resulted in larger variations in the modelled Δ CoM velocity, compared to those resulting from changes in the duration or amplitude, see figure 2.
IV. DISCUSSION
A simple inverted pendulum model was able to model representative CoM trajectories from the generated CoP trajectories as input. To control the CoM velocity after a perturbation, subjects used all CoP parameters. However, in the experimental data these parameters were also related with each other. When uncoupling the effect of these parameters in the model, the shape of the CoP trajectory, represented by the CoP shift that is reached halfway the DSP, had the largest influence on the changes of the CoM velocity during the DSP. Shifting the load earlier or later to the leading leg helps in increasing or decreasing the CoM velocity. This will help in counteracting the effect of the perturbation and returning to the baseline CoM velocity.
REFERENCES
[1] H. Reimann, T. D. Fettrow, E. D. Thompson, P. Agada, B. J. McFadyen, and J. J. Jeka, “Complementary mechanisms for upright balance during walking,” PLoS One, vol. 12, no. 2, pp. 1–16, 2017.
[2] M. Vlutters, E. H. F. van Asseldonk, and H. van der Kooij, “Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking,” J. Exp. Biol., vol. 219, no. 10, pp. 1514–1523, 2016.
[3] Y. Jian, D. Winter, M. Ishac, and L. Gilchrist, “Trajectory of the body COG and COP during initiation and termination of gait,” Gait Posture, vol. 1, no. 1, pp. 9–22
Original languageEnglish
Publication statusPublished - 14 May 2020
EventDynamic Walking Conference 2020 - Online Conference
Duration: 11 May 202014 May 2020

Conference

ConferenceDynamic Walking Conference 2020
CityOnline Conference
Period11/05/2014/05/20

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