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      Linking whole-body angular momentum and step placement during perturbed human walking

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          ABSTRACT

          Human locomotion is remarkably robust to environmental disturbances. Previous studies have thoroughly investigated how perturbations influence body dynamics and what recovery strategies are used to regain balance. Fewer studies have attempted to establish formal links between balance and the recovery strategies that are executed to regain stability. We hypothesized that there would be a strong relationship between the magnitude of imbalance and recovery strategy during perturbed walking. To test this hypothesis, we applied transient ground surface translations that varied in magnitude, direction and onset time while 11 healthy participants walked on a treadmill. We measured stability using integrated whole-body angular momentum (iWBAM) and recovery strategy using step placement. We found the strongest relationships between iWBAM and step placement in the frontal plane for earlier perturbation onset times in the perturbed step ( R 2=0.52, 0.50) and later perturbation onset times in the recovery step ( R 2=0.18, 0.25), while correlations were very weak in the sagittal plane (all R 2≤0.13). These findings suggest that iWBAM influences step placement, particularly in the frontal plane, and that this influence is sensitive to perturbation onset time. Lastly, this investigation is accompanied by an open-source dataset to facilitate research on balance and recovery strategies in response to multifactorial ground surface perturbations, including 96 perturbation conditions spanning all combinations of three magnitudes, eight directions and four gait cycle onset times.

          Abstract

          Summary: Investigation of human walking during perturbations varying in magnitude, direction and timing indicates a significant influence of all three variables on whole-body angular momentum and step placement as well as strong correlations between whole-body angular momentum and step placement in the frontal plane but not the sagittal plane.

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          Most cited references37

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          OpenSim: open-source software to create and analyze dynamic simulations of movement.

          Dynamic simulations of movement allow one to study neuromuscular coordination, analyze athletic performance, and estimate internal loading of the musculoskeletal system. Simulations can also be used to identify the sources of pathological movement and establish a scientific basis for treatment planning. We have developed a freely available, open-source software system (OpenSim) that lets users develop models of musculoskeletal structures and create dynamic simulations of a wide variety of movements. We are using this system to simulate the dynamics of individuals with pathological gait and to explore the biomechanical effects of treatments. OpenSim provides a platform on which the biomechanics community can build a library of simulations that can be exchanged, tested, analyzed, and improved through a multi-institutional collaboration. Developing software that enables a concerted effort from many investigators poses technical and sociological challenges. Meeting those challenges will accelerate the discovery of principles that govern movement control and improve treatments for individuals with movement pathologies.
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            The condition for dynamic stability.

            The well-known condition for standing stability in static situations is that the vertical projection of the centre of mass (CoM) should be within the base of support (BoS). On the basis of a simple inverted pendulum model, an extension of this rule is proposed for dynamical situations: the position of (the vertical projection of) the CoM plus its velocity times a factor (square root l/g) should be within the BoS, l being leg length and g the acceleration of gravity. It is proposed to name this vector quantity 'extrapolated centre of mass position' (XcoM). The definition suggests as a measure of stability the 'margin of stability' b, the minimum distance from XcoM to the boundaries of the BoS. An alternative measure is the temporal stability margin tau, the time in which the boundary of the BoS would be reached without intervention. Some experimental data of subjects standing on one or two feet, flatfoot and tiptoe, are presented to give an idea of the usual ranges of these margins of stability. Example data on walking are also presented.
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              Central programming of postural movements: adaptation to altered support-surface configurations.

              We studied the extent to which automatic postural actions in standing human subjects are organized by a limited repertoire of central motor programs. Subjects stood on support surfaces of various lengths, which forced them to adopt different postural movement strategies to compensate for the same external perturbations. We assessed whether a continuum or a limited set of muscle activation patterns was used to produce different movement patterns and the extent to which movement patterns were influenced by prior experience. Exposing subjects standing on a normal support surface to brief forward and backward horizontal surface perturbations elicited relatively stereotyped patterns of leg and trunk muscle activation with 73- to 110-ms latencies. Activity began in the ankle joint muscles and then radiated in sequence to thigh and then trunk muscles on the same dorsal or ventral aspect of the body. This activation pattern exerted compensatory torques about the ankle joints, which restored equilibrium by moving the body center of mass forward or backward. This pattern has been termed the ankle strategy because it restores equilibrium by moving the body primarily around the ankle joints. To successfully maintain balance while standing on a support surface short in relation to foot length, subjects activated leg and trunk muscles at similar latencies but organized the activity differently. The trunk and thigh muscles antagonistic to those used in the ankle strategy were activated in the opposite proximal-to-distal sequence, whereas the ankle muscles were generally unresponsive. This activation pattern produced a compensatory horizontal shear force against the support surface but little, if any, ankle torque. This pattern has been termed the hip strategy, because the resulting motion is focused primarily about the hip joints. Exposing subjects to horizontal surface perturbations while standing on support surfaces intermediate in length between the shortest and longest elicited more complex postural movements and associated muscle activation patterns that resembled ankle and hip strategies combined in different temporal relations. These complex postural movements were executed with combinations of torque and horizontal shear forces and motions of ankle and hip joints. During the first 5-20 practice trials immediately following changes from one support surface length to another, response latencies were unchanged. The activation patterns, however, were complex and resembled the patterns observed during well-practiced stance on surfaces of intermediate lengths.(ABSTRACT TRUNCATED AT 400 WORDS)
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                Author and article information

                Contributors
                Journal
                J Exp Biol
                J Exp Biol
                JEB
                The Journal of Experimental Biology
                The Company of Biologists Ltd
                0022-0949
                1477-9145
                15 March 2023
                29 March 2023
                29 March 2023
                : 226
                : 6
                : jeb244760
                Affiliations
                [ 1 ]George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, GA 30332, USA
                [ 2 ]Institute for Robotics and Intelligent Machines, Georgia Institute of Technology , Atlanta, GA 30332, USA
                [ 3 ]Parker H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology , Atlanta, GA 30332, USA
                [ 4 ]Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology , Atlanta, GA 30332, USA
                [ 5 ]School of Biological Sciences, Georgia Institute of Technology , Atlanta, GA 30332, USA
                Author notes
                [* ]Author for correspondence ( jleestma@ 123456gatech.edu )

                Competing interests

                The authors declare no competing or financial interests.

                Author information
                http://orcid.org/0000-0002-4435-4121
                http://orcid.org/0000-0001-9844-2859
                http://orcid.org/0000-0003-0743-0786
                http://orcid.org/0000-0002-5588-6297
                http://orcid.org/0000-0002-5376-2258
                Article
                JEB244760
                10.1242/jeb.244760
                10112983
                36752161
                58f4bf8a-66ef-46db-8ca1-b58a349ca573
                © 2023. Published by The Company of Biologists Ltd

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

                History
                : 10 July 2022
                : 30 January 2023
                Funding
                Funded by: National Science Foundation, http://dx.doi.org/10.13039/100000001;
                Award ID: 1324585
                Award ID: 1545287
                Funded by: Georgia Tech, http://dx.doi.org/10.13039/100006778;
                Categories
                Research Article

                Molecular biology
                balance recovery,whole-body angular momentum,foot placement,locomotion stability

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