Center of mass in analysis of dynamic stability during gait following stroke: A systematic review

The goal of this study was to validate dynamic stability and forward progression determinants for the alternate foot placement selection algorithm. Participants were asked to walk on level ground and avoid stepping, when present, on a virtual white planar obstacle. They had a one-step duration to select an alternate foot placement, with the task performed under two conditions: free (participants chose the alternate foot placement that was appropriate) and forced (a green arrow projected over the white planar obstacle cued the alternate foot placement). To validate the dynamic stability determinant, the distance between the extrapolated center of mass (COM) position, which incorporates the dynamics of the body, and the limits of the base of support was calculated in both anteroposterior (AP) and mediolateral (ML) directions in the double support phase. To address the second determinant, COM deviation from straight ahead was measured between adaptive and subsequent steps. The results of this study showed that long and lateral choices were dominant in the free condition, and these adjustments did not compromise stability in both adaptive and subsequent steps compared with the short and medial adjustments, which were infrequent and adversely affected stability. Therefore stability is critical when selecting an alternate foot placement in a cluttered terrain. In addition, changes in the plane of progression resulted in small deviations of COM from the endpoint goal. Forward progression of COM was maintained even for foot placement changes in the frontal plane, validating this determinant as part of the selection algorithm.

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Strategies for Dynamic Stability During Locomotion on a Slippery Surface: Effects of Prior Experience and Knowledge

Journal of Neurophysiology ◽

10.1152/jn.00691.2001 ◽

2002 ◽

Vol 88 (1) ◽

pp. 339-353 ◽

Cited By ~ 219

Author(s):

Daniel S. Marigold ◽

Aftab E. Patla

Keyword(s):

Dynamic Stability ◽

Time Course ◽

Imaging System ◽

Prior Experience ◽

Surface Condition ◽

Center Of Mass ◽

Whole Body ◽

Global Changes ◽

Slippery Surface ◽

Rate Of Loading

Falls due to slips are prevalent in everyday life. The purpose of this study was to determine the reactive recovery responses used to maintain dynamic stability during an unexpected slip, establish the time course of response adaptation to repeated slip perturbations, and distinguish the proactive strategies for negotiating a slippery surface. Twelve young adults participated in the study in which a slip was generated following foot contact on a set of steel free-wheeling rollers. Surface electromyographic (EMG) data were collected from rectus femoris, biceps femoris, tibialis anterior, and the medial head of gastrocnemius on the perturbed limb. Whole body kinematics were recorded using an optical imaging system: from this the center of mass, foot angle, and medial-lateral stability margins were determined. In addition, braking/loading and accelerating/unloading impulses while in contact with the rollers and the rate of loading the rollers were determined from ground reaction forces. Results demonstrate that the reactive recovery response to the first slip consisted of a rapid onset of a flexor synergy (146–199 ms), a large arm elevation strategy, and a modified swing limb trajectory. With repeated exposure to the slip perturbation, the CNS rapidly adapts within one slip trial through global changes. These changes include the attenuation of muscle response magnitude, reduced braking impulse, landing more flat-footed, and elevating the center of mass. Individuals implement a “surfing strategy” while on the rollers when knowledge of the surface condition was available before hand. Furthermore, knowledge of a slip results in a reduced braking impulse and rate of loading, a shift in medial-lateral center of mass closer to the support limb at foot contact on the rollers and a more flat foot landing. In conclusion, prior experience with the perturbations allows subsequent modification and knowledge of the surface condition results in proactive adjustments to safely traverse the slippery surface.

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A new approach to dynamic posture control

Robotica ◽

10.1017/s0263574797000544 ◽

1997 ◽

Vol 15 (4) ◽

pp. 449-459 ◽

Cited By ~ 7

Author(s):

O. Vanel ◽

P. Gorce

Keyword(s):

Real Time ◽

Dynamic Stability ◽

Center Of Mass ◽

Biped Robot ◽

Force Distribution ◽

Linear Programming Method ◽

Task Transition ◽

New Approach ◽

Simulation Results ◽

Dynamic Posture

In this paper, we propose an approach which ensures the dynamic stability of a biped robot called “BIPMAN”. It is based on the correction of the trunk center of mass acceleration and on the distribution of the forces exerted by the limbs on the trunk. This latter is performed by means of a linear programming method (the simplex method). The retained criterion allows to optimize force distribution as well as trunk roll and pitch angles. Weighting factors are introduced into this criterion in order to define criteria adapted to specific tasks. Modifying these factors is a solution to the task transition problem. Many simulation results are presented to demonstrate criteria and constraints influences on dynamic stability. They lead us to introduce a new approach called RTCA (Real Time Criteria and Constraints Adaptation). This relies on the analysis of position, velocity and acceleration vectors for criterion real time adaptation and on forces analysis for constraints real time adaptation. The RTCA approach is finally validated through simulations results for a specific task.

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A Systematic Review of Center of Mass as a Measure of Dynamic Postural Control Following Concussion

International Journal of Sports Physical Therapy ◽

10.26603/001c.27983 ◽

2021 ◽

Author(s):

Sarah Patejak ◽

Joshua Forrest ◽

Emily Harting ◽

Mable Sisk ◽

Eric Schussler

Keyword(s):

Systematic Review ◽

Postural Control ◽

Center Of Mass

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Dynamic and static stability in hexapedal runners.

Journal of Experimental Biology ◽

10.1242/jeb.197.1.251 ◽

1994 ◽

Vol 197 (1) ◽

pp. 251-269 ◽

Cited By ~ 3

Author(s):

L H Ting ◽

R Blickhan ◽

R J Full

Keyword(s):

Dynamic Stability ◽

Center Of Pressure ◽

Center Of Mass ◽

Stability Margin ◽

Static Stability ◽

Double Support ◽

Wide Range ◽

One Step ◽

Energy And Momentum ◽

Base Of Support

Stability is fundamental to the performance of terrestrial locomotion. Running cockroaches met the criteria for static stability over a wide range of speeds, yet several locomotor variables changed in a way that revealed an increase in the importance of dynamic stability as speed increased. Duty factors (the fraction of time that a leg spends on the ground relative to the stride period) decreased to 0.5 and below with an increase in speed. The duration of double support (i.e. when both tripods, or all six legs, were on the ground) decreased significantly with an increase in speed. All legs had similar touch-down phases in the tripod, but the shortest leg, the front one, lifted off before the middle and the rear leg, so that only two legs of the tripod were in contact with the ground at the highest speeds. Per cent stability margin (the shortest distance from the center of gravity to the boundaries of support, normalized to the maximum possible stability margin) decreased with increasing speed from 60% at 10 cms-1 to values less than zero at speeds faster than 50 cms-1, indicating instances of static instability at fast speeds. The center of mass moved rearward or posteriorly with respect to the base of support as speed increased. Moments about the center of mass, as shown by the center of pressure (the equivalent of a single 'effective' leg), were variable, but were balanced by opposing moments over a stride. Thus, hexapods can exploit the advantages of both static and dynamic stability. Static or quasi-static assumptions alone were insufficient to explain straight-ahead, constant-speed locomotion and may hinder discovery of behaviors that are dynamic, where kinetic energy and momentum can act as a bridge from one step to the next.

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Torque around the center of mass: dynamic stability during quadrupedal arboreal locomotion in the Siberian chipmunk (Tamias sibiricus)

Zoology ◽

10.1016/j.zool.2010.11.004 ◽

2011 ◽

Vol 114 (2) ◽

pp. 95-103 ◽

Cited By ~ 22

Author(s):

Andrew R. Lammers ◽

Ulrich Zurcher

Keyword(s):

Dynamic Stability ◽

Center Of Mass ◽

Siberian Chipmunk ◽

Tamias Sibiricus

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Effect of Externally Cued Training on Dynamic Stability Control During the Sit-to-Stand Task in People With Parkinson Disease

Physical Therapy ◽

10.2522/ptj.20100423 ◽

2013 ◽

Vol 93 (4) ◽

pp. 492-503 ◽

Cited By ~ 9

Author(s):

Tanvi Bhatt ◽

Feng Yang ◽

Margaret K.Y. Mak ◽

Christina W-Y. Hui-Chan ◽

Yi-Chung Pai

Keyword(s):

Dynamic Stability ◽

Center Of Mass ◽

Stability Control ◽

Sit To Stand ◽

Backward Stability ◽

Stability Limits ◽

Balance Loss ◽

Mass Position ◽

Dynamic Stability Control ◽

Forward Stability

Background Previous studies have shown that people with Parkinson disease (PD) have difficulty performing the sit-to-stand task because of mobility and stability-related impairments. Despite its importance, literature on the quantification of dynamic stability control in people with PD during this task is limited. Objective The study objective was to examine differences in dynamic stability control between people with PD and people who were healthy and the extent to which externally cued training could improve such control during the sit-to-stand task in people with PD. Design This was a quasi-experimental controlled trial. Methods The performance of 21 people with PD was compared with that of 12 older adults who dwelled in the community. People with PD were randomly assigned to 2 groups: a group that did not receive training and a group that received audiovisually cued training (3 times per week for 4 weeks) for speeding up performance on the sit-to-stand task. Outcome measures recorded at baseline and after 4 weeks included center-of-mass position, center-of-mass velocity, and stability against either backward or forward balance loss (backward or forward stability) at seat-off and movement termination. Results Compared with people who were healthy, people with PD had greater backward stability resulting from a more anterior center-of-mass position at seat-off. This feature, combined with decreased forward stability at movement termination, increased their risk of forward balance loss at movement termination. After training, people with PD achieved greater backward stability through increased forward center-of-mass velocity at seat-off and reduced the likelihood of forward balance loss at movement termination through a posterior shift in the center-of-mass position. Limitations The study applied stability limits derived from adults who were healthy to people with PD, and the suggested impact on the risk of balance loss and falling is based on these theoretical stability limits. Conclusions For people with PD, postural stability against backward balance loss at task initiation was increased at the expense of possible forward balance loss at task termination. Task-specific training with preparatory audiovisual cues resulted in improved overall dynamic stability against both forward and backward balance loss.

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Dynamic Margins of Stability During Robot-Assisted Walking in Able-Bodied Individuals: A Preliminary Study

Frontiers in Robotics and AI ◽

10.3389/frobt.2020.574365 ◽

2020 ◽

Vol 7 ◽

Author(s):

Arvind Ramanujam ◽

Kamyar Momeni ◽

Manikandan Ravi ◽

Jonathan Augustine ◽

Erica Garbarini ◽

...

Keyword(s):

Dynamic Stability ◽

Center Of Mass ◽

Spatial Location ◽

Careful Consideration ◽

Whole Body ◽

Control Mechanisms ◽

Overground Walking ◽

Robot Assisted ◽

Lateral Direction ◽

Stability Margins

Background: Gait analysis studies during robot-assisted walking have been predominantly focused on lower limb biomechanics. During robot-assisted walking, the users' interaction with the robot and their adaptations translate into altered gait mechanics. Hence, robust and objective metrics for quantifying walking performance during robot-assisted gait are especially relevant as it relates to dynamic stability. In this study, we assessed bi-planar dynamic stability margins for healthy adults during robot-assisted walking using EksoGT™, ReWalk™, and Indego® compared to independent overground walking at slow, self-selected, and fast speeds. Further, we examined the use of forearm crutches and its influence on dynamic gait stability margins.Methods: Kinematic data were collected at 60 Hz under several walking conditions with and without the robotic exoskeleton for six healthy controls. Outcome measures included (i) whole-body center of mass (CoM) and extrapolated CoM (XCoM), (ii) base of support (BoS), (iii) margin of stability (MoS) with respect to both feet and bilateral crutches.Results: Stability outcomes during exoskeleton-assisted walking at self-selected, comfortable walking speeds were significantly (p < 0.05) different compared to overground walking at self-selected speeds. Unlike overground walking, the control mechanisms for stability using these exoskeletons were not related to walking speed. MoSs were lower during the single support phase of gait, especially in the medial–lateral direction for all devices. MoSs relative to feet were significantly (p < 0.05) lower than those relative to crutches. The spatial location of crutches during exoskeleton-assisted walking pushed the whole-body CoM, during single support, beyond the lateral boundary of the lead foot, increasing the risk for falls if crutch slippage were to occur.Conclusion: Careful consideration of crutch placement is critical to ensuring that the margins of stability are always within the limits of the BoS to control stability and decrease fall risk.

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