scholarly journals Sensitivity of Dynamic Stability to Changes in Step Width During Treadmill Walking by Young Adults

2012 ◽  
Vol 28 (5) ◽  
pp. 616-621 ◽  
Author(s):  
Noah J. Rosenblatt ◽  
Christopher P. Hurt ◽  
Mark D. Grabiner
Keyword(s):  
Motor System ◽  
Center Of Mass ◽  
Treadmill Walking ◽  
Step Width ◽  
Foot Placement ◽  
Before And After ◽  
Theoretical Predictions ◽  
Young Subjects ◽  
Minimum Margin ◽  
Experimental Findings

Recent experimental findings support theoretical predictions that across walking conditions the motor system chooses foot placement to achieve a constant minimum “margin of stability” (MOSmin)—distance between the extrapolated center of mass and base of support. For example, while step width varies, similar average MOSmin exists between overground and treadmill walking and between overground and compliant/irregular surface walking. However, predictions regarding the invariance of MOSmin to step-by-step changes in foot placement cannot be verified by average values. The purpose of this study was to determine average changes in, and the sensitivity of MOSmin to varying step widths during two walking tasks. Eight young subjects walked on a dual-belt treadmill before and after receiving information that stepping on the physical gap between the belts causes no adverse effects. Information decreased step width by 17% (p = .01), whereas MOSmin was unaffected (p = .12). Regardless of information, subject-specific regressions between step-by-step values of step width and MOSmin explained, on average, only 5% of the shared variance (β = 0.11 ± 0.05). Thus, MOSmin appears to be insensitive to changing step width. Accordingly, during treadmill walking, step width is chosen to maintain MOSmin. If MOSmin remains insensitive to step width across other dynamic tasks, then assessing an individual’s stability while performing theses tasks could help describe the health of the motor system.

EXPERIENCE AND PRACTICE IN CARRYING A HEAVY, UNILATERAL LOAD: FOOTPRINT EVIDENCE

2017 ◽  
Vol 17 (01) ◽  
pp. 1750022 ◽  
Author(s):  
DAVID WEBB ◽  
SARA BRATSCH
Keyword(s):  
Anterior Part ◽  
Center Of Mass ◽  
Initial Study ◽  
Ease Of Use ◽  
Human Walking ◽  
Step Width ◽  
Heavy Load ◽  
Subtle Change ◽  
Foot Placement ◽  
Heavy Loads

Although a significant amount of research has examined the biomechanical effects of carrying a load on human walking, most has focussed on fore and aft loads, or evenly balanced loads. In addition, most research on human walking no longer considers footprint analysis, despite its ease of use and its effectiveness in studies of balance. However, one project, with a small number of subjects, suggested that people carrying a heavy load in one hand (e.g., a suitcase or toolbox) make two sorts of adjustments to the placement of their feet on the substrate. The first and most obvious change is a decrease in foot angle (in-toeing) on the unloaded side. This puts the anterior part of the foot further under the center of mass when carrying a load in the contralateral hand and has been amply documented in subsequent studies. The second and more subtle change is a decrease in step width, a practice which also moves the foot on the unloaded side closer to the center of mass. However, tests subsequent to the original study did not show a consistent or significant use of this technique. This discrepancy between original and subsequent results in step width can be explained by the level of expertise which various subjects have. Experience carrying heavy loads may be required for most subjects to develop ways of accommodating loads. For this project, subjects were tested under two conditions: carrying an empty canvas bag; carrying the same bag with 21% of their body weight in it. All subjects walked on paper runners, wearing paint-soaked socks to leave footprint trails. Subjects were asked to walk once with no weights followed by three more times with weights. They were then given 10–15[Formula: see text]min of practice with the weighted bag, then asked to repeat the protocol, for a total of eight trials (two unweighted and six weighted). Foot angle and step width were measured for all trials. Results show that practice does indeed make a difference in the use of a narrower step when carrying a heavy load. Specifically, the first three weighted trials show a decrease in step width that is nonsignificant, but the last three evince a significant reduction as compared to unweighted trials. In addition, lifetime experience carrying a heavy load led to more immediate changes in foot placement. We conclude that the initial study involved subjects who already had experience carrying a unilateral heavy load and that, as with other activities, mechanically more effective movements are acquired with greater experience and practice.

scholarly journals Stabilization Strategies for Fast Walking in Challenging Environments With Incomplete Spinal Cord Injury

2021 ◽  
Vol 2 ◽  
Author(s):  
Tara Cornwell ◽  
Jane Woodward ◽  
Wendy Ochs ◽  
Keith E. Gordon
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Walking Speed ◽  
Center Of Mass ◽  
Lateral Stability ◽  
Step Width ◽  
Incomplete Spinal Cord Injury ◽  
Foot Placement ◽  
Fast Speed ◽  
Cord Injury

Gait rehabilitation following incomplete spinal cord injury (iSCI) often aims to enhance speed and stability. Concurrently increasing both may be difficult though as certain stabilization strategies will be compromised at faster speeds. To evaluate the interaction between speed and lateral stability, we examined individuals with (n = 12) and without (n = 12) iSCI as they performed straight walking and lateral maneuvers at Preferred and Fast treadmill speeds. To better detect the effects of speed on stability, we challenged lateral stability with a movement amplification force field. The Amplification field, created by a cable-driven robot, applied lateral forces to the pelvis that were proportional to the real-time lateral center of mass (COM) velocity. While we expected individuals to maintain stability during straight walking at the Fast speed in normal conditions, we hypothesized that both groups would be less stable in the Amplification field at the Fast speed compared to the Preferred. However, we found no effects of speed or the interaction between speed and field on straight-walking stability [Lyapunov exponent or lateral margin of stability (MOS)]. Across all trials at the Fast speed compared to the Preferred, there was greater step width variability (p = 0.031) and a stronger correlation between lateral COM state at midstance and the subsequent lateral foot placement. These observations suggest that increased stepping variability at faster speeds may be beneficial for COM control. We hypothesized that during lateral maneuvers in the Amplification field, MOS on the Initiation and Termination steps would be smaller at the Fast speed than at the Preferred. We found no effect of speed on the Initiation step MOS within either field (p > 0.350) or group (p > 0.200). The Termination step MOS decreased at the Fast speed within the group without iSCI (p < 0.001), indicating a trade-off between lateral stability and forward walking speed. Unexpectedly, participants took more steps and time to complete maneuvers at the Fast treadmill speed in the Amplification field. This strategy prioritizing stability over speed was especially evident in the group with iSCI. Overall, individuals with iSCI were able to maintain lateral stability when walking fast in balance-challenging conditions but may have employed more cautious maneuver strategies.

scholarly journals The effect of external lateral stabilization on the control of mediolateral stability in walking and running

2018 ◽  
Author(s):  
Mohammadreza Mahaki ◽  
Sjoerd M Bruijn ◽  
Jaap H. van Dieën
Keyword(s):  
Active Control ◽  
Repeated Measures ◽  
Gait Cycle ◽  
Center Of Mass ◽  
Step Width ◽  
Kinematic Data ◽  
Foot Placement ◽  
Consumption Data ◽  
Mediolateral Stability

It is still unclear how humans control mediolateral (ML) stability in walking and even more so for running. Here, foot placement adjustment as a main mechanism of active control of mediolateral stability was compared between walking and running. Moreover, to verify the role of foot placement as a means of active control of ML stability and associated metabolic costs in both modes of locomotion, this study investigated the effect of external lateral stabilization on foot placement control. Ten young adults participated in this study. Kinematic data of the trunk (T6) and feet (heels) as well as breath-by-breath oxygen consumption data were recorded during walking and running on a treadmill in normal and stabilized conditions. Coordination between ML trunk Center of Mass (CoM) state and subsequent ML foot placement, step width, and step width variability were assessed. Two-way repeated measures ANOVAs (either normal or SPM1d) were used to test for effects of walking vs. running and of normal vs. stabilized locomotion. We found a stronger association between ML trunk CoM state and foot placement in walking than in running from 90-100% of the gait cycle and also a higher step width variability in walking, but no significant differences in step width. The association between trunk CoM state and foot placement was significantly decreased by external lateral stabilization in walking and running, and this reduction was stronger in walking than in running from 75-100% of gait cycle. Surprisingly, energy cost significantly increased by external lateral stabilization, which was more pronounced in running than walking. We conclude that ML foot placement is coordinated to the CoM kinematic state to stabilize both walking and running. This coordination is more tight in walking than in running and appears not to contribute substantially to the energy costs of either mode of locomotion.

scholarly journals Does increased gait variability improve stability when faced with an expected balance perturbation during treadmill walking?

2020 ◽  
Author(s):  
Jacqueline Nestico ◽  
Alison Novak ◽  
Stephen D. Perry ◽  
Avril Mansfield
Keyword(s):  
Research Question ◽  
Step Length ◽  
Gait Variability ◽  
Treadmill Walking ◽  
Step Width ◽  
Movement Variability ◽  
Foot Placement ◽  
Motion Simulator ◽  
Improve Stability

AbstractBackgroundCurrently, there is uncertainty as to whether movement variability is errorful or exploratory.Research questionThis study aimed to determine if gait variability represents exploration to improve stability. We hypothesized that 1) spatiotemporal gait features will be more variable prior to an expected perturbation than during unperturbed walking, and 2) increased spatiotemporal gait variability pre-perturbation will correlate with improved stability post-perturbation.MethodsSixteen healthy young adults completed 15 treadmill walking trials within a motion simulator under two conditions: unperturbed and expecting a perturbation. Participants were instructed not to expect a perturbation for unperturbed trials, and to expect a single transient medio-lateral balance perturbation for perturbed trials. Kinematic data were collected during the trials. Twenty steps were recorded post-perturbation. Unperturbed and pre-perturbation gait variabilities were defined by the short- and long-term variabilities of step length, width, and time, using 100 steps from pre-perturbation and unperturbed trials. Paired t-tests identified between-condition differences in variabilities. Stability was defined as the number of steps to centre of mass restabilization post-perturbation. Multiple regression analyses determined the effect of pre-perturbation variability on stability.ResultsLong-term step width variability was significantly higher pre-perturbation compared to unperturbed walking (mean difference=0.28cm, p=0.0073), with no significant differences between conditions for step length or time variabilities. There was no significant relationship between pre-perturbation variability and post-perturbation restabilization.SignificanceIncreased pre-perturbation step width variability was neither beneficial nor detrimental to stability. However, the increased variability in medio-lateral foot placement suggests that participants adopted an exploratory strategy in anticipation of a perturbation.

scholarly journals Effects of vestibular stimulation on gait stability and variability

2021 ◽  
Author(s):  
Rina M. Magnani ◽  
Jaap H. van Dieën ◽  
Sjoerd M. Bruijn
Keyword(s):  
Muscle Activity ◽  
Center Of Mass ◽  
Mass Movement ◽  
Stable Condition ◽  
Vestibular Stimulation ◽  
Step Width ◽  
Gait Stability ◽  
Foot Placement ◽  
Vestibular Information ◽  
Narrow Base

AbstractVestibular information modulates muscle activity during gait, presumably to contribute stability, because noisy electrical vestibular stimulation perturbs gait stability. An important mechanism to stabilize gait in the mediolateral direction is to coordinate foot placement based on a sensory estimate of the trunk center of mass state, to which vestibular information appears to contribute. We, therefore expected that noisy vestibular stimulation would decrease the correlation between foot placement and trunk center of mass state. Moreover, as vestibular modulation of muscle activity during gait depends on step width, we expected stronger effects for narrow-base than normal walking, and smaller effects for wide-base walking. In eleven healthy subjects we measured the kinematics of the trunk (as a proxy of the center of mass), and feet, while they walked on a treadmill in six conditions, including three different step widths: control (preferred step width), narrow-base (steps smaller than hip width), and wide-base (with steps greater than hip width). The three conditions were conducted with and without a bipolar electrical stimulus, applied behind the ears (5 mA). Walking with EVS reduced gait stability but increased the foot placement to center of mass correlation in different step width conditions. The narrow-base walking was the most stable condition and showed a stronger correlation between foot placement and center of mass state. We argue that EVS destabilized gait, but that this was partially compensated for by tightened control over foot placement, which would require successful use of other than vestibular sensory inputs, to estimate center of mass movement.

ADRENOCORTICAL RESPONSE TO NON-EXHAUSTIVE MUSCULAR EXERCISE

1972 ◽  
Vol 70 (1) ◽  
pp. 73-80 ◽  
Author(s):  
L. W. Raymond ◽  
J. Sode ◽  
J. R. Tucci
Keyword(s):  
Treadmill Exercise ◽  
Serum Cortisol ◽  
Treadmill Walking ◽  
Exhaustive Exercise ◽  
Muscular Exercise ◽  
Adrenocortical Response ◽  
Exercise Tachycardia ◽  
Before And After

ABSTRACT Treadmill walking produced a prompt reduction in serum cortisol in 10 of 12 healthy military men. In contrast, two subjects, with pre-exercise tachycardia and apprehension, showed an increase in serum cortisol with treadmill exercise. In each group, the changes produced by exercise were still evident 30 and 60 minutes after the 30-minute treadmill walk. Urine collected before and after exercise contained similar amounts of 11-hydroxy- and 17-hydroxycorticosteroid material. These results may be explained by an increase in cortisol utilization during exercise and/or by a change in its distribution. The data indicate that in the absence of psychic factors, non-exhaustive exercise is not associated with pituitary adrenocortical activation.

scholarly journals Transfer and generalization of learned manipulation between unimanual and bimanual tasks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Trevor Lee-Miller ◽  
Marco Santello ◽  
Andrew M. Gordon
Keyword(s):  
Learning Transfer ◽  
Center Of Pressure ◽  
Center Of Mass ◽  
Pressure Point ◽  
Torque Generation ◽  
Before And After ◽  
Object Center ◽  
High Level ◽  
Bimanual Grasping ◽  
Partial Learning

AbstractSuccessful object manipulation, such as preventing object roll, relies on the modulation of forces and centers of pressure (point of application of digits on each grasp surface) prior to lift onset to generate a compensatory torque. Whether or not generalization of learned manipulation can occur after adding or removing effectors is not known. We examined this by recruiting participants to perform lifts in unimanual and bimanual grasps and analyzed results before and after transfer. Our results show partial generalization of learned manipulation occurred when switching from a (1) unimanual to bimanual grasp regardless of object center of mass, and (2) bimanual to unimanual grasp when the center of mass was on the thumb side. Partial generalization was driven by the modulation of effectors’ center of pressure, in the appropriate direction but of insufficient magnitude, while load forces did not contribute to torque generation after transfer. In addition, we show that the combination of effector forces and centers of pressure in the generation of compensatory torque differ between unimanual and bimanual grasping. These findings highlight that (1) high-level representations of learned manipulation enable only partial learning transfer when adding or removing effectors, and (2) such partial generalization is mainly driven by modulation of effectors’ center of pressure.

scholarly journals Measurements of the differential cross sections of the production of Z + jets and γ + jets and of Z boson emission collinear with a jet in pp collisions at $$ \sqrt{s} $$ = 13 TeV

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
◽  
A. M. Sirunyan ◽  
A. Tumasyan ◽  
W. Adam ◽  
F. Ambrogi ◽  
...  
Keyword(s):  
Cross Sections ◽  
Differential Cross ◽  
Z Boson ◽  
Center Of Mass ◽  
Z Bosons ◽  
Differential Cross Sections ◽  
Pp Collisions ◽  
Center Of Mass Energy ◽  
Cms Experiment ◽  
Theoretical Predictions

Abstract Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet.

Detection of Vehicle Tripped and Untripped Rollovers by a Novel Index With Mass-Center-Position Estimations

2017 ◽  
Author(s):  
Fengchen Wang ◽  
Yan Chen
Keyword(s):  
Load Transfer ◽  
Center Of Mass ◽  
Roll Motion ◽  
Mass Center ◽  
Motion Models ◽  
Center Position ◽  
Before And After ◽  
Vehicle Rollover ◽  
Lift Off ◽  
Rollover Index

This paper presents a novel mass-center-position (MCP) metric for vehicle rollover propensity detection. MCP is first determined by estimating the positions of the center of mass of one sprung mass and two unsprung masses with two switchable roll motion models, before and after tire lift-off. The roll motion information without saturation can then be provided through MCP continuously. Moreover, to detect completed rollover statues for both tripped and untripped rollovers, the criteria are derived from d’Alembert principle and moment balance conditions based on MCP. In addition to tire lift-off, three new rollover statues, rollover threshold, rollover occurrence, and vehicle jumping into air can be all identified by the proposed criteria. Compared with an existing rollover index, lateral load transfer ratio, the fishhook maneuver simulation results in CarSim® for an E-class SUV show that MCP metric can successfully predict the vehicle impending rollover without saturation for untripped rollovers. Tripped rollovers caused by a triangle road bump are also successfully detected in the simulation. Thus, MCP metric can be successfully applied for rollover propensity prediction.

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