Biology subjects

Dean, J. C.

Publications and source records attributed to Dean, J. C..

7 recordsLinked to original sources

bioRxiv2025

Frequency-dependent effects of hip abductor vibration and surface translation on mediolateral sway

The control of mediolateral standing balance is altered in many clinical populations, due in part to disrupted sensorimotor processing. Sensory perturbations, as evoked by musculotendon vibration, can provide insight into the contributions of individual sources of sensory feedback to this control. The purpose of this study was to investigate whether hip abductor vibration can elicit mediolateral sway at frequencies <1 Hz, which dominate standing posture. Secondarily, we quantified the effects of mediolateral surface translations in this frequency range. Participants (n=12) without neurological or orthopedic conditions completed a series of standing trials in which we quantified center of pressure motion. In a subset of trials, time-varying hip abductor vibration was delivered, with vibration intensity following sum-of-sine trajectories with frequency content from 0.1-0.9 Hz. In other trials, the standing surface translated mediolaterally following similar trajectories. Participants were not provided instructions regarding how to respond to the stimuli. Vibration significantly increased mediolateral sway for frequencies greater than 0.5 Hz, while surface translation caused substantial sway increases throughout the investigated frequency range. The effects of vibration were observed in the frequency range typically interpreted as reflecting feedback-driven corrective responses, suggesting the potential of this approach to influence balance performance through sensory augmentation.

bioengineering↗

bioRxiv2023

Force-field perturbations and muscle vibration strengthen stability-related foot placement responses during steady-state gait

Mediolateral gait stability can be maintained by coordinating our foot placement with respect to the center-of-mass (CoM) kinematic state. Neurological impairments can reduce the degree of foot placement control. For individuals with such impairments, interventions that could improve foot placement control could thus contribute to improved gait stability. In this study we aimed to better understand two potential interventions, by investigating their effect in neurologically intact individuals. The degree of foot placement control can be quantified based on a foot placement model, in which the CoM position and velocity during swing predict subsequent foot placement. Previously, perturbing foot placement with a force-field resulted in an enhanced degree of foot placement control as an after-effect. Moreover, muscle vibration enhanced the degree of foot placement control through sensory augmentation whilst the vibration was applied. Here, we replicated these two findings and further investigated whether Q1) sensory augmentation leads to an after-effect and Q2) whether combining sensory augmentation with force-field perturbations leads to a larger after-effect, as compared to force-field perturbations only. In addition, we evaluated several potential contributors to the degree of foot placement control, by considering foot placement errors, CoM variability and the CoM position gain ({beta}pos) of the foot placement model, next to the R2 measure as the degree of foot placement control. Sensory augmentation led to a higher degree of foot placement control as an after-effect (Q1). However, combining sensory augmentation and force-field perturbations did not lead to a larger after-effect, as compared to following force-field perturbations only (Q2). Furthermore, we showed that, the improved degree of foot placement control following force-field perturbations and during/following muscle vibration, did not reflect diminished foot placement errors. Rather, participants demonstrated a stronger active response (higher {beta}pos) as well as higher CoM variability.

biophysics↗

bioRxiv2022

Relationships between post-stroke mediolateral stepping characteristics, walking speed, balance performance, and balance confidence

BackgroundMany people with chronic stroke (PwCS) exhibit walking balance deficits linked to increased fall risk and decreased balance confidence. One potential contributor to these balance deficits is a decreased ability to modulate mediolateral stepping behavior based on pelvis motion. This behavior, hereby termed mediolateral step modulation, is thought to be an important balance strategy but can be disrupted in PwCS. Research QuestionAre biomechanical metrics of mediolateral step modulation related to common clinical balance measures among PwCS? MethodsIn this cross-sectional study, 93 PwCS walked on a treadmill at their self-selected speed for 3-minutes. We quantified mediolateral step modulation for both paretic and non-paretic steps by calculating partial correlations between mediolateral pelvis displacement at the start of each step and step width ({rho}SW), mediolateral foot placement relative to the pelvis ({rho}FP), and final mediolateral location of the pelvis ({rho}PD) at the end of the step. We also assessed several common clinical balance measures (Functional Gait Assessment [FGA], Activities-specific Balance Confidence scale [ABC], self-reported fear of falling and fall history). We performed Spearman correlations to relate each biomechanical metric of step modulation to FGA and ABC scores. We performed Wilcoxon rank sum tests to compare each biomechanical metric between individuals with and without a fear of falling and a history of falls. ResultsOnly {rho}FP for paretic steps was significantly related to all four clinical balance measures; higher paretic {rho}FP values tended to be observed in participants with higher FGA scores, with higher ABC scores, without a fear of falling and without a history of falls. However, the strength of each of these relationships was only weak to moderate. SignificanceWhile the present results do not provide insight into causality, they justify future work investigating whether interventions designed to increase {rho}FP can improve clinical measures of post-stroke balance in parallel.

bioengineering↗

bioRxiv2020

Augmented hip proprioception influences mediolateral foot placement during walking

Hip abductor proprioception contributes to the control of mediolateral foot placement, which varies with step-by-step fluctuations in pelvis dynamics. While prior work has used hip abductor vibration as a sensory perturbation to investigate this role of hip proprioception, we here tested whether time-varying vibration can predictably manipulate the relationship between pelvis dynamics and foot placement. We compared participants (n=32; divided into two groups of 16 with slightly different vibration control) gait behavior across four treadmill walking conditions: 1) No feedback; 2) Random feedback, with vibration unrelated to pelvis motion; 3) Augmented feedback, with vibration designed to evoke proprioceptive feedback paralleling the actual pelvis motion; 4) Disrupted feedback, with vibration designed to evoke proprioceptive feedback inversely related to pelvis motion. We hypothesized that the relationship between pelvis dynamics and foot placement would be strengthened by Augmented feedback but weakened by Disrupted feedback. For both participant groups, the strength of the relationship between pelvis dynamics at the start of a step and foot placement at the end of a step was significantly (p[≤]0.0002) influenced by the feedback condition. This metric was highest with Augmented feedback, but not significantly reduced with Disrupted feedback, partially supporting our hypotheses. Our approach to augmenting proprioceptive feedback during gait may have implications for clinical populations with a weakened relationship between pelvis motion and foot placement.

bioengineering↗

bioRxiv2020

Effects of targeted assistance and perturbations on the relationship between pelvis motion and step width in people with chronic stroke

BackgroundPeople with chronic stroke (PwCS) often exhibit a weakened relationship between pelvis motion and paretic step width, a behavior important for gait stabilization. We have developed a force-field able to manipulate this relationship on a step-by-step basis. ObjectiveThe objective of this study was to investigate the effects of a single exposure to our novel force-field on the step-by-step modulation of paretic step width among PwCS, quantified by the partial correlation between mediolateral pelvis displacement at the start of a step and paretic step width (step start paretic {rho}disp). MethodsFollowing a 3-minute period of normal walking, participants were exposed to 5-minutes of either force-field assistance (n=10; pushing the swing leg toward a mechanically-appropriate step width) or perturbations (n=10; pushing the swing leg away from a mechanically-appropriate step width). This period of assistance or perturbations was followed by a 1-minute catch period to identify any after-effects, a sign of sensorimotor adaptation. ResultsWe found that assistance did not have a significant direct effect or after-effect on step start paretic {rho}disp. In contrast, perturbations directly reduced step start paretic {rho}disp (p=0.004), but were followed by an after-effect in which this metric was increased above the baseline level (p=0.02). ConclusionsThese initial results suggest that PwCS have the ability to strengthen the link between pelvis motion and paretic foot placement if exposed to a novel mechanical environment, which may benefit gait stability. Future work is needed to determine whether this effect can be extended with repeated exposure to force-field perturbations.

bioengineering↗

bioRxiv2019

Altered active control of step width in response to mediolateral leg perturbations while walking

During human walking, step width is predicted by mediolateral motion of the pelvis, a relationship that can be attributed to a combination of passive body dynamics and active sensorimotor control. The purpose of the present study was to investigate whether humans modulate the active control of step width in response to a novel mechanical environment. Participants were repeatedly exposed to a force-field that either assisted or perturbed the normal relationship between pelvis motion and step width, separated by washout periods to detect the presence of potential after-effects. As intended, force-field assistance directly strengthened the relationship between pelvis displacement and step width. This relationship remained strengthened with repeated exposure to assistance, and returned to baseline afterward, providing minimal evidence for assistance-driven changes in active control. In contrast, force-field perturbations directly weakened the relationship between pelvis motion and step width. Repeated exposure to perturbations diminished this negative direct effect, and produced larger positive after-effects once the perturbations ceased. Both of these results provide evidence of gradual changes in active control in response to perturbations. In the longer term, these methods may be useful for improving deficits in the active control of step width often observed among clinical populations with poor walking balance.

bioengineering↗

bioRxiv2019

Application of a novel force-field to manipulate the relationship between pelvis motion and step width in human walking

Motion of the pelvis throughout a step predicts step width during human walking. This behavior is often considered an important component of ensuring bipedal stability, but can be disrupted in populations with neurological injuries. The purpose of this study was to determine whether a novel force-field that exerts mediolateral forces on the legs can manipulate the relationship between pelvis motion and step width, providing proof-of-concept for a future clinical intervention. We designed a force-field able to: 1) minimize the delivered mediolateral forces (Transparent mode); 2) apply mediolateral forces to assist the leg toward mechanically-appropriate step widths (Assistive mode); and 3) apply mediolateral forces to perturb the leg away from mechanically-appropriate step widths (Perturbing mode). Neurologically-intact participants were randomly assigned to either the Assistive group (n=12) or Perturbing group (n=12), and performed a series of walking trials in which they interfaced with the force-field. We quantified the step-by-step relationship between mediolateral pelvis displacement and step width using partial correlations. Walking in the Transparent force-field had a minimal effect on this relationship. However, force-field assistance directly strengthened the relationship between pelvis displacement and step width, whereas force-field perturbations weakened this relationship. Both assistance and perturbations were followed by short-lived effects during a wash-out period, in which the relationship between pelvis displacement and step width differed from the baseline value. The present results demonstrate that the link between pelvis motion and step width can be manipulated through mechanical means, which may be useful for retraining gait balance in clinical populations.

bioengineering↗