Biology subjects

Bruijn, S.

Publications and source records attributed to Bruijn, S..

8 recordsLinked to original sources

bioRxiv2026

Cortico-muscular control of postural balance in older adults - effects of training on functional connectivity

BackgroundBalance training in older adults can lead to reduced centre of mass accelerations and reduced angular momenta after perturbations of unipedal stance, reflecting an enhanced ability to recover balance. It has been suggested that the co-occurring changes in muscle synergies indicated strategy-specific adaptations in feedback control. MethodsWe investigated the cortical involvement in such adaptations by focusing on the interaction between muscle synergies and cortical activity after perturbations. Twenty older adults (>65 years) underwent short-term and three-week long-term balance training, and we assessed their recovery from unpredictable mediolateral perturbations during unipedal stance. We measured high-density EEG and activation of leg and trunk muscles. The representations of the balance-related muscle synergies were localised in the cortex using coherence-based beamformers in the {beta}-frequency band. ResultsBalance performance was accompanied by task-specific {beta}-band activation in the somatotopic representation of the lower extremities in the primary motor cortex. The {beta}-power significantly dropped during the response to perturbations, while the coherence with the activation of muscle synergies significantly increased, especially for synergies active in the early stage of balance recovery. The task-related changes in cortico-synergy coherence, especially during the later phase of balance recovery, were significantly affected by short-term training. ConclusionRefinements of feedback control seem to underlie balance improvements in older adults. The significant changes in the cortico-synergy interaction after balance training suggest cortical involvement in these refinements.

neuroscience↗

bioRxiv2025

The Impact of Visual Perturbations on Balance Control during Walking

Visual perturbations may lead to an illusory self-motion and affect balance control. We studied effects of different visual perturbations in 16 healthy young participants walking on a treadmill, by assessing foot placement and center of mass (CoM) states. Three different visual perturbations were applied: fixating on a stationary target while the background moved to the right (MB), tracking the target moving rightward over a stationary background with head rotation (MT-HR), and tracking the moving target with eye movement only (MT-EM). Deviations of foot placement, CoM and trunk orientation due to the visual perturbation were assessed. Linear models were fit to the kinematic data to predict foot placement from CoM state at mid-swing. Over the whole trial, MT-HR and MT-EM caused an increase in step width variability, CoM position variability and RMS of foot placement errors simultaneously. During visual perturbation epochs specifically, in MB, a left deviation of foot and CoM trajectories was observed from the start of the background movement. In MT-HR and MT-EM, a right deviation of foot and CoM trajectories was observed only after the target had stopped moving. Contrary to our expectations, foot placement errors did not coincide with subsequent CoM deviations in the opposite direction. An obvious change in frontal plane trunk orientation was found only in MT-HR. While all visual perturbations affected control of the CoM trajectory in the frontal plane, these effects appeared caused by effects on control of heading as well. Head rotation appears to additionally disturb balance through a coupling with trunk orientation. Summary statementVisual perturbations during walking alter foot placement and body motion in humans, revealing how eye and head movements influence walking balance.

neuroscience↗

bioRxiv2025

Corticospinal Excitability in Response to Mediolateral Gait Instability

Unpredictable gait disturbances, particularly in the mediolateral direction, pose a significant challenge to stability and are a common contributor to falls. Although the corticospinal tract is critical for gait and postural control, its response to such instabilities remains unclear. To investigate if corticospinal excitability increases during laterally destabilised gait, single-pulse transcranial magnetic stimulations were delivered over the primary motor cortex of 15 healthy individuals during steady-state and laterally destabilised treadmill gait. Full-body kinematics were recorded using an optoelectronic motion capture system. Stimulations with coil displacement >5 mm from the targeted location were excluded. Corticospinal excitability was quantified for four upper- and three lower-leg muscles by the motor evoked potential (MEP) amplitude and compared between steady-state and destabilised gait. Destabilisation resulted in a wider step width and shorter stride duration with increased variability and greater dynamic instability. Foot placement control was increased at mid-swing, along with greater average foot placement error. No differences in corticospinal excitability were observed in the lower-leg muscles. All upper-leg muscles demonstrated greater absolute MEPs in destabilised relative to steady-state gait. After normalising MEP to the pre-stimulus muscle activity, these periods became less pronounced, however, increases were observed in all but the gastrocnemius muscles. These findings suggest heightened readiness of the corticospinal tract projecting to upper-leg muscles during destabilised gait, which could reflect general stabilising strategies such as decreasing stride time and increasing step width. KEY POINTSO_LIMaintaining stability during bipedal gait requires precise control, especially when confronted with unpredictable mediolateral disturbances, a common contributor to falls. C_LIO_LIWhen walking on a treadmill that was laterally destablised, participants adopted a cautious walking strategy characterised by wider step width, shorter stride duration and increased variability. C_LIO_LICorticospinal excitability to upper-leg muscles was greater in destabilised than steady-state gait, corticospinal excitability to lower-leg muscles remained largely unchanged. C_LIO_LIThe observed increases in corticospinal excitability to upper-leg muscles likely reflect a general stabilisation strategy in response to a laterally destabilised walking surface. C_LIO_LIIncreases in MEP gain (MEP amplitude relative to ongoing muscle activity) suggest that changes in corticospinal excitability may reflect additional roles beyond modulating the ongoing muscle activity. C_LI

animal behavior and cognition↗

bioRxiv2023

Machine learning approaches to predicting whether muscles can be elicited via TMS

BackgroundTranscranial magnetic stimulation (TMS) is a valuable technique for assessing the function of the motor cortex and cortico-muscular pathways. TMS activates the motoneurons in the cortex, and this activation is transmitted through the cortico-muscular pathway, after which it can be measured as a motor evoked potential (MEP) in the muscles. The position and orientation of the TMS coil and the intensity used to deliver a TMS pulse are considered central TMS setup parameters influencing the presence/absence of MEPs. New MethodWe sought to predict the presence of MEPs from TMS setup parameters using machine learning. We trained different machine learners using either within-subject or between-subject designs. ResultsWe obtained prediction accuracies of on average 77% and 65% with maxima up to up to 90% and 72% within and between subjects, respectively. Across the board, a bagging ensemble appeared to be the most suitable approach to predict the presence of MEPs, although a comparably simple logistic regression model also performed well. ConclusionsWhile the prediction between subjects clearly leaves room for improvement, the within-subject performance encourages to supplement TMS by machine learning to improve its diagnostic capacity with respect to motor impairment.

neuroscience↗

bioRxiv2023

ASSESSMENT OF STABILIZING FEEDBACK CONTROL OF WALKING, A TUTORIAL

Walking without falling requires stabilization of the trajectory of the body center of mass relative to the base of support. Model studies suggest that this requires active, feedback control, i.e., the nervous system must process sensory information on the state of the body to generate descending motor commands to the muscles to stabilize walking, especially in the mediolateral direction. Stabilization of bipedal gait is challenging and can be impaired in older and diseased individuals. In this tutorial, we illustrate how gait analysis can be used to assess the stabilizing feedback control of gait. We present methods ranging from those that require limited input data (e.g. position data of markers placed on the feet and pelvis only) to those that require full-body kinematics and electromyography. Analyses range from simple kinematics analyses to inverse dynamics. These methods assess stabilizing feedback control of human walking at three levels: 1) the level of center of mass movement and horizontal ground reaction forces, 2) the level of center of mass movement and foot placement and 3) the level of center of mass movement and the joint moments or muscle activity. We show how these can be calculated and provide a GitHub repository (https://github.com/VU-HMS/Tutorial-stabilizing-walking) which contains open access Matlab and Python code to calculate these. Finally, we discuss what information on feedback control can be learned from each of these.

neuroscience↗

bioRxiv2020

The validation of new phase-dependent gait stability measures: a modeling approach

Identification of individuals at risk of falling is important when designing fall prevention methods. Current measures that estimate gait stability and robustness appear limited in predicting falls in older adults. Inspired by recent findings on changes in phase-dependent local stability within a gait cycle, we devised several phase-dependent stability measures and tested for their usefulness to predict gait robustness in compass walker models. These measures are closely related to the often-employed maximum finite-time Lyapunov exponent and maximum Floquet multiplier that both assess a systems response to infinitesimal perturbations. As such, they entail linearizing the system but this is realized in a rotating hypersurface orthogonal to the period-one solution followed by estimating the trajectory-normal divergence rate of the swing phases and the foot strikes. We correlated the measures with gait robustness, i.e. the largest perturbation a walker can handle, in two compass walker models with either point or circular feet to estimate their prediction accuracy. To also test for the dependence of the measures under state space transform, we represented the point-feet walker in both Euler-Lagrange and Hamiltonian canonical form. Our simulations revealed that for most of the measures their correlation with gait robustness differs between models and between different state space forms. In particular the latter may jeopardize many stability measures predictive capacity for gait robustness. The only exception that consistently displayed strong correlations is the divergence of foot strike. Our results admit challenges of using phase-dependent stability measures as objective means to estimate the risk of falling.

bioengineering↗

bioRxiv2020

How does external lateral stabilization constrain normal gait, apart from improving medio-lateral gait stability?

BackgroundThe effect of external lateral stabilization on medio-lateral gait stability has been investigated previously. However, existing lateral stabilization devices not only constrains lateral motions, but also transverse and frontal pelvis rotations. This study aimed to investigate the effect of external lateral stabilization with and without constrained transverse pelvis rotation on mechanical and metabolic gait features. MethodsWe undertook 2 experiments with eleven and ten young adult subjects, respectively. Experiment 2 supplemented experiment 1, as it considered several potential confounding factors in the design and set-up of experiment 1. Kinematic, kinetic, and breath-by-breath oxygen consumption data were recorded during 3 walking conditions (normal walking (Normal), lateral stabilization with (Free) and without transverse pelvis rotation (Restricted)) and at 3 speeds (0.83, 1.25, and 1.66 m/s) for each condition. ResultsExternal lateral stabilization significantly reduced the amplitudes of the transverse and frontal pelvis rotations, medio-lateral pelvis displacement, transverse thorax rotation, arm swing, and step width. The amplitudes of free vertical moment, anterior-posterior and vertical pelvis displacements, step length, and energy cost were not significantly influenced by external lateral stabilization. The removal of transverse pelvis rotation restriction by our experimental set-up resulted in significantly higher transverse pelvis rotation, although it remained significantly less than Normal condition. In concert, concomitant gait features such as transverse thorax rotation and arm swing were not significantly influenced by our new set-up. ConclusionExisting lateral stabilization set-ups not only constrain medio-lateral motions (i.e. medio-lateral pelvis displacement), but also constrains other movements such as transverse and frontal pelvis rotations, which leads to several other gait changes such as reduced transverse thorax rotation, and arm swing. Our new setup allowed for more transverse pelvis rotation, however, this did not result in more normal pelvis rotation, arm swing, etc. Hence, to provide medio-lateral support without constraining other gait variables, more elaborate set-ups are needed. Unless such a set-up is realized the observed side effects need to be taken into account when interpreting the effects of lateral stabilization as reported in previous studies.

bioengineering↗

bioRxiv2019

The effect of anteroposterior perturbations on the control of the center of mass during treadmill walking

Shifts of the center of pressure (CoP) through modulation of foot placement and ankle moments (CoP-mechanism) cause accelerations of the center of mass (CoM) that can be used to stabilize gait. An additional mechanism that can be used to stabilize gait, is the counter-rotation mechanism, i.e., changing the angular momentum of segments around the CoM to change the direction of the ground reaction force. The relative contribution of these mechanisms to the control of the CoM is unknown. Therefore, we aimed to determine the relative contribution of these mechanisms to control the CoM in the anteroposterior (AP) direction during a normal step and the first recovery step after perturbation in healthy adults. Nineteen healthy subjects walked on a split-belt treadmill and received unexpected belt acceleration perturbations of various magnitudes applied immediately after right heel-strike. Full-body kinematic and force plate data were obtained to calculate the contributions of the CoP-mechanism and the counter-rotation mechanism to control the CoM. We found that the CoP-mechanism contributed to corrections of the CoM acceleration after the AP perturbations, while the counter-rotation mechanism actually contributed to CoM acceleration in the direction of the perturbation, but only in the initial phases of the first step after the perturbation. The counter-rotation mechanism appeared to prevent interference with the gait pattern, rather than using it to control the CoM after the perturbation. Understanding the mechanisms used to stabilize gait may have implications for the design of therapeutic interventions that aim to decrease fall incidence. Summary statementUnderstanding the mechanisms used to stabilize gait during unperturbed and perturbed walking may have implications for the design of therapeutic interventions that aim to decrease fall incidence.

bioengineering↗