Biology subjects

van Dieen, J.

Publications and source records attributed to van Dieen, J..

3 recordsLinked to original sources

bioRxiv2022

Standing balance in aging is robust against head rotation during visual tracking.

Standing balance is relatively more unstable when visually pursuing a moving target than when fixating a stationary one. These effects are common across age groups if the head is restrained during visual task performance. The present study focused on the role of the head motion on standing balance during the pursuit of a moving target as a function of age. Three predictions were tested: a) standing balance is compromised to a greater extent in older than young adults by gaze target pursuit compared to fixation, b) older adults pursue a moving target with greater and more variable head rotation than young adults, and c) greater and more variable head rotation during the gaze pursuit task is associated with greater postural sway. Twenty-two (22) older (age: 71.7{+/-}8.1, 12 M / 10 F) and twenty-three (23) young adults (age: 23.6{+/-}2.5, 12 M / 11 F) stood on a force plate in front of a 60-inch monitor while performing two visual tasks: fixation at a stationary target and gaze pursuit of a horizontally moving target. Centre of pressure (CoP) and head kinematics were synchronously recorded with the Vicon motion analysis system, while head-unconstrained gaze was captured by the Pupil Labs Invisible mobile tracking system. Postural sway, reflected in the interquartile CoP range and the root mean square (RMS) of CoP velocity increased during the gaze pursuit compared to the fixation task (p<.05), and this effect was more pronounced in older than young participants (p<.05). Older adults pursued the moving target employing more variable (p=.022) head yaw rotation than young participants although the amplitude of head rotation was not systematically different between groups (p=. 077). The amplitude and variance of head yaw rotation did not correlate with postural sway measures. Results suggest that older adults may engage more variable head rotation when tracking a moving target to compensate for age-related deficits in eye smooth pursuit movement. However, this strategy does not seem to compromise standing balance.

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↗

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↗