Biology subjects

Bruijn, S.

Publications and source records attributed to Bruijn, S..

3 recordsLinked to original sources

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↗