Biology subjects

Kistemaker, D.

Publications and source records attributed to Kistemaker, D..

4 recordsLinked to original sources

bioRxiv2022

Is phase-dependent stability related to phase-dependent gait robustness?

Predicting gait robustness is paramount for targeting interventions to prevent falls. Our analysis of a compass walker model revealed that phase-dependent stability measures have limited capacity to predict overall gait robustness. Interestingly, these measures vary substantially over the gait cycle which seemingly aligns with the robustness of both humans and walking models that likewise depends on the phase at which perturbations occur. To explore this in depth, we again used a compass walker model that can walk stably and periodically and applied forward and backward perturbations (instantaneous changes in angular velocities) to the stance or swing leg at multiple instants during the single-stance phase. We then estimated the degree to which phase-dependent stability measures correlate with phase-dependent gait robustness, quantified as the maximal perturbation-induced change in mechanical energy that the walker could tolerate without falling within 50 steps. We found that these phase-dependent stability measures did not adequately predict phase-dependent gait robustness in the compass walker model. We therefore conclude that these measures are unlikely to provide reliable predictions of gait robustness or fall risk in humans.

physiology↗

bioRxiv2022

The energetic effect of hip flexion and retraction in walking at different speeds: a modeling study

In human walking, power for propulsion is generated primarily via ankle and hip muscles. The addition of a passive hip spring to simple bipedal models appears more efficient than using only push-off impulse, at least, when hip spring associated energetic costs are not considered. Hip flexion and retraction torques, however, are not free, as they are produced by muscles demanding metabolic energy. Studies evaluating the inclusion of hip actuation costs, especially during the swing phase, and the hip actuations energetic benefits are few and far between. It is also unknown whether these possible benefits/effects may depend on speed. We simulated a planar flat-feet model walking stably over a range of speeds. We asked whether the addition of independent hip flexion and retraction remains energetically beneficial when considering work-based metabolic cost of transport (MCOT) with different efficiencies of doing positive and negative work. We found asymmetric hip actuation can reduce the estimated MCOT relative to ankle actuation by up to 6%, but only at medium speeds. The corresponding optimal strategy is zero hip flexion and some hip retraction actuation. The reason for this reduced MCOT is a reduction in collision loss being larger than the associated increase in hip negative work. Both terms require positive mechanical work to compensate, yielding a larger reduction in metabolic work per step than the reduction in step length. Our study shows how ankle actuation, hip flexion, and retraction actuation can be coordinated to reduce MCOT.

physiology↗

bioRxiv2022

Does ankle push-off correct for errors in anterior-posterior foot placement relative to center-of-mass state?

I.Understanding the mechanisms humans use to stabilize walking is vital for predicting falls in elderly. Modeling studies identified two potential mechanisms to stabilize gait in the anterior-posterior direction: foot placement control and ankle push-off control: Foot placement depends on position and velocity of the center-of-mass (CoM) and push-off modulates with deviations between actual and predicted CoM trajectories. While both control mechanisms have been reported in humans, it is unknown whether especially the latter one is employed in unperturbed steady-state walking. On the one hand, the covariance between CoM states and anterior-posterior foot placement served as a measure of foot placement control. On the other hand, we determined variations in ankle push-off as a function of differences between the actual foot placement and the one predicted from CoM states. We estimated the corresponding correlations and consider them indictors for push-off control based on foot placement errors. We found ankle push-off torque to be correlated to the foot placement error in 30 participants when walking at normal and slow speed, with mean correlation values of up to 0.45. Our study suggests that humans use a push-off strategy for correcting foot placement errors in steady-state walking.

physiology↗

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↗