Parcourir HE Louvain en Hainaut par auteur "White, Olivier"
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Adiabatic Invariant of Center-of-Mass Motion during Walking as a Dynamical Stability Constraint on Stride Interval Variability and Predictability
09 septembre 2022, HE Louvain en HainautArticle scientifiqueHuman walking exhibits properties of both stability and variability. On the one hand, the variability of the interval of time between heel strikes is autocorrelated, i.e., not randomly organized. On the other hand, walking is highly stereotyped and arguments from general mechanics suggest that the stability of gait can be assessed according to invariant properties. This study aims at proposing ... -
Adiabatic invariants drive rhythmic human motion in variable gravity
01 décembre 2020, CeREF TechniqueArticle scientifiqueVoluntary human movements are stereotyped. When modeled in the framework of classical mechanics they are expected to minimize cost functions that may include energy, a natural candidate from a physiological point of view also. In time-changing environments, however, energy is no longer conserved—regardless of frictional energy dissipation—and it is therefore not the preferred candidate for any cost ... -
Benefits of nonlinear analysis indices of walking stride interval in the evaluation of neurodegenerative diseases
12 décembre 2020, HE Louvain en HainautArticle scientifiqueIndices characterising the long-range temporal structure of walking stride interval (SI) variability such as Hurst exponent (H) and fractal dimension (D) may be used in addition to indices measuring the amount of variability like the coefficient of variation (CV). We assess the added value of the former indices in a clinical neurological context. Our aim is to demonstrate that they provide a clinical ... -
Diffusion in Phase Space as a Tool to Assess Variability of Vertical Centre-of-Mass Motion during Long-Range Walking
06 février 2023, CeREF SantéCeREF TechniqueArticle scientifiqueWhen a Hamiltonian system undergoes a stochastic, time-dependent anharmonic perturbation, the values of its adiabatic invariants as a function of time follow a distribution whose shape obeys a Fokker–Planck equation. The effective dynamics of the body’s centre-of-mass during human walking is expected to represent such a stochastically perturbed dynamical system. By studying, in phase space, the ... -
Fine adaptive precision grip control without maximum pinch strength changes after upper limb neurodynamic mobilization
30 juin 2021, HE Louvain en HainautArticle scientifiqueBefore and immediately after passive upper limb neurodynamic mobilizations targeting the median nerve, grip ( GF ) and load ( LF ) forces applied by the thumb, index and major fingers (three-jaw chuck pinch) were collected using a manipulandum during three different grip precision tasks: grip-lifthold- replace (GLHR), vertical oscillations (OSC), and vertical oscillations with up and down ... -
Fractal analyses reveal independent complexity and predictability of gait
28 novembre 2017, HE Louvain en HainautLivre/Ouvrage ou monographieLocomotion is a natural task that has been assessed for decades and used as a proxy to highlight impairments of various origins. So far, most studies adopted classical linear analy- ses of spatio-temporal gait parameters. Here, we use more advanced, yet not less practical, non-linear techniques to analyse gait time series of healthy subjects. We aimed at finding more sensitive indexes related to ... -
Higher-derivative harmonic oscillators: stability of classical dynamics and adiabatic invariants
06 janvier 2019, CERISICArticle scientifiquehe status of classical stability in higher-deriv- ative systems is still subject to discussions. In this note, we argue that, contrary to general belief, many higher-derivative systems are classically stable. The main tool to see this prop- erty are Nekhoroshev’s estimates relying on the action-angle formulation of classical mechanics. The latter formulation can be reached provided the Hamiltonian ... -
Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights
05 août 2021, CeREF TechniqueArticle scientifiqueThe role of gravity in human motor control is at the same time obvious and difficult to isolate. It can be assessed by performing experiments in variable gravity. We propose that adiabatic invariant theory may be used to reveal nearly conserved quantities in human voluntary rhythmic motion, an individual being seen as a complex time-dependent dynamical system with bounded motion in phase space. ...