A new statistical test based on the wavelet cross-spectrum to detect time–frequency dependence between non-stationary signals: Application to the analysis of cortico-muscular interactions

The study of the correlations that may exist between neurophysiological signals is at the heart of modern techniques for data analysis in neuroscience. Wavelet coherence is a popular method to construct a time-frequency map that can be used to analyze the time-frequency correlations be- tween two time series. Coherence is a normalized measure of dependence, for which it is possible to construct confidence intervals, and that is commonly considered as being more interpretable than the wavelet cross-spectrum (WCS). In this paper, we provide empirical and theoretical arguments to show that a significant level of wavelet coherence does not necessarily correspond to a significant level of dependence between random signals, especially when the number of trials is small. In such cases, we demonstrate that the WCS is a much better measure of statistical dependence, and a new statistical test to detect significant values of the cross-spectrum is proposed. This test clearly outperforms the limitations of coherence analysis while still allowing a consistent estimation of the time-frequency correlations between two non-stationary stochastic processes. Simulated data are used to investigate the advantages of this new approach over coherence analysis. The method is also applied to experimental data sets to analyze the time-frequency correlations that may exist between electroencephalogram (EEG) and surface electromyogram (EMG)

A KINEMATIC AND DYNAMIC ANALYSIS OF ELITE ALPINE SKIERS

The knowledge of the internal forces and torques acting on a joint during a physical activity as well as a clear description of the motion performed by an elite athlete is of top most interest for rehabilitation, teaching or training purposes. Nevertheless, the motion of the athletes can be strongly affected by the evolution of the equipment design. For example, great changes in terms of angular motion and ground reaction have been revealed in alpine skiing when comparing conventional and carving turns (Yoneyama, 2000). More recently, MCJller and Schwameder (2003) have carried out a comparative study between conventional and carving ski turn based upon kinematics, plantar pressure and EMG records. Coupling 3D video analysis and forceplate acquisition, the present work aims at recording the displacements of whole body segments as well as ground reaction in order to analyze the turning motion of elite alpine skiers

3D KINEMATIC AND KINETIC ANALYSIS OF JAVELIN THROWING PERFORMANCE

Major studies on javelin throwing have focused more recently on kinematics studies, in two, and later, in three dimensions (3D), especially to analyse high performances (Bartlell & Best, 1988). However, there is a lack of literature reporting on kinetics data in javelin throwing event (Bartonietz, 2000). The main objective of this study is to develop a 3D kinematics and kinetics analysis of the final release phase of the javelin throw to explain javelin throwing performance

Neuro-biomécanique de la redondance musculaire – Modélisation musculo-squelettique et contrôle moteur de la co-contraction agoniste / antagoniste

This document summarizes the scientific route that I have followed since 2003 to develop my research activities on the issue of muscular redundancy. Throughout my career, I have deepened this subject by focusing on the functional roles of agonist/antagonist co-contraction and on the central nervous mechanisms controlling antagonist muscles activity during voluntary and involuntary contractions in man, with the aims to optimize motor performance in the healthy subject and to improve motor function in the brain or spinal cord injured subjects. To address this issue, my scientific works shifted from a strictly biomechanical approach to a multidisciplinary multimodal approach at the intersection of biomechanics, neuroscience and signal processing. The main research topics that I have developed relate to musculoskeletal modeling of muscular redundancy, to the study of the factors of modulation of healthy and pathological agonist/antagonist co-contraction, to the study of the cerebral correlates of antagonist muscles activity, and finally to the contribution of cortico-muscular and intermuscular interactions to the control of agonist/antagonist co-contraction. By pursuing the original approach in which I am engaged in the field of neuro-biomechanics, this work will deepen the analysis of co-contraction through a broader definition and an open vision to new scientific fields. It will also contribute to a better understanding of the functional role and the mechanisms involved in the control of muscular redundancy from both a fundamental and clinical perspective.Ce document est la synthèse du cheminement scientifique que j’ai suivi depuis 2003 pour développer mes activités de recherche sur la question de la redondance musculaire. Tout au long de mon parcours, j’ai approfondi ce sujet en m’intéressant aux rôles fonctionnels de la co-contraction agoniste / antagoniste et aux mécanismes nerveux centraux de contrôle de l’activité musculaire antagoniste lors de contractions volontaires et involontaires chez l’homme, avec des visées dans les domaines entrecroisés de l’optimisation de la performance motrice chez le sujet sain et l’amélioration de la fonction motrice chez le patient cérébro- ou médullo-lésé. Pour traiter cette question, ma démarche scientifique m’a fait passer d’une approche strictement biomécanique à une approche multimodale réellement pluridisciplinaire au croisement de la biomécanique, des neurosciences et du traitement du signal. Les principales thématiques de recherche que j’ai développées concernent la modélisation musculo-squelettique de la redondance musculaire, l’étude des facteurs de modulation de la co-contraction agoniste / antagoniste saine et pathologique, l’étude des corrélats cérébraux de l’activité des muscles antagonistes, et enfin la contribution des interactions cortico-musculaires et intermusculaires au contrôle de la co-contraction agoniste / antagoniste. En poursuivant la démarche originale dans laquelle je m’inscris dans le domaine de la neuro-biomécanique, ces travaux approfondiront l’analyse de la co-contraction à travers une définition élargie et une vision ouverte à de nouveaux champs scientifiques. Ils contribueront également à mieux comprendre le rôle fonctionnel et les mécanismes impliqués dans le contrôle de la redondance musculaire dans une double perspective fondamentale et clinique

Estimation des efforts musculaires à partir de données périphériques : application à l'analyse de la coordination pluri-articulaire

The aim of the present work was first to develop numerical methods in order to generate satisfactory estimates of the net, agonist and antagonist moments created by the muscles crossing a joint. Secondly, these methods were applied for the investigation of the pluri-articular coordination during "stepping-in-place". The inverse dynamics problem was solved by using static optimization of joint accelerations. This procedure provides estimations of the net moments that best agree with all kinematic and dynamic data, while respecting all equilibrium equations. The agonist and antagonist moments are calculated under dynamic contractions by using a method that includes firstly an isometric calibration test, and secondly an optimization procedure with kinematic, dynamic and electromyographic data as inputs. The model accounts for muscle dynamics and muscle functions in order to obtain physiologically realistic solutions of the moments as well as reliable estimates of the cocontraction index. These models are applied to study the coordination of "stepping-in-place" in the face of an externally applied perturbation at the knee joint. Because of redundancy, the musculoskeletal system can locally cope with the perturbation by increasing the participation of extensor muscles to control the kinematic at the knee joint. By implementing this strategy, the kinematic of the movement remains unchanged and the control of equilibrium is preserved.L'objectif de ce travail était d'une part de développer des méthodes numériques permettant d'estimer de manière satisfaisante les moments résultant, agoniste et antagoniste développés autour d'une articulation et, d'autre part, d'appliquer ces méthodes à l'analyse de la coordination pluri-articulaire d'un mouvement de piétinement. Le problème de la dynamique inverse est résolu à l'aide d'une méthode d'optimisation statique des accélérations qui permet d'estimer les moments résultants en accord avec toutes les mesures cinématiques et dynamiques, tout en respectant les conditions d'équilibre mécanique de chaque segment. Les moments musculaires agoniste et antagoniste sont estimés en conditions dynamiques à l'aide d'une méthode qui comprend une étape de calibration isométrique et une procédure d'optimisation numérique qui utilise les données cinématiques, dynamiques et électromyographiques en entrée. Le modèle tient compte du comportement mécanique des muscles et de leur fonction anatomique pour obtenir une estimation physiologiquement réaliste des moments et un indice de co-contraction fiable a chaque instant du mouvement. Ces modèles sont appliqués à l'étude de la coordination pluri-articulaire d'un mouvement de piétinement, perturbé par le port d'un système élastique à l'articulation du genou. La redondance du système musculo-squelettique permet de gérer localement la perturbation en accroissant la participation des muscles extenseurs au contrôle de la cinématique du genou. Cette stratégie permet de conserver la même cinématique du mouvement et ainsi préserve l'équilibre dynamique du piétinement

Training-related changes in the EMG–moment relationship during isometric contractions: Further evidence of improved control of muscle activation in strength-trained men?

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Influence of sporting expertise on the EMG–torque relationship during isometric contraction in man

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Estimation des efforts musculaires à partir de données périphériques (application à l'analyse de la coordination pluri-articulaire)

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Estimation of knee muscle moments from an EMG-assisted optimization method during dynamic contractions

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A method to combine numerical optimization and EMG data for the estimation of joint moments under dynamic conditions

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