How does practise of internal Chinese martial arts influence postural reaction control?

International audienceThe aim of this study was to determine the effects of Chinese martial arts practice on postural reaction control after perturbation. Participants standing in Romberg tandem posture were subjected to an unexpected lateral platform translation with the eyes open or closed at two translation amplitudes. The peak displacement of the centre of pressure and of the centre of mass, and the onset latency of muscular activity (tibialis anterior, gastrocnemius, lumbodorsal muscular group, and rectus abdominis), were evaluated for martial arts practitioners and for sport and non-sport participants. Compared with the sport and non-sport participants, the martial arts group showed lower maximal centre of pressure and centre of mass peak displacements in both the lateral and anterior-posterior directions, but no difference was found in the onset of muscular responses. We conclude that martial arts practice influences postural reaction control during a fixed-support strategy in a tandem task. The martial arts group used the ankle joint more frequently than the sport and non-sport participants, especially in the eyes-closed conditions. Our results suggest that the better balance recovery in the martial arts group is a consequence of better control of biomechanical properties of the lower limbs (e.g. through muscular response by co-contraction), not a change in the neuromuscular temporal pattern

Coordination of upper and lower body during balance recovery following a support translation

International audienceStrategies for recovery of posture were studied after lateral mechanical perturbations. 11 participants standing in tandem stance were unexpectedly submitted to lateral support translations with the eyes open or closed at two translation amplitudes. The trajectories of the center of mass of the upper and lower body and muscle activities allowed identification of three strategies, involving either the ankle or the hip only, or both. Hip use increased with vision and with amplitude of perturbation. Short-to-medium latency electromyographic activities were observed in leg and trunk muscles, and long-latency responses in the back leg muscles. Vision increased the activity of both leg and trunk muscles but did not influence the onset of the muscular responses. These data suggest a hierarchy in the selection of these different strategies: the hip is mobilized when the perturbation is more destabilizing but this strategy has a cost and needs specific sensory information supplied by vision

Ajustements posturaux réactionnels suite à une perturbation mécanique médio-latérale (facteur inertiel, influence visuelle et rôle de la raideur sur la détermination des stratégies articulaires)

En vue d étudier les ajustements posturaux réactionnels (APR) latéraux nous avons développé un paradigme de perturbation utilisant une translation latérale inattendue courte et soudaine de la surface d appui. Les sujets debout, pieds alignés (i.e. posture en tandem), devaient maintenir leur posture verticale après la translation sans changer la position de leurs pieds ni de leurs bras. Une première étude a montré, suite à la perturbation, l existence d un de placement passif latéral du centre de masse (CM) antérieur au déplacement latéral du centre de pression (CP) et antérieur également à l activité électromyographique. Cette observation suggère l existence d une composante inertielle induite par la translation de la surface de support. Cette composante influencerait la réponse posturale (le déplacement latéral précoce du CP en direction opposée à la translation, ainsi que son déplacement antéropostérieur). La vision influencerait quant à elle le déplacement latéral plus tardif du CP (direction de la translation). Pourtant, même si la vision intervient dans la réaction d équilibration elle n influence pas la régulation posturale durant toute la durée de la tâche, ce qui suggère une discontinuité des processus de contrôle visuel dans une tâche réactionnelle. Néanmoins, la vision réduit l amplitude de déplacement du tronc, et l amplitude de déplacement du bassin est réduite par l intensité de la perturbation. Une deuxième étude a montré que la translation latérale de la surface d appui pouvait ou non créer une dissociation des déplacements latéraux des centres de masse (CM) de la partie haute (au dessus du bassin) et basse du corps (en dessous du bassin). Utilisant la phase relative de ces déplacements, nous avons défini trois types de stratégies articulaires (cheville, hanche et combinée). Ainsi, nous avons montré que l intensité de la perturbation ainsi que la vision influençaient la fréquence d apparition d une stratégie par rapport à une autre. De plus, les participants ont montré, suivant la translation latérale, un déplacement du corps en direction A/P (déplacement du CM, du CP et activités musculaires des jambes et du tronc). La latence de déplacement du CP en direction A/P étant plus courte que celle du déplacement latéral cela signifie que les participants utilisent le plan d appui le plus large comme stratégie de conservation de l équilibre postural médio-latéral. Afin de réguler leur équilibre, les participants montrent des réponses musculaires réflexes et automatiques (jambes et tronc), et une réponse fonctionnelle à longue latence (jambes). Contrairement à ce qui était attendu, l absence de vision diminue l activité phasique des muscles antagonistes des jambes ceci pourrait donc permettre au système de contrôle postural d évaluer plus efficacement le moment de force exercé à partir des chevilles. Une troisième étude a montré qu un groupe de pratiquants d arts martiaux chinois internes (MA) révélait un contrôle postural plus performant (réduction des déplacements du CM et du CP) que celui d un groupe de sportifs juniors et seniors, et d un groupe de non sportifs, sans montrer une organisation temporelle neuromusculaire différente. De plus, le groupe MA a utilisé préférentiellement la stratégie de cheville, surtout en l absence de vision, et a montré une tendance à utiliser une raideur articulaire plus importante, avec ou sans vision. Ces résultats suggèrent que le système postural pourrait bénéficier, afin de répondre à une perturbation externe, d un système de réglage de la raideur articulaire qui serait implémenté par des entrées somatosensorielles, renseignant sur l effet mécanique de la perturbation sur la posture. Ainsi ce système d ajustement de la raideur pourrait permettre de fournir un processus de réglage en ligne de la posture, et ainsi serait le principal responsable du maintien de la géométrie corporelle et de l équilibre postural dans une situation de perturbation.In order to study postural reaction adjustments (PRA) we develop a paradigm of disturbance using an unexpected short lateral translation of the support surface. Participants in upright posture, with feet aligned (tandem posture), had to resume and maintain this posture after the translation without changing the position of their feet or of their arms. The first study showed, following the disturbance, a passive lateral displacement of the centre of mass (CM) prior to the lateral displacement of the centre of pressure (CP) and the electromyographic activity, this corresponding to the inertial effect induced by the support surface translation. This component influences the early lateral displacement of the CP (i.e. in the opposite direction to the translation) and its antero-posterior displacement. The subsequent lateral displacement of the CP (in the direction of the translation) appeared influenced by vision. However, even if vision influences the postural reaction it does not influence posture regulation during all the duration of the task, this observation underline that visual process are discontinuous during reactional balance task. Nevertheless, it was found that with vision the lateral trunk displacement was reduced and hip displacement was diminished by the perturbation intensity. The second study showed that in response to the lateral translation different patterns of association of the lateral displacements of the centres of masses (CM) of the upper part (above the hip) and lower (below the hip) could be generated. Using the relative phase of these displacements, we defined three types of joint strategies (ankle, hip and combined). We then showed that both disturbance intensity and vision influenced the frequency of appearance of one strategy compared to another. In addition, participants showed a displacement in A/P direction following the lateral translation (as shown by displacements of CM and CP, and muscular activities of the legs and trunk). The onset latency of the CP displacement in A/P direction being shorter than for its lateral displacement indicates that this postural reaction is to use the widest dimension of the support surface and this constitutes a conservative strategy to the medio-lateral postural imbalance. Participants showed reflexes and automatic muscles responses (legs and trunk), followed by a long latency functional response (legs). The frequency of the phasic activity of the antagonistic muscles of the legs increases with vision, thus in the absence of vision the postural control system evaluates more effectively the moment of force exerted especially at the ankles, this preserving the inverted pendulum strategy. The third study showed that a group of subjects practicing Chinese martial arts (MA) achieved a more effective postural control (reduction of CM and CP displacements) than groups of young and senior sportives, and a group of non sportives, without showing any difference in temporal neuromuscular organization. Moreover, for the MA group the ankle strategy was used more, especially in the absence of vision, and this group showed a tendency to use a greater joint stiffness both with and without vision. These results suggest that the postural system, reacting to an external perturbation, could be making use of a regulation system of joint stiffness which could be implemented by somatosensory inputs informing on the mechanical effect of the disturbance on the posture. Thus, this system, regulating joint stiffness, could provide an on-line process for posture regulation, and thus would be the main factor responsible for the maintenance of body geometry and postural balance in a perturbation context.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

L'autisme : une pathologie du codage temporel ?

Autorisation No.2100 : TIPA est la revue du Laboratoire Parole et LangageInternational audienceIn this article, we present the final report of a cooperative project that was conducted by a group of clinicians and three groups of researchers belonging to CNRS or University. The aim of this project was to test a novel unifiying hypothesis in autism : are the communicative and interactive disorders in autism correlated with a temporal processing impairment of sensory and motor events. Autistic children and adolescents were tested in three experimental tasks aimed at testing i) motion vision, ii) phonems categorial perception and iii) motor anticipation. Results indicate that performance of autistic subjects is limited comparatively to that of normal control subjects in each task, which suppose that they have difficulties in processing sensory inputs and producing motor outputs online. These difficulties could account for their communicative and interactive impairments. Neurophysiological explanations involving cerebellum are proposed to explain this temporal processing deficit. Reeducational pathways using slowed down visual motion and speech flow are also suggested.Nous présentons dans cet article la synthèse d'un projet coopératif qui a regroupé une équipe de cliniciens hospitaliers et trois équipes de chercheurs du CNRS et de l'Université, et destiné à tester une nouvelle hypothèse unificatrice dans l'autisme. La question était de savoir si les troubles communicatifs et relationnels typiques de l'autisme sont corrélés à des troubles du traitement temporel des événements sensoriels et moteurs. Des enfants et adolescents autistes ont été testés dans trois types de tâches expérimentales visant à tester i) la vision du mouvement, ii) la perception catégorielle de phonèmes et iii) l'anticipation motrice. Les résultats montrent que dans chacun de ces trois domaines, les performances des sujets autistes sont limitées par rapport à celles des sujets témoins, et témoignent d'une difficulté à traiter les événements sensoriels et produire des événements moteurs en temps réel. Cette difficulté pourrait rendre compte des anomalies communicatives et relationnelles des sujets autistes. Des explications neurophysiologiques de ce déficit du traitement temporel impliquant notamment le cervelet sont proposées. Des voies de rééducation utilisant le ralentissement des mouvements visuels et du flux verbal sont également suggérées

Numerical investigation into the inclination effect on conjugate pool boiling and the condensation of steam in a passive heat removal system

In this study, the effect of the tube inclination angle on simultaneous condensation inside and pool boiling outside a smooth tube is investigated numerically. Such conjugate phase-change phenomena happen in many heat exchangers, particularly in passive heat removal systems. The simulated domain is a pool filled with water liquid at atmospheric pressure, with a submerged tube with inner and outer diameters of 19 mm and 25 mm respectively. The fluid inside the tube is considered to be the steam at the saturation temperature of 250 °C, which is a very common operating condition in many heat removal systems. The flow field is considered to be turbulent, unsteady and three dimensional. The effect of conduction through the tube thickness is also taken into account. The Eulerian-Eulerian multiphase flow approach is utilized to express the governing equation of the problem. ANSYS FLUENT 17.1 is also used to solve the governing equations. The effects of various parameters, such as tube orientation, steam mass flux and inlet steam quality on the condensation and pool boiling heat transfer coefficients, are investigated. The results show good agreement with the available experimental data. The condensation heat transfer coefficient is found to increase with an increase in the inlet steam quality and steam mass flow rate. The results of the effect of inclination on the heat transfer coefficient are also compatible with the previous experimental works. Moreover, the results show that there is a partial maximum point for the total heat transfer coefficient at an inclination angle between θ = −60° and θ = −30°.http://www.elsevier.com/locate/ijhmt2019-07-01hj2018Mechanical and Aeronautical Engineerin