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

Port-en-Bessin-Huppain – Le Mont-Castel

Le Mont-Castel est un plateau côtier d’une vingtaine d’hectares qui domine la commune de Port-en-Bessin à une dizaine de kilomètres à l’ouest de la capitale de cité gallo-romaine des Baïocasses Bayeux/Augustodurum. Il s’intègre au fond d’une plaine d’environ 400 ha entourée d’une couronne de reliefs bien marqués sur lesquels au moins deux autres sites fortifiés ont déjà été repérés : le Mont-Cauvin, sur la commune d’Étreham (Bronze final IIIb, prospections aériennes G. Hulin et S. Normant 200..

Port-en-Bessin-Huppain – Le Mont Castel

Depuis trois ans, le site du Mont Castel fait l’objet de fouilles archéologiques programmées à la fin de l’été. Cette année, c’est principalement l’occupation de la fin de l’indépendance gauloise qui a fait l’objet d’un travail de fond. Il est désormais possible de dresser dans ces grandes lignes les modalités d’occupation du site. Nous rappellerons toutefois, avant de présenter l’occupation de La Tène D2b, que le site est fortifié et occupé dès le Bronze final IIIa et fait l’objet durant le ..

Role of the Amygdala in Antidepressant Effects on Hippocampal Cell Proliferation and Survival and on Depression-like Behavior in the Rat

The stimulation of adult hippocampal neurogenesis by antidepressants has been associated with multiple molecular pathways, but the potential influence exerted by other brain areas has received much less attention. The basolateral complex of the amygdala (BLA), a region involved in anxiety and a site of action of antidepressants, has been implicated in both basal and stress-induced changes in neural plasticity in the dentate gyrus. We investigated here whether the BLA modulates the effects of the SSRI antidepressant fluoxetine on hippocampal cell proliferation and survival in relation to a behavioral index of depression-like behavior (forced swim test). We used a lesion approach targeting the BLA along with a chronic treatment with fluoxetine, and monitored basal anxiety levels given the important role of this behavioral trait in the progress of depression. Chronic fluoxetine treatment had a positive effect on hippocampal cell survival only when the BLA was lesioned. Anxiety was related to hippocampal cell survival in opposite ways in sham- and BLA-lesioned animals (i.e., negatively in sham- and positively in BLA-lesioned animals). Both BLA lesions and low anxiety were critical factors to enable a negative relationship between cell proliferation and depression-like behavior. Therefore, our study highlights a role for the amygdala on fluoxetine-stimulated cell survival and on the establishment of a link between cell proliferation and depression-like behavior. It also reveals an important modulatory role for anxiety on cell proliferation involving both BLA-dependent and –independent mechanisms. Our findings underscore the amygdala as a potential target to modulate antidepressants' action in hippocampal neurogenesis and in their link to depression-like behaviors

Modélisation biomécanique de la nage avec palmes

Ce travail doctoral a pour objectif de mettre en place des méthodes permettant de quantifier les efforts subits par le nageur avec palme, lors de la pratique de 3 activités (Natation, Randonnée Aquatique et Body-Board). Pour ce faire, un modèle utilisant des procédures de dynamique inverse a été mis en place. Dans la première phase de cette étude, la cinématique tridimensionnelle des 3 segments du membre inférieur gauche a été analysée. Il en résulte 3 cinématiques fondamentalement différentes. Avec un modèle type Bottum-Up, la mesure d efforts distaux est nécessaire. Un robot palmeur a donc été développé, afin de reproduire la cinématique du pied pour chacune des ces pratiques et ainsi permettre une mesure fiable des forces et moments au centre articulaire de la cheville. Ainsi, nous avons quantifié via le modèle, les moments au genou et à la hanche. Ainsi, via le robot nous pouvons quantifier l effet d un design de palme sur les efforts subit par l utilisateur à la cheville, et s assurer par le modèle que les efforts ne sont pas répercutés sur le genou ou la hanche. En plus de cette étude biomécanique, une analyse de l activité musculaire a été réalisée sur les principaux muscles moteurs du membre inférieur, pour différentes cinématiques et différents designs de palme. Les résultats nous ont prouvé que le design de la palme a un effet non uniforme sur l ensemble des muscles, et que pour chacune des pratiques, les demandes musculaires ne sont pas similaires.The present work had in objective to develop some methods to quantify the joint torque endured by a fin swimmer during is activity for 3 sports (Swimming, Snorkeling, Body-Board). In this way, a model using inverse dynamic methods has been done. During the first step of this study, the 3D kinematic of each activity was mad on the 3 segments of the lower limbs, and this allows defining 3 specifics motions. For a Bottom-Up model, a forces measurement on distal segment is needed to make the calculation. So, a swimming fin robot has been develop to reproduce the foot kinematics for each activity and measure all forces and torques on the ankle joint. By this way, with all this inputs, by the model we can quantify the demands on knee and hip. With this robot, we measure the effect of design modification on muscular request on the joint ankle, and by the model we assure torques are not postpone on knee or hip. In addition to this biomechanical study, a muscular activities study has been realise on the main muscle, and this for different kinematics and different fin blade shapes. The results acknowledge that the fin designs differentiate the effect on specific muscles, and that for each activity the muscular requests are not the same.AIX-MARSEILLE2-Bib.electronique (130559901) / SudocSudocFranceF

Influence of additional load on the moments of the agonist and antagonist muscle groups at the knee joint during closed chain exercise

International audienceThe present study investigated the influence of additional loads on the knee net joint moment, flexor and extensor muscle group moments, and cocontraction index during a closed chain exercise. Loads of 8, 28, or 48 kg (i.e., respectively, 11.1 +/- 1.5%, 38.8 +/- 5.3%, and 66.4 +/- 9.0% of body mass) were added to subjects during dynamic half squats. The flexor and extensor muscular moments and the amount of cocontraction were estimated at the knee joint using an EMG-and-optimization model that includes kinematics, ground reaction, and EMG measurements as inputs. In general, our results showed a significant influence of the Load factor on the net knee joint moment, the extensor muscular moment, and the flexor muscle group moment (all Anova p <.05). Hence we confirmed an increase in muscle moments with increasing load and moreover, we also showed an original ``more than proportional'' evolution of the flexor and extensor muscle group moments relative to the knee net joint moment. An influence of the Phase (i.e., descent vs. ascent) factor was also seen, revealing different activation strategies from the central nervous system depending on the mode of contraction of the agonist muscle group. The results of the present work could find applications in clinical fields, especially for rehabilitation protocols. (C) 2007 Elsevier Ltd. All rights reserved

A two-step EMG-and-optimization process to estimate muscle force during dynamic movement

International audienceThe present study proposed a two-step EMG-and-optimization method for muscle force estimation in dynamic condition. Considering the strengths and the limitations of existing methods, the proposed approach exploited the advantages of min/max optimization with constraints on the contributions of the flexor and extensor muscle groups to the net joint moment estimated through an EMG-to-moment approach. Our methodology was tested at the knee joint during dynamic half squats, and was compared with traditional min/max optimization. In general, results showed significant differences in muscle force estimates from EMG-and-optimization method when compared with those from traditional min/max optimization. Muscle forces were higher - especially in the antagonist muscles - and more consistent with EMG patterns because of the ability of the proposed approach to properly account for agonist/antagonist cocontraction. In addition, muscle forces agree with mechanical constraints regarding the net, the agonist, and the antagonist moments, thus greatly improving the confidence in muscle force estimates. The proposed two-step EMG-and-optimization method for muscle force estimation is easy to implement with relatively low computational requirements and, thus, could offer interesting advantages for various applications in many fields, including rehabilitation, clinical, and sports biomechanics

Ultrasound-based subject-specific parameters improve fascicle behaviour estimation in Hill-type muscle model

International audienceThe estimation of muscle fascicle behaviour is decisive in a Hill-type model as they are related to muscle force by the force – length –velocity relationship and the tendon force – strain relationship. This study was aimed at investigating the influence of subject-specific tendon force – strain relationship and initial fascicle geometry (IFG) on the estimation of muscle forces and fascicle behaviour during isometric contractions. Ultrasonography was used to estimate the in vivo muscle fascicle behaviour and compare the muscle fascicle length and pennation angle estimated from the Hill-type model. The calibration – prediction process of the electromyography-driven model was performed using generic or subject-specific tendon definition with or without IFG as constraint. The combination of subject-specific tendon definition and IFG led to muscle fascicle behaviour closer to ultrasound data and significant lower forces of the ankle dorsiflexor and plantarflexor muscles compared to the other conditions. Thus, subject-specific ultrasound measurements improve the accuracy of Hill-type models on muscle fascicle behaviour

Subject-specific tendon-aponeurosis definition in Hill-type model predicts higher muscle forces in dynamic tasks.

Neuromusculoskeletal models are a common method to estimate muscle forces. Developing accurate neuromusculoskeletal models is a challenging task due to the complexity of the system and large inter-subject variability. The estimation of muscles force is based on the mechanical properties of tendon-aponeurosis complex. Most neuromusculoskeletal models use a generic definition of the tendon-aponeurosis complex based on in vitro test, perhaps limiting their validity. Ultrasonography allows subject-specific estimates of the tendon-aponeurosis complex's mechanical properties. The aim of this study was to investigate the influence of subject-specific mechanical properties of the tendon-aponeurosis complex on a neuromusculoskeletal model of the ankle joint. Seven subjects performed isometric contractions from which the tendon-aponeurosis force-strain relationship was estimated. Hopping and running tasks were performed and muscle forces were estimated using subject-specific tendon-aponeurosis and generic tendon properties. Two ultrasound probes positioned over the muscle-tendon junction and the mid-belly were combined with motion capture to estimate the in vivo tendon and aponeurosis strain of the medial head of gastrocnemius muscle. The tendon-aponeurosis force-strain relationship was scaled for the other ankle muscles based on tendon and aponeurosis length of each muscle measured by ultrasonography. The EMG-driven model was calibrated twice - using the generic tendon definition and a subject-specific tendon-aponeurosis force-strain definition. The use of subject-specific tendon-aponeurosis definition leads to a higher muscle force estimate for the soleus muscle and the plantar-flexor group, and to a better model prediction of the ankle joint moment compared to the model estimate which used a generic definition. Furthermore, the subject-specific tendon-aponeurosis definition leads to a decoupling behaviour between the muscle fibre and muscle-tendon unit in agreement with previous experiments using ultrasonography. These results indicate the use of subject-specific tendon-aponeurosis definitions in a neuromusculoskeletal model produce better agreement with measured external loads and more physiological model behaviour

A method to characterize in vivo tendon force-strain relationship by combining ultrasonography, motion capture and loading rates

International audienceThe ultrasonography contributes to investigate in vivo tendon force–strain relationship during isometric contraction. In previous studies, different methods are available to estimate the tendon strain, using different loading rates and models to fit the tendon force–strain relationship. This study was aimed to propose a standard method to characterize the in vivo tendon force–strain relationship. We investigated the influence on the force–strain relationship for medialis gastrocnemius (MG) of (1) one method which takes into account probe and joint movements to estimate the instantaneous tendon length, (2) models used to fit the force–strain relationship for uniaxial test (polynomial vs. Ogden), and (3) the loading rate on tendon strain. Subjects performed ramp-up contraction during isometric contractions at two different target speeds: 1.5 s and minimal time with ultrasound probe fixed over the muscle–tendon junction of the MG muscle. The used method requires three markers on ultrasound probe and a marker on calcaneum to take into account all movements, and was compared to the strain estimated using ultrasound images only. The method using ultrasound image only overestimated the tendon strain from 40% of maximal force. The polynomial model showed similar fitting results than the Ogden model (R 2 ¼0.98). A loading rate effect was found on tendon strain, showing a higher strain when loading rate decreases. The characterization of tendon force–strain relationship needs to be standardized by taking into account all movements to estimate tendon strain and controlling the loading rate. The polynomial model appears to be appropriate to represent the tendon force–strain relationship