The nervous system does not compensate for an acute change in the balance of passive force between synergist muscles

It is unclear how muscle activation strategies adapt to differential acute changes in the biomechanical characteristics between synergist muscles. This issue is fundamental to understanding the control of almost every joint in the body. The aim of this human experiment was to determine whether the relative activation of the heads of the triceps surae [gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and soleus (SOL)] compensates for differential changes in passive force between these muscles. Twenty-four participants performed isometric ankle plantarflexion at 20 N m and 20% of the active torque measured during a maximal contraction, at three ankle angles (30\ua0deg of plantarflexion, 0 and 25\ua0deg of dorsiflexion; knee fully extended). Myoelectric activity (electromyography, EMG) provided an index of neural drive. Muscle shear modulus (elastography) provided an index of muscle force. Passive dorsiflexion induced a much larger increase in passive shear modulus for GM (+657.6±257.7%) than for GL (+488.7±257.9%) and SOL (+106.6±93.0%). However, the neural drive during submaximal tasks did not compensate for this change in the balance of the passive force. Instead, when considering the contraction at 20% MVC, GL root mean square (RMS) EMG was reduced at both 0\ua0deg (-39.4±34.5%) and 25\ua0deg dorsiflexion (-20.6±58.6%) compared with 30\ua0deg plantarflexion, while GM and SOL RMS EMG did not change. As a result, the GM/GL ratio of shear modulus was higher at 0\ua0deg and 25\ua0deg dorsiflexion than at 30\ua0deg plantarflexion, indicating that the greater the dorsiflexion angle, the stronger the bias of force to GM compared with GL. The magnitude of this change in force balance varied greatly between participants

THE EFFECT OF THE ERGOMETER DESIGN ON PELVIC TWIST AND LOWERBACK FLEXION IN ELITE ROWERS

Pelvic twist and lower-back flexion are considered as two important risk factors regarding lower-back injuries in rowers training frequently on ergometers. Mobile ergometers could be helpful because their design decreases the inertial loads that the rower has to overcome at the catch. Hence, the purpose of this study was to investigate pelvic twist and lower-back flexion with respect to the ergometer design. These two kinematic parameters were examined on ten elite rowers during one stationary and two mobile ergometer sessions performed at 20 strokes per minutes. The differences related to pelvic twist and lower-back flexion were very small. These findings suggested that further studies should be performed at higher paces and focused on the whole trunk motion and muscle activity to offer an overview of the influence of the ergometer design

APPLIED SESSION: ELASTOGRAPHY FOR MUSCLE BIOMECHANICS

The purpose of this applied session is to demonstrate the potential of shear wave elastography for the study of muscle biomechanics using both real-time demo and recent results, with a special focus on sport applications (stretching, fatigue, pain, damage)

L'Âge du Bronze moyen atlantique au prisme de la parure : recherches sur les ornements corporels en bronze de France atlantique et des régions voisines entre le milieu du XVe et la fin du XIVe siècle avant notre ère

During the second part of the Middle Bronze Age, between, XVth and beginning of the XIIIth century BC, many bronze bracelets, anklets, pins and torcs are produced and buried in the northern part of Atlantic Europe, mainly within hoards. This constitutes a peculiar moment, in which this hoard phenomenon evolves, particularly through a significant increase of the buried and immersed metallic mass. If it is evidently consistent with a strong increase of the production, it does not completely explain the plethoric quantity of bronze objects removed from the economic circulation.Through the detailed inventory of bronze ornaments and their typo-technologic classification, but also their spatial and statistics analysis, it has been showed that the ornament typological attribution required being as accurate as other object categories, providing crucial information about cultural interpretation. This revised classification identifies 14 types of pin, 2 of torcs and 27 of bracelets and anklets. These types form the major part of Middle Bronze Age 2 bronze ornament production yet discovered in Atlantic France, including imitating productions and importations from neighbouring areas.Concerning the technological aspect, one of the main contributions of this research is the demonstration of the predominant use of lost-wax-casting technique in the production of plain bracelets and anklets. A technique of wax slicing has been highlighted: clear examples from Bignan and Trégueux hoards indicate that strips and coils were cut in a wax drafts then individually curved and decorated, before smelting.This study concerns a wide geographical area, allowing considering different production/diffusion networks. Local specificities have been identified through the presence of types whose area of diffusion is clearly restricted/which have a restricted area of diffusion or by the hoard composition distinguishable from the neighbouring areas.Several groups are identified at a regional scale, characterized by the burying of a certain type of ornaments whose morphology and ornamentation are specific of a distinct area. The precise typo-technological analysis identify/allows to identify productions which are preferentially deposited in a specific area, but also to recognize the possible importations, affinities and influences visible through ornaments. Interactions between these groups have been estimated at different scales, allowing clarifying the outlines of the Atlantic space.Long-distance trades have been detected during Middle Bronze Age through the importation of materials (Baltic amber, Middle East glass, etc.), but also ornaments, particularly visible between Atlantic France, the South of England, Luneburg and Schleswig-Holstein. If it is not possible to reconstruct precisely the nature of these trades, it could be tempting to interpret them in terms of people circulation, maybe by matrimonial exchanges. Ornaments are often use in this context in modern or ancient societies.Finally, bronze ornaments are proven to be excellent indicators for the study of Atlantic Middle Bronze Age societies. This research has contributed to a better understanding of this period from a cultural, socio-economic, technical and symbolic matter.Au cours de la seconde partie de l’âge du Bronze moyen, soit entre le XVe et le début du XIIIe siècle avant notre ère, des bracelets, parures de cheville, épingles et torques sont produits et enfouis en quantité importante dans la moitié nord de l’Europe atlantique, essentiellement en contexte de dépôt non funéraire. Il s’agit d’un moment particulier, au cours duquel ce phénomène des dépôts évolue, notamment à travers l’accroissement considérable de la masse métallique enfouie et immergée. S’il concorde certainement avec une forte augmentation de la production, elle ne suffit pas à expliquer la quantité pléthorique d’objets en bronze retirés du circuit économique.Par l’inventaire détaillé des ornements corporels en bronze et leur classement typo-technologique, ainsi qu’à travers des analyses spatiales et statistiques, il a été démontré que l’attribution typologique des objets de parure nécessitait d’être affinée et aussi précise que pour les autres catégories d’objets, fournissant des informations cruciales d’un point de vue culturel. Cette classification renouvelée distingue désormais 14 types d’épingles, 2 types de torques et 27 types de parures annulaires, au sein desquels se répartit l’essentiel des productions de parure du Bronze moyen atlantique 2 mises au jour en France atlantique, y compris les productions imitées ou importées depuis les régions voisines.D’un point de vue technologique, l’un des apports majeurs de ce travail est la démonstration de l’emploi prédominant de la technique de la fonte à la cire perdue pour la fabrication des parures annulaires à tige pleine. Des modalités de découpe de la cire ont également pu être identifiées. L’hypothèse avancée et étayée par des exemples concrets irait dans le sens de la segmentation de colombins et de plaques de cire, permettant l’obtention de préformes, ensuite cintrées et décorées individuellement avant la fonte.Le fait de mener cette étude sur une aire géographique étendue a permis d’envisager différents réseaux de production/diffusion des parures en bronze. Des particularismes locaux ont notamment pu être identifiés, caractérisés par le dépôt de types d’objets dont la diffusion est extrêmement restreinte, ou encore par des associations d’objets dans les dépôts qui dénotent avec celles des zones directement voisines géographiquement.À l’échelle régionale, plusieurs groupes ont pu être identifiés, caractérisés par l’enfouissement de certains types de parures dont la combinaison entre la morphologie et le décor lui sont propres. L’analyse typo-technologique fine a permis de déterminer quelles étaient les productions enfouies préférentiellement dans une zone, mais aussi de repérer les éventuelles importations, affinités ou influences visibles à travers les ornements corporels. Les interactions à différentes échelles entre les groupes ont ainsi pu être évaluées, permettant de préciser les contours du domaine atlantique. Des échanges à très longue distance ont eu lieu durant le Bronze moyen, visibles notamment par l’importation de matériaux (ambre balte, verre proche-oriental, etc.), mais aussi d’objets de parure, particulièrement visibles entre la France atlantique, le sud de l’Angleterre, le Lüneburg et le Schleswig-Holstein. Si la nature de ces échanges ne peut à ce jour être envisagée précisément, il est tentant de l’interpréter en termes de circulation d’individus, peut-être par le biais d’échanges matrimoniaux. Les parures annulaires sous toutes leurs formes sont en effet très souvent sollicitées dans ce cadre, dans les sociétés actuelles ou passées.En définitive, les ornements corporels en bronze s’avèrent être d’excellents indicateurs, justifiant le choix de ce prisme pour l’étude des sociétés du Bronze moyen atlantique. Ce travail a participé à caractériser plus précisément cette période, mais ouvre également de nombreuses perspectives, aussi bien sur les plans culturels que socio-économiques, techniques et symboliques

ELECTROMECHANICAL DELAY AND ITS MECHANISMS ARE NOT IMPAIRED FOLLOWING ECCENTRIC EXERCISE

The aim of the present study was to assess the effect of exercise-induced muscle damage on both electrochemical and mechanical components involved in the electromechanical delay in the gastrocnemius medialis muscle. 15 healthy participants completed 10 sets of 30 maximal eccentric contractions of the plantar flexor muscles at a constant angular velocity of 45°.s-1. Delayed onset muscular soreness, maximal isometric torque, and electromechanical delay were measured before, 1h, and 48h following eccentric exercise. The present study revealed that the time required for both electrochemical and mechanical process involved in electromechanical delay are not impaired by exercise induced muscle damage. This study suggests that the long lasting reduction in force after eccentric exercise cannot be associated to an alteration of the force transmission efficiency

A KINEMATIC MODEL TO PERSONALIZE BOAT SETTINGS IN ORDER TO TARGET A GIVEN RANGE OF MOTION IN SCULLING

The boat settings is a complex topic in rowing as many parts of both boat and oars can be set. The amplitude of the rowing stroke, one main parameter of performance in rowing (Smith & Loschner, 2002), is directly affected by these choices. Surprisingly, the scientific literature is very poor on this subject and boat and oars settings are mainly based on rowers' and coaches' experiences (Nolte, 2011). Most of the time, all crew members have the same settings, while they can display various segment anthropometries and joint flexibilities. Therefore, this study aimed to implement and validate a numeric kinematic model to individualize boat settings in order that scullers can reach given catch and finish angles. For that purpose, it is possible to adjust both inboard of the rigging (boat) and spread (oar) lengths. The inputs of the model should be measured using simple testing that can be performed by coaches and athletes

Coordination interindividuelle et performance en aviron

Cette étude visait à analyser les phénomènes associés à la coordination entre les rameurs d’un équipage au cours d’une course d’aviron, en articulant une analyse des cours d’expérience des rameurs, et une analyse de paramètres mécaniques corrélatifs de leur activité durant la course. Elle a été conçue afin (a) d’améliorer la compréhension de la performance collective et d’optimiser l’entraînement en aviron, et (b) d’explorer la fécondité d’une méthode permettant de décrire les processus de coordination conjointement aux niveaux significatif et non significatif de leur activité pour les acteurs. Deux équipages féminins ont volontairement participé à cette étude. Leur activité a été étudiée in situ lors de deux courses contre la montre, en référence au cadre théorique et méthodologique du cours d’action. Des mesures mécaniques ont conjointement été collectées, permettant de calculer un ensemble de paramètres mécaniques relatifs aux performances des rameurs et à leur coordination. Les résultats présentent, dans la première partie, les phénomènes significatifs pour les rameuses liés à leur coordination. Trois phénomènes ont été mis en évidence : (a) une sensibilité particulière des rameuses à l’état de la coordination, (b) une interprétation récurrente de l’activité de leur partenaire, et (c) quatre modalités typiques d’ajustements mutuels. Dans la deuxième partie, une étude de cas présente l’analyse d’un moment d’une course vécu par les rameuses comme un dysfonctionnement de leur coordination, sur la base de l’articulation d’une analyse des cours d’expérience et de paramètres mécaniques. Ces résultats sont discutés à trois niveaux, répondant aux visées empiriques, méthodologiques et pratiques de l’étude.The aim of this study was to analyse the phenomena associated with coordination between a crew of rowers during a race by confronting an analysis of the rowers’ courses of experience and an analysis of correlative mechanical parameters of their activity during the race. It was designed (a) to acquire a better understanding of performance and to optimize the rowers’ training, and (b) to explore the usefulness of a method that describes the processes of coordination at both significant and non-significant levels for the actors. Two female crews volunteered to participate in the study. Their activity was studied in situ during two time trials, relating to the theoretical and methodological framework of the course of action (Theureau, 2006). Mechanical measurements were collected, enabling a set of parameters on the rowers’ performance and coordination to be calculated. The results are presented in two parts. The first describes the significant phenomena for the rowers related to their coordination. Three phenomena were highlighted: (a) a particular sensitivity to their state of coordination, (b) a recurring interpretation of their partners’ activity, and (c) four typical ways of making mutual adjustments. In the second part, a case study analyses one specific moment in a race, experienced by the rowers as a malfunctioning of their coordination, by confronting analyses of the rowers’ courses of experience and mechanical parameters. These findings are discussed at three levels, answering the empirical, methodological and practical aims of the study

Rate of force development relationships to muscle architecture and contractile behavior in the human vastus lateralis

In this study, we tested the hypotheses that (i) rate of force development (RFD) is correlated to muscle architecture and dynamics and that (ii) force–length–velocity properties limit knee extensor RFD. Twenty-one healthy participants were tested using ultrasonography and dynamometry. Vastus lateralis optimal fascicle length, fascicle velocity, change in pennation angle, change in muscle length, architectural gear ratio, and force were measured during rapid fixed-end contractions at 60° knee angle to determine RFD. Isokinetic and isometric tests were used to estimate individual force–length–velocity properties, to evaluate force production relative to maximal potential. Correlation analyses were performed between force and muscle parameters for the first three 50 ms intervals. RFD was not related to optimal fascicle length for any measured time interval, but RFD was positively correlated to fascicle shortening velocity during all intervals (r = 0.49–0.69). Except for the first interval, RFD was also related to trigonometry-based changes in muscle length and pennation angle (r = 0.45–0.63) but not to architectural gear ratio. Participants reached their individual vastus lateralis force–length–velocity potential (i.e. their theoretical maximal force at a given length and shortening velocity) after 62 ± 24 ms. Our results confirm the theoretical importance of fascicle shortening velocity and force–length–velocity properties for rapid force production and suggest a role of fascicle rotation.publishedVersio

ROWING APPLIED SESSION IMPROVING ROWING PERFORMANCE AND MINIMISING INJURY

Competitive rowing has been practiced for millennia as evidenced by Egyptian wall paintings from 2500 BC. Boats from the First Egyptian Dynasty were 25 m long and 2 m wide had 30 rowers. Rowing races were conducted in Ancient Greece as part of festivals and games (Virgil, 19 – 30 BC) and in Rome regattas were organized for entertainment. The complexity of rowing boats probably reached their peak with the Greek Triremes which had 170 rowers in three banks. Today, in the modern day Olympics, there are 14 different events from the single scull to the sweep eight with coxswain. Further, ergometer rowing is an international sport in its own right. Both on-water and ergometer rowing are activities that are enjoyed recreationally and as a form of fitness training. Whatever the motivation for involvement in rowing, an understanding of the mechanisms of performance and injury can deepen appreciation of the sport. Progress will be made towards optimizing performance and minimizing injury when the relevant determinants are known. They can be grouped by their association with the rower, boat, oar and environment