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International audience; Lateral epicondylitis, also known as tennis elbow, is a major health issue among tennis players. This musculo-skeletal disorder affects hand extensor tendons, results in substantial pain and impairments for sporting and everyday activities and requires several weeks of recovery. Unfortunately, prevention remains limited by the lack of data regarding biomechanical risk factors, especially because in vivo evaluation of hand tendon forces remains challenging. Electromyography-informed musculo-skeletal modeling is a noninvasive approach to provide physiological estimation of tendon forces based on motion capture and electromyography but was never applied to study hand tendon loading during tennis playing. The objective of this study was to develop such electromyography-informed musculo-skeletal model to provide new insight into hand tendon loading in tennis players. The model was tested with three-dimensional kinematics and electromyography data of two players performing forehand drives at two-shot speeds and with three rackets. Muscle forces increased with shot speed but were moderately affected by racket properties. Wrist prime extensors withstood the highest forces, but their relative implication compared to flexors depended on the player-specific grip force and racket motion strategy. When normalizing wrist extensor forces by shot speed and grip strength, up to threefold differences were observed between players, suggesting that gesture technique, for example, grip position or joint motion coordination, could play a role in the overloading of wrist extensor tendons. This study provided a new methodology for in situ analysis of hand biomechanical loadings during tennis gesture and shed a new light on lateral epicondylitis risk factors.

International audience; Current intervertebral disc finite element models are hard to validate since they describe multi-physical phenomena and contain a huge number of material properties. This work aims to simplify numerical validation/identification studies by prioritizing the sensitivity of intervertebral disc behavior to mechanical properties. A 3D fiber-reinforced hyperelastic model of a C6-C7 intervertebral disc is used to carry out the parametric study. 10 parameters describing the extracellular matrix and the collagen network behaviors are included in the parametric study. The influence of varying these parameters on the disc response is estimated during physiological movements of the head, including compression, lateral bending, flexion, and axial rotation. The obtained results highlight the high sensitivity of the disc behavior to the stiffness of the annulus fibrosus extracellular matrix for all the studied loads with a relative increase in the disc apparent stiffness by 67% for compression and by 57% for axial rotation when the annulus stiffness increases from 0.4 to 2 MPa. It is also shown that varying collagen network orientation, stiffness, and stiffening in the studied configuration range have a noticeable effect on rotational motions with a relative apparent stiffness difference reaching 6.8%, 10%, and 22%, respectively, in lateral bending. However, the collagen orientation does not affect disc response to axial load.

International audience; Cell competition is a widespread process leading to the expansion of one cell population through the elimination and replacement of another. A large number of genetic alterations can lead to either competitive elimination of the mutated population or expansion of the mutated cells through the elimination of the neighbouring cells. Several processes have been proposed to participate in the preferential elimination of one cell population, including competition for limiting extracellular pro-survival factors, communication through direct cell–cell contact, or differential sensitivity to mechanical stress. Recent quantitative studies of cell competition have also demonstrated the strong impact of the shape of the interfaces between the two populations. Here, we discuss the direct and indirect contribution of mechanical cues to cell competition, where they act either as modulators of competitive interactions or as direct drivers of cell elimination. We first discuss how mechanics can regulate contact-dependent and diffusion-based competition by modulating the shape of the interface between the two populations. We then describe the direct contribution of mechanical stress to cell elimination and competition for space. Finally, we discuss how mechanical feedback also influences compensatory growth and triggers preferential expansion of one population.

Background: Previous studies focusing on the effects of knee surgery on hindfoot alignment have suggested some degree of compensation between the knee and the hindfoot. However, these studies did not investigate a preoperative relationship in patients without end-stage knee osteoarthritis using 3-dimensional (3D) biometrics. The purpose of this study was to investigate the relationship between knee and hindfoot alignment using 3D weightbearing imaging. Methods: This retrospective comparative study included 95 lower limbs with weightbearing computed tomography and low-dose biplanar radiograph investigations. Cases with a history that may have caused a change in lower limb alignment were excluded. Hindfoot and knee alignments were measured using foot ankle offset (FAO) and hip-knee-ankle (HKA) angle, respectively. Patients were separated into 3 groups according to the knee deformity to investigate the distribution of FAO in each group. Results: The mean (SD) FAO was 2% (7%) for the knee varus group, 1% (6%) for the neutral knee group, and 4% (5%) for the valgus knee group ( P = .12). Fifty-three percent of patients with knee valgus showed a pathological hindfoot valgus ( P = .04). We found a positive but moderate correlation between hindfoot valgus and HKA (ρ = 0.53; P = .01). Female sex was associated with higher FAO (3% ± 4% vs 0.6% ± 6%; P = .009). Conclusion: This feasibility study suggests a new opportunity using 3D biometrics to understand the relationship between knee and hindfoot alignment and to highlight different patterns of combined deformities in further investigations. Level of Evidence: Level III, comparative study.

International audience; Sound analysis by the cochlea relies on frequency tuning of mechanosensory hair cells along a tonotopic axis. To clarify the underlying biophysical mechanism, we have investigated the micromechanical properties of the hair cell's mechanoreceptive hair bundle within the apical half of the rat cochlea. We studied both inner and outer hair cells, which send nervous signals to the brain and amplify cochlear vibrations, respectively. We find that tonotopy is associated with gradients of stiffness and resting mechanical tension, with steeper gradients for outer hair cells, emphasizing the division of labor between the two hair-cell types. We demonstrate that tension in the tip links that convey force to the mechano-electrical transduction channels increases at reduced Ca 2+. Finally, we reveal gradients in stiffness and tension at the level of a single tip link. We conclude that mechanical gradients of the tip-link complex may help specify the characteristic frequency of the hair cell.

International audience; Chemical and physical properties of the environment control cell proliferation, differentiation, or apoptosis in the long term. However, to be able to move and migrate through a complex three-dimensional environment, cells must quickly adapt in the short term to the physical properties of their surroundings. Interactions with the extracellular matrix (ECM) occur through focal adhesions or hemidesmosomes via the engagement of integrins with fibrillar ECM proteins. Cells also interact with their neighbors, and this involves various types of intercellular adhesive structures such as tight junctions, cadherin-based adherens junctions, and desmosomes. Mechanobiology studies have shown that cell-ECM and cell-cell adhesions participate in mechanosensing to transduce mechanical cues into biochemical signals and conversely are responsible for the transmission of intracellular forces to the extra-cellular environment. As they migrate, cells use these adhesive structures to probe their surroundings, adapt their mechanical properties, and exert the appropriate forces required for their movements. The focus of this review is to give an overview of recent developments showing the bidirectional relationship between the physical properties of the environment and the cell mechanical responses during single and collective cell migration.

International audience; A general trait of living cells is their ability to exert contractile stresses on their surroundings and thus respond to substrate rigidity. At the cellular scale, this response affects cell shape, polarity, and ultimately migration. The regulation of cell shape together with rigidity sensing remains largely unknown. In this article we show that both substrate rigidity and cell shape contribute to drive actin organization and cell polarity. Increasing substrate rigidity affects bulk properties of the actin cytoskeleton by favoring long-lived actin stress fibers with increased nematic interactions, whereas cell shape imposes a local alignment of actin fibers at the cell periphery.

International audience; The regulation of morphogenesis by the basement membrane (BM) may rely on changes in its mechanical properties. To test this, we developed an atomic force microscopy-based method to measure BM mechanical stiffness during two key processes in Drosophila ovarian follicle development. First, follicle elongation depends on epithelial cells that collectively migrate, secreting BM fibrils perpendicularly to the anteroposterior axis. Our data show that BM stiffness increases during this migration and that fibril incorporation enhances BM stiffness. In addition, stiffness heterogeneity, due to oriented fibrils, is important for egg elongation. Second, epithelial cells change their shape from cuboidal to either squamous or columnar. We prove that BM softens around the squamous cells and that this softening depends on the TGF beta pathway. We also demonstrate that interactions between BM constituents are necessary for cell flattening. Altogether, these results show that BM mechanical properties are modified during development and that, in turn, such mechanical modifications influence both cell and tissue shapes.

International audience; Whisking rodents can discriminate finely textured objects using their vibrissae. The biomechanical and neural processes underlying such sensory tasks remain elusive. Here we combine the use of model micropatterned substrates and high-resolution videography of rats' whiskers during tactile exploration to study how texture information is mechanically encoded in the whisker motion. A biomechanical modeling of the whisker is developed, which yields quantitative predictions of the spectral and temporal characteristics of the observed whisker kinetics, for any given topography. These texture-induced whisker vibrations are then replayed via a multiwhisker stimulator while recording neuronal responses in the barrel field of the primary somatosensory cortex (S1bf). These results provide a comprehensive description of the transduction process at play during fine texture sensing in rats. They suggest that the sensory system operates through a vibratory amplitude modulation/demodulation scheme. Fine textural properties are encoded in the time-varying envelope of the whisker-resonant vibrations. This quantity is then recovered by neural demodulation, as it effectively drives the spiking-rate signal of a large fraction of S1 cortical neurons. This encoding/decoding scheme is shown to be robust against variations in exploratory conditions, such as the scanning speed or pad-to-substrate distance, thus allowing for reliable tactile discrimination in realistic conditions.

International audience; The leading front of a collectively migrating epithelium often destabilizes into multicellular migration fingers where a cell initially similar to the others becomes a leader cell while its neighbours do not alter. The determinants of these leader cells include mechanical and biochemical cues, often under the control of small GTPases. However, an accurate dynamic cartography of both mechanical and biochemical activities remains to be established. Here, by mapping the mechanical traction forces exerted on the surface by MDCK migration fingers, we show that these structures are mechanical global entities with the leader cells exerting a large traction force. Moreover, the spatial distribution of RhoA differential activity at the basal plane strikingly mirrors this force cartography. We propose that RhoA controls the development of these fingers through mechanical cues: the leader cell drags the structure and the peripheral pluricellular acto-myosin cable prevents the initiation of new leader cells.

International audience; We introduce an intrinsically multiplexed and easy to implement method to apply an external force to a biomolecule and thus probe its interaction with a second biomolecule or, more generally, its environment (for example, the cell membrane). We take advantage of the hydrodynamic interaction with a controlled fluid flow within a microfluidic channel to apply a force. By labeling the biomolecule with a nanoparticle that acts as a kite and increases the hydrodynamic interaction with the fluid, the drag induced by convection becomes important. We use this approach to track the motion of single membrane receptors, the Clostridium perfringens ε-toxin (CPεT) receptors that are confined in lipid raft platforms, and probe their interaction with the environment. Under external force, we observe displacements over distances up to 10 times the confining domain diameter due to elastic deformation of a barrier and return to the initial position after the flow is stopped. Receptors can also jump over such barriers. Analysis of the receptor motion characteristics before, during, and after a force is applied via the flow indicates that the receptors are displaced together with their confining raft platform. Experiments before and after incubation with latrunculin B reveal that the barriers are part of the actin cytoskeleton and have an average spring constant of 2.5 ± 0.6 pN/μm before vs. 0.6 ± 0.2 pN/μm after partial actin depolymerization. Our data, in combination with our previous work demonstrating that the ε-toxin receptor confinement is not influenced by the cytoskeleton, imply that it is the raft platform and its constituents rather than the receptor itself that encounters and deforms the barriers formed by the actin cytoskeleton.

International audience; We studied prey processing in the Siamese fighting fish (Betta splendens), involving slow, easily observed head-bobbing movements, which were compared with prey processing in other aquatic feeding vertebrates. We hypothesized that head-bobbing is a unique prey-processing behaviour, which alternatively could be structurally and functionally analogous with raking in basal teleosts, or with pharyngognathy in neoteleosts. Modulation of head-bobbing was elicited by prey with different motility and toughness. Head-bobbing involved sustained mouth occlusion and pronounced cranial elevation, similar to raking. However, the hyoid and pectoral girdle were protracted, and not retracted as in both raking and pharyngognathy. High-speed videofluoroscopy of hyoid movements confirmed that head-bobbing differs from other known aquatic prey-processing behaviours. Nevertheless, head-bobbing and other prey-processing behaviours converge on a recurrent functional theme in the trophic ecology of aquatic feeding vertebrates; the use of intraoral and oropharyngeal dentition surfaces to immobilize, reduce and process relatively large, tough or motile prey. Prey processing outside the pharyngeal region has not been described for neoteleosts previously, but morphological evidence suggests that relatives of Betta might use similar processing behaviours. Thus, our results suggest that pharyngognathy did not out-compete ancestral prey-processing mechanisms completely during the evolution of neoteleosts.

International audience; Thanks to their immune properties, the mesenchymal stem cells (MSC) are a promising source for cell therapy. Current clinical trials show that MSC administrated to patients can treat different diseases (graft-versus-host disease (GVHD), liver cirrhosis, systemic lupus, erythematosus, rheumatoid arthritis, type I diabetes…). In this case, the most common mode of cell administration is the intravenous injection, and the hemodynamic environment of cells induced by blood circulation could interfere on their behavior during the migration and homing towards the injured site. After a brief review of the mechanobiology concept, this paper will help in understanding how the mechanical environment could interact with MSC behavior once they are injected to patient in cell-based treatment.

International audience; BACKGROUND:Identification of transmural extent and degree of non-viability after ST-segment elevation myocardial infarction (STEMI) is clinically important. The objective of the present study was to assess the regional mechanics and temporal deformation patterns using speckle tracking echocardiography (STE) in acute and later phases of STEMI to predict myocardial damage in these patients.METHODS AND RESULTS:Ninety-eight patients with first STEMI underwent both echocardiography and cardiac magnetic resonance imaging in acute phase and at 6 months follow-up with 2D STE-derived measurements of peak longitudinal strain (PLS), Pre-STretch index (PST) and post-systolic deformation index (PSI). For each segment, late gadolinium enhancement (LGE) was defined as transmural (LGE >66 %) or non-transmural (

International audience; Ubiquitin inclusions represent a cytopathological hallmark of ALS. The ubiquitin-dependent protein degradation pathway may also be involved in the pathophysiology of SOD1 mutated ALS cases as demonstrated in transgenic animals. UBE2H is an ubiquitin conjugating enzyme known to act on histones and cytoskeletal proteins, both involved in the degenerative pathway of the motor neuron. We screened the whole coding sequence of the UBE2H gene in 24 sporadic ALS (SALS) patients using single strand conformation polymorphism (SSCP). All variants detected by SSCP were analysed by genomic DNA sequencing. We found one known polymorphism (rs12539800) and two new synonymous single nucleotide polymorphisms (SNP) (nG78A and nG501A). The allele distribution of the rs12539800 (A336G) SNP were tested for association in 252 SALS patients and 357 controls. The allele and genotype distributions were identical in the two groups. The UBE2H gene is not implicated in SALS; however, the ubiquitin pathway is worthy of further investigation in ALS.

Resume Objectif. – Mesures des resistances maximales a la rupture des ligaments pelviens utilises dans les cures de prolapsus et d'incontinence urinaire. Patientes et methodes. – Nos mesures sont effectuees a partir de ligaments pelviens de cadavres. Nous avons disseque 29 bassins de cadavres feminins dont les modes de conservation differaient. Dix cadavres etaient frais congeles, dix frais et neuf formoles. Sur chacun, nous avons disseque le ligament pre-vertebral au niveau du promontoire, les ligaments pectines, sacro-epineux et les arcs tendineux du fascia pelvien. Une evaluation subjective clinique de la qualite ligamentaire par l'examen et la palpation digitale nous a permis d'effectuer une classification en trois groupes de qualite : A, B et C. Ces memes ligaments etaient ensuite aiguilles par un fil, prenant l'ensemble de leur epaisseur, et les ligaments etaient soumis a une traction dans l'axe du vagin jusqu'a obtenir leur rupture. L'appareil de mesure est un dynamometre de type Samson, adapte a notre etude. La resistance a la rupture des ligaments est rapportee en newtons. Resultats. – Il existe une grande variabilite dans les mesures de resistance maximale a la rupture des ligaments. Les valeurs minimales obtenues sont de l'ordre de 22 newtons, et proches de 200 newtons pour les valeurs maximales. Les resultats montrent une grande disparite. Le ligament pre-vertebral est en moyenne plus resistant. Lorsqu'on compare la resistance en fonction des trois modes de conservation, il n'existe une difference significative de resistance que pour les ligaments pre-vertebraux aux depens des sujets formoles. Pour tous les autres ligaments il n'existe pas de difference significative en fonction du mode de conservation. On ne retrouve pas de difference significative entre les mesures droite et gauche pour les ligaments bilateraux. Le ligament pectine est significativement plus resistant que le ligament sacro-epineux et que les arcs tendineux du fascia pelvien. Il existe un lien significatif entre l'appreciation subjective de la qualite ligamentaire et les mesures objectives de resistance. Discussion et conclusion. – La litterature ne donne pas de reference concernant la resistance a la rupture des ligaments pelviens. Ces ligaments sont pourtant utilises couramment dans presque toutes les interventions de cures de prolapsus ou d'incontinence urinaire. Les resultats rapportes permettent de constater que ces ligaments sont de resistance tres variable d'une patiente a l'autre, d'un ligament a l'autre, voire chez une meme patiente et pour un meme ligament d'un cote a l'autre. Ces observations pourraient permettre d'expliquer certains echecs des techniques chirurgicales et soulignent l'interet de rechercher des techniques d'evaluation de ces resistances en pre-operatoire. Ceci nous permettrait de modifier les indications chirurgicales en fonction de la qualite des ligaments. L'evaluation subjective per-operatoire de la resistance est globalement correlee aux mesures objectives et devrait donc etre un element determinant dans le choix per-operatoire des ligaments de suspension pour les montages chirurgicaux.

Epithelial spreading is a common and fundamental aspect of various developmental and disease-related processes such as epithelial closure and wound healing. A key challenge for epithelial tissues undergoing spreading is to increase their surface area without disrupting epithelial integrity. Here we show that orienting cell divisions by tension constitutes an efficient mechanism by which the Enveloping Cell Layer (EVL) releases anisotropic tension while undergoing spreading during zebrafish epiboly. The control of EVL cell-division orientation by tension involves cell elongation and requires myosin II activity to align the mitotic spindle with the main tension axis. We also found that in the absence of tension-oriented cell divisions and in the presence of increased tissue tension, EVL cells undergo ectopic fusions, suggesting that the reduction of tension anisotropy by oriented cell divisions is required to prevent EVL cells from fusing. We conclude that cell-division orientation by tension constitutes a key mechanism for limiting tension anisotropy and thus promoting tissue spreading during EVL epiboly., Comment: Methods, supplementary information and associated references are available in the published online version of the paper at http://www.nature.com/doifinder/10.1038/ncb2869

Opinion/Feedback Amputation of a limb is always perceived as a catastrophe. The principles underlying creation of a stump adapted to modern prosthetic fittings must be fully understood and the patient managed by a multidisciplinary team. In paediatric patients, preserving residual limb length is a crucial point that should be assessed according to the expected growth potential. Advances in prosthetic fittings have led to changes in the overall concept of socket design, which seeks to achieve three objectives: to maximise the weight-bearing surface area, to eliminate friction of the skin on the socket, and to eliminate lever-arm effects. The introduction on the market of new materials has contributed substantially to advances in prosthetic fittings. These advances require the use of new criteria for stump quality and optimisation, which exert a considerable influence on prosthesis function. Prosthetic fitting and specific management of psychological and social problems are provided during an inpatient stay in a physical medicine department, by a team of physicians, other healthcare professionals, social workers, and educators. Three-dimensional imaging and gait analysis provide valuable information. Amputation of a limb is always perceived as a catastrophe. The principles underlying creation of a stump adapted to modern prosthetic fittings must be fully understood and the patient managed by a multidisciplinary team. In paediatric patients, preserving residual limb length is a crucial point that should be assessed according to the expected growth potential. Advances in prosthetic fittings have led to changes in the overall concept of socket design, which seeks to achieve three objectives: to maximise the weight-bearing surface area, to eliminate friction of the skin on the socket, and to eliminate lever-arm effects. The introduction on the market of new materials has contributed substantially to advances in prosthetic fittings. These advances require the use of new criteria for stump quality and optimisation, which exert a considerable influence on prosthesis function. Prosthetic fitting and specific management of psychological and social problems are provided during an inpatient stay in a physical medicine department, by a team of physicians, other healthcare professionals, social workers, and educators. Three-dimensional imaging and gait analysis provide valuable information.

International audience; This article quantitatively investigates ultrasound propagation in numerical anisotropic porous media with finite-difference simulations in 3D. The propagation media consist of clusters of ellipsoidal scatterers randomly distributed in water, mimicking the anisotropic structure of cancellous bone. Velocities and attenuation coefficients of the ensemble-averaged transmitted wave (also known as the coherent wave) are measured in various configurations. As in real cancellous bone, one or two longitudinal modes emerge, depending on the micro-structure. The results are confronted with two standard theoretical approaches: Biot's theory, usually invoked in porous media, and the Independent Scattering Approximation (ISA), a classical first-order approach of multiple scattering theory. On the one hand, when only one longitudinal wave is observed, it is found that at porosities higher than 90% the ISA successfully predicts the attenuation coefficient (unlike Biot's theory), as well as the existence of negative dispersion. On the other hand, the ISA is not well suited to study two-wave propagation, unlike Biot's model, at least as far as wave speeds are concerned. No free fitting parameters were used for the application of Biot's theory. Finally we investigate the phase-shift between waves in the fluid and the solid structure, and compare them to Biot's predictions of in-phase and out-of-phase motions.

Aim: Atomic force microscopy nanoindentation of myofibers was used to assess and quantitatively diagnose muscular dystrophies from human patients. Materials & methods: Myofibers were probed from fresh or frozen muscle biopsies from human dystrophic patients and healthy volunteers, as well as mice models, and Young’s modulus stiffness values were determined. Results: Fibers displaying abnormally low mechanical stability were detected in biopsies from patients affected by 11 distinct muscle diseases, and Young’s modulus values were commensurate to the severity of the disease. Abnormal myofiber resistance was also observed from consulting patients whose muscle condition could not be detected or unambiguously diagnosed otherwise. Discussion & conclusion: This study provides a proof-of-concept that atomic force microscopy yields a quantitative read-out of human muscle function from clinical biopsies, and that it may thereby complement current muscular dystrophy diagnosis.

International audience; This study aimed to first investigate synchronous (SYN) versus asynchronous (ASY) mode of propulsion and, second, investigate the wheel camber effects on sprinting performance as well as temporal parameters. Seven wheelchair basketball players performed four maximal eight-second sprints on a wheelchair ergometer. They repeated the test according to two modes of propulsion (SYN and ASY) and two wheel cambers (9° and 15°). The mean maximal velocity and push power output was greater in the synchronous mode compared to the asynchronous mode for both camber angles. However, the fluctuation in the velocity profile is inferior for ASY versus SYN mode for both camber angles. Greater push time/cycle time (Pt/Ct) and arm frequency (AF) for synchronous mode versus asynchronous mode and inversely, lesser Ct and rest time (Rt) values for the synchronous mode, for which greater velocity were observed. SYN mode leads to better performance than ASY mode in terms of maximal propulsion velocity. However, ASY propulsion allows greater continuity of the hand-rim force application, reducing fluctuations in the velocity profile. The camber angle had no effect on ASY and SYN mean maximal velocity and push power output. The study of wheelchair propulsion strategies is important for better understanding physiological and biomechanical impacts of wheelchair propulsion for individuals with disabilities. From a kinematical point of view, this study highlights synchronous mode of propulsion to be more efficient, with regards to mean maximal velocity reaching during maximal sprinting exercises. Even if this study focuses on well-trained wheelchair athletes, results from this study could complement the knowledge on the physiological and biomechanical adaptations to wheelchair propulsion and therefore, might be interesting for wheelchair modifications for purposes of rehabilitation.

International audience; Acoustic communication is widespread in animals. According to the sensory drive hypothesis [Endler JA (1993) Philos Trans R Soc Lond B Biol Sci 340(1292):215-225], communication signals and perceptual systems have coevolved. A clear illustration of this is the evolution of the tetrapod middle ear, adapted to life on land. Here we report the discovery of a bone conduction-mediated stimulation of the ear by wave propagation in Sechellophryne gardineri, one of the world's smallest terrestrial tetrapods, which lacks a middle ear yet produces acoustic signals. Based on X-ray synchrotron holotomography, we measured the biomechanical properties of the otic tissues and modeled the acoustic propagation. Our models show how bone conduction enhanced by the resonating role of the mouth allows these seemingly deaf frogs to communicate effectively without a middle ear.

International audience; The tailbud is the posterior leading edge of the growing vertebrate embryo and consists of motile progenitors of the axial skeleton, musculature and spinal cord. We measure the 3D cell flow field of the zebrafish tailbud and identify changes in tissue fluidity revealed by reductions in the coherence of cell motion without alteration of cell velocities. We find a directed posterior flow wherein the polarization between individual cell motion is high, reflecting ordered collective migration. At the posterior tip of the tailbud, this flow makes sharp bilateral turns facilitated by extensive cell mixing due to increased directional variability of individual cell motions. Inhibition of Wnt or Fgf signaling or cadherin 2 function reduces the coherence of the flow but has different consequences for trunk and tail extension. Modeling and additional data analyses suggest that the balance between the coherence and rate of cell flow determines whether body elongation is linear or whether congestion forms within the flow and the body axis becomes contorted.

Measurements of the tensile and bending strength of samples of vaginal tissue collected during corrective surgery of prolapse.Our measurements were conducted on two samples of vaginal tissue 2 cm x 2 cm collected during surgical correction of prolapse by vaginal route in 16 post-menopausal patients. The samples were collected from posterior vaginal fundus, were orientated, and then fixed on a plate holding the edges and allowing the tissue to be stretched over an orifice of 1 cm. The tensile measurements were made using a suture passed over this distance of 1 cm in one of the two samples by recording the strength curve in order to evaluate the force at rupture of the collagen fibres. The second sample was prepared in the same way and a piston of 1 cm diameter was made to penetrate to determine the strength of breakage of the fibres. The pressure and tensile strength curves were recorded up to rupture of the sample, as was the value of the tissue elongation.There was a great variability in the measurements of maximum strength at rupture of the vaginal samples and in the elongation before rupture of the samples. The mean rupture values in tensile tests were 44 and 59 N in bending with extremes of 12 and 130 N. The values of elongation before rupture of a 10 mm sample were 23 mm in tensile tests and 11 mm in bending tests. There was a great variability of results from one patient to another. There was no relation between the values observed and the patient age. There was a statistical relation between the elongation values of the samples and the maximum force before rupture in both the tensile and bending tests. There was also a relation between the measurement of the maximum force at rupture in bending and in tensile tests although there was no such relation in terms of the values of elongation before rupture.There is no published reference concerning the strength at rupture or the tensile strength curves for human vaginal tissues. Vaginal tissues are however commonly used as a suspension component in the vast majority of operations for correcting prolapse or urinary incontinence. These suspensions are made by passing a suture through the thickness of the vaginal tissue. The results that we report do however show that these vaginal tissues are very variable in strength from one patient to another. The same finding was made in terms of the elongation values for the vaginal tissue before rupture. The values in bending tests showed that the highest rupture force values and the greatest mean elongation before rupture were lower than in tensile tests.These findings could explain some failures of these surgical procedures, which are all based on the tensile strength properties. Finally these results could be included in modelling of the reaction of vaginal tissues to the pressure experienced within the vagina.

SUMMARY Microstructure–function relationships remain poorly understood in primary bone tissues. The relationship between bone growth rate and bone tissue type, although documented in some species by previous works, remains somewhat unclear and controversial. We assessed this relationship in a species with extreme adaptations, the king penguin (Aptenodytes patagonicus). These birds have a peculiar growth, interrupted 3 months after hatching by the austral winter. Before this interruption, chicks undergo extremely rapid statural and ponderal growth. We recorded experimentally (by means of fluorescent labelling) the growth rate of bone tissue in four long bones(humerus, radius, femur and tibiotarsus) of four king penguin chicks during their fastest phase of growth (3–5 weeks after hatching) and identified the associated bone tissue types (`laminar', `longitudinal', `reticular' or`radial' fibro-lamellar bone tissue). We found the highest bone tissue growth rate known to date, up to 171 μm day–1 (mean 55 μm day–1). There was a highly significant relationship between bone tissue type and growth rate (P

Objectives : To measure the strength at tearing of pelvic ligaments used in the cure of prolapse and urinary incontinence. Material and methods : We performed our measurements on pelvis ligaments from cadaveric specimens. We dissected 29 human female pelvis cadavers of which storage conditions differed. Ten were frozen, 10 fresh and 9 were stored in formalin. In each cadaver we dissected pre-vertebral ligaments at promontory and right and left symmetrical ligaments. These were the iliopectineal, sacrospinous and arcus tendineus of pelvic fascia. A subjective clinical evaluation of the ligament properties was performed by visual observation as well as finger palpation. Ligaments were classified into three groups. Group A contained high quality ligaments, in terms of thickness and apparent strength following finger palpation. Ligaments of doubtful quality were classified in group B and low apparent quality ligaments in group C. Then the ligaments were stitched by a suture taking the entire ligament and a force was applied on the vagina axis until tearing. The device used for strength measurement during traction was a SAMSON type force gauge, model EASY, serial number SMS-R-ES 300N manufactured by Andilog that was developed for the purpose of our study. Measurements were given in Newton (N). Results : There was a great variability in the values obtained at tearing with minimal values at around 20 N and maximal values at 200 N. Individually measured, ligament strength varied between individuals, and for the same patient between the type of ligaments and the side. The pre-vertebral ligament was on average the strongest. There was no significant difference according to the storage condition except for the pre-vertebral ligament in formalin cadavers. For bilateral ligaments, there was no difference between the left and right side. The iliopectineal ligament was statistically significantly stronger than the sacrospinous and arcus tendineus of pelvic fascia. There was a correlation between subjective evaluation and objective strength measurements. Discussion : No papers have been published on the strength of pelvic ligaments at tearing. These are however routinely used in the cure of prolapse and urinary incontinence. Our results show that there is a great variability in strength between individuals, and for a same patient between the types of ligaments and side. These observations could explain some of the surgical intervention failures and demonstrate the importance of per-operative strength evaluation. Per-operative subjective evaluation of strength is related to objective measurements and could be used to determine the type of ligaments to be used for surgical suspension. Freezing does not damage pre-vertebral ligament strength and further studies are required to evaluate elasticity of pelvic ligaments.

International audience; 1. The organisation of the muscular activities responsible for the termination of gait, their modulation as a function of the rate of progression and the associated mechanical effects were investigated in normal adults, using EMG, force plate and kinematic recordings. In particular, the braking actions in reaction to a visual cue presented at the instant of heel-strike were analysed quantitatively, with a focus on representative leg and thigh muscles of the weight-supporting (stance) and oscillating (swing) limb, during walk-and-stop trials performed at three different velocities. 2. In the stance limb, the EMG associated with braking started approximately 150 ms after the stop signal and, on average, displayed a distal-to-proximal activation sequence that primarily involved the posterior muscle groups (soleus, SOL, and hamstring, HAM). With the exception of SOL, which showed a single EMG burst, EMG patterns consisted of two or three progressively larger components occurring reciprocally in antagonistic muscles. Increasing walking speed yielded a significant reduction of the activity in distal muscles, and a simultaneous increment in proximal muscles. The mechanical effect of the earlier braking actions, estimated from the backward-directed wave of the horizontal ground reaction force, decreased in a velocity-dependent manner. 3. In the swing limb the braking activities began approximately 330 ms after the stop signal and, on average, revealed a proximal-to-distal activation sequence with the extensor groups (quadriceps, QUAD, and SOL) playing a prominent role. They always consisted of single EMG bursts, largely co-activated in the antagonist muscles. The onset latencies of the individual components showed a close correlation, and the spatio-temporal parameters were always scaled in parallel. Unlike the stance limb, the mechanical braking action associated with the final contact of the swing limb increased with walking speed. 4. The results indicate that the muscle synergies responsible for the rapid termination of gait in response to a ground-contact visual cue are produced by a relatively flexible set of motor commands modulated according to different velocity-dependent strategies in the weight-bearing limb, and by a single, fairly robust motor programme in the swing limb. Mechanical constraints related to the relative position of the centre of foot pressure and centre of body mass at the time the braking commands begin to affect external forces, may condition the difference between the two sides of the body.

The present study was designed to determine whether fatigue alters the ability to estimate an index of individual muscle force from shear elastic modulus measurements ( experiment I), and to test the ability of this technique to highlight changes in load sharing within a redundant muscle group during an isometric fatiguing task ( experiment II). Twelve subjects participated in experiment I, which consisted of smooth linear torque ramps from 0 to 80% of maximal voluntary contraction (MVC) performed before and after an isometric fatigue protocol, beginning at 40% of MVC and stopped when the force production dropped below 30% of MVC. Although the relationships between modulus and torque were very similar for pre- and postfatigue [root mean square deviation (RMSdeviation) = 3.7 ± 2.6% of MVC], the relationships between electromyography activity level and torque were greatly altered by fatigue (RMSdeviation = 10.3 ± 2.6% of MVC). During the fatiguing contraction, shear elastic modulus provided a significantly lower RMSdeviation between measured torque and estimated torque than electromyography activity level (5.7 ± 0.9 vs. 15.3 ± 3.8% of MVC). Experiment II performed with eight participants consisted of an isometric knee extension at 25% of MVC sustained until exhaustion. Opposite changes in shear elastic modulus were observed between synergists (vastus medialis, vastus lateralis, and rectus femoris) of some participants, reflecting changes in load sharing. In conclusion, despite the fact that we did not directly estimate muscle force (in Newtons), this is the first demonstration of an experimental technique to accurately quantify relative changes in force in an individual human muscle during a fatiguing contraction.

The purpose of this study was to measure the effects of drafting on energy expenditure in in-line skating, and to investigate whether the "benefit of drafting", i.e. the decrease in energy expenditure, was different between two velocities and two distances separating the two skaters.Eight recreational in-line skaters performed six exercises of 6 min, at 2 velocities (V(1) = 5.51+/-0.45 m x sec(-1); V(2) = 7.01+/-0.67 m x sec(-1)) in 3 conditions (ND = without drafting; D(1)=0.74-0.87 m "close"; D(2) = 1.19-1.36 m "far"). Collection of expired gas was carried out using a breath-by-breath portable gas analyser K4(b2) and the distance between the skaters was measured by video analysis.The skaters' energy expenditure was reduced in all drafting conditions; between D(1) and ND by 9.6+/-4.4% at V(1) and by 2.7+/-3.3% at V(2); between D(2) and ND by 8.8+/-6.0% at V(1) and by 4.2+/-4.8% at V(2). This reduction was significantly (p0.05) more important at V(1) than V(2) and no differences were observed between D(1) and D(2).In in-line skating, the technical difficulties for drafting efficiently, especially while cornering, resulted in a reduced "benefit of drafting" at high velocity than in other sports. Moreover, the need for the subject to adjust their own cycle frequency to that of the lead skater while drafting "close" would explain partly that there were no significant differences between drafting at D(1) and D(2). These results suggest that the drafting technique should be emphasized in training, especially in non-skilled skaters at high velocities and when cornering.