The variational theory of complex rays for the calculation of medium-frequency vibrations

A new approach called the ``variational theory of complex rays’’ (VTCR) is developed for calculating the vibrations of weakly damped elastic structures in the medium-frequency range. Here, the emphasis is put on the most fundamental aspects. The effective quantities (elastic energy, vibration intensity, etc.) are evaluated after solving a small system of equations which does not derive from a finite element discretization of the structure. Numerical examples related to plates show the appeal and the possibilities of the VTCR

LOW BACK PAIN: BIOMECHANICS ANALYSIS AND PREVENTION

Epidemiological studies have shown that lower back pain from golf represent 25% of all golf related injuries. A review of the literature shows that the etiology is pluri-factorial, with general and specific risk factors. For the average players and the elite players, the mechanical loadings on the lumbar spine must be analyzed during all the golf swing. The specific risk factors, as range of motion restriction, abnormal muscle recruitment, excessive X-factor, important right side bending with high velocity lumbar rotation (crunch factor) are essential elements to be considered in a prevention strategy. Golf can aggravate pre-existing low back pain, especially in a context of overuse, without correct warm-up and with important golf swing technical fault but golf could also be an efficient treatment when it is practiced in good conditions

INFLUENCE OF PLAYING SURFACE ON KNEE LOADS DURING RUNNING, SIDESTEP CUTTING AND DROP JUMPING

The purpose of this study was to analyse the influence of 3 different playing surfaces on knee load during sport tasks. 15 young skilled rugby players (17-19 year old) performed running, sidestep cutting and drop jumping tasks on 3 different tracks; i.e. a natural turf, an artificial turf and an hybrid turf (natural grass rooted in artificial rootzone). Kinematic analysis and inverse dynamic methods were applied to assess the knee loads during these exercises. A special attention was paid to knee valgus and internal rotation moments related to ACL injury risk. Results showed that moment of knee valgus during running and sidestep cutting were significantly higher on artificial turf compared with natural ones (3.73 ± 1.13 vs. 1.98 ±. 0.83 N.m.kg-1). In the same way, internal rotation moments in sidestep cutting displayed higher values on artificial track than natural grass (2.97 ± 1.21 vs. 2.51 ±. 1.15 N.m.kg-1). Furthermore, hybrid turf exhibited the lowest knee moments except for the running task. In conclusion, the type of the playing surface play an important role in knee loads related to ACL injury risk

SPRING JUMPERS VS POWER JUMPERS: ROLE OF THE ANKLE JOINT IN ELITE WUSHU PERFORMANCE AND INJURY RISK

The purpose of this study was to characterize two jumping strategies observed in elite wushu athletes: power and spring jumping. Inverse dynamics analysis was conducted on 12 male wushu athletes performing squat jumps, drop jumps and wushu-specific acrobatic jumps. Ankle laxity and Achilles tendon elasticity were also measured. Spring jumpers showed lower ankle laxity and a bilinear evolution of overall ankle stiffness during the concentric phase of the stance, compared to power jumpers. They also showed higher peak valgus reaction moments at the knee joint. Tendon elasticity was similar between groups. As spring jumping strategy is more efficient in terms of energy expenditure and fatigue dependence, lower limb injury risk can be higher. Attention must be paid to athlete-specific jumping strategies for personalized conditioning and injury prevention

Spring jumpers vs power jumpers: ankle joint behavior in elite wushu athletes and implications for performance and injury risk

Wushu, better known as kungfu, is the modern athletic form of Chinese martial arts, and consists of performing a routine of martial arts movements as well as acrobatic jumps. Since those acrobatic jumps are performed on a hard floor, vertical jump height plays a major role in elite performance. Wushu coaches often mention two differ- ent types of athletes: spring jumpers and power jumpers. From this empirical point of view, spring jumpers seem to jump more easily. As in many sports, wushu jumps are performed with a run up followed by a stance phase with eccentric and concentric phases, often referred to as a ‘stretch-short- ening cycle’ (SSC). Vertical jump height, in this case, is the result of three main components acting during the concentric phase: muscle fiber shortening, coordination between joints and recoil of elastic energy stored during the eccentric phase. Whereas the squat jump exercise (SJ) is used to evaluate the first component, the drop jump (DJ) can be used as a standard exercise to analyze the whole SSC. The overall ability of an athlete to benefit from a previous eccentric phase can be evaluated by pre-stretch augmentation (PSA), defined as the ratio of DJ and SJ performances (Kubo et al. 2007). Ankle behavior can be characterized by the evolution of joint torque, obtained with inverse dynamics, with respect to joint angle during the different phases of the support phase, with the slope being considered as overall joint stiffness. The aim of this study was to characterize spring and power jumpers in elite wushu athletes in terms of PSA, ankle laxity, and overall ankle stiffness during the concen- tric phase. The influence of the chosen jumping strategies on performance and injury risk will be also discussed

Vibrational analysis of structures with stochastic interfaces in the medium-frequency range: Experimental validation on a touch screen

This paper proposes a dedicated approach and its experimental validation when dealing with structures (including stochastic parameters, such as interface parameters) in medium-frequency vibrations. The first ingredient is the use of a dedicated approach – the Variational Theory of Complex Rays (VTCR) – to solve the medium-frequency problem. The VTCR, which uses two-scale shape functions verifying the dynamic equation and the constitutive relation, can be viewed as a means of expressing the power balance at the different interfaces between substructures. The second ingredient is the use of the Polynomial Chaos Expansion (PCE) to calculate the random response. Since the only uncertain parameters are those which appear in the interface equations (which, in this application, are the complex connection stiffness parameters), this approach leads to very low computation costs. This method is validated on a new kind of touch screen. The simulated mobilities are compared with experimental ones obtained with a laser vibrometer and a good agreement is founded on a large medium-frequency bandwidth

Intervertebral disc characterization by shear wave elastography: an in-vitro preliminary study

Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. While geometrical personalization of the spine is no more an issue, thanks to recent technological advances, non-invasive personalization of soft tissue’s mechanical properties remains a challenge. Ultrasound elastography is a relatively recent measurement technique allowing the evaluation of soft tissue’s elastic modulus through the measurement of shear wave speed (SWS). The aim of this study was to determine the feasibility of elastographic measurements in intervertebral disc (IVD). An in-vitro approach was chosen to test the hypothesis that SWS can be used to evaluate IVD mechanical properties and to assess measurement repeatability. Eleven oxtail IVDs were tested in compression to determine their stiffness and apparent elastic modulus at rest and at 400 N. Elastographic measurements were performed in these two conditions and compared to these mechanical parameters. The protocol was repeated six times to determine elastographic measurement repeatability. Average SWS over all samples was 5.3 ± 1.0 m/s, with a repeatability of 7 % at rest and 4.6 % at 400 N; stiffness and apparent elastic modulus were 266.3 ± 70.5 N/mm and 5.4 ± 1.1 MPa at rest, respectively, while at 400 N they were 781.0 ± 153.8 N/mm and 13.2 ± 2.4 MPa. Correlations were found between elastographic measurements and IVD mechanical properties; these preliminary results are promising for further in-vivo application.The authors are grateful to the ParisTech BiomecAM chair program on subject-specific musculoskeletal modelling for funding (with the support of Proteor, ParisTech and Yves Cotrel Foundations)

Comparison of hip joint mechanical energetics in table tennis forehand and backhand drives: a preliminary study

Hip joints are highly involved in table tennis. Some authors found both pelvic angular velocity and hip joint torques are related to the racket velocity. Others have also demonstrated how some of the best players have higher ranges of motion of the lower-limb joints. Therefore, the mechanical work generated by the playing-side-hip can be seen as indicator of the playing intensity associated with different strokes. The aim of this study was to quantify the hip joint mechanical work and power during four classical strokes. Motion capture acquisitions were performed on two international players. A biplanar radiographic acquisition was also performed to personalize the biomechanical model. Hip joint velocity and torques were calculated on the dominant side, allowing mechanical power and work to be calculated between the end of backswing and the ball impact. The highest level of mechanical work from the hip joint was found for forehand drive against backspin and forehand topspin drive with pivot. A backhand drive required the lowest hip mechanical work, and the forehand drive against topspin was found to be intermediate. The lower work required from the backhand stroke makes it suitable as a waiting stroke

Contribution à la reconstruction 3D des membres inférieurs reconstruits à partir des radios biplanes pour l'application à la planification et au suivi des chirurgies

Pour comprendre et diagnostiquer les pathologies qui affectent l organisation spatialede notre squelette, il est essentiel d aborder ces problématiques en 3D. Le CT-Scan et l IRMsont des modalités d imagerie couramment utilisées en milieu clinique pour étudier en 3D notresystème musculosquelettique. La plupart de ces systèmes d imagerie proposent une acquisitioncouchée sur laquelle les effets gravitaires ne sont pas pris en compte. Le CT-Scan est unemodalité particulièrement irradiante et l IRM est plus spécifiquement dédiée à l étude des tissusmous. Le système EOS permet de reconstruire en 3D les os à partir d une paire deradiographies biplanes à faible dose d irradiation. En plus, le système EOS propose uneacquisition en position debout, prenant en compte les effets gravitaires. Cette thèse contribue àl amélioration des méthodes de reconstruction 3D des membres inférieurs à partir des radiosbiplanes. Dans le cadre de thèse on a proposé et évalué : 1) Une méthode de reconstruction3D des membres inférieurs s appuyant sur des modèles paramétrés et des inférencesstatistiques. 2) Une méthode d auto-amélioration de la reconstruction 3D des membresinférieurs en utilisant du traitement d images local et le recalcul d inférences statistiques. 3)Enfin, des méthodes utilisant des critères de similarité d images et des critères morphologiquespour détecter de manière automatique le côté médial et latéral du fémur et du tibia. Le but estd éviter l inversion par l opérateur de condyles fémoraux et plateaux tibiaux, affectant la valeurdes paramètres cliniques, surtout les torsions. La méthode de reconstruction proposée dans lecadre de cette thèse est intégrée dans le logiciel sterEOS® et utilisée dans une soixantained hôpitaux au monde. Les méthodes développées dans le cadre de cette thèse ont permis deprogresser vers la reconstruction semi-automatisée, précise et robuste du membre inférieurFor a better understanding and diagnosis of the pathologies affecting the spatialorganization of our skeleton it is necessary to address them in 3D. CT-Scan and MRI areimaging modalities commonly used to study the musculoskeletal system in 3D. Moreover,patients are recorded in reclining position thus gravity effect can t be taken into account.Furthermore, CT-Scan exposes patient to high radiation doses and MRI is used mostly tocharacterize soft tissues. With the EOS system, from a pair of low dose biplanar radiographs wecan reconstruct bones in 3D, and the radiographs are recorded in standing position thus gravityeffects are considered. This thesis contributes to the improvement of the 3D reconstructionmethods of lower limbs from biplanar radiographs. In this thesis we have proposed andevaluated: 1) A 3D reconstruction method of the lower limbs based on parametric models andstatistical inferences. 2) A method for the auto-improvement of the 3D reconstruction of thelower limbs. This method combines image processing and the recalculation of the statisticalinferences. 3) Finally, methods based on similarity measures and shape criteria were used todetect automatically the medial and lateral side of the femur and tibia. The aim of thesemethods is to avoid the inversion of the femoral and tibial condyles in biplanar radiographs.These inversions have an impact in the calculation of clinical measurements, particularly thetorsional ones. The reconstruction method proposed in this thesis is already integrated withinthe sterEOS® software, available in 60 hospitals around the world. The methods developed inthis thesis have led us to a semi-automatic, accurate and robust reconstruction of lower limbs.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF