Analyse biomécanique de l'appui sportif : contributions méthodologiques et application au saut en kungfu wushu

Sports biomechanics aims at better understanding performance mechanisms, to improve them while limiting injury risk. At elite level, stances are a key aspect of performance. Often used in gait analysis, inverse dynamics enables quantification of mechanical actions during motion. However, there are some limits to this method, two of which can become important when studying sports stances: soft tissue artifact and accuracy of dynamic wrenches. The first objective of this work is to propose methodological adaptations for inverse dynamics analysis of sports stances. Firstly, the benefit of the “mean joint centers” method, based on the use of rigid clusters, is shown for segment kinematics acquisition. Secondly, the influences of the sampling frequency and the differentiation method on the calculation of accelerations are evaluated. Thirdly, the validation of a personalized volumetric model enabling better estimation of segment inertial parameters than common proportional models is presented. The second objective of this work is the application of the methods proposed to the analysis of the ankle joint mechanical behavior during plyometric jumps, and to personalized evaluation of the lower limb injury risk in elite wushu athletes. These analyses have been performed in parallel to specific measures of athletes' characteristics, such as the ankle range of motion and the shear modulii of different structures of the triceps surae, using shear wave elastography. Perspectives for training application will be discussed, to address the evolution of training habits and personalized injury prevention.L'analyse biomécanique du geste sportif vise à mieux comprendre les mécanismes de la performance, en vue de l'améliorer tout en limitant le risque de blessures. Dans le sport de haut niveau, les appuis constituent une des clés de la performance. Couramment utilisée pour l'analyse de la marche, la dynamique inverse permet de quantifier les actions inter-segmentaires, potentiellement traumatiques, au cours du mouvement. Cette méthode comporte toutefois certains biais, dont deux peuvent être particulièrement importants au cours de mouvements sportifs à fortes accélérations : l'artefact des tissus mous et la précision du torseur dynamique. Ce travail a pour premier objectif de proposer des adaptations méthodologiques pour l'analyse par dynamique inverse d'appuis sportifs. D'abord, l'intérêt de la méthode des « centres articulaires moyens », basée sur l'utilisation de clusters rigides, est montré pour l'acquisition de la cinématique segmentaire. Ensuite, l'influence de la fréquence d'échantillonnage et de la méthode de dérivation discrète sur le calcul des accélérations est évaluée. Enfin, la validation d'un modèle volumique personnalisé permettant une meilleure estimation des paramètres inertiels que les modèles proportionnels couramment utilisés est présentée. Le second objectif de ce travail consiste en l'application des méthodes ainsi développées à l'analyse du comportement mécanique de la cheville au cours de sauts de type pliométrique et à l'évaluation personnalisée du risque de blessures du membre inférieur chez des athlètes d'élite en kungfu wushu. Ces analyses seront faites en parallèle de la mesure de caractéristiques spécifiques de l'athlète, telles que l'amplitude articulaire de la cheville et les modules d'élasticité de différentes structures du triceps sural obtenus par élastographie. Les perspectives pour l'application à l'entraînement seront abordées, en termes d'évolution des pratiques et de prévention personnalisée des blessures

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

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

Biomechanics of sports stances : methodological contributions and application to jumps in wushu

L'analyse biomécanique du geste sportif vise à mieux comprendre les mécanismes de la performance, en vue de l'améliorer tout en limitant le risque de blessures. Dans le sport de haut niveau, les appuis constituent une des clés de la performance. Couramment utilisée pour l'analyse de la marche, la dynamique inverse permet de quantifier les actions inter-segmentaires, potentiellement traumatiques, au cours du mouvement. Cette méthode comporte toutefois certains biais, dont deux peuvent être particulièrement importants au cours de mouvements sportifs à fortes accélérations : l'artefact des tissus mous et la précision du torseur dynamique. Ce travail a pour premier objectif de proposer des adaptations méthodologiques pour l'analyse par dynamique inverse d'appuis sportifs. D'abord, l'intérêt de la méthode des « centres articulaires moyens », basée sur l'utilisation de clusters rigides, est montré pour l'acquisition de la cinématique segmentaire. Ensuite, l'influence de la fréquence d'échantillonnage et de la méthode de dérivation discrète sur le calcul des accélérations est évaluée. Enfin, la validation d'un modèle volumique personnalisé permettant une meilleure estimation des paramètres inertiels que les modèles proportionnels couramment utilisés est présentée. Le second objectif de ce travail consiste en l'application des méthodes ainsi développées à l'analyse du comportement mécanique de la cheville au cours de sauts de type pliométrique et à l'évaluation personnalisée du risque de blessures du membre inférieur chez des athlètes d'élite en kungfu wushu. Ces analyses seront faites en parallèle de la mesure de caractéristiques spécifiques de l'athlète, telles que l'amplitude articulaire de la cheville et les modules d'élasticité de différentes structures du triceps sural obtenus par élastographie. Les perspectives pour l'application à l'entraînement seront abordées, en termes d'évolution des pratiques et de prévention personnalisée des blessures.Sports biomechanics aims at better understanding performance mechanisms, to improve them while limiting injury risk. At elite level, stances are a key aspect of performance. Often used in gait analysis, inverse dynamics enables quantification of mechanical actions during motion. However, there are some limits to this method, two of which can become important when studying sports stances: soft tissue artifact and accuracy of dynamic wrenches. The first objective of this work is to propose methodological adaptations for inverse dynamics analysis of sports stances. Firstly, the benefit of the “mean joint centers” method, based on the use of rigid clusters, is shown for segment kinematics acquisition. Secondly, the influences of the sampling frequency and the differentiation method on the calculation of accelerations are evaluated. Thirdly, the validation of a personalized volumetric model enabling better estimation of segment inertial parameters than common proportional models is presented. The second objective of this work is the application of the methods proposed to the analysis of the ankle joint mechanical behavior during plyometric jumps, and to personalized evaluation of the lower limb injury risk in elite wushu athletes. These analyses have been performed in parallel to specific measures of athletes' characteristics, such as the ankle range of motion and the shear modulii of different structures of the triceps surae, using shear wave elastography. Perspectives for training application will be discussed, to address the evolution of training habits and personalized injury prevention