MINIMAXX PLAYER LOAD AS AN INDEX OF THE CENTER OF MASS DISPLACEMENT? A VALIDATION STUDY

The purpose of this study was to assess the concurrent validity of the player load computed by the MinimaxX accelerometers by comparing it to the player load computed by a gold standard method based on in series force platforms. Fourteen participants were instrumented with two accelerometers (MinimaxX S4, Catapult, Australia) during specific team sport displacements performed on the force plates. Pearson correlation coefficients were ranged from 0.74 to 0.93 while the coefficients of variation varied from 6.9 to 16.4%. The standard error of the estimate was small

Lower Limb Mechanical Properties: Significant References Omitted

International audienceWe read with attention the recent narrative literature review by Pearson and McMahon [1]. We were very surprised and quite disappointed by the amount of relevant literature omitted by the authors on lower limb mechanical properties and, specifically, how ‘limb stiffness’ could affect performance and risk of injury. Although this review focuses on muscle-tendon unit (MTU) stiffness, the more global vertical, leg and joint stiffness (i.e. referred to as limb stiffness, collectively) are also reviewed, as the authors assume that limb stiffness is primarily controlled by MTU stiffness

Interactions between fascicles and tendinous tissues in gastrocnemius medialis and vastus lateralis during drop landing

Animal tendons have been shown to act as shock absorbers to protect muscle fascicles from exercise-induced damage during landing tasks. Meanwhile, the contribution of tendinous tissues to damping activities such as landing has been less explored in humans. The aim of this study was to analyze in vivo fascicle-tendon interactions during drop landing to better understand their role in energy dissipation. Ultrafast ultrasound images of the gastrocnemius medialis (GM) and vastus lateralis (VL), lower limb electromyographic activity, 2-D kinematics, and ground reaction forces were collected from twelve participants during single- and double-leg drop landings from various heights. For both muscles, length changes were higher in tendinous tissues than in fascicles, demonstrating their key role in protecting fascicles from rapid active lengthening. Increasing landing height increased lengthening and peak lengthening velocity of VL fascicle and GM architectural gear ratio, whereas GM fascicle displayed similar length and velocity patterns. Single-leg landing lengthens the tendinous tissues of GM and, to a greater degree, VL muscles, without affecting the fascicles. These findings demonstrate the adjustment in fascicle-tendon interactions to withstand mechanical demand through the tendon buffer action and fascicle rotation. The higher VL fascicle contribution to negative work as the drop height increases would suggest muscle-specific damping responses during drop landing. This can originate from the distal-to-proximal sequence of joint kinetics, from differences in muscle and tendon functions (one- and two-joint muscles), architectural and morphological properties (eg, tendon stiffness), as well as from the muscle activity of the GM and VL muscles.Enzo Hollville is funded by the Natural Grass company. We warmly thank Hugo Hauraix for his technical support

A simple method for measuring power, force, velocity properties, and mechanical effectiveness in sprint running

International audienceThis study aimed to validate a simple field method for determining force– and power–velocity relationships and mechanical effectiveness of force application during sprint running. The proposed method, based on an inverse dynamic approach applied to the body center of mass, estimates the step-averaged ground reaction forces in runner's sagittal plane of motion during overground sprint acceleration from only anthropometric and spatio-temporal data. Force– and power–velocity relationships, the associated variables, and mechanical effectiveness were determined (a) on nine sprinters using both the proposed method and force plate measurements and (b) on six other sprinters using the proposed method during several consecutive trials to assess the inter-trial reliability. The low bias (<5%) and narrow limits of agreement between both methods for maximal horizontal force (638 ± 84 N), velocity (10.5 ± 0.74 m/s), and power output (1680 ± 280 W); for the slope of the force–velocity relationships ; and for the mechanical effectiveness of force application showed high concurrent validity of the proposed method. The low standard errors of measurements between trials (<5%) highlighted the high reliability of the method. These findings support the validity of the proposed simple method, convenient for field use, to determine power, force, velocity properties, and mechanical effectiveness in sprint running

Muscle volume quantification: guiding transformers with anatomical priors

Muscle volume is a useful quantitative biomarker in sports, but also for the follow-up of degenerative musculo-skelletal diseases. In addition to volume, other shape biomarkers can be extracted by segmenting the muscles of interest from medical images. Manual segmentation is still today the gold standard for such measurements despite being very time-consuming. We propose a method for automatic segmentation of 18 muscles of the lower limb on 3D Magnetic Resonance Images to assist such morphometric analysis. By their nature, the tissue of different muscles is undistinguishable when observed in MR Images. Thus, muscle segmentation algorithms cannot rely on appearance but only on contour cues. However, such contours are hard to detect and their thickness varies across subjects. To cope with the above challenges, we propose a segmentation approach based on a hybrid architecture, combining convolutional and visual transformer blocks. We investigate for the first time the behaviour of such hybrid architectures in the context of muscle segmentation for shape analysis. Considering the consistent anatomical muscle configuration, we rely on transformer blocks to capture the longrange relations between the muscles. To further exploit the anatomical priors, a second contribution of this work consists in adding a regularisation loss based on an adjacency matrix of plausible muscle neighbourhoods estimated from the training data. Our experimental results on a unique database of elite athletes show it is possible to train complex hybrid models from a relatively small database of large volumes, while the anatomical prior regularisation favours better predictions

EVALUATION OF RESPONSE IN MALIGNANT TUMORS TREATED WITH TARGETED AGENTS.

To focus on the role of new imaging-based criteria for monitoring targeted therapies in malignant tumors in assessing treatment success, in identifying complications and in decision-making for subsequent therapy

Intrinsic ankle and hopping leg-spring stiffness in distance runners and aerobic gymnasts

International audienceThe objective of this study was to examine the contribution of intrinsic ankle stiffness to leg-spring stiffness in high level athletes using various musculotendinous solicitations. Eight aerobic gymnasts (G), 10 long-distance runners (R) and 7 controls (C) were evaluated using quick-release or sinusoidal perturbation tests in order to quantify their respective plantarflexor musculotendinous (SI MT), ankle musculoarticular active (SI MA) and passive (K P) stiffness. Leg-spring stiffness (K leg) was measured during vertical hopping. Runners and gymnasts presented significantly higher SI MT values (P<0.01) than controls: 60.4 (±14.1) rad-1 .kg 2/3 for G, 72.7 (±23.8) rad-1 .kg 2/3 for R and 38.8 (±6.5) for C. In addition, normalized K leg were not significantly different between G, R and C. It appeared that intrinsic ankle stiffness had no influence on leg-spring stiffness. The adaptation of SI MT seems to concern specifically the active part of the series elastic component in runners. The results suggested that the number of stretch-shortening cycles during daily practice sessions, rather than their intensity, act as the determinant for this component

Utilisation des dynamomètres isocinétiques pour la caractérisation des propriétés mécaniques passives du système musculo-articulaire

International audienceTraditionally, isokinetic dynamometers have been used to measure variables associated with strength, power and endurance characteristics of muscle. Much less attention has been given to their potential for measuring the passive mechanical properties of the musculoarticular system (MAS). These dynamometers are configured in order to i) mobilise passively the joint at low speeds and over all the range of motion, ii) maintain a steady level of stretching or stress, iii) realise a loading–unloading protocol, iv) apply cyclic stretching on the MAS. The mechanical behaviour of the MAS can be characterised by stiffness and viscoelasticity properties. Other methods allowed, either to control the passive conditions of the method as the surface electromyography, or to reach the mechanical properties of the muscle-tendon complex.Les dynamomètres isocinétiques sont classiquement utilisés pour la mesure des variables caractéristiques du muscle (force, puissance, endurance, etc.), moins d’attention a été apportée aux possibilités qu’ils offrent de mesurer les propriétés passives du système musculoarticulaire (SMA). Ces systèmes sont configurés de façon i) à mobiliser passivement l’articulation à des vitesses faibles et sur la quasi-totalité de l’amplitude articulaire, ii) à maintenir un niveau constant d’étirement ou de contrainte, iii) à réaliser un protocole de charge-décharge, iv) à solliciter de façon cyclique le SMA. Le comportement mécanique du SMA peut être caractérisé par ses propriétés de raideur et viscoélasticité. D’autres méthodes ont permis, soit de contrôler les conditions passives de la méthode comme l’électromyographie de surface, soit d’accéder aux propriétés mécaniques du complexe muscle-tendon (CMT)

Evaluation des propriétés mécaniques de la cheville chez des sauteurs en longueur, triple sauteurs, gymnastes aérobic et coureurs de fond "elites"

ObjectifL'objet de cette étude est d'analyser les éventuelles modifications des propriétés mécaniques musculo-tendineuses des fléchisseurs plantaires chez des sportifs de haut niveau d'activités sportives sollicitant différemment l'articulation de la cheville. Par ailleurs, les relations de ces propriétés mécaniques avec, d'une part, les propriétés de raideur du système musculo-squelettique global et d'autre part, les performances lors de sauts verticaux sont également analysées.MéthodologieTrente cinq sujets masculins [8 sauteurs (groupe S); triple saut, n=3; saut en longueur, n=5) 8 spécialistes d'aérobic sportive (groupe A), 10 spécialistes de course à pied de demi-fond ou de fond (groupe C), tous d'un niveau national ou international, et 9 sujets témoins (groupe T)] participent à l'étude. Ils sont évalués à partir des tests de quick-release et de perturbations sinusoïdales pour la détermination des propriétés de raideur musculo-tendineuse (iRMT) et musculo-articulaire active (iRMA) et passive (Kp), respectivement. Par ailleurs, des tests de sauts verticaux permettent de déterminer la raideur musculo-squelettique globale (KMI) et les hauteurs maximales atteintes (Hmax, HCMJ et HSJ).Résultats et discussionL'analyse montre un effet significatif (P0,05) avec les autres groupes.L'influence d'iRMT sur KMI reste limitée. De plus, en ce qui concerne la raideur mesurée en condition de sauts verticaux (KMI), elle est corrélée à Hmax pour les groupes S (R= -0,89; P<0,005) et A (R= -0.89; P<0,05). Pour les gymnastes, KMI est également corrélée négativement à HCMJ (R= -0,90; P<0.05). Les corrélations entre la raideur musculo-squelettique (KMI), mesurée pendant le test des rebonds, et la hauteur lors de ce test (Hmax) sont négatives pour le groupe de sauteurs et de gymnastes. Autrement dit, plus la compliance des membres inférieurs est grande et plus l'athlète saute haut. Les observations contradictoires concernant les adaptations des propriétés mécaniques chez les sportifs de haut niveau et leur influence sur la performance mettent en évidence la complexité des relations entre les caractéristiques élastiques des différentes structures anatomiques sollicitées lors des activités de type SSC.ConclusionNotre étude montre que pour résoudre la balance entre compliance et raideur, l'adaptation des propriétés mécaniques intrinsèques se réalise dans le sens d'une raideur accrue chez les sportifs de haut niveau afin de transmettre la force de manière plus efficace à la périphérie lors de la phase de restitution. Ce sont les athlètes dont le fonctionnement neuromusculaire permettra de contre-balancer cette augmentation de raideur, nécessaire par ailleurs, qui présenteront les performances les plus élevées