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International audience; Patellar tendinopathy is a chronic overuse injury of the patellar tendon which is prevalent in jump-landing activities. Sports activities can require jumping not only with a vertical component but also in a forward direction. It is yet unknown how jumping in the forward direction may affect patellar tendon forces. The main purpose of this study was to compare PTF between landings preceded by a vertical jump and a forward jump in volleyball players. The second purpose was to compare two different estimation methods of the patellar tendon force. Fifteen male volleyball players performed vertical and forward jump-landing tasks at a controlled jump height, while kinetics and kinematics were recorded. Patellar tendon forces were calculated through two estimation methods based on inverse dynamic and static optimization procedures, using a musculoskeletal model. Results showed that forward jump-landing generated higher patellar tendon forces compared to vertical jump-landing for both estimation methods. Surprisingly, although the static optimization method considered muscle co-contraction, the inverse kinematic method provided statistically significant higher patellar tendon force values. These findings highlight that limiting the forward velocity component of the aerial phase appears to reduce the load on the patellar tendon during landing and may help to prevent patellar tendinopathy.

Supplemental material, sj-docx-1-pip-10.1177_17543371211041220 for Increasing the longitudinal bending stiffness of runners’ habitual shoes:An appropriate choice for improving running performance? by Nicolas Flores, Guillaume Rao, Eric Berton and Nicolas Delattre in Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology

International audience; Based on a previous study that demonstrated the beneficial effects of sonification on cycling performance, this study investigated which kinematic and muscular activities were changed to pedal effectively. An online error-based sonification strategy was developed, such that, when negative torque was applied to the pedal, a squeak sound was produced in real-time in the corresponding headphone. Participants completed four 6-min cycling trials with resistance values associated with their first ventilatory threshold. Different auditory display conditions were used for each trial (Silent, Right, Left, Stereo), where sonification was only presented for 20 s at the start of minutes 1, 2, 3, and 4. Joint kinematics and right leg muscular activities of 10 muscles were simultaneously recorded. Our results showed participants were more effective at pedalling when presented sonification, which was consistent with previously reported findings. In comparison to the Silent condition, sonification significantly limited ankle and knee joint ranges of motion and reduced muscular activations. These findings suggest performance-based sonification significantly affected participants to reduce the complexity of the task by altering the coordination of the degrees of freedom. By making these significant changes to their patterns, participants improved their cycling performance despite lowering joint ranges of motion and muscular activations.

International audience; Objectives.-In cycling, the interaction between the athlete and his bike is crucial for the resulting performance with frame geometry and bike-setup being known to affect the biomechanical and physiological outputs. Road and Olympic crosscountry (XCO) bike frames are routinely used in training programs, despite having different frame configurations. The present study compared biomechanical indices of the pedalling techniques between road and off-road bike frames. Equipment and methods.-Ten XCO mountain bikers of national level performed two sessions on their personal bikes. For each frame, the athletes achieved one-minute tests at 65%, 90% and 115% of their maximal aerobic power (MAP) while recording 3D pedal forces. Together with various frame and bike-setup measurements, the peak of effective force, corresponding crank angle, global and instantaneous index of efficiency were compared for Power and Frame statistical effect. Results.-The frame geometry and bike-setup showed significant differences between the road and XCO frames. The Power factor significantly (P < 0.05) influenced the biomechanical indices of pedalling technique, but no effect of the Frame on any variable was reported. We posit that an internal reorganization was adopted by each cyclist to retrieve a specific and individual pedalling pattern regardless of the frame type. Such results can have important implications for training.; Objectifs.-En cyclisme, l'interaction entre l'athlète et son vélo est cruciale pour la performance , la géométrie du cadre et la configuration du vélo étant connues pour affecter les données biomécaniques et physiologiques. Les cadres de vélo de route et de crosscountry olympique (XCO) sont couramment utilisés dans les programmes d'entraînement, malgré des configurations de cadres différentes. La présente étude a comparé les indices biomécaniques des techniques de pédalage entfre les cadres de vélo de route et de vélo tout-terrain. Matériels et méthodes.-Dix Vététistes XCO de niveau national ont effectué deux séances sur leur vélos personnels. Pour chaque cadre, les athlètes ont réalisé des tests d'une minute à 65 %, 90 % et 115 % de leur puissance aérobique maximale (PMA) tandis que les forces 3D aux pédales étaient enregistrés. En plus des diverses mesures du cadre et de la configuration du vélo, le pic de force effective, l'angle de manivelle correspondant, l'indice global et instantané d'efficacité ont été comparés en observant les effets statistiques de la puissance et du cadre. Résultats.-La géométrie du cadre et la configuration du vélo ont montré des différences signi-ficatives entre le cadre de route et le cadre XCO. Le facteur de puissance (n < 0,05) a influencé de façon significative les indices biomécaniques de la technique de pédalage, mais aucun effet du cadre n'a été rapporté, sur aucune variable. Nous supposons qu'une réorganisation interne a été adoptée par chaque cycliste pour retrouver un modèle de pédalage spécifique et individuel quel que soit le type de cadre. De tels résultats peuvent avoir des implications importantes pour l'entraînement.

International audience; Purpose This study focused on the effects of shoe energy return and shoe longitudinal bending stiffness on the energetic cost and biomechanics of running. Methods The energetic cost of running and biomechanical variables altering running economy (ground contact times, stride frequency, vertical and leg stiffness, ground reaction force impulses, alignment between the resultant ground reaction force and the leg) were measured for nineteen male recreational runners. Participants ran overground under their ventilatory anaerobic threshold (10.8 ± 1.1 km h −1 on average) using four shoe prototypes with features combining low or high magnitudes of energy return and longitudinal bending stiffness. Results Neither the energy return, nor the longitudinal bending stiffness, or the interaction of these shoe features altered the energetic cost of running. High energy return shoes induced significant increased ground contact time from 274.5 ± 18.3 to 277.1 ± 18.7 ms, and significant decreased stride frequency from 1.34 ± 0.05 to 1.33 ± 0.05 Hz. High bending stiffness shoes induced significant increased ground contact time from 273.8 ± 18.2 to 277.9 ± 18.7 ms, significant increased vertical stiffness from 23.2 ± 3.4 to 23.8 ± 3.0 kN m −1 , and significant decreased net vertical impulse from 245.4 ± 17.2 to 241.7 ± 17.5 BW ms. Conclusions Increased energy return and longitudinal bending stiffness induced subtle changes in the running biomechanics, but did not induce any decrease in the energetic cost of running.

International audience; The dynamical systems approach addresses Bernstein's degrees of freedom problem by assuming that the neuro-musculo-skeletal system transiently assembles and dismantles its components into functional units (or synergies) to meet task demands. Strikingly, little is known from a dynamical point of view about the functioning of the muscular subsystem in this process. To investigate the interaction between the dynamical organisation at muscular and behavioural levels, we searched for specific signatures of a phase transition in muscular coordination when a transition is displayed at the behavioural level. Our results provide evidence that, during Fitts' task when behaviour switches to a different dynamical regime, muscular activation displays typical signatures of a phase transition; a reorganisation in muscular coordination patterns accompanied by a peak in the variability of muscle activation. This suggests that consistent changes occur in coordination processes across the different levels of description (i.e., behaviour and muscles). Specifically, in Fitts' task, target size acts as a control parameter that induces a destabilisation and a reorganisation of coordination patterns at different levels of the neuro-musculo-skeletal system.

International audience; The aim of this article is to characterise the extent to which the dynamic behaviour of a tennis racket is dependent on its mechanical characteristics and the modulation of the player's grip force. This problem is addressed through steps involving both experiment and modelling. The first step was a free boundary condition modal analysis on five commercial rackets. Operational modal analyses were carried out under " slight " , " medium " and " strong " grip force conditions. Modal frequencies and damping factors were then obtained using a high-resolution method. Results indicated that the dynamic behaviour of a racket is not only determined by its mechanical characteristics, but is also highly dependent on the player's grip force. Depending on the grip force intensity, the first two bending modes and the first torsional mode frequencies respectively decreased and increased while damping factors increased. The second step considered the design of a phenomenological hand-gripped racket model. This model is fruitful in that it easily predicts the potential variations in a racket's dynamic behaviour according to the player's grip force. These results provide a new perspective on the player/ racket interaction optimisation by revealing how grip force can drive racket dynamic behaviour, and hence underlining the necessity of taking the player into account in the racket design process.

The present work had two objectives : On the one hand, to provide a triple methodological contribution to the analysis of motor coordination. Firstly, this contribution consists in analysing the sensibility of an inverse dynamics procedure to the quality of the anthropometric input data. A recommendation for the use of a BSP estimation method was provided to compute the net joint moments in a better way. Secondly, an evolution of a biomechanical model that includes the kinematics, BSP, groud reaction and EMG as input data into a numerical optimization process was proposed to estimate the moments developed by the knee flexor and extensor muscle groups under muscle fatigue condition. The loss of force production capacity due to fatigue was taken into account in the numerical procedure by means of a frequency analysis of the EMG signal. The spectral analysis was carried out using wavelet transform. Thirdly, a procedure was developed to estimate the individual muscle tension with an optimal prediction of the co-contraction. On the other hand, an analysis of the muscular coordination was carried out during squat exercises when faced with either an internal or an external perturbation. The external perturbation results from supplementary loads added to the subjects while muscle fatigue of the agonist muscle group qualified the internal perturbation. Our results show an exploitation of the muscle redundancy both to stabilize the joint and to produce coordinated motions. Moreover, the exploitation of the muscle redundancy in presence of fatigue differs from that observed when adding load. Thus, the Central Nervous System exploits differently, but always in an optimal sense, the muscular redundancy when faced with a perturbation., Ce travail doctoral poursuivait deux objectifs : D'une part, proposer une triple contribution méthodologique à l'analyse de la coordination motrice. Cette contribution consiste premièrement à analyser la sensibilité des résultats d'une procédure de dynamique inverse à la qualité des données d'entrée anthropométriques et à proposer une recommendation quant à la méthode d'estimation des BSP à utiliser pour déterminer au mieux les moments musculaires nets. Deuxièmement, une évolution d'un modèle biomécanique associant des données périphériques de différente nature (cinématique, anthropométrie, torseur dynamique externe, EMG) dans une procédure d'optimisation numérique et permettant d'estimer les moments développés par les groupes musculaires agoniste et antagoniste de l'articulation du genou est présentée. Les évolutions apportées visent à prendre en compte la baisse de capacit'e de production de force du groupe musculaire dûe à la fatigue en se basant sur une analyse fréquentielle du signal EMG réalisée par une transformée en ondelettes. Troisièmement, une méthode d'estimation des tensions musculaires est développée avec pour objectif une prédiction optimale de l'activité musculaire antagoniste. D'autre part, analyser la coordination musculaire lors d'une tâche de "squat" réalisée en présence d'une perturbation interne ou externe des conditions de réalisation de la tâche. L'ajout d'une charge supplémentaire modifiait les conditions externes de réalisation de la tâche tandis que la présence d'une fatigue musculaire représentait une perturbation interne. Les résultats de l'analyse de la coordination musculaire montrent une exploitation de la redondance musculaire orientée vers la stabilité de l'articulation et la production de mouvements coordonnés. De plus, la gestion de cette redondance en présence de fatigue diffère de celle observée lors de l'ajout d'une charge. Le Système Nerveux Central exploite donc différemment, mais toujours de manière optimale, la redondance musculaire pour faire face à une perturbation.