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The wrist and finger extensors play a crucial role in the muscle coordination during grasping tasks. Nevertheless, few data are available regarding their force-generating capacities. The objective of this study was to provide a model of the force-length-activation relationships of the hand extensors using non-invasive methods. The extensor carpi radialis (ECR) and the extensor digitorum communis (EDC) were studied as representative of wrist and finger extensors. Ten participants performed isometric extension force-varying contractions in different postures on an ergometer recording resultant moment. The joint angle, the myotendinous junction displacement and activation were synchronously tracked using motion capture, ultrasound and electromyography. Muscle force was estimated via a musculoskeletal model using the measured joint angle and moment. The force-length-activation relationship was then obtained by fitting a force-length model at different activation levels to the measured data. The obtained relationships agreed with previously reported data regarding muscle architecture, sarcomere length and activation-dependent shift of optimal length. Muscle forces estimated from kinematics and electromyography using the force-length-activation relationships were comparable, below 15% differences, to those estimated from moment via the musculoskeletal model. The obtained quantitative data provides a new insight into the different muscle mechanics of finger and wrist extensors. Graphical abstract By combining in vivo data (kinematics, dynamometry, electromyography, ultrasonography) during isometric force-varying contractions with musculoskeletal modelling, the force-length-activation relationships of both finger and wrist extensors were obtained. The results provided a new insight into the role of hand extensors in the generation and control of hand movements.

Ankle sprains are the most common injury in regular badminton players and usually occur at the end of a match or training. The purpose of the present study was to examine the influence of fatigue produced by badminton practice on the lower limb biomechanics of badminton players. It was hypothesized that fatigue induces ankle kinematic and lower leg muscle activity changes which may increase the risk of ankle sprain. Ankle kinematics, ankle kinetics and muscles activities of 17 regular badminton players were recorded during lateral jumps before and after an intense badminton practice session. Post-fatigue, ankle inversion at foot strike and peak ankle inversion increased (+2.6°

Although shoe friction has been widely studied in occupational ergonomics, information was lacking about friction in sport shoes. The purpose of the study was to examine the neuromechanical adaptations to different shoe-surface interface in an aerobic-gym specific movement. Sixteen females performed 10 change of direction movements in two shoe conditions differing by their outsoles (ethyl-vinyl-acetate: EVA and rubber: RB) to ensure significant differences in mechanical coefficients of friction (EVA = 0.73 ± 0.07 and RB = 1.46 ± 0.15). The kinematics, kinetics and muscle activities of the right lower-limb were analysed. Statistical parametric mapping was used to investigate the kinematics and kinetics adaptation to the different shoe-surface coefficients of friction. The participants had a longer stance duration in the EVA compared to the RB condition (526 ± 160 ms vs. 430 ± 151 ms, p .001). The ankle and knee joints powers and works were lower during both the braking and the push-off phases in the EVA as compared to the RB condition. Preactivation of the agonist muscles (soleus, gastrocnemius medialis and vastus medialis) decreased in the EVA compared to the RB condition (-28.5%, -26.5% and -49.0%, respectively). Performing a change of direction movement with slippery shoes reduced the ankle and knee joints loadings, but impaired the stretch-shortening cycle performance. Participants demonstrated thus a different neuromechanical strategy to control their movement which was associated with a reduced performance.

Summary Objective Epidemiological studies examined injuries in European and Asian badminton players but no study directly compared these 2 populations. Therefore, the objective of this study was to examine whether differences existed between French and Chinese regular badminton players (RBP) in terms of injury. Methods An online questionnaire was completed by 113 French and 117 Chinese RBP. The two populations were matched for distribution of genders, ages, skill levels and badminton exposure. Chi-square tests (χ2) were conducted to determine differences in injuries distribution between the two populations. Results A higher percentage of French RBP reported to have experienced at least one injury over the 5 past years compared with Chinese RBP (66% vs. 45%, respectively, χ2 = 10.3, P = 0.001). For the upper limb, French players experienced more shoulder/arm injuries (59% vs. 32%, respectively, P Conclusions The most common injury reported was the ankle sprain, which generally occurred during a jump landing upon backward and lateral movements (60%) or during forward lunge (26%). As more than half of the ankle sprains were moderate or severe, a particular attention should be paid to the effects of footwear and court surface characteristics on the biomechanics of badminton players.

Resume Objectifs L’objectif de cette revue etait d’examiner, chez les enfants, l’influence des chaussures minimalistes sur la biomecanique de course et d’etablir une analyse theorique de l’influence de ce type de chaussure sur le risque de blessure. Actualites Entre 8 et 15 ans, les stress repetes induits par la pratique sportive reguliere et les poussees de croissance que connaissent les enfants sportifs les rendent enclins aux blessures de sur-sollicitation. Les plus communes pour le membre inferieur sont les maladies d’Osgood-Schlatter et de Sever. Le premier lien entre le corps et le sol etant la chaussure, cette derniere peut etre de premiere importance concernant le risque d’apparition de ces pathologies. Il est suggere que l’utilisation de chaussures minimalistes modifierait la biomecanique de course et donc potentiellement le risque de blessure. Perspectives et projets De futures investigations sont necessaires pour identifier, au cours du temps, si les enfants adaptent ou non leur motricite a l’utilisation de chaussures minimalistes et si le port de ces dernieres influence le risque de blessure de sur-sollicitation. Conclusion Par rapport aux chaussures conventionnelles, l’utilisation de chaussures minimalistes induit generalement un placement du pied plus a plat avec une cheville plus en flexion plantaire lors de l’impact avec le sol et une flexion du genou moins importante pendant la phase d’appui. Il semble que ces modifications conduisent a une reduction des forces de tension au niveau du genou et qu’elles pourraient diminuer le risque de maladie d’Osgood-Schlatter. Concernant la maladie de Sever, l’analyse biomecanique n’est pas concluante a cause de la complexite de sa patho-mecanique. Le port de chaussures minimalistes devrait diminuer les forces compressives sous le talon par une redistribution de la pression sur l’ensemble de la face plantaire ou sous l’avant-pied mais pourrait en contrepartie augmenter les forces de tension au niveau de l’insertion du tendon d’Achille sur le calcaneum.

IF=0.885; International audience; Footwear fit is very important in tennis, directly influencing comfort, security and performance. Within the current literature, there are no in-depth studies regarding the fit of tennis shoes, resulting in a lack of knowledge regarding the effect of player expertise on fit preference. Therefore, the main purpose of this study was to determine optimal inner-shoe dimensions for tennis players. A total of 34 tennis players were recruited and divided into two groups based on frequency of play (occasional and regular). Each subject’s feet were measured, and they were then asked to assess each of the four tennis shoes, which varied in dimension, through the use of a questionnaire. A repeated measure analysis of variance and Pearson’s correlation coefficient were performed to analyse shoe–foot dimensional difference and subjective fit rating. The analysis of variance revealed significant differences on fit rating between shoes. Correlations were found between shoe–foot dimensional differences at length, metatarsal width and metatarsal girth. The optimal shoe length was determined to be nearly 10 mm longer than the foot for both occasional and regular players; the optimal shoe metatarsal width was 8.4 mm less than the foot for regular players; the optimal shoe metatarsal girth was 9.5 mm less than the foot for occasional players and 14.7 mm less than the foot for regular players.

International audience; Introduction Because the hand joints possess a broad range of motion, the muscle length can vary importantly which might result in significant variations of the muscle force-generating capacities. However, facing the complexity of this musculoskeletal system, no study has examined the effect of hand muscle length change on muscle force. This study aimed to characterize the force-length relationship of muscles involved in wrist and metacarpophalangeal flexion.Methods Eleven participants performed two sessions: (i) one for the wrist flexor muscles and (ii) one for the finger flexor muscles. For each session, the participants performed two maximal voluntary contractions and then two progressive isometric ramps from 0% to 100% of their maximal force capacity at five different wrist/metacarpophalangeal angles. Torque, kinematic, and electromyographic data were recorded. An ultrasound scanner was used to measure the myotendinous junction displacement of flexor carpi radialis (FCR) and flexor digitorum superficialis (FDS) during isometric contractions. A three-dimensional relationship between muscle length, force, and activation level was modeled using optimization procedure.Results Globally, the FCR was stronger and shorter compared with FDS. The results showed that the three-dimensional relationships fitted well the experimental data (mean R-2 = 0.92 0.07 and 0.87 +/- 0.11 for FCR and FDS, respectively). Using joint angle and EMG data, this approach allows to estimate the muscle force with low estimation errors (9% of F-max).Conclusions This study proposes a new method to investigate the force-length relationship by combining ultrasound measurement, musculoskeletal modeling and optimization procedures. The data and relationships provide a new insight into hand biomechanics and muscle function that could be useful for designing hand tools or surgical operations.

Badminton is a popular sport practiced by more than 200 millions of players (Fahlstrom & Soderman, 2007). Due to the rapidity of the game, the repetition and the intensity of the player’s movements...

International audience

Worldwide, tennis is practiced by millions of children, several thousands being intensive players. The participation in high-performance training programmes and competition places them at risk to e...

International audience; Athletic children are prone to overuse injuries, especially at the heel and knee. Since footwear is an extrinsic factor of lower limb injury risk, the aim of this study was to assess the influence of shoe aging on children running biomechanics. Fourteen children active in sports participated in a laboratory biomechanical evaluation. A new pair of shoes was provided to each participant at an inclusion visit. Four months later, the participants performed a running task and their kinematics and kinetics were assessed both with their used shoes and with a new pair of shoes identical to the first. Furthermore, mechanical cushioning properties of shoes were evaluated before and after in-vivo aging. After 4 months of use, the sole stiffness increased by 16% and the energy loss capacity decreased by 18% (p < 0.001). No ankle or knee kinematic adjustment was found at foot strike in used shoes but changes were observed later during stance. Running with used shoes produced a higher loading rate of the vertical ground reaction force (+ 23%, p = 0.016), suggesting higher compressive forces under the heel and placing children at risk to experience impact-related injuries. Nevertheless, the decreased peak ankle and knee power absorption in used shoes (-11%, p = 0.010 and -12%, p = 0.029, respectively) suggests a lower ankle and knee joints loading during the absorption phase that may be beneficial regarding stretch-related injuries.

International audience; Compared to traditional tennis shoes, using 0-drop shoes was shown to induce an immediate switch from rear- to forefoot strike pattern to perform an open stance tennis forehand for 30% of children tennis players. The purpose of the study was to examine the long-term effects of a gradual reduction in the shoe drop on the biomechanics of children tennis players performing open stance forehands. Thirty children tennis players participated in 2 laboratory biomechanical test sessions (intermediate: +4 months and final: +8 months) after an inclusion visit where they were randomly assigned to control (CON) or experimental (EXP) group. CON received 12-mm-drop shoes twice, whereas EXP received 8mm then 4-mm-drop shoes. Strike index indicated that all CON were rearfoot strikers in intermediate and final test sessions. All EXP were rearfoot strikers in intermediate test session, but half the group switched towards a forefoot strike pattern in final test session. This switch resulted in a decreased loading rate of the ground reaction force (-73%, p=.005) but increased peak ankle plantarflexors moment (+47%, p=.050) and peak ankle power absorption (+107%, p=.005) for these participants compared with CON. Biomechanical changes associated with the long-term use of partial minimalist shoes suggest a reduction in heel compressive forces but an increase in Achilles tendon tensile forces.

IF=1.55; International audience; This study investigated the immediate effects of reducing the shoe drop (i.e. the difference between the heel and the forefoot height) on the kinematics and kinetics of the lower extremities of children tennis players performing a tennis-specific movement. Thirteen children tennis players performed a series of simulated open stance forehands wearing 3 pairs of shoes differing only in the drop: 0 (D0), 6 (D6) and the control condition of 12mm (D12). Two embedded forceplates and a motion capture system were used to analyse the ground reaction forces and ankle and knee joint angles and moments of the leading lower limb. In D6 compared with D12, the peak impact force was reduced by 24% (p=.004) and the ankle was less dorsiflexed at foot strike (p=.037). In D0 compared with D12, the peak impact force was reduced by 17% (p=.049), the ankle was less dorsiflexed at foot strike (p=.045) and the knee was more flexed at foot strike (p=.007). In addition, 4 out of 13 participants (31%) presented a forefoot strike pattern for some of the trials in D0. No difference was observed across shoe conditions for the peak knee extensor moment (p=.658) or the peak ankle plantarflexor moment (p=.071). The results provide preliminary data supporting the hypothesis that for children tennis players, using a 6-mm lower shoe drop might reduce heel impact forces and thus limit potentially impact-related injuries.

IF=1.56; International audience; Footwear comfort is essential and pressure distribution on the foot was shown as a relevant objective measurement to assess it. However, asperities on the foot sides, especially the metatarsals and the instep, make its evaluation difficult with available equipment. Thus, a sock equipped with textile pressure sensors was designed. Results from the mechanical tests showed a high linearity of the sensor response under incremental loadings and allowed to determine the regression equation to convert voltage values into pressure measurements. The sensor response was also highly repeatable and the creep under constant loading was low. Pressure measurements on human feet associated with a perception questionnaire exhibited that significant relationships existed between pressure and comfort perceived on the first, the third and the fifth metatarsals and top of the instep. Practitioner Summary: A sock equipped with textile sensors was validated for measuring the pressure on the foot top, medial and lateral sides to evaluate footwear comfort. This device may be relevant to help individuals with low sensitivity, such as children, elderly or neuropathic, to choose the shoes that fit the best.

IF=1.866; International audience; The purpose of this study was to determine the optimal inner-shoe volume for children tennis players. Sixteen participants, aged from 8 to 12 years old assessed comfort of 6 shoes, which were a combination of 3 lasts (thin, medium and wide) and 2 upper constructions (flexible and stiff), while a sock equipped with textile sensors was measuring the pressure applied on their foot. The thin last was based on the proportion of an adult last. The widest shoes produced the lowest pressure on the 1st and 5th metatarsal heads, the medial midfoot and the medial and lateral heel (p < 0.05), whilst they were perceived the most comfortable for the 3rd and 5th metatarsal heads, the 5th metatarsal base and the medial and lateral heel (p < 0.05). These outcomes indicated that footwear manufacturers should design wider shoes for children than for adults

Tennis is practised by a large number of children. This sport is characterised by repeated high-intensity runs comprising acceleration–decelerations and changes of direction, which generate large b...