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International audience; Aim: Defining the origins of muscle injury has important rehabilitation and exercise applications. However, current knowledge of muscle damage mechanics in human remains unclear in vivo. This study aimed to determine the relationships between muscle–tendon unit mechanics during maximal eccentric contractions and the extent of subsequent functional impairments induced by muscle damage.Methods: The length of the muscle–tendon unit, fascicles and tendinous tissues was continuously measured on the gastrocnemius medialis using ultrasonography, in time with torque, during 10 sets of 30 maximal eccentric contractions of plantar flexors at 45°s -1, in seventeen participants.Results: Muscle–tendon unit, fascicles and tendinous tissues were stretched up to 4.44 ± 0.33 cm, 2.31 ± 0.64 cm and 1.92 ± 0.61 cm respectively. Fascicle stretch length, lengthening amplitude and negative fascicle work beyond slack length were significantly correlated with the force decrease 48 h post-exercise (r=0.51, 0.47 and 0.68, respectively; P

International audience

Eccentric training is a mechanical loading classically used in clinical environment to rehabilitate patients with tendinopathies. In this context, eccentric training is supposed to alter tendon mechanical properties but interaction with the other components of the muscle-tendon complex remains unclear. The aim of this study was to determine the specific effects of 14 wk of eccentric training on muscle and tendon mechanical properties assessed in active and passive conditions in vivo. Twenty-four subjects were randomly divided into a trained group ( n = 11) and a control group ( n = 13). Stiffness of the active and passive parts of the series elastic component of plantar flexors were determined using a fast stretch during submaximal isometric contraction, Achilles tendon stiffness and dissipative properties were assessed during isometric plantar flexion, and passive stiffness of gastrocnemii muscles and Achilles tendon were determined using ultrasonography while ankle joint was passively moved. A significant decrease in the active part of the series elastic component stiffness was found ( P < 0.05). In contrast, a significant increase in Achilles tendon stiffness determined under passive conditions was observed ( P < 0.05). No significant change in triceps surae muscles and Achilles tendon geometrical parameters was shown ( P > 0.05). Specific changes in muscle and tendon involved in plantar flexion are mainly due to changes in intrinsic mechanical properties of muscle and tendon tissues. Specific assessment of both Achilles tendon and plantar flexor muscles allowed a better understanding of the functional behavior of the muscle-tendon complex and its adaptation to eccentric training.

The aim of the present study was to compare the effects of ankle muscle fatigue on postural control when plantarflexors (PFs) and dorsiflexors (DFs) are fatigued simultaneously compared with separately. This study also investigated the recovery of postural control after fatigue. Sixteen adults (eight women and eight men) performed postural trials before and after an isokinetic fatigue task involving either (i) only PFs (308 s 1 ), (ii) only DFs (1208 s 1 ), or (iii) both PFs and DFs simultaneously. The fatigue task involved maximal contractions repeated until the torque produced decreased below 50% of the maximal torque. Postural trials lasted 30 s and were performed on one leg with eyes open (EO) or eyes closed (EC). Sway area, medio-lateral (ML) and antero-posterior (AP) positions and velocities were calculated from the center of pressure displacements. With EO, no effect of fatigue was found on postural variables. With EC, sway area and AP velocity increased only when both PFs and DFs were fatigued simultaneously. An effect of fatigue present only when both muscle groups are fatigued simultaneously could be due to impairment in the compensatory activity between agonist and antagonist muscles and/or a greater decrease in proprioception due to a greater number of fatigued muscles. In addition, when PFs and DFs were fatigued simultaneously, sway area and AP velocity returned to pre-fatigue values within 2 min, whereas a posterior shift in AP position persisted for 10 min. This last result may suggest a longer-lasting change in postural strategy needed for optimal postural control.

The aims of this study were to determine the effects of plyometric training on both active and passive parts of the series elastic component (SEC) stiffness, and on geometrical parameters [i.e., muscle architecture, muscle and tendon cross-sectional area (CSA)] of the plantarflexors muscle-tendon complex to assess possible specific adaptations of the elastic properties. Nineteen subjects were randomly divided into a trained group and a control group. Active and passive components of the SEC stiffness were determined using a fast stretch during submaximal voluntary isometric plantarflexor activity. Geometrical parameters of the triceps surae muscles and the Achilles tendon were determined using ultrasonography. A significant increase in the passive component of the SEC stiffness was found (p0.05). In contrast, a significant decrease in the active part of the SEC stiffness was observed (p0.05). No significant changes in plantarflexor muscles CSA, architecture and Achilles tendon CSA were seen (p0.05). Thus, plyometric training led to specific adaptations within each part of the SEC. Theses adaptations could increase both the efficiency of the energy storage-recoil process and muscular tension transmission leading to an increase in jump performances.

The aim of this study was to determine whether high inter-individual variability of the electromyographic (EMG) patterns during pedaling is accompanied by variability in the pedal force application patterns. Eleven male experienced cyclists were tested at two submaximal power outputs (150 and 250 W). Pedal force components (effective and total forces) and index of mechanical effectiveness were measured continuously using instrumented pedals and were synchronized with surface electromyography signals measured in ten lower limb muscles. The intersubject variability of EMG and mechanical patterns was assessed using standard deviation, mean deviation, variance ratio and coefficient of cross-correlation (\( \overline {R_{0} } , \) with lag time = 0). The results demonstrated a high intersubject variability of EMG patterns at both exercise intensities for biarticular muscles as a whole (and especially for Gastrocnemius lateralis and Rectus femoris) and for one monoarticular muscle (Tibialis anterior). However, this heterogeneity of EMG patterns is not accompanied by a so high intersubject variability in pedal force application patterns. A very low variability in the three mechanical profiles (effective force, total force and index of mechanical effectiveness) was obtained in the propulsive downstroke phase, although a greater variability in these mechanical patterns was found during upstroke and around the top dead center, and at 250 W when compared to 150 W. Overall, these results provide additional evidence for redundancy in the neuromuscular system.

CCC:000355836600018; International audience; Objective: In contrast to conventional (CONV) neuromuscular electrical stimulation (NMES), the use of "wide-pulse, high-frequencies" (WPHF) can generate higher forces than expected by the direct activation of motor axons alone. We aimed at investigating the occurrence, magnitude, variability and underlying neuromuscular mechanisms of these "Extra Forces" (EF). Methods: Electrically-evoked isometric plantar flexion force was recorded in 42 healthy subjects. Additionally, twitch potentiation, H-reflex and M-wave responses were assessed in 13 participants. CONV (25 Hz, 0.05 ms) and WPHF (100 Hz, 1 ms) NMES consisted of five stimulation trains (20 s on-90 s off). Results: K-means clustering analysis disclosed a responder rate of almost 60%. Within this group of responders, force significantly increased from 4% to 16% of the maximal voluntary contraction force and H-reflexes were depressed after WPHF NMES. In contrast, non-responders showed neither EF nor H-reflex depression. Twitch potentiation and resting EMG data were similar between groups. Interestingly, a large inter-and intrasubject variability of EF was observed. Conclusion: The responder percentage was overestimated in previous studies. Significance: This study proposes a novel methodological framework for unraveling the neurophysiological mechanisms involved in EF and provides further evidence for a central contribution to EF in responders. (C) 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

International audience; Purpose: The purpose of this study was to compare neuromuscular adaptations induced by work-matched isoload (IL) versus isokinetic (IK) eccentric resistance training. Methods: A total of 31 healthy subjects completed a 9-wk IL (n = 11) or IK (n = 10) training program for the knee extensors or did not train (control group; n = 10). The IL and IK programs consisted of 20 training sessions, which entailed three to five sets of eight repetitions in the respective modalities. The amount of work and the mean angular velocity were strictly matched between IL and IK conditions. Neuromuscular tests were performed before and after training and consisted of the assessment of quadriceps muscle strength, muscle architecture (vastus lateralis), EMG activity, and antagonist coactivation. Results: IL, but not IK, eccentric resistance training enhanced eccentric strength at short muscle length (+20%), high-velocity eccentric strength (+15%), muscle thickness (+10%), and fascicle angle measured at rest (+11%; P G 0.05). Agonist EMG activity increased almost similarly for the two modalities, whereas antagonist coactivation was unaffected by training. Conclusions: IL proved to be more effective than IK training for improving quadriceps muscle strength and structure. It is conjectured that the rapid acceleration of the load in the early phase of IL eccentric movements (i.e., at short muscle lengths), which results in greater torque and angular velocities compared with IK actions, is the main determinant of strength and neuromuscular adaptations to eccentric training. These findings have important consequences for the optimization of IL and IK eccentric exercise for resistance training and rehabilitation purposes.

The assessment of Achilles tendon mechanical properties in vivo has received much attention in the literature. Many studies investigated mechanical properties by assessing tendon stiffness. Despite tendon dissipative properties being representative of a storage-recoil process, its determination has received minimal attention in the literature. The aim of this study was to determine if Achilles tendon stiffness is associated with dissipative properties. The cross-sectional area, stiffness and dissipation coefficient of the Achilles tendon were measured in 35 subjects. No significant correlation was found between stiffness and the dissipation coefficient, irrespective of stiffness normalization with cross-sectional area (P > 0.05). Thus, it appears that both stiffness and dissipative properties must be assessed to determine the storage-recoil process capacities of the Achilles tendon in order to precisely characterize changes in the tendon mechanical properties after chronic interventions or rehabilitation programs.

To evaluate the physiological demands and effects of different pacing strategies on performance during the new combined event (CE) of the modern pentathlon (consisting of three pistol shooting sessions interspersed by three 1-km running legs). Nine elite pentathletes realised five tests: a free-paced CE during an international competition; an incremental running test to determine \( \dot{V}{\text{O}}_{{2\max }} \) and its related velocity (\( v\dot{V}{\text{O}}_{{2\max }} \)) and three experimental time-trial CE, where the pacing strategy was manipulated (CEref, CE100%, CE105%). CEref reproduced the international competition strategy with a 170-m fast running start within the first 2 km. CE100% and CE105% imposed a constant strategy over km-1 and km-2 with a velocity of 100 and 105% of the mean speed adopted over the same sections during the international competition, respectively. Km-3 was always self-paced. The subjects ran CEref at 99 ± 4% of \( v\dot{V}{\text{O}}_{{2\max }} \) and reached 100 ± 5, 100 ± 7, 99 ± 8% of \( \dot{V}{\text{O}}_{{2\max }} \) at the end of kilometres 1, 2 and 3, respectively (\( \dot{V}{\text{O}}_{{2\max }} \): 72 ± 6 mL O2 min−1 kg−1), with a peak blood lactate concentration of 13.6 ± 1.5 mmol L−1. No significant differences in overall performance were found between the pacing conditions (753 ± 30, 770 ± 39, 768 ± 27 s for CEref, CE100% and CE105%, respectively, p = 0.63), but all of the shooting performance parameters were only stable in CEref. Completion of CE by elite pentathletes elicits a maximal aerobic contribution coupled with a high glycolytic supply. Manipulating the mean running speed over km-1 and km-2 had strong influence on the overall pacing strategy and induced minor differences in shooting performance, but it did not affect overall performance.

The aim of this study was to determine the effects of 14 wk of plyometric training on mechanical properties of the Achilles tendon. Nineteen subjects were randomly assigned to trained or control group. Cross-sectional area (CSA), stiffness, and dissipation coefficient of the Achilles tendon were measured before and after the training period. In the trained group, a decrease in dissipation coefficient (−35.0%; P < 0.05) and an upward trend in stiffness (+24.1%) of the Achilles tendon was found, without any changes in Achilles tendon CSA ( P > 0.05). Plyometric training enhances the muscular tension transmission mainly through a reduction in energy dissipated by the tendon. The lack of changes in the Achilles tendon CSA indicates that changes in mechanical properties would mainly result from a qualitative change in tendinous tissues rather than from changes in the geometry of the Achilles tendon.

The aim of this study was to investigate the reliability of an in vivo adaptation of the short range stiffness experiment associated with the application of a mathematical model to determine the stiffness of both torque dependent and independent components of the plantarflexors series elastic component. Fourteen subjects participated in this study. The experimental protocol consisted of quickly moving the ankle joint in dorsiflexion during constant voluntary isometric plantarflexion at 7 submaximal torque levels. Relationships between joint stiffness and torque were established and the stiffness of both torque dependent and independent components were determined using the alpha method. The day-to-day reliability was assessed for joint stiffness and stiffness of both torque dependent and independent components (ICC higher than 0.88 and CVs lower than 6.0%). This method could then be used to better understand adaptive subjacent mechanisms to assess the effects of training protocols, and the rehabilitation of neuromuscular pathologies or traumatisms.

International audience; The present study aimed to standardize isotonic (IT) and isokinetic (IK) eccentric exercises by equalizing the amount of work and the angular velocity at two intensity levels, to be able to compare specific effects of these exercise modes on the neuromuscular system. Fourteen subjects participated in three test sessions consisting of two IT and two IK sets on a customized isokinetic dynamometer. IT sets were comprised of 8 eccentric contractions of the knee extensors at 120% of the maximal repetition (1RM) in the first two sessions, and 100% in the third session. IK sets were performed at the same mean angular IT velocity and stopped when the amount of work performed corresponded to the IT set. External work, angular velocity and Root Mean Square (RMS) of electromyographic activity of three superficial muscles of the quadriceps femoris were calculated. Results showed concordance of work and angular velocity for each test session. Both modes involved the same number of repetitions at 120% and fewer repetitions in IK mode at 100% of 1RM. Work and RMS values remained steady in all sets. This study allowed the standardization of isotonic and isokinetic eccentric exercises, a first step before determining their specific effects on neuromuscular function.

While the passive mechanical properties of a musculo-articular complex can be determined using the relationship between the articular angle and the passive torque developed in resistance to motion, the properties of different structures of the musculo-articular complex cannot be easily assessed. Recently, an elegant method has been proposed to estimate the passive length–tension properties of gastrocnemius muscle–tendon unit ( Hoang et al., 2005 ). In the present paper, two improvements of this method are proposed to decrease the number of parameters required to assess the passive length–tension relationship from 9 to 2. Furthermore, these two parameters have physical meaning as they represent a passive muscle–tendon stiffness index ( α ) and the muscle–tendon slack length ( l 0 ). α and l 0 are relevant clinical parameters to study the chronic effects of aging, training protocols or neuromuscular pathologies on the passive mechanical properties of the muscle–tendon unit. Eight healthy subjects performed passive loading/unloading cycles at 5°/s with knee angle at 6 knee angles to assess the torque–angle relationships and to apply the modified method. Numerical optimization was used to minimize the squared error between the experimental and the modeled relationships. The experiment was performed twice to assess the reliability of α and l 0 across days. The results showed that the reliability of the two parameters was good ( α : ICC=0.82, SEM=6.1 m −1 , CV=6.3% and l 0 : ICC=0.83, SEM=0.29 cm, CV=0.9%). Using a sensitivity analysis, it was shown that the numerical solution was unique. Overall, the findings may provide increased interest in the method proposed by Hoang et al. (2005) .

International audience; The purpose of this study was to investigate the influence of upper-limb inertia on the force-velocity relationship and maximal power during concentric bench press exercise. Reference peak force values (Fpeakp) measured with a force plate positioned below the bench were compared to those measured simultaneously with a kinematic device fixed on the barbell by taking (Fpeakt) or not taking (Fpeakb) upper-limb inertia into account. Thirteen men (27.8 6 4.1 years, 184.6 6 5.5 cm, 99.5 6 18.6 kg) performed all-out concentric bench press exercise against 8 loads ranging between 7 and 74 kg. The results showed that for each load, Fpeakb was significantly less than Fpeakp (P , 0.0001), whereas no significant difference was found between Fpeakp and Fpeakt. The values of maximal force (F0), maximal velocity (V0), optimal velocity (Vopt), and maximal power (Pmax), extrapolated from the force-and power-velocity relationships determined with the kinematic device, were significantly underestimated when upper-limb inertia was ignored. The results underline the importance of taking account of the total inertia of the moving system to ensure precise evaluation of upper-limb muscular characteristics in all-out concentric bench press exercise with a kinematic device. A major application of this study would be to develop precise upper-limb muscular characteristic evaluation in laboratory and field conditions by using a simple and cheap kinematic device.

Passive muscle stretching can be used in vivo to assess the viscoelastic properties of the entire musculo-articular complex, but does not allow the specific determination of the muscle or tendon viscoelasticity. In this respect, the local muscle hardness (LMH) of the gastrocnemius medialis (GM) belly was measured during a passive ankle stretching of 10 subjects using transient elastography. A Biodex isokinetic dynamometer was used to stretch ankle plantar flexors, to measure ankle angle, and the passive torque developed by the ankle joint in resistance to the stretch. Results show that the LMH increased during the stretching protocol, with an averaged ratio between maximal LMH and minimal LMH of 2.6270.46. Furthermore, LMH–passive torque relationships were nicely fitted using a linear model with mean correlation coefficients (R 2 ) of 0.82870.099. A good reproducibility was found for the maximal passive torque (ICC ¼ 0.976, SEM ¼ 2.9 N m, CV ¼ 5.5%) and the y-intercept of the LMH–passive torque relationship (ICC ¼ 0.893, SEM ¼ 105 Pa, CV ¼ 7.8%). However, the reproducibility was low for the slope of this relationship (ICC ¼ 0.631, SEM ¼ 10.35 m � 2 ,C V¼ 60.4%). The y-intercept of the LMH–passive torque relationship was not significantly changed after 10 min of static stretching. This result confirms the finding of a previous study indicating that changes in passive torque following static stretching could be explained by an acute increase in muscle length without any changes in musculo-articular intrinsic mechanical properties. r 2008 Elsevier Ltd. All rights reserved.

International audience

Characterization of interpersonal coordination modes within a basket-ball team. The aim of our study was to analyze the construction of a collective activity. We focused on interpersonal coordination process within a basket-ball team during a match. We characterized the way how basketball players took mutually into account their respective activities. In order to consider in the same time both units of analysis, the individual one and the collective one, this study referred to the framework of the course of action theory (Theureau, 2006). Results allowed us to specify the relational network between players, the various coordination modes between two players and the different forms of team coordination. These results are discussed with regard to the nature of interactions within the team, and with regard to the notion of a collective action plan : they highlighted that some collective activity construction modalities are based on local overlapping coordination. These results thus question the status of a collective plan (as a scheme shared by all the players)., Caractérisation de modes de coordination interpersonnels dans une équipe de basket-ball. Le but de notre étude était d'analyser la construction d'une activité collective. Nous nous sommes concentrés sur le processus de coordination interpersonnel dans une équipe de basket-ball pendant un match(une allumette). Nous avons caractérisé la voie comment les basketteurs ont pris mutuellement en considération leurs activités respectives. Pour considérer dans le même temps les deux unités d'analyse, le individuel et le collectif, cette étude a mentionné la structure du cours de théorie d'action (Theureau, 2006). Les résultats nous ont permis de spécifier le réseau relationnel entre des acteurs(joueurs), les modes de coordination divers entre deux acteurs(joueurs) et les formes(formulaires) différentes de coordination d'équipe. Ces résultats sont discutés en ce qui concerne la nature d'interactions dans l'équipe et en ce qui concerne la notion d'un plan d'action collectif : ils ont mis en évidence(ont surligné) ces quelques modalités de construction d'activité collectives sont basé sur la coordination de chevauchement locale. Ces résultats mettent ainsi en doute le statut d'un plan collectif (comme un plan(arrangement) partagé par tous les acteurs(joueurs)).

Cette étude porte sur un " format pédagogique " ancien et très répandu : le cours dialogué. À partir d'une étude en géographie, à l'école primaire, l'activité en classe a été analysée à deux niveaux, individuel et collectif. Les préoccupations et émotions qui orientent l'activité individuelle de l'enseignante et des élèves ont été décrites. Puis, à partir de l'enchaînement des questions, réponses et évaluations, des structures d'articulation des activités individuelles ont été identifiées. Elles ont permis de modéliser le cours dialogué et de mettre en évidence sa stabilité et sa viabilité. Nous considérons que ces caractéristiques contribuent à expliquer sa pérennité et sa vitalité.