Search

This study aimed to quantify in- and between-match characteristics and mechanical workload variations elicited by a congested schedule in high-level female ice hockey. Six players were monitored during four international pre-season exhibition matches against the same opponent. Two different methods (Player Load and Accel'Rate) were used to assess specific mechanical workload. Number of shifts and effective playing time per shift were significantly higher for period 2 (p = 0.03 for both). Mechanical workload intensity (i.e., relative and peak workload) showed a significant (p ≤ 0.05) decrease from period 1 to period 2 and period 3 (

The application of a series of extremely high accelerative motor-driven quick releases while muscles contract isometrically (i.e. slack test) has been proposed to assess unloaded velocity in human muscle. This study aimed to measure gastrocnemius medialis fascicle (VF) and tendinous tissues shortening velocity during motor-driven quick releases performed at various activation levels to assess the applicability of the slack test method in human. Maximal fascicle shortening velocity and joint velocity recorded during quick releases and during fast contraction without external load (ballistic condition) were compared. Gastrocnemius medialis fascicle behaviour was investigated from 25 participants using high-frame rate ultrasound during quick releases performed at various activation levels (from 0% to 60% of maximal voluntary isometric torque) and ballistic contractions. Unloaded joint velocity calculated using the slack test method increased whereas VF decreased with muscle activation level (P≤0.03). Passive and low-level quick releases elicited higher VF values (≥ 41.4±9.7 cm.s−1) compared to ballistic condition (36.3±8.7 cm.s−1), while quick releases applied at 60% of maximal voluntary isometric torque produced the lowest VF. These findings suggest that initial fascicle length, complex fascicle-tendon interactions, unloading reflex and motor-driven movement pattern strongly influence and limit the shortening velocity achieved during the slack test. Furthermore, VF elicited by quick releases is likely to reflect substantial contributions of passive processes. Therefore, the slack test is not appropriate to assess maximal muscle shortening velocity in vivo.

The objective of this study was to characterize the mechanics of maximal running sprint acceleration in high-level athletes. Four elite (100-m best time 9.95-10.29 s) and five sub-elite (10.40-10.60 s) sprinters performed seven sprints in overground conditions. A single virtual 40-m sprint was reconstructed and kinetics parameters were calculated for each step using a force platform system and video analyses. Anteroposterior force (FY), power (PY), and the ratio of the horizontal force component to the resultant (total) force (RF, which reflects the orientation of the resultant ground reaction force for each support phase) were computed as a function of velocity (V). FY-V, RF-V, and PY-V relationships were well described by significant linear (mean R(2) of 0.892 ± 0.049 and 0.950 ± 0.023) and quadratic (mean R(2) = 0.732 ± 0.114) models, respectively. The current study allows a better understanding of the mechanics of the sprint acceleration notably by modeling the relationships between the forward velocity and the main mechanical key variables of the sprint. As these findings partly concern world-class sprinters tested in overground conditions, they give new insights into some aspects of the biomechanical limits of human locomotion.

Purpose: The aim of this study was to evaluate concomitantly the changes in leg-spring behavior and the associated modifications in the lower limb muscular activity during a constant pace run to exhaustion at severe intensity. Methods: Twelve trained runners performed a running test at the velocity associated with _ VO 2max (5.1 70.3 m s −1 ; mean time to exhaustion: 3537 69 s). Running step spatiotemporal parameters and spring-mass stiffness were calculated from vertical and horizontal components of ground reaction force measured by a 6.60 m long force platform system. The myoelectrical activity was measured by wireless surface electrodes on eight lower limb muscles. Results: The leg stiffness decreased significantly (−8.9%; Po 0.05) while the vertical stiffness did not change along the exhaustive exercise. Peak vertical force (−3.5%; Po 0.001) and aerial time (−9.7%; P o0.001) decreased and contact time significantly increased (+4.6%; Po 0.05). The myoelectrical activity decreased significantly for triceps surae but neither vastus medialis nor vastus lateralis presented significant change. Both rectus and biceps femoris increased in the early phase of swing (+14.7%; P o0.05) and during the pre-activation phase (+16.2%; Po 0.05). Conclusion: The decrease in leg spring-stiffness associated with the decrease in peak vertical ground reaction force was consistent with the decline in plantarflexor activity. The biarticular rectus femoris and biceps femoris seem to play a major role in the mechanical and spatiotemporal adjustments of stride pattern with the occurrence of fatigue during such exhaustive run.

International audience; This study tested the relationship between the magnitude of muscle damage and both central and peripheral modulations during and after eccentric contractions of plantar flexors. Eleven participants performed 10 sets of 30 maximal eccentric contractions of the plantar flexors at 45 • ·s −1. Maximal voluntary torque, evoked torque (peripheral component) and voluntary activation (central component) were assessed before, during, immediately after (POST) and 48 h after (48 h) the eccentric exercise. Voluntary eccentric torque progressively decreased (up to −36%) concomitantly to a significant alteration of evoked torque (up to −34%) and voluntary activation (up to −13%) during the exercise. Voluntary isometric torque (−48 ± 7%), evoked torque (−41 ± 14%) and voluntary activation (−13 ± 11%) decreased at POST, but only voluntary isometric torque (−19 ± 6%) and evoked torque (−10 ± 18%) remained depressed at 48 h. Neither changes in voluntary activation nor evoked torque during the exercise were related to the magnitude of muscle damage markers, but the evoked torque decrement at 48 h was significantly correlated with the changes in voluntary activation (r = −0.71) and evoked torque (r = 0.77) at POST. Our findings show that neuromuscular responses observed during eccentric contractions were not associated with muscle damage. Conversely, central and peripheral impairments observed immediately after the exercise reflect the long-lasting reduction in force-generating capacity.

International audience; Purpose: Maximal cycling exercise has been widely used to describe the power-velocity characteristics of lower-limb extensor muscles. This study investigated the contribution of each functional sector (i.e., extension, flexion, and transitions sectors) on the total force produced over a complete pedaling cycle. We also examined the ratio of effective force to the total pedal force, termed index of mechanical effectiveness (IE), in explaining differences in power between subjects.Methods: Two-dimensional pedal forces and crank angles were measured during a cycling force-velocity test performed by 14 active men. Mean values of forces, power output, and IE over four functional angular sectors were assessed: top = 330°-30°, downstroke = 30°-150°, bottom = 150°-210°, and upstroke = 210°-330°.Results: Linear and quadratic force-velocity and power-velocity relationships were obtained for downstroke and upstroke. Maximal power output (P max ") generated over these two sectors represented, respectively, 73.6% ± 2.6% and 10.3% ± 1.8% of P max assessed over the entire cycle. In the whole group, P max over the complete cycle was significantly related to P max during the downstroke and upstroke. IE significantly decreased with pedaling rate, especially in bottom and upstroke. There were significant relationships between power output and IE for top and upstroke when the pedaling rate was below or around the optimal value and in all the sectors at very high cadences.Conclusions: Although data from force-velocity test primarily characterize the muscular function involved in the downstroke phase, they also reflect the flexor muscles' ability to actively pull on the pedal during the upstroke. IE influences the power output in the upstroke phase and near the top dead center, and IE accounts for differences in power between subjects at high pedaling rates.

Inspiratory premotor potentials reflect the involvement of premotor cortical networks in the compensation of mechanical respiratory loading. Electromagnetic pollution and movement artefacts make them difficult to record, particularly in clinical environment. In 7 healthy subjects, we tested a simplified recording setup (single vs. linked earlobe reference, bandwidth restriction from 0.05–500 to 0.1–500 Hz) to identify premotor potentials during volitional inspiratory manoeuvres. Pre-triggered ensemble averaging of Cz EEG epochs starting 2.5 s before the onset of inspiration was used to identify the potentials. The simplified setup reliably detected the potentials identified by the conventional setup (Cohen's Kappa score of 1). It slightly underestimated the slope of the potentials ( P = 0.0156). In conclusion, using a single earlobe reference and a restricted filtering bandwidth does not impair the detection of inspiratory premotor potentials. This could make the study of respiratory premotor potentials easier in difficult clinical environments.

International audience; The purpose of this study was to evaluate the accuracy and the reliability a new running computer system (RS800sd, Polar®, Kempele, Finland) which includes the measurement of running speed (RS) and stride rate (SR). Eight well-trained triathletes participated in this study. First, they completed an incremental continuous maximum test on a treadmill (from 12 km.h-1 9 to 18 km.h-1) at 0% grade. Secondly, the subjects took part in a second test to determine RS800sd intra-reproductibility to evaluate running speed. They ran twice during 5 minutes at a pace corresponding to their maximal lactate steady-state. During these two tests, RS and SR were recorded by the RS800sd system, by an optical sensor system (for RS) and a force-sensitive device (for SR). No difference was found between the RS800sd system and the reference systems both for RS (ICC=0.95) and SR (ICC=0.69). Moreover RS measures were statistically repeatable (r2=0.97, P

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.

Faced with mechanical inspiratory loading, awake animals and anaesthetized humans develop alveolar hypoventilation, whereas awake humans do defend ventilation. This points to a suprapontine compensatory mechanism instead of or in addition to the ‘traditional’ brainstem respiratory regulation. This study assesses the role of the cortical pre-motor representation of inspiratory muscles in this behaviour. Ten healthy subjects (age 19–34 years, three men) were studied during quiet breathing, CO2-stimulated breathing, inspiratory resistive loading, inspiratory threshold loading, and during self-paced voluntary sniffs. Pre-triggered ensemble averaging of Cz EEG epochs starting 2.5 s before the onset of inspiration was used to look for pre-motor activity. Pre-motor potentials were present during voluntary sniffs in all subjects (average latency (±s.d.): 1325 ± 521 ms), but also during inspiratory threshold loading (1427 ± 537 ms) and during inspiratory resistive loading (1109 ± 465 ms). Pre-motor potentials were systematically followed by motor potentials during inspiratory loading. Pre-motor potentials were lacking during quiet breathing (except in one case) and during CO2-stimulated breathing (except in two cases). The same pattern was observed during repeated experiments at an interval of several weeks in a subset of three subjects. The behavioural component of inspiratory loading compensation in awake humans could thus depend on higher cortical motor areas. Demonstrating a similar role of the cerebral cortex in the compensation of disease-related inspiratory loads (e.g. asthma attacks) would have important pathophysiological implications: it could for example contribute to explain why sleep is both altered and deleterious in such situations.

Epub 2015 Jul 17; Overground sprint studies have shown the importance of net horizontal ground reaction force impulse (IMPH) for acceleration performance, but only investigated one or two steps over the acceleration phase, and not in elite sprinters. The main aim of this study was to distinguish between propulsive (IMPH+) and braking (IMPH−) components of the IMPH and seek whether, for an expected higher IMPH, faster elite sprinters produce greater IMPH+, smaller IMPH−, or both.Nine high-level sprinters (100-m best times range: 9.95–10.60 s) performed 7 sprints (2×10 m, 2×15 m, 20 m, 30 m and 40 m) during which ground reaction force was measured by a 6.60 m force platform system. By placing the starting-blocks further from the force plates at each trial, and pooling the data, we could assess the mechanics of an entire “virtual” 40-m acceleration.IMPH and IMPH+ were significantly correlated with 40-m mean speed (r=0.868 and 0.802, respectively; P

Objectives: To determine whether the integrated electromyographic signal of two lower limb muscles indicates preferred cadence during a two hour cycling task. Methods: Eight male triathletes performed right isometric maximum voluntary contraction (MVC) knee extension and plantar flexion before (P1) and after (P2) a two hour laboratory cycle at 65% of maximal aerobic power. Freely chosen cadence (FCC) was also determined, also at 65% of maximal aerobic power, from five randomised three minute sessions at 50, 65, 80, 95, and 110 rpm. The integrated electromyographic signal of the vastus lateralis and gastrocnemius lateralis muscles was recorded during MVC and the cycle task. Results: The FCC decreased significantly (p Conclusion: The decrease in FCC observed at the end of the cycle task may be due to changes in the muscle fibre recruitment pattern with increasing exercise duration and cadence.

De nombreuses travaux ont pu suggerer qu'il serait possible d'ameliorer la vitesse de realisation d’un mouvement, en effectuant immediatement avant, un effort quasi maximal. Le but de ce travail est d'eprouver cette possibilite en mesurant les effets immediats d'un effort concentrique quasi maximal sur trois types d’efforts explosifs : un effort concentrique realise a vitesse maximale, un rebond pliometrique et un geste technique (le passement file remonte a l’appui tendu renverse). Methodologie : 20 gymnastes feminines, appartenant aux poles France et Espoirs de Creteil, Dijon, l'INSEP, Marseille et St Etienne (âge = 14.5 ans + 2) ont participe a cette etude. Protocole 1: combinaison de charge lourd-leger : l'effort explosif est un demi-squat a 30% du 1RM, realise dans une presse oblique a 45°, avant et immediatement apres l’effort quasimaximal. L’effort quasi maximal effectue dans la meme presse oblique, est compose d’une serie de 3 demi-squats a 85% de la force concentrique maximale du jour (1RM). Les vitesses du plateau mobile de la presse mesurees 50 et 100ms apres le debut du mouvement, ainsi que la vitesse maximale sont retenues comme indice de performance. Protocole 2 : combinaison concentrique - pliometrique : le rebond pliometrique, est effectue sur une plateforme de force type KISTLER , a partir d'un banc de 35 cm de haut, avant et immediatement apres l’effort quasi-maximal (3 demi-squats presse a 85% du 1RM). Le temps de vol, le temps de contact et le rapport temps de vol/temps de contact (reactivite) ont ete retenus comme indices de la performance sur cette epreuve. Analyses electromyographiques (EMG): dans les deux protocoles, l’activite EMG des principaux muscles agonistes (Vastus Medialis, Gactrocnemius) est enregistree pendant toute la duree des efforts. L’ EMG est quantifie en utilisant la valeur integree du signal (EMGi). Protocole 3 : combinaison concentrique - technique : la vitesse d’ouverture de l’angle brastronc au cours de la phase de remontee du corps vers l’equilibre, a ete analysee, avant et apres un effort d’antepulsion quasi maximal des bras, au moyen d’une analyse videographique 2D. Analyses statistiques : Les variations des indices de performances et des valeurs EMGi, avant et apres l’effort quasi maximal, ont ete analysees, au moyen d’une analyse de variance (ANOVA) par mesures repetees a deux facteurs (serie*avant/apres) au seuil p

International audience; This study aimed to evaluate the validity and test–retest reliability of trunk muscle strength testing performed with a latest-generation isokinetic dynamometer. Eccentric, isometric, and concentric peak torque of the trunk flexor and extensor muscles was measured in 15 healthy subjects. Muscle cross sectional area (CSA) and surface electromyographic (EMG) activity were respectively correlated to peak torque and submaximal isometric torque for erector spinae and rectus abdominis muscles. Reliability of peak torque measurements was determined during test and retest sessions. Significant correlations were consistently observed between muscle CSA and peak torque for all contraction types (r = 0.74À0.85; P < 0.001) and between EMG activity and submaximal isometric torque (r P 0.99; P < 0.05), for both extensor and flexor muscles. Intraclass correlation coefficients were comprised between 0.87 and 0.95, and standard errors of measurement were lower than 9% for all contraction modes. The mean difference in peak torque between test and retest ranged from À3.7% to 3.7% with no significant mean directional bias. Overall, our findings establish the validity of torque measurements using the tested trunk module. Also considering the excellent test–retest reliability of peak torque measurements, we conclude that this latest-generation isokinetic dynamometer could be used with confidence to evaluate trunk muscle function for clinical or athletic purposes.

International audience; Purpose: This study aimed to investigate the coordination of lower limb muscles during a specific fencing gesture in relation to its mechanical effectiveness. Methods: Maximal isokinetic concentric and isometric plantarflexor, dorsiflexor, knee and hip extensor and flexor torques of 10 female elite saber fencers were assessed and compared between both legs. Sabers completed three trials of a specific fencing gesture (i.e., marché-fente) on a 6.60-m-long force platform system. Surface EMG activities of 15 lower limb muscles were recorded in time with ground reaction forces and separated into four distinct assault phases. EMG signals were normalized to the muscle activity assessed during maximal isometric contraction. Mechanical and EMG data were compared between both legs over the entire assault and in each phase (ANOVA). Potential correlations between muscle strength and average EMG activities were tested (Bravais–Pearson coefficient). Results: EMG activity patterns showed that rear hip and knee extensor and plantarflexor muscles were mainly activated during propulsive (concentric) phases, while front hip and knee extensor muscles were strongly solicited during the final braking (eccentric) phase to decelerate the body mass. Although fencers presented greater maximal hip (+10%) and knee (+26%) extensor strength in the front than in the rear leg (P G 0.05), rear hip and knee extensor strength was significantly correlated to the maximal anteroposterior velocity (r = 0.60–0.81). Moreover, muscle activity of the rear extensors was related to average velocity during the second propulsive phase (phase 3). Conclusions: This study gathers the first evidence of a crucial role of the rear extensor muscles in fencing speed performance. Such findings suggest interesting perspectives in the definition of specific training or rehabilitation programs for elite fencers.

International audience; Aim: Changes in muscle stiffness after exercise-induced muscle damage have been classically inferred from passive torque–angle curves. Elasto-graphic techniques can be used to estimate the shear modulus of a localized muscular area. This study aimed to quantify the changes in shear elastic modulus in different regions of the elbow flexors after eccentric exercise and their relation to muscle length. Methods: Shear elastic modulus and transverse relaxation time (T 2) were measured in the biceps brachii and brachialis muscles of sixteen participants , before, 1 h, 48 h and 21 days after three sets of ten maximal isoki-netic eccentric contractions performed at 120° s À1. Results: The shear elastic modulus of the elbow flexors significantly increased 1 h (+46%; P = 0.005), with no significant change at 48 h and 21D, post-exercise. In contrast, T 2 was not modified at 1 h but significantly increased at 48 h (+15%; P < 0.05). The increase in shear elastic modulus was more pronounced at long muscle lengths and reached a similar extent in the different regions of the elbow flexors. The normalized hysteresis area of shear elastic modulus–length relationship for the biceps brachii increased 1 h post-exercise (31%) in comparison with the pre-exercise value (18%), but was not significantly altered after five stretching cycles (P = 0.63). Conclusion: Our results show homogeneous changes in muscle shear elastic modulus within and between elbow flexors. The greater increase in shear elastic modulus observed at long muscle lengths suggests the putative involvement of both cross-bridges number and titin in the modifications of muscle shear elastic modulus after damaging exercise.

Background: Localized cooling has been proposed as an effective strategy to limit the deleterious effects of exercise-induced muscle damage on neuromuscular function. However, the literature reports conflicting results. Purpose: This randomized controlled trial aimed to determine the effects of a new treatment, localized air-pulsed cryotherapy (–30°C), on the recovery time-course of neuromuscular function following a strenuous eccentric exercise. Study Design: Controlled laboratory study. Methods: A total of 24 participants were included in either a control group (CONT) or a cryotherapy group (CRYO). Immediately after 3 sets of 20 maximal isokinetic eccentric contractions of elbow flexors, and then 1, 2, and 3 days after exercise, the CRYO group received a cryotherapy treatment (3 × 4 minutes at −30°C separated by 1 minute). The day before and 1, 2, 3, 7, and 14 days after exercise, several parameters were quantified: maximal isometric torque and its associated maximal electromyographic activity recorded by a 64-channel electrode, delayed-onset muscle soreness (DOMS), biceps brachii transverse relaxation time (T2) measured using magnetic resonance imaging, creatine kinase activity, interleukin-6, and C-reactive protein. Results: Maximal isometric torque decreased similarly for the CONT (–33% ± 4%) and CRYO groups (−31% ± 6%). No intergroup differences were found for DOMS, electromyographic activity, creatine kinase activity, and T2 level averaged across the whole biceps brachii. C-reactive protein significantly increased for CONT (+93% at 72 hours, P < .05) but not for CRYO. Spatial analysis showed that cryotherapy delayed the significant increase of T2 and the decrease of electromyographic activity level for CRYO compared with CONT (between day 1 and day 3) in the medio-distal part of the biceps brachii. Conclusion: Although some indicators of muscle damage after severe eccentric exercise were delayed (ie, local formation of edema and decrease of muscle activity) by repeated air-pulsed cryotherapy, we provide evidence that this cooling procedure failed to improve long-term recovery of muscle performance. Clinical Relevance: Four applications of air-pulsed cryotherapy in the 3 days after a strenuous eccentric exercise are ineffective overall in promoting long-term muscle recovery. Further studies taking into account the amount of exercise-induced muscle damage would allow investigators to make stronger conclusions regarding the inefficiency of this recovery modality.

The aim of this study was to evaluate concomitantly the changes in leg-spring behavior and the associated modifications in the lower limb muscular activity during a constant pace run to exhaustion at severe intensity.Twelve trained runners performed a running test at the velocity associated with VO(2max) (5.1 ± 0.3 ms(-1); mean time to exhaustion: 353 ± 69s). Running step spatiotemporal parameters and spring-mass stiffness were calculated from vertical and horizontal components of ground reaction force measured by a 6.60 m long force platform system. The myoelectrical activity was measured by wireless surface electrodes on eight lower limb muscles.The leg stiffness decreased significantly (-8.9%; P0.05) while the vertical stiffness did not change along the exhaustive exercise. Peak vertical force (-3.5%; P0.001) and aerial time (-9.7%; P0.001) decreased and contact time significantly increased (+4.6%; P0.05). The myoelectrical activity decreased significantly for triceps surae but neither vastus medialis nor vastus lateralis presented significant change. Both rectus and biceps femoris increased in the early phase of swing (+14.7%; P0.05) and during the pre-activation phase (+16.2%; P0.05).The decrease in leg spring-stiffness associated with the decrease in peak vertical ground reaction force was consistent with the decline in plantarflexor activity. The biarticular rectus femoris and biceps femoris seem to play a major role in the mechanical and spatiotemporal adjustments of stride pattern with the occurrence of fatigue during such exhaustive run.

International audience; Purpose: This study was designed to assess muscle coordination during a specific all-out sprint cycling task (Sprint). The aim was to estimate the EMG activity level of each muscle group by referring to the submaximal cycling condition (Sub150 W) and to test the hypothesis that a maximal activity is reached for all of the muscles during Sprint.Methods: Fifteen well-trained cyclists were tested during submaximal and sprint cycling exercises and a series of maximal voluntary contractions (MVCs) in isometric and isokinetic modes (MVC at the three lower limb joints). Crank torque and surface EMG signals for 11 lower limb muscles were continuously measured.Results:Results showed that Sprint induced a very large increase of EMG activity level for the hip flexors (multiplied by 7–9 from 150 W to Sprint) and the knee flexors and hip extensors (multiplied by 5–7), whereas plantar flexors and knee extensors demonstrated a lower increase (multiplied by 2–3). During Sprint, EMG activity level failed to reach a maximal value for hamstrings, tibialis anterior, tensor fasciae latae, and gluteus maximus (i.e.

International audience; In sport, high training load required to reach peak performance push human adaptation to their limits. 3 In that process, athletes may experience general fatigue, impaired performance and may be identified 4 as overreached (OR). When this state lasts for several months, an overtraining syndrome is diagnosed 5 (OT). Until now, no variable per se can detect OR, a requirement to prevent the transition from OR to 6 OT. It encouraged us to further investigate OR using a multivariate approach including physiological, 7 biomechanical, cognitive and perceptive monitoring. Twenty-four highly trained triathletes were 8 separated into an overload group and a normo-trained group (NT) during three weeks of training. 9 Given the decrement of their running performance, eleven triathletes were diagnosed as OR after this 10 period. A discriminant analysis showed that the changes of eight parameters measured during a 11 maximal incremental test could explain 98.2% of the OR state (lactataemia, heart rate, biomechanical 12 parameters and effort perception). Variations in heart rate and lactataemia were the two most 13 discriminating factors. When the multifactorial analysis was restricted to these variables, the 14 classification score reached 89.5%. Catecholamines and creatine kinase concentrations at rest did not 15 change significantly in both groups. Running pattern was preserved and cognitive performance 16 decrement was observed only at exhaustion in OR subjects. This study showed that monitoring various 17 variables is required to prevent the transition between NT and OR. It emphasized that an OR index, 18 which combines heart rate and blood lactate concentration changes after a strenuous training period, 19 could be helpful to routinely detect OR.

International audience; The 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

The purpose of the present study was to determine whether muscle synergies are constrained by changes in the mechanics of pedaling. The decomposition algorithm used to identify muscle synergies was based on two components: “muscle synergy vectors,” which represent the relative weighting of each muscle within each synergy, and “synergy activation coefficients,” which represent the relative contribution of muscle synergy to the overall muscle activity pattern. We hypothesized that muscle synergy vectors would remain fixed but that synergy activation coefficients could vary, resulting in observed variations in individual electromyographic (EMG) patterns. Eleven cyclists were tested during a submaximal pedaling exercise and five all-out sprints. The effects of torque, maximal torque-velocity combination, and posture were studied. First, muscle synergies were extracted from each pedaling exercise independently using non-negative matrix factorization. Then, to cross-validate the results, muscle synergies were extracted from the entire data pooled across all conditions, and muscle synergy vectors extracted from the submaximal exercise were used to reconstruct EMG patterns of the five all-out sprints. Whatever the mechanical constraints, three muscle synergies accounted for the majority of variability [mean variance accounted for (VAF) = 93.3 ± 1.6%, VAFmuscle> 82.5%] in the EMG signals of 11 lower limb muscles. In addition, there was a robust consistency in the muscle synergy vectors. This high similarity in the composition of the three extracted synergies was accompanied by slight adaptations in their activation coefficients in response to extreme changes in torque and posture. Thus, our results support the hypothesis that these muscle synergies reflect a neural control strategy, with only a few timing adjustments in their activation regarding the mechanical constraints.

Purpose: This study investigated the effects of a combined endurance and strength training on the physiological and neuromuscular parameters during a 2-h cycling test. Methods: Fourteen triathletes were assigned to an endurance-strength training group and an enduranceonly training group. They performed three experimental trials before and after training: an incremental cycling test to exhaustion, a maximal concentric lower-limbs strength measurement and a 2-h cycling exercise. Physiological parameters, free cycling chosen cadence and the EMG of Vastus Lateralis (VL) and Rectus Femoris (RF) were analysed during the 2-h cycling task before and after a strength training programme of 5 weeks (three times per week). Results: The results showed that the maximum strength and the isometric maximal voluntary contraction (isoMVC) after training were significantly higher (P < 0.01) and lower (P < 0.01) than those before training, respectively, in endurance-strength training group and endurance-only group. The physiological variables measured during the cycling tests and the progressive increase (P < 0.01) in EMGi(VL) and EMGi(RF) throughout the 2-h cycling test did not differ between the two groups before and after training, except for the variation of EMGi(VL) over the cycle time which was stabilized during the second hour of the 2-h cycling test due to training in endurance-strength training group. The decrease in free cycling chosen cadence observed in pre-training (P < 0.01) was also replaced by a steady free cycling chosen cadence for the endurance-strength training group during the second hour of exercise. Conclusion: This study confirmed the decrease in the free cycling chosen cadence with exercise duration and demonstrated that a specific combined endurance and strength training can prevent this decrease during a 2-h constant cycling exercise. 2009 Published by Elsevier Ltd.

International audience; Purpose: This study investigated neuromuscular fatigue following high versus low-intensity eccentric exercise corresponding to the same amount of work.Methods: Ten volunteers performed two eccentric exercises of the elbow flexors: a high-intensity versus a low-intensity exercise. Maximal voluntary contraction torque and surface electromyography of the biceps brachii muscle were recorded before, immediately and 48 h after exercises. Maximal voluntary activation level, neural (M-wave) and contractile (muscular twitch) properties of the biceps brachii muscle were analysed using electrical stimulation techniques.Results: Maximal voluntary contraction torque was significantly (P < 0.01) reduced immediately and 48 h after exercise but the reduction was not different between the two conditions. Electromyography associated with maximal voluntary contraction significantly decreased (P < 0.05) immediately and 48 h after exercise for both conditions while maximal voluntary activation level was only significantly reduced immediately after the high-intensity exercise. Peak twitch alterations were observed immediately and 48 h after exercise for both conditions while M-wave did not change.Conclusion: High and low-intensity eccentric exercises with the same amount of work induced the same reduction in maximal strength capacities of the biceps brachii muscles. The magnitude of peripheral and central fatigue was very similar in both conditions.

International audience; Purpose: Alterations of the mechanical patterns during an exhaustive pedaling exercise have been previously shown. We designed the present study to test the hypothesis that these alterations in the biomechanics of pedaling, which occur during exhaustive exercise, are linked to changes in the activity patterns of lower limb muscles. Methods: Ten well-trained cyclists were tested during a limited time to exhaustion, performing 80% of maximal power tolerated. Pedal force components were measured continuously using instrumented pedals and were synchronized with surface EMG signals measured in 10 lower limb muscles. Results: The results confirmed most of the alterations of the mechanical patterns previously described in the literature. The magnitude of the root mean squared of the EMG during the complete cycle (RMS cycle) for tibialis anterior and gastrocnemius medialis decreased significantly (P G 0.05) from 85% and 75% of T lim , respectively. A higher RMS cycle was obtained for gluteus maximus (P G 0.01) and biceps femoris (P G 0.05) from 75% of T lim. The k values that resulted from the cross-correlation technique indicated that the activities of six muscles (gastrocnemius medialis, gastrocnemius lateralis, tibialis anterior, vastus lateralis, vastus medialis, and rectus femoris) were shifted forward in the cycle at the end of the exercise. Conclusions: The large increases in activity for gluteus maximus and biceps femoris, which are in accordance with the increase in force production during the propulsive phase, could be considered as instinctive coordination strategies that compensate for potential fatigue and loss of force of the knee extensors (i.e., vastus lateralis and vastus medialis) by a higher moment of the hip extensors.

International audience; Purpose: We compared incline and level training sessions as usually used in elite 400-m runners through stride kinematics and muscular activity measurements. Methods: Nine highly trained 400-m ramiers (international and French national level) performed two maximal velocity sprints: 1) 300-m on level ground (LEV) and 2) 250-m on an incline ground (INC) characterized by a mean ± SD grade of 5.4 ± 0.7%. Kinematics (250 Hz) and electromyography parameters (root mean square [RMS] and integrated electromyography [iEMG] measurements) were analyzed (from 40-to 50-m phases). Results: INC induced a decrease in running velocity compared to LEV (6.28 ± 0.38 vs 7.56 ± 0.38 ms-1) explained by a reduction in stride length (-14.2%) and stride rate (-7.4%) and by an increase in push-off time (+26.4%). Kinematics analysis indicated that the lower limbs were more flexed during INC running. Concerning the level of activity of the lower limb muscles, the major findings pointed out the decrease in RMS for semitendinosus and biceps femoris muscles during the contact phase and for vastus lateralis during its concentric phase. However, iEMG of both semitendinosus and biceps femoris muscles remained constant during both contact and push-off phases. Conclusion: Our results are clearly different from those of previous studies carried out at similar absolute velocities in both LEV and INC conditions, which were not the case in this study. The lower running velocity marking INC running was associated with a decrease in the activation of the hamstrings. Trainers should particularly consider this lower level of activation of the hamstrings muscles during INC maximal sprint.

International audience; The aim of this study was to characterize the influence of intrinsic musculotendinous and musculoartic-ular stiffness of plantarflexor muscles on (1) the overall musculoskeletal stiffness and (2) the performance during stretch-shortening cycles-type exercise. The influence of plyometric training background on these relationships was also analyzed. Musculotendinous (SI MT), passive (K P) and active (SI MA) musculoarticular stiffnesses were quantified, using quick-release and sinusoidal perturbation tests, on nine French elite long or triple jumpers (athlete group, AG) and nine control subjects (CG). These ergometric parameters were related with the lower-limb stiffness (K leg) and the maximal performance (H max) measured from a force platform during vertical hopping. AG showed a significantly higher SI MT (2.76 rad-1), K P (55.6 N m rad-1), K leg (30.3 kN m-1) and H max (0.48 m) compared to CG (1.83 rad-1 , 37.8 N m rad-1 , 19.6 kN m-1 and 0.38 m, respectively). K leg was not significantly correlated with any of the intrinsic stiffness parameters (SI MT , SI MA or K P). For AG, a strong and negative correlation was observed between H max and K leg. These data indicate that, while elite jumpers presented higher stiffness of both musculotendi-nous and passive musculoarticular structures, a high compliance of musculoskeletal system was beneficial to optimize the performance in vertical hopping for these athletes. We suggested that neuromuscular strategies were designed to counterbalance this higher intrinsic stiffness to solve the problem of the conflicting requirement of the musculotendinous elements: increase in compliance to enhance the elastic recoil and increase in stiffness for a better force transmission to the periphery.

International audience; The aim of this study was to investigate the effect of concentric or eccentric fatiguing exercise on cycling pattern. Eleven well trained cyclists completed three sessions of cycling (control cycling test (CTRL), cycling following concentric (CC) or eccentric (ECC) knee contractions) at a mean power of 276.8 ± 26.6 Watts. Concentric and eccentric knee contractions were performed at a load corresponding to 80% of one repetition maximum with both legs. Before and after CTRL, CC or ECC knee contractions and after cycling, a maximal voluntary contraction (MVC) test was performed. Cardiorespiratory, mechanical and electromyographic activity (EMG) of the rectus femoris, vastus lateralis and biceps femoris muscles were recorded during cycling. A significant decrease in MVC values was observed after CC and ECC exercises and after the cycling. ECC exercise induced a significant decrease in EMG root mean square during MVC and a decrease in pedal rate during cycling. EMG values of the three muscles were significantly higher during cycling exercise following CC exercise when compared to CTRL. The main finding of this study was that a prior ECC exercise induces a greater neuromuscular fatigue than a CC exercise, and changes in cycling pattern.

International audience; Assessment of intra-session repeatability of muscle activation pattern is of considerable relevance for research settings, especially when used to determine changes over time. However, the repeatability of lower limb muscles activation pattern during pedaling is not fully established. Thus, we tested the intra-session repeatability of the activation pattern of 10 lower limb muscles during a sub-maximal cycling exercise. Eleven triathletes participated to this study. The experimental session consisted in a reference sub-maximal cycling exercise (i.e. 150 W) performed before and after a 53-min simulated training session (mean power output = 200 ± 12 W). Repeatability of EMG patterns was assessed in terms of muscle activity level (i.e. RMS of the mean pedaling cycle and burst) and muscle activation timing (i.e. onset and offset of the EMG burst) for the 10 following lower limb muscles: gluteus maximus (GMax), semimembranosus (SM), Biceps femoris (BF), vastus medialis (VM), rectus femoris (RF), vastus lateralis (VL), gastrocnemius medianus (GM) and lateralis (GL), soleus (SOL) and tibialis anterior (TA). No significant differences concerning the muscle activation level were found between test and retest for all the muscles investigated. Only VM, SOL and TA showed significant differences in muscle activation timing parameters. Whereas ICC and SEM values confirmed this weak repeatability, cross-correlation coefficients suggest a good repeatability of the activation timing parameters for all the studied muscles. Overall, the main finding of this work is the good repeatability of the EMG pattern during pedaling both in term of muscle activity level and muscle activation timing.

We tested the hypothesis that time course of O (2) uptake (VO (2)) measured during a supramaximal exercise performed in the field is driven to maximal oxygen uptake (VO (2max)). On an outdoor track, five middle-distance male runners first performed a test to determine VO (2max) and a supramaximal 800-m running test at least two days apart. VO (2) response was measured from the start to the end of exercise with the use of a miniaturised telemetric gas exchange system (Cosmed K4). VO (2max) was reached by all subjects 45 +/- 11 s (mean +/- SD) after the onset of the 800-m race (i.e., 316 +/- 75 m), and was maintained during the next 33 +/- 6 s (i.e., 219 +/- 41 m). The mean relative exercise intensity of the 800 m was 120 % VO (2max). An unexpected significant decrease in VO (2) (24.1 +/- 7.0 %; p0.05) was observed in all subjects during the final 38 +/- 17 s (i.e., the last 265 +/- 104 m). We concluded that, at onset of a simulated 800 m running event, VO (2) is quickly projected towards the VO (2max), and then becomes limited by the achievable VO (2max). This race profile shown by all athletes is in some contrast to what can be expected from earlier findings in a laboratory setting.

During hopping in place or running, human legs normally behave like compression springs, so that the overall musculo-skeletal (MS) system can be described as a simple spring-mass model (McMahon and...

Resume Objectif – Determiner la part de chaque systeme energetique aux differents moments d'un 800 m couru sur le mode de competition en mesurant en continu la consommation d'oxygene et la vitesse reelle de course. Materiels et methodes – Cinq athletes ont ainsi effectue sur une piste de 400 m, un test progressif de determination de la consommation d'oxygene maximale et de la vitesse maximale aerobie ainsi qu'un exercice supramaximal de 800 m. Resultats – Ils mettent en evidence une depense energetique globale et un deficit d'oxygene evalue a 31,9 % quasi-identiques a ceux obtenus au cours d'un 800 m realise sur tapis roulant mais montrent une repartition differente du deficit d'oxygene. Ceci suggere que la cinetique des vitesses a une incidence determinante aussi bien sur la contribution anaerobie qu'aerobie lorsque existent des variations de vitesse importantes.

Abstract This paper describes a field drilling experiment in a preselected section of a well, performed to test an electric high-data-rate telemetry system. The system uses wired pipes from the surface to an intermediate position and an electrical cable inside the drill pipes and the bottom hole assembly to complete the transmission link. Data are transmitted up from the downhole sensor package to the surface computer unit. The process enables continuous transmission of downhole data while drilling or not, at a sampling rate for instance of 360 times per second of four drilling parameters among the variables to be collected. The field results indicate that this telemetry system is adaptable, reliable and able to transmit numerous and accurate data for hours. The process should not be considered as a competitor with commercial MWD systems, but, at a high rate and with greater accuracy, it enables an analysis to be made of downhole drilling variables such as drill string vibrations, actual environmental conditions or dynamic bit behavior. INTRODUCTION AND SYSTEM CONCEPT AND DESIGN The idea of transmitting electric signals along a drill string was recognized over 60 years ago. Nowadays the oil industry uses measurement while - drilling on a large scale to enhance well safety, evaluate the formation, analyze and control the drilling process, etc. Information is acquired downhole and sent to the surface through either the drilling fluid (mud pulse or continuous wave process), the earth (electromagnetic process), or an electrical conductor inside the drillstem. Mud or electromagnetic-based telemetry systems have proven to be commercially viable. Nevertheless their data transmission rate is low, i.e. from one to several tens of bits,/second, and such a rate cannot be used to transmit a high level of information or to analyze any quick dynamic behavior of a downhole parameter efficiently. Present system design, called TRAFOR, as implemented by the Institute Francis du Petrole (IFP), is based on a 30,000 bits/second downhole-to-surface transmission system. This range is similar to those chosen for other field tested telemetry systems. P. 95^

Studying composition and dynamics of forest stand is an essential step in order to practice sustainable management for tropical moist forest. This study aims to understand the effects of different logging intensities on forest stands located in particular geographic areas in the Congo Basin. The following questions are addressed: (1) Does floristic composition of forest stands vary according to climate and geographic conditions? (2) Does logging triggers growth of all tree species, when logging intensity is sufficient? (3) Does logging enable to reduce mortality of helophilious species while increasing their recruitment, as well as increasing the mortality rate of shade tolerant species? (4) Does diversity increase after logging? The data come from the IFO-DANZER permanent device located in north Republic of Congo. Four different areas were analysed, including two areas which undertook logging activities. Every area contains between 28 and 502 tree.ha-1 with a logging activity of 1 to 9 tree.ha-1 (0,7 à 9,1 m2.ha-1). Forest stands located on (grès horizontaux) and (schistes quartzitiques) are less dense and diverse than those located on (formation schisto-calicaro-gréseuse ou alluvionnaire). Logging does not have an impact on species? diversity but increases the presence of heliophilious species. The effect of logging on growth speed is more important when the logging intensity is stronger. This effect is even more visible when the area is dense. Logged parcels tend to have a lower mortality rate and a higher recruitment rate than non-logged parcels.; Etudier la composition et la dynamique d'un peuplement est une étape indispensable pour pouvoir mettre en oeuvre une gestion durable de la forêt tropicale humide. Cette étude a pour but de comprendre l'effet de l'exploitation forestière à différentes intensités sur des peuplements situés dans des zones à conditions environnementales particulières dans le bassin du Congo. Elle vise à répondre aux questions suivantes : (1) La composition floristique des peuplements diffère-t-elle selon des variables de station ? (2) L'exploitation entraine-t-elle une augmentation de la croissance de toutes les espèces d'arbre, lorsque son intensité est suffisante ? (3) L'exploitation entraine-t-elle une diminution de la mortalité des espèces héliophiles mais une augmentation de leur recrutement ainsi qu'une augmentation du taux de mortalité des espèces tolérantes à l'ombre ? (4) La diversité augmente-t-elle après l'exploitation ? Les données proviennent du dispositif permanent de la concession IFO-DANZER située au nord de la République du Congo. Quatre zones différentes ont été analysées dont deux zones qui ont subi une exploitation. Chaque zone compte entre 28 et 502 arbres.ha-1 et l'exploitation a porté sur 1 à 9 tiges.ha- 1 (soit 0,7 à 9,1 m2.ha-1). Les peuplements situés sur grès horizontaux et sur schistes quartzitiques sont moins denses et moins divers que ceux situés sur une formation schisto-calcairo-gréseuse ou alluvionnaire. L'exploitation n'entraine pas de changement dans la diversité mais favorise l'apparition d'espèces héliophiles. L'effet de l'exploitation sur la vitesse de croissance est plus important lorsque l'intensité d'exploitation a été plus forte. Cet effet est d'autant plus visible lorsque la zone est dense. Les parcelles exploitées ont tendance à afficher un taux de mortalité plus faible et un taux de recrutement plus élevé que les parcelles non exploitées.