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International audience; On-chip study of blood flow has emerged as a powerful tool to assess the contribution of each component of blood to its overall function. Blood has indeed many functions, from gas and nutrient transport to immune response and thermal regulation. Red blood cells play a central role therein, in particular through their specific mechanical properties, that directly influence pressure regulation, oxygen perfusion, or platelet and white cells segregation towards endothelial walls. As the bloom of in-vitro studies has led to the apparition of various storage and sample preparation protocols, we address the question of the robustness of the results involving cell mechanical behavior against this diversity. The effects of three conservation media (EDTA, citrate and glucose-albumin-sodium-phosphate) and storage time on the red blood cell mechanical behavior are assessed under different flow conditions: cell deformability by ektacytometry, shape recovery of cells flowing out of a microfluidic constriction, and cell flipping dynamics under shear flow. The impact of buffer solutions (phosphate-buffered saline and density-matched suspension using iodixanol/Optiprep) are also studied by investigating individual cell flipping dynamics, relative viscosity of cell suspensions and cell structuration under Poiseuille flow. Our results reveal that storing blood samples up to seven days after withdrawal and suspending them in adequate density-matched buffer solutions has in most experiments a moderate effect on the overall mechanical response, with a possible rapid evolution in the first three days after sample collection. SIGNIFICANCE Blood is in intimate contact with all organs in the body, supplying oxygen, nutrients and drugs while removing waste. It carries cells involved in immune response, wound repair and tumor dissemination. Blood is easily collected, revealing the presence of disease through biomarker analysis. It is storable and transfusable. Thus, blood is the subject of many in-vitro studies for research and medical purposes. Guidelines associated to sample preparation or storage conditions have been established, but these may affect its mechanical behavior. In this collaborative study, we provide new guidelines to minimize the impact of specific experimental requirements (e.g. density matching, blood freshness) by focusing on the single or collective motion of red blood cells in a large range of flow conditions.

Objective To investigate the effects of focal muscle fatigue induced by electromyostimulation (EMS) on Anticipatory Postural Adjustments (APAs) during arm flexions performed at maximal velocity. Methods Fifteen healthy subjects performed self-paced arm flexions at maximal velocity before and after the completion of fatiguing electromyostimulation programs involving the medial and anterior deltoids and aiming to degrade movement peak acceleration. APA timing and magnitude were measured using surface electromyography. Results Following muscle fatigue, despite a lower mechanical disturbance evidenced by significant decreased peak accelerations (−12%, p p >.11 for all analyses). Conclusion The fatigue signals evoked by externally-generated contractions seem to be gated by the Central Nervous System and result in postural strategy changes which aim to increase the postural safety margin. Significance EMS is widely used in rehabilitation and training programs for its neuromuscular function-related benefits. However and from a motor control viewpoint, the present results show that the use of EMS can lead to acute inaccuracies in predictive motor control. We propose that clinicians should investigate the chronic and global effects of EMS on motor control.

article i nfo Background: The variability of peroneal reaction time measurements is a major problem when using this parameter to control rehabilitation or proprioceptive training processes. In order to control peroneal reaction time values, some extrinsic factors should be considered. The purpose of this study was to measure peroneal reaction time in unipodal stance for two different destabilization axes. Methods: The peroneal reaction time of 10 healthy subjects was measured from kinematic and electromyograhic data in an experimental study using an ankle destabilization device. Findings: Inapreliminaryanalysis,resultsshowedthatthedestabilizationaxisorientationdidnotaffectperoneal reaction time values (68.5 ms, standard deviation=9.5 ms and 71.5 ms, standard deviation=8 ms for destabilizations in the frontal plane and around the Henke's axis, respectively). However, the inter-trial variance of inversion velocity peaks explained between 40% and 49% of the peroneal reaction time variance. When trials were selected on the basis of homogeneous inversion velocity peaks, results showed that peroneal reaction time values for the peroneus brevis were shorter during inversion movements performed around the physiological Henke's tilting axis (63 ms, standard deviation=9 ms vs. 71 ms, standard deviation=8 ms). Interpretation: Our findings evidenced that tilting axis orientation must be considered as an extrinsic factor that may influence peroneal reaction time. Moreover it also seems necessary to consider inversion speed values to adequately compare peroneal reaction time values.

The study investigated the effects of an unilateral ankle muscle fatigue onto independent postural control parameters including the trajectories of the estimated resultant CoP (CoPres) and his components: the centre of gravity (CG) and CoP–CG trajectories. Nine healthy men realized series of 10 toe-lift immediately followed by 10 knee flexions until exhaustion with one (Ex) leg. Maximal isometric voluntary contractions, postural sway measures of each leg, and muscular activities of the ankle muscles were recorded before and immediately after the fatiguing exercise. As expected, the latter induced a decrease in maximal voluntary peak force associated with a greater variability of the relative contribution of each leg on the CoPres, enhanced all postural parameters of the non-exercised leg. A significant decreased of the tibialis anterior EMG activity for the Ex leg and an increased one for the NoEx leg. Finally, following unilateral fatigue, the body sway destabilisation seemed to occur only along the medio-lateral (ML) axis. The enhanced and greater variability of the variance along ML axis might be explained by the recourse at the loading–unloading strategy choice and suggests a central attempt to compensate for pain sensation.

The main objective of this study was to examine whether static and dynamic signals from a non-fatigued reference ankle can differently improve the movement accuracy of a fatigued ankle. To address this question, subjects performed an ankle-matching task in a control condition and in a condition of local fatigue induced in the right tibialis anterior, in two matching conditions. In a bilateral condition, the matching task was completed with the two ankles simultaneously. In a unilateral condition subjects had to match the exact target position with the left non-fatigued ankle first and then tried to match the target position with the right fatigued ankle. Results showed that the final accuracy of the right fatigued ankle was degraded when matched with both ankles simultaneously while, for the unilateral condition, the final accuracy remained constant whether the ankle was fatigued or not. In addition, the EMG activity of the right tibialis increased significantly in the acceleration portion of the ankle movement for the unilateral condition. These results suggest that the CNS was able to integrate the correct static positional signals originating from the left reference ankle, to improve the movement accuracy of the controlateral fatigued ankle. This compensation of lateralized fatigue is operated in a feedforward manner.

BACKGROUND Soft tissue surgery to address in-toeing gait in young cerebral palsy (CP) patients may be an alternative in some cases to femoral derotation osteotomy (FDO), which is the currently accepted treatment. The relative contribution of muscular contracture, spasticity and bone deformity is still controversial. In this study, we determined the outcomes of soft tissue surgery on hip internal rotation (HIR) when femoral anteversion was less than 45° and the soft tissues were identified as being the cause. METHODS This prospective study included select adolescent patients who were operated in the context of single-event multilevel surgery. The soft tissues' contribution to the HIR was identified beforehand. The surgical procedures focused on the hamstrings, adductor magnus and gluteus minimus muscles. RESULTS Over a 6-year period, 21 patients (mean age 14 years) and 25 lower limbs were treated. The HIR improved by an average of 17.4°±4.8° (95% CI). The gait deviation index and gait profile score also improved significantly. At a mean follow-up of 36 months, no loss of correction had occurred. DISCUSSION In-toeing gait in CP patents is due to the action of retracted and/or spastic muscles and the presence of excessive bone torsion. When femoral anteversion

Resume Introduction Les lesions musculaires des ischiojambiers sont une problematique importante chez les sportifs du fait de leur frequence, de leur taux de recidive et de leur impact. Leur incidence ne cesse de croitre malgre la multiplication des etudes scientifiques sur ce sujet. L’objectif principal de notre etude etait d’evaluer les connaissances et les attitudes des medecins pouvant y etre confrontes. Methodes Nous avons realise une etude observationnelle, descriptive, transversale, declarative aupres de medecins francais confrontes a la prise en charge des patients presentant une lesion musculaire des ischiojambiers, par le biais d’un questionnaire electronique. Une analyse descriptive a ete faite dans un premier temps. Puis une analyse comparative a ete effectuee entre les medecins ayant ou non beneficie d’une formation specifique en medecine du sport. Resultats Les donnees de 559 questionnaires ont ete inclus dans l’analyse. Il y avait 402 medecins sans formation en medecine du sport (NFMDS) et 157 medecins avec formation (FMDS). Les medecins FMDS semblaient plus souvent confrontes a la prise en charge de lesion musculaire des ischiojambiers que ceux NFMDS. La note moyenne d’auto-evaluation des connaissances par les medecins etait de 4,8 ± 2,2 sur 10 ; elle etait superieure dans le groupe FMDS par rapport au groupe NFMDS. Les principaux facteurs de risque et les moyens de les prevenir etaient connus de la plupart des medecins, surtout par le groupe FMDS. Concernant la prise en charge initiale, le protocole POLICE (Protection Optimal Loading Ice Contention Elevation) etait bien integre par les medecins. La prescription d’anti-inflammatoires non steroidiens etait acceptee par les medecins NFMDS et refutee par les FMDS. L’imagerie etait plebiscitee par une majorite de medecins surtout l’echographie, a visee pronostique principalement. Les grands principes de la reeducation etaient connus majoritairement par les medecins FMDS. Les medecins NFMDS s’accordaient a laisser le soin au kinesitherapeute d’organiser la reeducation. Enfin, les medecins interroges acceptaient l’ensemble des parametres cliniques proposes pour determiner le retour au sport et refutaient l’interet de l’imagerie a ce sujet. Conclusion Les grands principes de la prise en charge des lesions musculaires des ischiojambiers semblent integres par les medecins y faisant face. Ces lesions sont plus frequemment rencontrees par les medecins ayant beneficie d’une formation en medecine du sport dont les connaissances a ce sujet sont plus en adequation avec les donnees de la science.

Resume Objectif Realiser un etat des lieux des connaissances actuelles concernant la prevention des blessures chez le skieur alpin de competition, âge de 14 a 19 ans, en suivant la sequence de prevention des blessures en 4 etapes de van Mechelen et al. (1992). Methode Une revue systematique a ete effectuee en novembre 2018 en utilisant deux moteurs de recherche (« Pub Med » et « Science Direct ») et les mots cles suivants : « Injury », « Sports injuries », « Young », « Adolescent », « Epidemiology », « Risk factor », « Prevention », « Alpine skiing » et « Alpine ski » pour inclure les articles traitant de l’epidemiologie, l’identification de facteurs de risque, la mise en place et/ou l’evaluation des programmes de prevention des blessures du skieur alpin de competition âge de 14 a 19 ans. Resultats Cinq etudes rapportaient des resultats concernant l’epidemiologie des blessures du skieur alpin de competition âge de 14 a 19 ans ; ces blessures etaient majoritairement localisees au genou concernant les ligaments et la blessure la plus frequente etait la lesion du ligament croise anterieur (LCA). Deux etudes identifiaient l’asymetrie de force entre les muscles flechisseurs et extenseurs du rachis, ainsi que l’asymetrie de performance au one leg hop test comme facteurs de risque de lesion du LCA. Une etude a rapporte qu’un programme de prevention base sur l’amelioration du controle neuromusculaire des membres inferieurs et le renforcement des muscles du rachis limitait le nombre de lesions du LCA. Discussion et conclusion Les lesions du LCA etaient les plus frequentes chez le skieur alpin de competition âge de 14 a 19 ans;un faible controle neuromusculaire ainsi qu’une asymetrie de musculature du tronc seraient predictifs de cette lesion, et il semblerait que la mise en place d’un programme de prevention puisse diminuer la survenue de cette blessure. Cependant, d’autres etudes longitudinales cherchant a identifier les facteurs de risque potentiels, leur evolution dans le temps et leur modification par des programmes de prevention sont necessaires. Niveau de preuve 4.

Introduction Variations in the length of lateral extra-articular reconstruction (LER) have been widely investigated during knee flexion but there is no information about length changes during pivot shift. This study sought to assess the changes in LER tension during weightbearing knee flexion in a normal knee and in a computer-simulated pivot-shift scenario. Hypothesis Placing the femoral tunnel posterior and proximal to the lateral femoral epicondyle allows the LER to tighten early in the flexion range during weightbearing (squatting motion) and simulated pivot-shift. Material and methods A computer model was used to simulate weightbearing knee flexion and pivot shift scenarios. Changes in LER tension were calculated in both scenarios by estimating the distance between six femoral attachment sites (posterior and proximal to the lateral femoral epicondyle) and two tibial tunnel locations: Gerdy's tubercle (GT) and the anterolateral ligament (ALL) anatomic attachment site. Results Independent of the location of the femoral and tibial tunnels, the LER tightened by up to 22% of its resting length during the early portion of weightbearing knee flexion and then relaxed from 40° to 60° of knee flexion. The ALL tibial tunnel position allowed complete LER relaxation at 60° flexion whereas LER using the GT tibial tunnel position remained tighter. In the simulated pivot-shift test, and for all femoral tunnel locations, the LER tightened by 20% to 34% of its resting value for the GT tibial tunnel position and by 11% to 26% for the ALL tibial tunnel position. Discussion During weightbearing knee flexion, placing the femoral tunnel proximal and posterior to the femoral epicondyle was associated with LER tightening in the early degrees of flexion and LER relaxation between 40 and 60° flexion. LER tightening occurred during a simulated pivot-shift test supporting the concept that a posterior and proximal femoral LER tunnel position is most effective during weightbearing knee flexion and altered knee kinematics.

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The hip is the joint most exposed to orthopaedic complications in cerebral palsy (CP), which is the main cause of spasticity in paediatric patients. The initial immaturity of the hip allows the forces applied by the spastic and retracted muscles to displace the femoral head, eventually causing it to dislocate. The risk of hip dislocation increases with the severity and extent of CP, exceeding 70% in the most severe cases. Hip dislocation causes pain in up to 30% of cases, carries a risk of orthopaedic and cutaneous complications and hinders patient installation and nursing care. These adverse outcomes warrant routine screening, which has been proven effective in lessening the frequency and severity of hip displacement. Preventive techniques including physical therapy, orthoses and treatments to alleviate spasticity are strongly recommended in every case. The beneficial effects of treating spasticity, if needed via neurosurgical procedures, have been convincingly established. Orthopaedic surgery is required when prevention fails. Soft-tissue release is designed to correct the asymmetry in the forces applied by the muscles. Femoral osteotomy creates the possibility for spontaneous correction of secondary acetabular dysplasia. Progress has been made in standardising the use of multilevel surgery involving the soft tissues, femur and pelvis, which is often effective in correcting the morphological abnormalities and stabilising the joint. When hip pain or alterations are severe, hip resection or total hip arthroplasty are highly effective in alleviating the pain and improving patient comfort. The spastic hip is a complex condition in which currently available screening protocols and treatment strategies have been proven effective in benefitting patient outcomes.

To compare the effects of local-vibration and active warm-up on knee extensors muscle stiffness and neuromuscular performance.Experimental crossover study.Thirteen participants performed three 15-min warm-up protocols of control (CON), active (ACT) and local-vibration (LV) in separate testing session. Passive stiffness of vastus lateralis (VL) and vastus medialis (VM) by shear wave elastography and neuromuscular performance were assessed before and 2-min after each condition.A decrease in muscle stiffness was reported after ACT for VL (-16.0±6.6%; p0.001) and VM (-10.2±8.7%; p=0.03) while no changes were reported after CON (p=0.46 and p=0.34 for VL and VM, respectively) and LV (p=0.07 and p=0.46 for VL and VM, respectively). Maximal jump performances increased during squat (+8.5±6.6%; p0.001) and countermovement jump (+5.2±5.8%; p0.001) after ACT while no changes were reported after CON and LV during squat (p=0.16 and p=0.81, respectively) and countermovement jump (p=0.18 and p=0.31, respectively). We further report that each condition was ineffective to inducing changes in maximal voluntary isometric contraction force (p=0.18), rate of force development (p=0.92), twitch parameters (p0.05) as well as central modulations as reported by the unchanged voluntary activation level (p=0.24) and maximal electromyography (EMG) recorded from the VL (p=0.44).The active warm-up acutely reduced muscle stiffness and increased muscle performance during maximal dynamic tasks. With regard to LV, further studies are required to determine optimal parameters (frequency, amplitude, duration) to significantly increase muscle performance.

Background The variation of the anterolateral ligament (ALL) length during knee motion is still unclear, and the knee position in which a reconstruction graft should be tensioned remains controversial. The objective of this study was to determine the variation of the ALL length during knee motion using a three-dimensional optoelectronic system. Methods Kinematic analyses of 20 cadaveric knees were performed using a Motion Analysis® system. The variability of the measurements made during the five acquisition cycles was studied. Reliability was evaluated by two separate measurement sessions, with complete system reinstallation, using different cadavers and a new operator. The ALL length was analysed from extension to full flexion in three rotational conditions. Findings When analysing the reliability of the five cycles, 82% of the measurements we found to have an Intra Class Correlation (ICC) >0.85. The reproducibility of inter-sessional measures by different operators and different cadavers was either good (ICC >0.75) or excellent (ICC >0.85). The ALL length was maximum in full internal rotation with the knee at 25° of flexion. Interpretation This three-dimensional optoelectronic protocol allowed us to analyse the variation of the ALL length during intact knee motion with good reliability and the required accuracy to analyse this variable. The maximal length and highest tension of the ALL was reported at 25° of knee flexion in internal rotation, suggesting this as the optimal position for the knee joint when tensioning an ALL reconstruction.

International audience; Hydroxyurea (HU) has been suggested to act as a nitric oxide (NO) donor in sickle cell anemia (SCA). However, little is known about the HU NO-related effects on red blood cell (RBC) physiology and NO signalling pathway. Thirty-four patients with SCA (22 under HU treatment (HU+) and 12 without (HU-)) and 17 healthy subjects (AA) were included. RBC nitrite content, deformability and reactive oxygen species (ROS) levels were measured. RBC NO-synthase (RBC-NOS) signalling pathway was assessed by the measurement of RBC-NOS serine 1177 and RBC-AKT serine 473 phosphorylation. We also investigated the in vitro effects of Sodium Nitroprusside (SNP), a NO donor, on the same parameters in SCA RBC. RBC nitrite content was higher in HU+ than in HU-and AA. RBC deformability was decreased in SCA patients compared to AA but the decrease was more pronounced in HU-. RBC ROS level was increased in SCA compared to AA but the level was higher in HU-than in HU+. RBC-NOS serine 1177 and RBC-AKT serine 473 phosphorylation were decreased in HU+ compared to HU-and AA. SCA RBC treated with SNP showed increased deformability, reduced ROS content and a decrease in AKT and RBC-NOS phosphorylation. Our study suggests that HU, through its effects on foetal hemoglobin and possibly on NO delivery, would modulate RBC NO signalling pathway, RBC rheology and oxidative stress.

Shoulder performance and sensorimotor control assessments help to identify shoulder instabilities and document the rehabilitation progress. Testing seated subjects in a position of hand prehension requires less controlled adjustments to maintain body balance in a clinically relevant situation. The objective of this work was to determine the test–retest repeatability of a novel shoulder stability test in seated subjects with the ipsi-lateral hand in prehension during four arm loading conditions. Able-bodied subjects were seated on a rigid chair fixed to a force plate. A horizontally and posteriorly directed force was applied to the hand for four 4 loading conditions ranging from 0 to 3 kg. Ten postural balance parameters were calculated from the center of pressure displacements and its corresponding free moments. Intra-class correlation coefficients were calculated for three consecutive trials and for four loading conditions. Generally, the intra-class correlations values increased gradually with the load and varied from 0.727 to 0.948. Tz values increased non-linearly with the applied load. The test–retest reliability of a new shoulder stability test in seated able-bodied subjects was high with sufficient loading (3 kg) and 3 trials.

Resume Nous proposons une methode generale et analytique de description des limites de l'espace de travail plan, c'est-a-dire la frontiere de la partie de l'espace du plan atteinte par l'extremite d'un bras humain ou de robot. La methode proposee est decomposee en trois etapes independantes, aucune ne faisant appel a des calculs de derivees, de determinants ou de valeurs propres, ou utilisant des methodes de resolution numerique de problemes non lineaires, tous souvent utilises dans la litterature. La premiere etape, deja presentee dans des travaux precedents, consiste a interpreter de facon geometrique la necessaire degenerescence de la matrice jacobienne de la fonction de position, au bord de l'espace de travail et une condition d'alignement de certaines articulations permet de determiner une reunion d'arcs de cercle qui contiennent la frontiere. Ensuite, pour chacun des arcs de cercle, l'etude de la variation infinitesimale d'un point par rapport a ce cercle permet d'eliminer tout ou partie des arcs de cercle precedemment definis, qui n'est pas sur la frontiere. Enfin, un parcours global de la reunion des arcs de cercle permet de determiner la frontiere exterieure ainsi que la frontiere interieure de l'eventuel trou de l'espace de travail qui contient l'origine.

The objective of this study was to investigate the pressure applied by superimposed bandages and to compare it with the pressure applied by single-component bandages.Six different bandages, composed of one elastic bandage, one nonelastic bandage, or both, were applied in a spiral pattern on both legs of 25 patients at risk of venous thrombosis as a consequence of central or peripheral motor deficiency. Pressure was measured at four measurement points on the leg (B1 and C on the medial and lateral sides of the leg) and in three positions: supine, sitting, and standing.The two single bandages applied similar pressure in the supine position. Their superimposition showed different pressure levels (P .05) but similar static stiffness index, depending on the order in which the bandage components were applied on the leg. The highest interface pressure was measured at point B1 on the medial side of the leg. This point also showed the highest pressure increase from supine to standing position. The pressure applied by the superimposition of two bandages was computed as a linear combination of the pressure applied by each single component (with a constant term set to 0). However, this linear combination did not properly fit the experimental pressure measurements.The order of bandage application showed a significant impact on interface pressure. However, the poor correlation between the pressure applied by each bandage component and the pressure resulting from their superimposition underlined the poor understanding of interface pressure generated by the superimposition of compression bandages and should lead to further investigations.

Background The aim of this study was to determine the clinical efficacy of minimally invasive endoscopic ulnar nerve release at midterm follow-up. Methods This was a retrospective, consecutive, single-center study. The inclusion criterion was presentation of the patient with isolated and stable cubital tunnel syndrome. The surgical technique described by Hoffmann and Siemionow in 2006 was used for all patients. The cubital tunnel syndrome was graded by Dellon's classification and scored as described by MacDermid and Grewal in 2013. Results Sixty patients underwent surgery (62 cubital tunnel operations). Fifty-three patients were included in the study. The mean follow-up was 17 months (6-34). In the preoperative period, according to Dellon's classification, 8 patients were grade 1, 29 patients were grade 2, and 16 patients were grade 3. After surgery, according to the MacDermid score, 45 patients (84.9%) had good or excellent results, 6 (11.3%) had moderate results, and 2 (3.8%) had poor results. The mean preoperative score was 103.1 (25-181), and the mean postoperative score was 26.3 (0-135). By comparison with standard surgical technique, the endoscopic technique appears to be reliable with a similar success rate and functional improvement. The advantages are the minimally invasive portion of the surgical technique. Endoscopic control allowed complete release of the ulnar nerve with few complications. Conclusion The endoscopic technique as described by Hoffman et al had similar efficacy to open surgical techniques with the advantage of being minimally invasive.

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Background The objective of this study was to provide preliminary measures of the distance between the supraspinatus, infraspinatus, and subscapularis footprints and the acromion, coracoacromial ligament, and coracoid process, during dynamic arm elevations through the entire range-of-motion. Methods Two healthy men performed maximum adduction, flexion, abduction, and extension with the arm internally, neutrally, and externally rotated. The distance between each rotator cuff footprint and the acromion, coracoacromial ligament, and coracoid process was measured from glenohumeral kinematics obtained from markers fitted to intracortical pins combined with the scapular and humeral 3D geometry obtained from CT-scan. Results All footprints moved to be less than 10 mm to the acromion, coracoacromial ligament and coracoid process. They got closer to the acromion than to the other parts of the coracoacromial arch. The acromion-supraspinatus and acromion-infraspinatus distances were minimal during abduction and flexion. The acromion-subscapularis distance was minimal when the arm was in external and neutral rotation during both adduction and flexion. Conclusions The present study provides benchmark results of the distance between the rotator cuff footprints and the coracoacromial arch that may guide future clinical research. Pressure transducers should be positioned throughout the coracoacromial arch to provide comprehensive assessment of the compression undergone by the rotator cuff tendons. Common shoulder examination tests, that require flexion and internal rotation movements, may be refined since the supraspinatus footprint was the closest to the coracoacromial arch during abduction. Larger scale investigations may be needed to identify more accurate shoulder examination tests.

Background Acquisition and consolidation of a new motor skill occurs gradually over long time span. Motor imagery (MI) and brain stimulation have been showed as beneficial approaches that boost motor learning, but little is known about the extent of their combined effects. Objective Here, we aimed to investigate, for the first time, whether delivering multiple sessions of transcranial direct current stimulation (tDCS) over primary motor cortex during physical and MI practice might improve implicit motor sequence learning in a young population. Methods Participants practiced a serial reaction time task (SRTT) either physically or through MI, and concomitantly received either an anodal (excitatory) or sham stimulation over the primary motor cortex during three successive days. The effect of anodal tDCS on the general motor skill and sequence specific learning were assessed on both acquisition (within-day) and consolidation (between-day) processes. We further compared the magnitude of motor learning reached after a single and three daily sessions of tDCS. Results The main finding showed that anodal tDCS boosted MI practice, but not physical practice, during the first acquisition session. A second major result showed that compared to sham stimulation, multiple daily session of anodal tDCS, for both types of practice, resulted in greater implicit motor sequence learning rather than a single session of stimulation. Conclusions The present study is of particular importance in the context of rehabilitation, where we postulate that scheduling mental training when patients are not able to perform physical movement might beneficiate from concomitant and consecutive brain stimulation sessions over M1 to promote functional recovery.

International audience; The knee is the largest joint in the body and supports high loads, up to several times the body weight. It is vulnerable to injury during sport or professional activities, potentially leading to chronic knee instability. This instability is a functional issue to the patient and is characterized by a “wobbly” feeling. Different internal structures take part in joint stabilization by passive (ligaments, capsule) or active (neuro-muscular system and proprioception) action. The most common injury involves the anterior cruciate ligament (ACL) complete or partial rupture: it is involved in 24% of all knee injuries and 59% of ligamentous injuries [1]. In the United States,the annual incidence in the general population is approximately 1 in 3500 with 100,000 ACL reconstructions performed each year [2, 3]. These conditions are a huge burden on individualsand healthcare systems. Diagnosis of knee instability involves a discussion with the patient and a clinical examination, usually the Lachman test. It consists in a manual anterior translation of the tibia aiming at putting the ACL in tension. By practice, the examiner is able to grade the laxity by severity [4]. However, its sensitivity and specificity to detect complete ACL ruptures depends on the experience of the examiner, the patient’s body type and the delay between the accident and examination [5]. In order to reduce this variability, arthrometers were developed.These devices apply an increasing force to induce a postero-anterior drawer and measure the corresponding translation. Displacement-load curves of the healthy and injured knees are compared; ACL rupture is ascertained when differential laxity is higher than a certain threshold. Well-known arthrometer devices are the KT-1000 developed by [6] and the GNRB® [7]. The former is very popular and has been widely studied; its sensitivity to detect complete ACL ruptures is 77% and its specificity 90% (threshold: differential laxity of 3 mm at 130 N). Thelatter was developed recently; two studies [5, 7] highlighted the superiority of this device compared to similar apparatus. A differential threshold of 3 mm at 134 N is used to determine complete rupture: its sensitivity is 70% and specificity 99%. This arthrometer device is also used to diagnose partial ruptures (threshold of 1.5 mm at 134 N) with a sensitivity of 80% and a specificity of 87%.Knee braces or orthoses are usually part of the standard therapy for knee instability and are commonly prescribed by physicians and medical practitioners. Their claimed mechanical effects are to support/align the joint and increase proprioceptive input [8]. However, very few studies actually show significant actions, from biomechanical studies to therapeutic trials [9, 10]. Mechanical/ physiological effects have been emphasized, but the mechanisms of action have been poorly characterized [8, 9, 10, 11, 12, 13]. What is more, subjective evaluations of patients highlight a large demand for these products; therefore, their efficiency is still widely discussed among medical experts. In particular, therelative importance of the two principal stabilizing mechanisms is not known:- joint stiffening by adding supporting structures, e.g. hinged bars secured to the joint by straps and fabric (passive mechanism)- neuromuscular control enhancement by proprioceptive effect (active mechanism)As a consequence of these uncertainties, medical practitioners and manufacturers still lack a simple evaluation tool for knee orthoses. A French committee of experts highlighted this problem [14] and stated that orthoses must be evaluated by taking both the mechanisms of action and the desired therapeutic effects into account.Although the passive action of knee braces to prevent a drawer motion has already been characterized on surrogate limbs [15, 16, 17], only one attempt has been made to link these measures to corresponding expected in-vivo actions through numerical modelling [18, 19], highlighting a passive stiffening much lower than what is brought by intact ligaments. However, a real clinical study is still needed to validate the numerical results and investigate the influence of patient-specific factors such as morphology, injury severity, neuromuscular adaptation and instability feeling control.This study is aimed at objectively quantifying the joint stiffening action of various commercial braces in-vivo using a GNRB® arthrometer on a number of pathological patients.

The effects of exercise on decision-making performance have been studied using a wide variety of cognitive tasks and exercise interventions. Although the current literature supports a beneficial influence of acute exercise on cognitive performance, the mechanisms underlying this phenomenon have not yet been elucidated. We review studies that used single-pulse transcranial magnetic stimulation (TMS) to probe the excitability of motor structures during whole-body exercise and present a framework to account for the facilitating effects of acute exercise on motor processes. Recent results suggest that, even in the absence of fatigue, the increase in corticospinal excitability classically reported during submaximal and exhausting exercises may be accompanied by a reduction in intracortical inhibition. We propose that reduced intracortical inhibition elicits an adaptive central mechanism that counteracts the progressive reduction in muscle responsiveness caused by peripheral fatigue. Such a reduction would render the motor cortex more sensitive to upstream influences, thus causing increased corticospinal excitability. Furthermore, reduction of intracortical inhibition may account for the more efficient descending drive and for the improvement of reaction time performance during exercise. The adaptive modulation in intracortical inhibition could be implemented through a general increase in reticular activation that would further account for enhanced sensory sensitivity.

International audience; Projections from the somesthetic cortex are believed to be involved in the modulation of motor cortical excitability by muscle vibration. The aim of the present pilot study was to analyse the effects of a vibration intervention on short-latency afferent inhibition (SAI), long-latency afferent inhibition (LAI), and afferent facilitation (AF), three intracortical mechanisms reflecting sensorimotor integration. Abductor pollicis brevis (APB) SAI, AF and LAI were investigated on 10 subjects by conditioning test transcranial magnetic stimulation pulses with median nerve electrical stimulation at inter-stimuli intervals in the range 15-25 ms, 25-60 ms, and 100-200 ms, respectively. Test motor evoked potentials (MEPs) were compared to unconditioned MEPs. Measurements were performed before and just after 15 min of vibration applied to the muscle belly of APB at a frequency of 80 Hz. SAI and LAI responses were significantly reduced compared to unconditioned test MEPs (P=0.039 and P

International audience; The age-related decrease in neuromuscular performance is usually accentuated in very old age (> 80 yr) as evidenced by a marked reduction in maximal force production. However, little is known about the ability to rapidly produce force, which limits daily activities and increase the risk of falling. We aimed to assess rapid force production characteristics and rate of muscle activation of the knee extensors in 15 very old (82 +/- 1 yr) vs 12 young (24 +/- 4 yr) men. Maximal force (F-max) and maximal rate of force development (RFDmax) were determined during separated specific isometric contractions. EMG from the vastus lateralis was analyzed to assess the rate of EMG rise (RER). Finally, RFD and RER were examined at time intervals of 0-50, 50-100, 100-200, 0-200 ms and 0-30, 0-50, 0-75 ms, respectively. We reported lower F-max (414 +/- 91 N vs. 661 +/- 139 N) and absolute REDmax (8720 +/- 2056 N*s(-1) vs. 5700 +/- 2474 N*s(-1)) in the very old men compared to young men (P < 0.01). When normalized to F-max, RFD(max )was similar between groups. Normalized RFD at 0-50 and 0-200 ms were lower (- 34% and - 46%, P = 0.04) for the very old men, while no difference was observed at 50-100 ms and 100-200 ms. RER values were higher (similar to 346%, P < 0.01) for the young men at every time interval. These data suggest that the decline in REDmax is associated with the decrease in F-max. Impairments in RFD were accentuated in the first phase of the contraction, which has been associated in the literature with impairments in neural factors associated with aging.

International audience; Alteration of Soleus (SOL) H-reflex has been reported after prolonged vibratory exposure and it was hypothesized that presynaptic inhibition, known to depress the H-reflex during vibration, largely contributed to the H-reflex changes. To confirm this hypothesis, the purpose of the present study was to quantify the SOL H-reflex changes between sitting and standing positions (postural modulation) with or without the after-effects of 1h of Achilles tendon vibration. Indeed, postural modulation of the SOL H-reflex has been reported to inform on the level of presynaptic inhibition exerted on Ia afferents. SOL H-reflex and M waves were measured in healthy voluntary subjects in both sitting and standing positions before and after 1h of Achilles vibration (frequency: 50 Hz) applied in sitting position (vibration group, n=11) or before and after 1h of sitting position only (control group, n=6). SOL H(max)/M(max) ratios were calculated. Furthermore, in order to quantify presynaptic inhibition induced by prolonged vibration, an index of SOL H-reflex postural modulation was calculated as the standing H(max)/M(max) ratio relative to the sitting one. After 1h of Achilles tendon vibration, a significant decrease in the SOL H(max)/M(max) ratio was observed both in sitting and standing positions (p

Background: Medial patellofemoral ligament reconstruction is currently the technique of choice for the treatment of patellar instability. But what should be the most appropriate graft tension for optimal restoration of patellofemoral kinematics? Methods: Six freshly frozen cadaveric knees were studied, the three bone segments were respectively equipped with opto-reflective markers. The acquisitions were made using the Motion Analysis System®. Six successive acquisitions were performed for each knee under different levels of graft tension. Findings: With an intact medial patellofemoral ligament, the medial patellar tilt increased up to a mean value of 2.02° (SD 3.1), the medial patellar translation gradually increased up to a mean value of 3.3 mm (SD 2.25) with a slight lateral rotation over the first 30° of knee flexion with a maximum mean value of 1.22° (SD 0.8) at 20° of knee flexion. Reconstruction of the medial patellofemoral ligament was performed using different levels of tension applied to the graft. Only 10 N of graft tension could restore normal patellar tilt, lateral shift and rotation, with results approximating those measured on healthy knee. Interpretation: This study confirms the role of the medial patellofemoral ligament in providing adequate patellar stability during the first 30° of knee flexion. According to our findings, a 10 N tension applied to the graft appears sufficient to ensure proper control of patellar tracking whereas 20, 30 and 40 N of tension are excessive tension values inducing a major overcorrection in all studied parameters. Medial patello-femoral ligament reconstruction Patellar tilt - Patellar rotation - Patellar translation - Patellar instability

Objective Spatial dysgraphia, frequently observed after a right hemisphere stroke, associates signs of spatial compression in relation to spatial neglect, and a tilted writing which remains to be explained. Here we present a case study suggesting that tilted writing is due to a tilted representation of the vertical. Material/patients and methods JW, a 75-year-old patient who underwent a right hemisphere hemorrhage showed a pusher syndrome and a writing tilted 11.1° upwardly, consistent through many tests, without other signs of spatial dysgraphia. We comprehensively assessed and followed most aspects of spatial cognition, until nine months post-stroke. For writing assessments, head and trunk were kept upright, and JW was instructed to write with the right (non-paretic) hand, on a paper sheet affixed onto a graphic tablet (to quantify writing orientation and time) positioned in front him on a slanted table (30°). The writing was tested with or without visual clues, and after a modulation of verticality perception. Results One month post-stroke, spatial neglect was severe with predominant signs of body neglect. Subjective straight-ahead was normal. Visual (VV) and postural (PV) perceptions of the vertical were tilted of 11°, counterclockwise. This transmodal tilt was similar both in direction and magnitude to the tilt found congruent on all features of writing: margin, lines, and letters. At 3 months the writing was found slower than a control subject when JW was instructed to write on blank paper (1.67 vs. 0.82 s/letter; P Discussion – conclusion After a right hemisphere stroke, a tilted writing is likely a sign of a tilted verticality representation.

International audience; Clinical studies frequently report an increase in stiffness and a loss of range of motion at joints placed in disuse or immobilization. This is notably the case for subjects maintained in bed for a long period, whilst their joints are not affected. Recently we documented on healthy subjects the benefit in terms of force and activation capacities of the triceps surae offered by vibrations applied to the Achilles tendon. Knowing that stiffness changes may contribute to force changes, the aim of the present study was to investigate the effects of tendon vibration on the triceps surae stiffness of healthy subjects. The vibration program consisted in 14 days of 1h daily Achilles tendon vibration applied at rest. Nineteen healthy students were involved in this study. Before and at the end of the vibration program, musculo-tendinous stiffness in active conditions was determined by use of a quick-release test. Passive stiffness was also analyzed by a flexibility test: passive torque-angle relationships were established from maximal plantar-flexion to maximal dorsiflexion. Passive stiffness indexes at 10°, 15° and 20° dorsiflexion were defined as the slope of the relationships at the corresponding angle. Tendinous reflex, influenced by stiffness values, was also investigated as well as the H reflex to obtain an index of the central reflex excitability. After the program, musculo-tendinous stiffness was significantly decreased (p=.01). At the same time, maximal passive dorsiflexion was increased (p=.005) and passive stiffness indexes at 10°, 15° and 20° dorsiflexion decreased (p

Our aim was to clarify the relationship between power output and the different mechanical parameters influencing it during squat jumps, and to further use this relationship in a new computation method to evaluate power output in field conditions. Based on fundamental laws of mechanics, computations were developed to express force, velocity and power generated during one squat jump. This computation method was validated on eleven physically active men performing two maximal squat jumps. During each trial, mean force, velocity and power were calculated during push-off from both force plate measurements and the proposed computations. Differences between the two methods were not significant and lower than 3% for force, velocity and power. The validity of the computation method was also highlighted by Bland and Altman analyses and linear regressions close to the identity line (P

International audience