Influence of Force-Length Relationship and Task-Specific Constraints on Finger Force-Generating Capacities

Grip strength loss in extended and flexed wrist postures has been explained by reduced force-generating capacities of extrinsic finger flexor resulting from non-optimal length, owing to the force-length relationship. Recent works suggested that other muscles, especially wrist extensors, participate in this grip strength loss. The objective of this study was to clarify the role of the force-length relationship in finger force production. 18 participants performed maximal isometric finger force production during pinch grip (Pinch) and four-finger pressing (Press) tasks in four different wrist postures (extended, flexed, neutral, spontaneous). The maximum finger force (MFF), finger and wrist joint angles, as well as activation of four muscles were determined using dynamometry, motion capture, and electromyography. The force and length of the four muscles were estimated from joint angles and muscle activation using a musculoskeletal model. MFF decreased for flexed wrist during Pinch but remained stable across wrist postures during Press. The results suggested that the loss of pinch grip force in deviated wrist posture is partially related to force-length relationship of finger extensors. In opposition, MFF during Press was not influenced by the modulation of muscle capacities but was probably first limited by mechanical and neural factors related to finger interdependenceComment: Annals of Biomedical Engineering, 202

A severe case of Plasmodium falciparum malaria imported by a French traveler from Cameroon to French Guiana despite regular intake of Artemisia annua herbal tea

The use of herbal tea with Artemisia annua by travelers and traditional communities in Africa has increased in recent years as a supposed form of malaria prophylaxis, although its use is not recommended due to lack of efficacy. The risk of severe malaria complications that can lead to death is real regarding said behavior, and awareness needs to be raised. We report a case of severe Plasmodium falciparum malaria imported in the Amazon rainforest by a traveler returning from Cameroon who treated himself with Artemisia annua herbal tea

Role of the force-length relationship on muscle coordination and force production with the hand : a biomechanical modeling approach

La main nous permet de réaliser au quotidien une multitude de tâches en interaction avec notre environnement impliquant des niveaux de force élevés ou des gestes fins. Comment le système neuro-musculosquelettique coordonne-t-il ces multiples structures pour produire un geste ou une force, reste un questionnement majeur pour la compréhension du mouvement humain du fait d'un manque de données quantifiées pour la main. Mes travaux de thèse avaient pour but d’explorer le rôle de la mécanique musculaire, en particulier des aspects de « force-longueur », sur les coordinations musculaires et la capacité à produire de la force avec la main. Pour y arriver, j’ai développé un modèle musculosquelettique de la main et un protocole de mesure permettant d’étudier l’effet de la posture et de l’activation sur la force maximale que le muscle peut produire. Ces outils ont été employés dans deux études s’intéressant aux facteurs associés aux dimensions de l’objet et aux types d’application de force, préhension ou appui. Ces études ont permis de montrer que selon la tâche, les capacités d’un muscle spécifique semblent guider les variations de la force maximale que l’on peut exercer, notamment les extenseurs des doigts ou du poignet, dans les tâches préhensiles. Ces travaux doctoraux suggèrent que lors de la préhension les capacités musculaires exercent une influence forte sur les coordinations musculaires et sur les niveaux de force exercés avec la main. Ils apportent aussi des données essentielle pour les ergonomes et la compréhension des facteurs de risque des troubles musculosquelettiques en reliant directement une posture à un état favorable du système musculosquelettique.The hand allows us to perform a multitude of tasks in daily interaction with our environment, to manipulate objects of various shapes and weights, involving high levels of force or fine gestures. How the neuro-musculoskeletal system coordinates these multiple structures to produce a force remains a major question in the understanding of human movement. In particular, there is little understanding of how the force production capabilities of each muscle influence their coordination to accomplish a task due to a lack of quantified data. The aim of this thesis work was to explore the role of muscle mechanics, in particular aspects of ’force-length’, on muscle coordination and the ability to produce force with the hand. To achieve this, I developed a musculoskeletal model of the hand and a measurement protocol to study the effect of posture and activation on the maximum force that the muscle can produce. These tools were used in two studies that focused on factors associated with object size and the types of force application, grasping or supporting. This work showed that depending on the task, the ability of a specific muscle seemed to guide the variations of maximum hand force, notably the finger or wrist extensors in prehensile tasks. This doctoral work suggests that during prehension, muscular capabilities have a strong influence on muscle coordination and force levels exerted with the hand. They also provide essential data for ergonomists and the understanding of risk factors for musculoskeletal disorders by directly linking a posture to a favourable state of the musculoskeletal system

Complex couplings between joints, muscles and performance: the role of the wrist in grasping

International audienceThe relationship between posture, muscle length properties and performance remains unclear, because of a lack of quantitative data. Studies on grasping tasks suggested that wrist position could favour the extrinsic finger flexor in regards to their length to maximise grip force performance. The present study aimed at providing quantitative evidence of the links between wrist posture, muscle capacities and grip capabilities. it combines experimental measurements and a musculoskeletal model including the force-length relationship of the four prime muscles used in grasping. participants exerted their maximum grip force on a cylindrical dynamometer in four different wrist postures, including one freely chosen by participants (spontaneous). A musculoskeletal model computed the muscle force level and length from motion capture and muscle activation. Results revealed that participants exerted maximum grip force spontaneously, with a loss of force when using other postures. At muscle force and length level, grip force variation seems to be associated with all the muscles under study. This observation led to a first quantitative link between power grip, posture and muscle properties, which could provide more insight into neuromechanical interaction involved when grasping. the design of ergonomic devices could also benefit from this quantification of the relationship between wrist angle and muscle length properties

Using musculoskeletal modelling to clarify the effect of wrist posture on muscle force-generating capacities and maximal grip force during a power grip task

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Modelling force-length-activation relationships of wrist and finger extensor muscles

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

Characterization of the mechanical properties of the mouse Achilles tendon enthesis by microindentation. Effects of unloading and subsequent reloading

International audienceThe fibrocartilaginous tendon enthesis, i.e. the site where a tendon is attached to bone through a fibrocartilaginous tissue, is considered as a functionally graded interface. However, at local scale, a very limited number of studies have characterized micromechanical properties of this transitional tissue. The first goal of this work was to characterize the micromechanical properties of the mineralized part of the healthy Achilles tendon enthesis (ATE) through microindentation testing and to assess the degree of mineralization and of carbonation of mineral crystals by Raman spectroscopy. Since little is known about enthesis biological plasticity, our second objective was to examine the effects of unloading and reloading, using a mouse hindlimb-unloading model, on both the micromechanical properties and the mineral phase of the ATE. Elastic modulus, hardness, degree of mineralization, and degree of carbonation were assessed after 14 days of hindlimb suspension and again after a subsequent 6 days of reloading. The elastic modulus gradually increased along the mineralized part of the ATE from the tidemark to the subchondral bone, with the same trend being found for hardness. Whereas the degree of carbonation did not differ according to zone of measurement, the degree of mineralization increased by >70 % from tidemark to subchondral bone. Thus, the gradient in micromechanical properties is in part explained by a mineralization gradient. A 14-day unloading period did not appear to affect the gradient of micromechanical properties of the ATE, nor the degree of mineralization or carbonation. However, contrary to a short period of unloading, early return to normal mechanical load reduced the micromechanical properties gradient, regardless of carbonate-to-phosphate ratios, likely due to the more homogeneous degree of mineralization. These findings provide valuable data not only for tissue bioengineering, but also for musculoskeletal clinical studies and microgravity studies focusing on long-term space travel by astronauts

Outcomes of Bedaquiline Treatment in Patients with Multidrug-Resistant Tuberculosis

Bedaquiline is recommended by the World Health Organization for the treatment of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB). We pooled data from 5 cohorts of patients treated with bedaquiline in France, Georgia, Armenia, and South Africa and in a multicountry study. The rate of culture conversion to negative at 6 months (by the end of 6 months of treatment) was 78% (95% CI 73.5%–81.9%), and the treatment success rate was 65.8% (95% CI 59.9%–71.3%). Death rate was 11.7% (95% CI 7.0%–19.1%). Up to 91.1% (95% CI 82.2%–95.8%) of the patients experienced >1 adverse event, and 11.2% (95% CI 5.0%–23.2%) experienced a serious adverse event. Lung cavitations were consistently associated with unfavorable outcomes. The use of bedaquiline in MDR and XDR TB treatment regimens appears to be effective and safe across different settings, although the certainty of evidence was assessed as very low