Analyse biomécanique du mouvement de préhension contraint et altéré : indices quantitatifs de la gestion de la redondance motrice

Through the assessment of quantitative indexes, this work focused on the biomechanical analysis of the upper limb redundancy and motor coordination during a reach-to-grasp movement. Based on the Uncontrolled Manifold approach, we considered, on one hand, a particular aspect of the synergies, i.e. the covaration of elemental variables of a system that lead to a stabilization of a particular performance variable. In this framework, it was hypothesized that degrees of freedom were not frozen as suggested by Bernstein but combined in order to ensure performance and stability. On the other hand, we used a robotic index, the manipulability, allowing the assessment of wrist displacement capacities during the grasping task. The aim of the present work was to study the motor coordination during constrained and altered upper limb movements through the evaluation of these two. In this framework, the first analysis consisted in evaluating the effect of a spatial constraint materialized by an obstacle during the transport phase of the reach-to-grasp movement. The second part consisted in identifying motor coordination of the upper limb for spinal cord injury patients, especially quadriplegic patients, using both kinematics and electromyographic (EGM) analyses. Two experiments were conducted to record kinematics and EMG activity of upper limb muscles with adapted apparatus. In the presence of an obstacle, results showed that wrist Cartesian trajectory was stabilized through flexible combination of joint synergy. Also, the results showed an increase of goal equivalent configurations to stabilize the elbow trajectory when an obstacle was present. This result suggests that the increase of the joint angle flexibility may be a mechanism by which the central nervous system takes into account a spatial constraint during obstacle avoidance. In the same time, the increase of the manipulability of the wrist joint center was found. For quadriplegic patients, EMG analysis showed a compensation of the weakness or paralysis of particular muscles, particularly the triceps brachii, by an increase of the relative activation of the shoulder muscles. In addition, these subjects presented a variance decomposition similar to the one of the control group suggesting that, despite the presence of a motor deficiency, goal equivalent joint configuration during the execution of the movement are still present or have been recovered. Also, for manipulability, patients have strong similarities with the control group. Considering these results, we think that the exploration of synergies through the proposed indices could be an interesting tool to study the impact of external constraint and impairment on the biomechanical parameters of movement. These works open the way for interesting applications in the field of movement simulation by considering the variability of joint trajectories in relation to a performance variable. Also, they may be applied to the assessment of the coordination of impaired subjects in order to evaluate and improve rehabilitation programs by providing quantitative information on the contribution of all the degrees of freedom.Au travers de l'évaluation d'indices quantitatifs, ce travail se focalise sur l'analyse biomécanique de la redondance et des coordinations motrices du membre supérieur lors de la réalisation du mouvement de préhension. En nous basant sur la théorie de « l'uncontrolled manifold », nous abordons, d'une part, un aspect particulier de la notion de synergie qui est relatif à la covariation des paramètres d'état du système afin de stabiliser une variable de performance. En effet, la thématique de la redondance motrice qui est une des caractéristiques principale du système musculo-squelettique a été récemment reformulée. Dans ce cadre, il est postulé que les degrés de liberté ne sont jamais éliminés comme le suggère la théorie proposée par Bernstein mais combinés afin d'assurer performance et flexibilité. D'autre part, nous utilisons un indice issu de la robotique, la manipulabilité permettant d'évaluer les capacités de déplacement du poignet au cours de ce mouvement de saisie. L'objectif de ce travail consiste à appliquer ces deux analyses à des mouvements contraints ou altérés afin d'identifier les modifications de la coordination motrice par rapport à des conditions contrôles. Dans cette optique, la première analyse consiste à évaluer l'effet d'une contrainte spatiale matérialisée par un obstacle lors de la phase d'approche d'un mouvement de préhension par une mesure des paramètres cinématiques du membre supérieur. La seconde étude vise à identifier la coordination motrice du membre supérieur de sujets atteints d'une lésion médullaire et souffrants de tétraplégie par une analyse combinée des paramètres électromyographiques (EMG) de certains muscles impliqués et des paramètres cinématiques. Pour cela nous avons mis en place deux protocoles expérimentaux au cours desquels les angles articulaires du membre supérieur ainsi que le signal EMG ont été évalués par des moyens adaptés. En présence d'un obstacle, nos résultats montrent de manière classique que la position du poignet est stabilisée au travers d'une synergie articulaire. De plus, il semble que la présence d'une contrainte spatiale renforce les synergies pour stabiliser la trajectoire du coude dans la seconde partie du mouvement correspondant au franchissement de l'obstacle. Ce renforcement se caractérise par une utilisation accrue de configurations articulaires équivalentes. Ce résultat suggère que l'augmentation de la flexibilité des configurations articulaires serait un mécanisme par lequel le système nerveux central pourrait prendre en compte la présence d'une contrainte spatiale. Parallèlement, la présence de l'obstacle entraine des modifications de la manipulabilité du poignet. Pour les sujets souffrants de tétraplégie, l'analyse EMG a montré une compensation de la faiblesse ou la paralysie de certains muscles, le triceps brachial notamment, par une augmentation de l'activité relative des muscles de l'épaule. De plus, ces sujets présentent une décomposition de la variance des angles articulaires similaire à celle du groupe contrôle suggérant que, malgré la présence d'une déficience motrice, la flexibilité des configurations articulaire au cours de l'exécution du mouvement est toujours présente ou a été récupérée. De même pour la manipulabilité, les patients présentent de fortes similitudes avec les sujets valides avec, dans certains cas, des valeurs de manipulabilité du poignet supérieures. Ces résultats nous amènent à penser que l'étude des synergies au travers des indices proposés pourrait constituer un outil intéressant afin d'étudier l'impact d'une contrainte et d'une déficience motrice sur les paramètres biomécaniques du mouvement. Les présents travaux ouvrent des voies intéressantes pour des applications dans le domaine de la simulation du mouvement et de l'évaluation fonctionnelle de la coordination de sujets déficients moteurs en vue d'évaluer et améliorer la rééducation par l'apport d'informations quantitatives aux cliniciens

Postural prevalence, time of day and spent time activities during smartphone weekday use among students: A survey to prevent musculoskeletal disorders

The long time spent on smartphones in awkward postures exposes young users to the risk of developing musculoskeletal disorders (MSDs). This study aimed to investigate 1) how the duration of smartphone use varies by the time of day and activities and 2) the risks of MSDs based on an analysis of the postures used when interacting with smartphones. A cross-sectional survey was conducted among 263 university students. The duration of smartphone use during a typical weekday was investigated over four times of the day and seven activities. After checking for normality, a nonparametric Friedman test was used to study the differences in the time spent using a smartphone according to the time of day and activity. Postural prevalence during weekdays was analyzed using a taxonomy called SmarTaxo, consisting of 41 postures. The Rapid Upper Limb Assessment (RULA) ergonomic score was chosen to assess the MSD risks associated with each posture.Smartphone use was the highest in the evening (301.1 min; 95 % confidence interval [CI]: 277.4–324.8 min, p < 0.05). Texting (170.8 min; 95 % CI: 152.0–189.6 min) and watching videos (163.6 min; 95 % CI: 146.3–180.9 min) were the most common activities. Three sitting and two walking postures were primarily used in the morning (29.3–36.9 %), afternoon (27.0–44.4 %), and evening (28.9%–38.9 %). Standing postures were preferred in the morning and afternoon (36.9 % and 42.2 %, respectively), while one lying posture was widely reported in the evening (39.2 %). The RULA scores for these postures ranged from 3 to 4. However, four lying postures, often observed during the evening (frequency between 20.5 % and 37.6 % of the time), had RULA scores of 6. In conclusion, the study identified an existing MSD risk among smartphone users, especially with long durations of daily use. Special emphasis should be placed on addressing the reclining postures adopted during evening smartphone use, as they subject students to a significantly elevated risk of MSDs

Effect of day time on smartphone use posture and related musculoskeletal disorders risk: a survey among university students

Abstract Background Musculoskeletal disorders (MSDs) are one of the most important problems among young smartphone users worldwide. Portability leads to a wide variety of postures during the different activities of the day. The objective evaluation of these postures coupled with ergonomic tools allows evaluating the level of MSD risk to which users are exposed. Methods The purpose was to investigate the effect of the time of day on the posture adopted during smartphone use among university students. The study was conducted through a cross-sectional survey of 263 university sports students. Four time of day, i.e. morning, afternoon, evening and night, and a taxonomy of 41 postures called SmarTaxo were considered. SmarTaxo included 18 sitting, 11 standing, 10 lying and 2 walking postures and their ergonomic score. After checking the normality of the data, a non-parametric Kruskal–Wallis test was used to study the effect of the time of day on the use duration of the different postures. Results The total mean duration use per typical weekday was 5.39 ± 2.19 h for males and 5.15 ± 1.60 h for females with maximal duration during evening. The average smartphone use durations were statistically longer in afternoon and evening for all sitting (9.44 and 9.22 min respectively, p  5 h per day), young people will remain highly exposed to MSDs

Effect of the presence or absence of upper limb support on posture when a smartphone user is in a seated position under ambient light conditions

International audienceBackground: Home, public transport, work, the number of environmental positions constraining the use of smartphones is significant.Research question: How can the presence of an upper limb support influence the sitting posture of smartphone users under fixed illumination and brightness?Methods: Twelve subjects (21,6 ± 5,5 years old) performed web browsing under two environmental positions (POSITION): sitting with and without support (table). The users' postures were evaluated through relative kinematics joint angles analysis. A repeated measure analysis of variance and Tukey post-hoc tests were performed to test the effect of POSITION on posture.Results: In sitting position in front of a table, neck is less stressed (flexion < 10°) and trunk and shoulder are supported which suggests less constrains for the joints.Relevance to industry: To prevent injury or pain, the use of an upper limb support (to lean on) should be considered for people/workers who use the smartphone frequently

Identification of upper limb joint strategies in use of touch devices

International audienceRecent technological advancements have enabled the development of new communication devices and new ways to use them. Among them, touch technology is experiencing a major expansion. Indeed, its use is easy, intuitive and natural and is an excellent interface between human and machine. In this context, many studies have examined the development of touch screens whether for phones or tablets. The objective was to analyze how the user interacts with the screen to make it more ergonomic and easier to use. The results show that size, colours or locations of the interactive elements could influence the performance of the user. Although this approach is essential for the development of tactile devices, user motion analysis is equally: the upper limb is classically described as a multi-joint system with redundancy, which leads to the same movement on the screen with an infinite number of joint combinations. Very few studies have examined these biomechanical characteristics. However, such information may be relevant in the development of devices suitable for motor capabilities of users. The objective of this work was to analyze the joint organization of the upper limb during the interaction with a touch pad. Eleven healthy right handed subjects voluntarily participated to the experience. The task consisted in achieving five times a 16 pieces puzzle presented on a 10-inch touch pad. The pieces were randomly displayed at the bottom of the screen and a translucent guide was presented in the upper part. To perform the motion analysis, the trajectories of eighteen light reflective markers placed on the trunk and the right upper-limb were recorded using an optoelectronic system. Then, relative upper limb joint angles were computed according to the ISB instructions. A Hierarchy Ascending Classification was applied on the range of motion of the 15 degrees of freedom. Three groups of subjects emerged. The first one included six subjects that had an important solicitation of the proximal joints (shoulder and elbow) and a very low implication of the wrist. This organization was called “proximal strategy”. On the contrary, the second group (with five subjects) was characterized by an important mobilization of the wrist and a relative low involvement of the proximal joints. This organization was called “wrist strategy”. One subject had an important and equal solicitation of all de degrees of freedom characterizing a “neutral strategy”. From a biomechanical point of view, results revealed that there were different ways to interact with the touch pad and perform the task. This information would be relevant in the framework of ergonomics to adapt interfaces in relation to these different motor organizations. This is particularly relevant for patients with motor impairments. Indeed, the loss of a degree of freedom or control of a muscle due to trauma could significantly alter the motor organization and thus make interaction difficult or even impossible. However, future studies are needed to determine to what extent these organizations are stable drive and what are the parameters that can lead a subject to modify the organization of his gesture

Biomechanical analysis of interaction strategies using touchscreen: preliminary study

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Biomechanical analysis of upper limb during the use of touchscreen: motion strategies identification

International audienceNowadays touch technology is growing and developers try to make it ever more intuitive and easier to use. This present work focused on the upper limb joint coordination during the achievement of puzzles on touch screen. A 5-inch and 10-inch devices were used to perform 9 and 16 pieces puzzles dragged with digits. The conclusions showed an increase in joint solicitation with the number of piece and the touch screen size. Moreover, three interactions strategies proved to be an evidence: the 'wrist strategy' preferentially implying wrist flexion/extension, the 'elbow strategy' preferentially implying the elbow flexion/extension and the 'neutral strategy' mobilising equally the two joints. From an ergonomic point of view, the data about how the upper limb segments are mobilised while interacting with the screen could be relevant to increase the adaptability of the devices to the user, including users with motor impairments. Practitioner Summary: Information about the biomechanical organisation of movement during interaction with touch devices appears relevant in order to develop applications adapted to the motor capacities of users. From the analysis of joint angles when performing several times a puzzle with healthy subjects, three motor strategies were highlighted

Démarche de co-conception d'une méthode d'observation et d'évaluation multidimensionnelle de l'accessibilité au numérique

National audienceThis paper addresses the evaluation of technological devices for digital accessibility for people with disabilities or loss of independence. It builds on the work of a multidisciplinary consortium that has been set up at the national level to develop and propose a multidimensional evaluation and observation methodology based on an integrative co-design approach. The main qualitative and quantitative methods used by the partners in the field of digital accessibility are presented. Using both methods in the context of use is essential in order to model and characterise behaviours in terms of digital accessibility. The implementation of the methodology is illustrated by an exploratory study of five volunteers in a smart home environment.Cet article aborde la problématique de l’évaluation des dispositifs technologiques pour en mesurer l’accessibilité numérique par des personnes en situation de handicap ou de perte d’autonomie. Il s’appuie sur le travail d’un consortium pluridisciplinaire qui s’est constitué au niveau national pour élaborer et proposer une méthodologie d’évaluation et d’observation multidimensionnelle selon une démarche de co-conception intégrative. Les principales méthodes qualitatives et quantitatives utilisées par les partenaires dans le champ de l’accessibilité numérique sont présentées. Le croisement des deux méthodes à partir de contextes d’usage s’avère indispensable dans un but de modéliser et de qualifier les comportements dans l’accessibilité au numérique. La mise en oeuvre de la méthodologie est illustrée par une pré-étude sur cinq sujets tests au sein d’un environnement de maison intelligente

Méthode d'observation multimodale de l'accessibilité numérique pour les personnes âgées

International audienceCet article présente le projet MAN, de type mission AUTON du CNRS visant de proposer une méthode d'observation basée sur différents modalités en permettant d'analyser l'accessibilité numérique des personnes âgées. L'originalité du projet consiste dans la proposition de plusieurs indicateurs qualitatives et quantitatives qui par analyse croisée vont permettre l'analyse. Nous présentons principalement le corpus qui a été enregistré dans des conditions de Living Lab dans la MIB de Toulouse