Le mouvement nécessite la coordination de nombreux muscles. La manière dont le système nerveux adapte la commande motrice sous l’effet de contraintes telles que la fatigue ou la douleur n'est pas encore bien comprise, en particulier lors des tâches multi-segmentaires. Ce travail a démontré que lors d’une tache de pédalage sous-maximale, une pré-fatigue unilatérale du quadriceps entraîne une redistribution préférentielle de l'activité musculaire vers la jambe controlatérale pour compenser. Une seconde étude réalisée à puissance maximale (i.e sprint) a mis en évidence une diminution de l'activation des muscles synergistes, mais permettant le maintien de l’efficacité de pédalage. De façon originale, une amélioration de l'activation d'autres muscles a été observée, participant à augmenter la force produite lors de la phase de traction de la pédale pour les deux jambes. Enfin, en réponse à une douleur locale, les résultats d’une dernière étude suggèrent que, lorsqu'il existe une opportunité claire de compenser, des adaptations se produisent dans le but de diminuer la charge dans le tissu touché. Dans l'ensemble, cette thèse a démontré que les coordinations musculaires s'adaptent à la fatigue et à la douleur en exploitant les nombreux degrés de liberté disponibles dans cette tâche. Ces adaptations ont été discutées au regard des théories et lois de contrôle proposées dans la littérature incluant la minimisation de « fonctions de coût » (énergétique, mécanique et/ou nerveux) ou d’adaptation à la douleur, mais aussi des contraintes spécifiques de la tâche (orientation de la force externe à la pédale, transferts inter-segmentaires, couplage mécaniques et nerveux inter-jambes). / Movement requires the coordination of multiple muscles. How this is done during fatigue and pain is not well understood, particularly in multijoint tasks. This thesis investigated muscle coordination and the adaptations to local fatigue or pain during pedaling. Fatigue and pain was induced unilaterally on the quadriceps, which made it possible to determine the adaptations at these perturbed muscles, as well as between synergists, and muscles within the same leg and between legs. The thesis demonstrated that during submaximal pedaling, the unilateral pre-fatigue results in a predominant redistribution of muscle activity towards unaffected muscles at the contralateral leg. Another study performed in the same pre-fatigue condition but at maximal intensity, provided evidence that muscle coordination changes to decrease activation of ipsilateral synergist muscles allowing to maintain an effective force orientation at the pedal. Interestingly, we also observed an increase in activation of other muscles which participated to improve the total force produced during the flexion phase of both legs. Finally, another study that induced unilateral local pain, supported pain adaptation theories suggesting that when there is a clear opportunity to compensate, adaptations to pain occur to decrease load within the painful tissue. Overall this thesis demonstrated that muscle coordination readily adapts exploiting the many degrees of freedom available during pedaling. Both neural (between legs) and mechanical (between pedals) couplings in this specific task and the minimization of cost functions (neural, energetic, mechanical) or pain adaptation theories might explain these results.

The study of visually-guided reaching has been a meaningful tool to investigate sensory-motor coordination in typical development and different clinical paediatric populations. The aim of this study was to characterize the development of multi-joint reaching behaviour in children and youth, from 5 to 16 years of age, allowing us to capture changes that may occur into adolescence. Participants were 68 able-bodied children and youth, with no history of developmental, educational or social problems. A stratified recruitment strategy was used to adequately represent five age groups: I (5-6 years), II (7-8 years), III (9-10 years), IV (11-13 years) and V (14-16 years). A center-out reaching task was used as it allowed us to measure effects of limb mechanics during reaching. Different patterns of inter-segmental motions at the shoulder and elbow joints were needed to reach the different targets: flexion at both joints, extension at both joints, and a mixed-coordination pattern. Children were asked to reach quickly and accurately to 8 targets located at 45 degree intervals around the perimeter of a circle with a 6 cm radius. The development of reaching was described using non-parametric statistics. The global features of path length and total movement decreased as a function of increasing age, with less variability observed in older participants (p<0.05). This increased accuracy was explained by a significant reduction (p<0.05) in distance and direction error of the first movement component of the reach, indicative of the increasing ability of children to accurately plan movements based on an internal representation of the limb. These older children were also able to respond to the visual target more quickly (p<0.05). In general, initial direction errors and total movement time increased from a minimum for the 2-joint flexion coordination to a maximum for the mixed-coordination pattern. The magnitude of error, however, decreased as a function of age (p<0.05), and in particular for the mixed-coordination pattern (p<0.01). This center-out task is therefore considered to be responsive to observe effects of development and limb mechanics on performance. The established normative data set will provide a reference for the measures of performance in children with neurodevelopmental disorders. / Thesis (Master, Rehabilitation Science) -- Queen's University, 2009-11-30 11:29:28.718

No description available.

Purpose: To determine the reliability of early force production (50, 100, 150, 200, and 250 ms) relative to peak force (PF) during an isometric mid-thigh pull and to assess the relationships between these variables. Methods:: Male collegiate athletes (N = 29; age 21.1 [2.9] y, height 1.71 [0.07] m, body mass 71.3 [13.6] kg) performed isometric mid-thigh pulls during 2 separate testing sessions. Net PF and net force produced at each epoch were calculated. Within- and between-session reliabilities were determined using intraclass correlation coefficients and coefficient of variation percentages. In addition, Pearson correlation coefficients and coefficient of determination were calculated to examine the relationships between PF and time-specific force production. Results:: Net PF and time-specific force demonstrated very high to almost perfect reliability both within and between sessions (intraclass correlation coefficients .82–.97; coefficient of variation percentages 0.35%–1.23%). Similarly, time-specific force expressed as a percentage of PF demonstrated very high to almost perfect reliability both within and between sessions (intraclass correlation coefficients .76–.86; coefficient of variation percentages 0.32%–2.51%). Strong to nearly perfect relationships (r = .615–.881) exist between net PF and time-specific net force, with relationships improving over longer epochs. Conclusion:: Based on the smallest detectable difference, a change in force at 50 milliseconds expressed relative to PF > 10% and early force production (100, 150, 200, and 250 ms) expressed relative to PF of >2% should be considered meaningful. Expressing early force production as a percentage of PF is reliable and may provide greater insight into the adaptations to the previous training phase than PF alone.

VIBRATION AVOIDANCE, a technique to proactively remove unwanted or excessive vibrations in multi-joint industrial robots, has shown to be desired in various applications. A trade-off between vibration avoidance performance and path deviation has been thekey criteria for assessing the effectiveness and quality of an approach. The purpose of this thesis is to compare two proposed state-of-the-art vibration avoiding approaches: input shaping and extended flexible joint model combined with specialized compensation control and explore the fusion of them. Both approaches are first investigated and evaluated in simulation. A comparison is then conducted in the four presented baseline movements on a real robot. Among the two approaches, input shaping is less comprehensive but enables rapid identification, making it suitable for simple repetitive tasks. It is also found that joint-wise path generation used in input shaping causes a loss of path fidelity, but this problem is alleviated when using an extended flexible joint model combined with specialized compensation control. The latter approach preserves synchronicity across all joints and assures multi-input multi-output (MIMO)-path fidelity. The extended flexible joint model, which is identified through a nonlinear gray-box model, is also less susceptible to modeling errors. The performance comparison with two rudimentary digital filters exhibits promising results for both proposed solutions. Finally, a fusion of the two approaches is proposed as a final solution of this work. As a result, the collaborative approach is the closest to ideal vibration avoidance but suffers from greater path deviation. The extended flexible joint model combined with compensation results in the least deviation from the baseline trajectory among all tested approaches. / VIBRATIONSDÄMPNING, en teknik för att proaktivt undvika oönskade vibrationer i fleraxlade industrirobotar, har visat sig vara önskvärd i många olika applikationer. En avvägning mellan vibrationsdämpningens prestanda och avvikelser från rörelsebanan har varit viktiga kriterier för att bedöma effektiviteten och kvalitén av ett tillvägagångssätt. Syftet med denna avhandling är att jämföra två toppmoderna tillvägagångssätt för att undvika vibrationer: ingångsformning och utökad flexibel axelmodell kombinerad med specialiserad kompensationskontroll samt utforska sammanslagning av de två. Bägge tillvägagångssätt är först undersökta och utvärderade i en simulation. En jämförelsemellan de fyra standard robotrörelserna som är presenterade är sedan genomförd på en riktig robot. Mellan de två tillvägagångssätten är ingångsformning mindre förståeligt men möjliggör en snabb identifikation vilket gör den lämplig för simpla repetitiva uppgifter. Det fastställs även att axelvis generering av rörelsebanor som används med ingångsformning orsakar lägre noggrannhet och pålitlighet vad gäller avvikelser från rörelsebanan. Detta problem är inte lika påtagligt vid användning av utökad flexibel axelmodell kombinerad med specialiserad kompensationskontroll eftersom detta tillvägagångssätt bevarar synkroniciteten över samtliga axlar och garanterar multi-input multi-output (MIMO) följdriktighet. Den utökade flexibla axelmodellen, som identifieras med hjälp av en icke-linjär gray-box modell, är även mindre mottaglig för modelleringsfel. Prestandajämförelsen med två rudimentära digitala filter uppvisar lovande resultat för bägge föreslagna lösningar. Till sist, en sammanslagning av de två tillvägagångssätt är föreslagen som en slutgiltig lösning. Det sammanslagna tillvägagångssättet är närmast perfekt vibrationsdämpning men medför större avvikelser från rörelsebanan. Den utökade flexibla axelmodellen kombinerad med kompensation resulterar i minst avvikelse från rörelsebanan bland alla testade tillvägagångssätt.