Optimization has been used to simulate human neural control and resulting movement patterns. The short term aim was to develop the methodology required for solving the movement optimization problem often arising when modelling human movements. A long term aim is the contribution to increased knowledge about various human movements, wherein postures is one specific case. Simulation tools can give valuable information to improve orthopeadic treatments and technique for training and performance in sports. In one study a static 3D model with 30 muscle groups was used to analyse postures. The activation levels of these muscles are minimized in order to represent the individual’s choice of posture. Subject specific data in terms of anthropometry, strength and orthopedic aids serve as input. The specific aim of this part was to study effects from orthopedic treatment and altered abilities of the subject. Initial validation shows qualitative agreement of posture strategies but further details about passive stiffness and anthropometry are needed, especially to predict pelvis orientation. Four studies dealt with movement optimization. The main methodological advance was to introduce contact constraints to the movement optimization. A freetime multiple phase formulation was derived to be able to analyse movements where different constraints and degrees of freedom are present in subsequent phases of the movements. The athletic long jump, a two foot high jump, a backward somersault and rowing were used as applications with their different need of formulation. Maximum performance as well as least effort cost functions have been explored. Even though it has been a secondary aim in this work the results show reasonable agreement to expected movements in reality. Case specific subject properties and inclusion of muscle dynamics are required to draw conclusions about improvements in the sport activity, respectively. / <p>QC 20120910</p>

Children with myelomeningocele (MMC) usually have problems with daily life activities, but the background to their problems is not altogether obvious. An understanding of the possible causes of activity problems is a prerequisite for the effectiveness of physical therapy. The overall aim of the present studies was to identify impairments above the cele level, which might influence mobility in children with MMC (study I) and to analyse sitting posture (study II) and the movement characteristics of reaching movements (study III and IV). In total, 41 children and young adults with MMC and without mental retardation were investigated. Study I comprised 32 children, 6-11 years. Mobility and the caregiver assistance required for mobility were quantified according to the Paediatric Evaluation of Disability Inventory (PEDI) and correlation between mobility and neurological impairment, hand function and cognitive function were calculated. The results showed that nine children achieved independent mobility and that there was a moderate and significant correlation between the need for physical assistance and high cele level, impaired hand function and impaired cognitive function. In those children who used a wheelchair, only poor hand strength was significantly correlated with the need for caregiver assistance. Study II comprised 11 children, 10-13 years, and a control group of 20 healthy children. Sitting posture was investigated by using a force plate and analysed from the frequency and the amplitude of the postural sway. The reaction forces before and during rapid arm lift were also analysed. The result showed that children with MMC had significantly lower sway frequency compared to the controls. In both groups, the ground reaction forces were registered before the children lifted their arms. Study III and IV comprised 31 children and young adults, 9-19 years and 31 matched controls. Reaching movements were investigated with a digitising tablet, linked to a computer. The ability to program and execute reaching movements was analysed and also the ability to adapt reaching to new visuomotor conditions. The results showed that the MMC group had poorer precision, less straight movements and shorter deceleration phases as compared to the controls. In both groups the movements were pre-programmed. In addition, adaptation of reaching to new visuomotor conditions was poor in the MMC group as compared to the controls. In conclusion we found that impairments above the cele level influenced mobility and the control of sitting posture in children with MMC. Reduced precision and co-ordination of reaching, and also difficulties with motor adaptation, could partly explain thier problems with hand activities. These findings need to be considered in therapy programs for children and young adults with MMC.

Background: The latest generation of rear-end whiplash protection systems, as found in the WHIPS Volvo and SAHR Saab, have reduced injury rates by almost 50% in comparison with the previous generation of seat/head restraint systems. Occupant behaviour, such as seated posture and seat adjustment settings, may affect the injury risk. Method: Five studies were conducted. Studie I was an injury outcome study based on insurance data. Studies II-IV investigated seat adjustment, occupant backset, and cervical retraction for drivers and occupants in different postures and positions in the car, during stationary and driving conditions. Study V compared the occupant data from studies II and III with a vehicle testing tool, the BioRID dummy, using the protocols of the ISO, RCAR, and the RCAR-IIWPG. Results: Female drivers and passengers had a threefold increased risk for medically-impairing neck injury in rear-end impacts, compared to males. Driver position had a double risk compared with front passenger seat position. Female drivers adjusted the driver seat differently to male drivers; they sat higher and closer to the steering wheel and with more upright back support. The volunteers also adjusted their seat differently to the ISO, RCAR, and RCAR-IIWPG protocol settings; both sexes sat further away from the steering wheel, and seat back angle was more upright then in the protocols. In stationary cars, backset was highest in the rear seat position and lowest in the front passenger seat position. Males had a larger backset than females. Cervical retraction decreased and backset increased for both sexes when posture changed from self-selected posture to a slouched posture. The BioRID II dummy was found to represent 96th percentile female in stature, and a 69th percentile female in weight in the volunteer group. Conclusions: Risks in car rear-end impacts differ by sex and seated position. This thesis indicates the need for a 50th percentile female BioRID dummy and re-evaluation of the ISO, RCAR, and RCAR-IIWPG protocols, and further development of new safety systems to protect occupants in rear-end impacts.

Professional truck drivers are highly exposed to fatigue and work related injuries. Truck drivers are common victims of musculoskeletal disorders, frequently suffering from pain symptoms particularly in the neck, shoulder and lower back. This situation is believed to be a contributor to the high absenteeism in this job category. A high percentage of this problem is due to the adoption of an unhealthy driving posture resulting from inappropriate seat design. This incorrect and poor design is owing to the insufficient and obsolete anthropometrical data which has been used for decades for arranging and positioning components in the driver environment. The main objective of the present study was to create and construct a mathematical model which clarifies and predicts the drivers’ comfortable sitting posture and position. It was hypothesized that the length and height characteristics of some body segments as well as the body weight and waist circumference of the driver have a great impact on the selection of a specific sitting posture. The steering wheel positions as well as the pedal/floor locations were hypothesized to be highly correlated to the driver’s selected posture and the corresponding comfort. The effect of the seat position on posture selection and related comfort assessments constituted the other hypothesis of the study which received extra attention. A laboratory experiment on a Scania truck cab mock-up was conducted. The seat track travel along a vertical as well as horizontal forward-backward path was obtained by mounting the seat on the motorized rigid frame which allowed unrestricted vertical and fore-aft travel. The seat cushion angle and backrest angle were adjusted by pivoting the entire seat and backrest around a lateral axis and independently. The pedal components were mounted on a motorized platform, thus allowing unrestricted fore-aft and height travel without any changes in the pedal angles. The steering wheel was mounted on the instrument panel by two independent pneumatic axes which allowed a wide range of adjustments including tilting and moving along the sagittal plane for adjusting the height and distance. The test plan called for 55 international highly experienced heavy truck drivers. The drivers were recruited to span a large range of body weight and stature, in particular to ensure adequate representation of both the extreme as well as the normal group of drivers. The drivers filled in a general information questionnaire before undergoing the anthropometrical measurements and thereafter the test trials. The experiment contained a subset of test conditions with five different trials using random selection sampling procedure. Drivers were asked to adjust the components in a wide range of trajectory according to a written protocol. A sparse set of threedimensional body landmark locations and the corresponding comfort assessments were recorded. As the main part of the result, the mathematical models using multiple regression analyses on selected body landmarks as well as anthropometrical measures were developed which proposed a linear correlation between parameters. The differences between the observed data and the corresponding predicted data using the model were found to be minimal and almost dispensable. Additionally, the drivers preferred to sit in the rearmost position and at a rather high level relative to the rest of the available and adjustable area. Considering the normal adjustable seat area of the cab, only a very small part of the observed Hpoint data lies within this area while a large remaining amount of data lies outside of it. Moreover, the difference between the observation (plotted H-point data) and the neutral H-point was found to be significant. Furthermore, and since some of the data lies almost on the border of the adjustable area, it may indicate a reasonable tendency for even more seat adjustment in the backward direction. A conceptual model consisting of four different parameters was developed and presented in the end. These parameters of the model suggest being as key factors which play a central role on process of decision making regarding the selection of a desirable sitting posture. Any eventual modifications and adjustments for elimination or minimizing discrepancies, biases or obscured factors affecting the quality of the mathematical model would be a case for future study. The investigation of a complete assessment of comfort should be supplemented with an analysis of how many truck drivers are satisfied with the comfort in the end. / QC 20100824

Cette thèse traite de l'équilibre postural orthostatique chez l'Homme jeune ou âgé. Plusieurs sources d'informations sont utilisées (somesthésique, proprioceptive, vestibulaire et visuelle) pour maintenir la posture. Le but de la thèse est de montrer le rôle de la convergence des yeux (angle des axes optiques) qui varie selon la distance. L'Etude 1 montre que l'augmentation de la convergence, lorsqu'on fixe en vision proche ou lorsqu'on porte des prismes convergents, améliore la stabilité posturale. Cette amélioration est attribuée aux signaux efférents et proprioceptifs de la convergence. L'Etude 2 montre que la relation entre l'angle de convergence et la stabilité posturale n'existe qu'en vision binoculaire ; peut-être qu'en vision monoculaire, l'angle de convergence varie peu. L'Etude 3 apporte un regard nouveau sur le test de Romberg, traditionnellement considéré comme évaluant le rôle de la vision : la forte instabilité posturale avec les yeux fermés par rapport aux yeux ouverts est observée seulement en vision proche ou intermédiaire (< 90 cm). Ce résultat indique un rôle combiné de la vision et des signaux de la convergence. L'Etude 4 montre que l'exécution des saccades, horizontales ou verticales, améliore la stabilité posturale. Enfin, l'Etude 5 montre une instabilité posturale chez les personnes présentant des symptômes de fatigue visuelle, céphalées et vertiges associés à des troubles de la vergence. L'ensemble de ces études a une importance théorique et clinique et ouvre de nouvelles voies de recherche.

Le milieu des Services à l'automobile est un secteur d'activité comportant plusieurs travailleurs manuels. Depuis les dernières années, plusieurs études ont démontré que ce milieu est touché d'une manière importante par les troubles musculo-squelettiques aux membres supérieurs (TMS-MS). Les écrits associés aux peintres de carrosserie automobiles établissent un lien entre la charge statique, les postures de travail, les pistolets utilisés et le développement de TMS-MS. Cette étude avait pour objectif d'évaluer des stratégies utilisées lors de l'application de peinture à l'aide de deux types de pistolets par des peintres d'expérience ayant préalablement été observés par Giguère et al. (2007) lors d'une étude exploratoire portant sur les TMS-MS dans le secteur des Services à l'automobile. Ces stratégies avaient été identifiées en raison de leur potentiel à diminuer les contraintes physiques aux membres supérieurs associées à l'application de peinture pour différents plans, de hauteurs diverses. Dix sujets ont réalisé des manœuvres sur quatre sections différentes (portière basse, portière haute, capot et toit). Ces sujets devaient faire dix-huit conditions expérimentales qui furent créées à partir de la combinaison des variables indépendantes. Ces variables comportaient : la hauteur du plan de travail (standard et modifiée), la posture de travail (accroupie et debout), l'inclinaison de la surface (droit et incliné), le type de pistolets (standard et modifié). Les quatre variables n'ont pas été utilisées pour chacune des sections analysées. Tous les résultats ont été utilisés pour les analyses statistiques multifactorielles. L'activité musculaire a été mesurée avec l'électromyographie (EMG) de surface pour douze muscles du membre supérieur droit. L'évaluation des moments de force externes exercés par le pistolet a été faite. De plus, la vidéo a permis d'évaluer le positionnement angulaire des membres supérieurs pour les articulations de l'épaule et du coude. La perception psychophysique de l'effort associée aux différentes conditions expérimentales a aussi été recueillie pour chacun des sujets. Selon les résultats de l'EMG, l'optimisation de la hauteur de travail a permis de réduire les pourcentages de la contraction volontaire maximale pour le trapèze supérieur et le deltoïde antérieur aux conditions sur la section du toit. Cette baisse suggère que l'élévation du travailleur amène un effet positif sur sa posture, comme le témoigne la demande musculaire. Le muscle fléchisseur de l'épaule, qui est moins raccourci en raison de la baisse de l'angle relatif à l'articulation, déploie alors moins de force pour réaliser le même mouvement. De plus, l'inclinaison de la surface permet aussi de modifier la posture du travailleur. L'angle de 45 degrés à la section du capot permet le rapprochement des segments du travailleur et ainsi réduit le moment de force à l'épaule lors de l'application de peinture. Cette situation abaisse les %CVM des trapèzes supérieurs et deltoïdes antérieurs et les angles relatifs et absolus à l'articulation de l'épaule. Enfin, les résultats ont aussi démontré que l'utilisation du pistolet modifié présentait un effet significatif, mais que l'outil ne permettait pas de réduire de manière importante l'activation des muscles extenseurs et fléchisseurs du poignet. Bien que le centre de gravité de l'outil modifié à été mieux balancé, la déviation au poignet était quand même présente. Il serait intéressant de poursuivre cette étude en tentant de concevoir un type de poignée qui permettrait de réduire les contraintes physiques au poignet associées à la préhension du pistolet sur une surface horizontale. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : mécanique automobile, trouble musculo-squelettique au membre supérieur, ergonomie, électromyographie, biomécanique, pistolet à peinture, carrosserie

Intervertebral disc herniations have been indicated as a possible injury development pathway due to occupational vibration exposures in seated postures through epidemiological investigations. Little experimental evidence exists to corroborate the strong epidemiological link between intervertebral disc herniations and vibration exposures using basic scientific approaches. The purpose of the current investigation was to provide some basic experimental evidence of the epidemiological link between intervertebral herniation and exposure to vibration. Partial intervertebral disc herniations were created in in-vitro porcine functional spinal units using a herniation protocol of repetitive flexion/extension motions under modest compressive forces. After herniation initiation, functional spinal units were exposed to 8 different vibration and postural constraint loading protocols consisting of two postural conditions (full flexion and neutral) and 4 vibration loading conditions (whole-body vibration, shock loading, static compressive loads, and whole-body vibration in addition to shock loading) to assess the effects of vibration and posture on functional spinal unit damage progression. There were three main outcome variables used to quantify damage progression; average stiffness changes, herniation distance progression (distance of tracking changes), and specimen height changes, while cumulative loading factors were considered. Additionally the concordance between two types of contrast enhanced medical imaging (Computed Tomography and discograms) was qualified to a dissection ‘gold standard’, and an attempt was made to classify disc damage progression via three categorical variables. Concordance to a dissection ‘gold standard’ was higher for the Computed Tomography medical imaging type that for the Discograms. The categorical criteria used to qualify disc damage progression were insufficiently sensitive to detect damage progressions illustrated through dissection and medical imaging techniques. The partial herniation loading protocol was quantified to be more damaging overall to the functional spinal units compared to the vibration and postural constraint loading protocols. However, the vibration and postural constraint loading protocols provided sufficient mechanical insult to the functional spinal units to progress damage to the intervertebral discs. Vibration loading exposures were found to alter specimen height changes and distance of tracking changes, however posture had no significant effects on these variables. Neither posture nor vibration loading had any meaningful significant effects on average stiffness changes.

No description available.

Intervertebral disc herniations have been indicated as a possible injury development pathway due to occupational vibration exposures in seated postures through epidemiological investigations. Little experimental evidence exists to corroborate the strong epidemiological link between intervertebral disc herniations and vibration exposures using basic scientific approaches. The purpose of the current investigation was to provide some basic experimental evidence of the epidemiological link between intervertebral herniation and exposure to vibration. Partial intervertebral disc herniations were created in in-vitro porcine functional spinal units using a herniation protocol of repetitive flexion/extension motions under modest compressive forces. After herniation initiation, functional spinal units were exposed to 8 different vibration and postural constraint loading protocols consisting of two postural conditions (full flexion and neutral) and 4 vibration loading conditions (whole-body vibration, shock loading, static compressive loads, and whole-body vibration in addition to shock loading) to assess the effects of vibration and posture on functional spinal unit damage progression. There were three main outcome variables used to quantify damage progression; average stiffness changes, herniation distance progression (distance of tracking changes), and specimen height changes, while cumulative loading factors were considered. Additionally the concordance between two types of contrast enhanced medical imaging (Computed Tomography and discograms) was qualified to a dissection ‘gold standard’, and an attempt was made to classify disc damage progression via three categorical variables. Concordance to a dissection ‘gold standard’ was higher for the Computed Tomography medical imaging type that for the Discograms. The categorical criteria used to qualify disc damage progression were insufficiently sensitive to detect damage progressions illustrated through dissection and medical imaging techniques. The partial herniation loading protocol was quantified to be more damaging overall to the functional spinal units compared to the vibration and postural constraint loading protocols. However, the vibration and postural constraint loading protocols provided sufficient mechanical insult to the functional spinal units to progress damage to the intervertebral discs. Vibration loading exposures were found to alter specimen height changes and distance of tracking changes, however posture had no significant effects on these variables. Neither posture nor vibration loading had any meaningful significant effects on average stiffness changes.

Although people can typically maintain balance on moving trains, or press the appropriate button on an elevator with little conscious effort, the apparent ease of these sensorimotor tasks is courtesy of neural mechanisms that continuously interpret many sensory input signals to activate muscles throughout the body. The overall hypothesis of this work is that motor behaviors emerge from the interacting constraints and features of the nervous and musculoskeletal systems. The nervous system may simplify the control problem by recruiting muscles in groups called muscle synergies rather than individually. Because muscles cannot be recruited individually, muscle synergies may represent a neural constraint on behavior. However, the constraints of the musculoskeletal system and environment may also contribute to determining motor behaviors, and so must be considered in order to identify and interpret muscle synergies. Here, I integrated techniques from musculoskeletal modeling, control systems engineering, and data analysis to identify neural and biomechanical constraints that determine the muscle activity and ground reaction forces during the automatic postural response (APR) in cats. First, I quantified the musculoskeletal constraints on force production during postural tasks in a detailed, 3D musculoskeletal model of the cat hindlimb. I demonstrated that biomechanical constraints on force production in the isolated hindlimb do not uniquely determine the characteristic patterns of force activity observed during the APR. However, when I constrained the muscles in the model to activate in a few muscle synergies based on experimental data, the force production capability drastically changed, exhibiting a characteristic rotation with the limb axis as the limb posture was varied that closely matched experimental data. Finally, after extending the musculoskeletal model to be quadrupedal, I simulated the optimal feedforward control of individual muscles or muscle synergies to regulate the center of mass (CoM) during the postural task. I demonstrated that both muscle synergy control and optimal muscle control reproduced the characteristic force patterns observed during postural tasks. These results are consistent with the hypothesis that the nervous system may use a low-dimension control scheme based on muscle synergies to approximate the optimal motor solution for the postural task given the constraints of the musculoskeletal system. One primary contribution of this work was to demonstrate that the influences of biomechanical mechanisms in determining motor behaviors may be unclear in reduced models, a factor that may need to be considered in other studies of motor control. The biomechanical constraints on force production in the isolated hindlimb did not predict the stereotypical forces observed during the APR unless a muscle synergy organization was imposed, suggesting that neural constraints were critical in resolving musculoskeletal redundancy during the postural task. However, when the model was extended to represent the quadrupedal system in the context of the task, the optimal control of the musculoskeletal system predicted experimental force patterns in the absence of neural constraints. A second primary contribution of this work was to test predictions concerning muscle synergies developed in theoretical neuromechanical models in the context of a natural behavior, suggesting that these concepts may be generally useful for understanding motor control. It has previously been shown in abstract neuromechanical models that low-dimension motor solutions such as muscle synergies can emerge from the optimal control of individual muscles. This work demonstrates for the first time that low-dimension motor solutions can emerge from optimal muscle control in the context of a natural behavior and a realistic musculoskeletal model. This work also represents the first explicit comparison of muscle synergy control and optimal muscle control during a natural behavior. It demonstrates that an explicit low-dimension control scheme based on muscle synergies is competent for performance of the postural task across biomechanical conditions, and in fact, may approximate the motor solution predicted by optimal muscle control. This work advances our understanding how the constraints and features of the nervous and musculoskeletal systems interact to produce motor behaviors. In the future, this understanding may inform improved clinical interventions, prosthetic applications, and the general design of distributed, hierarchal systems.