Due to the large influx of computers in our daily lives, human-computer interaction has become crucially important. For a long time, focusing on what users need has been critical for designing interaction methods. However, new perspective tends to extend this attitude to encompass how human desires, interests, and ambitions can be met and supported. This implies that the way we interact with computers should be revisited. Centralizing human values rather than user needs is of the utmost importance for providing new interaction techniques. These values drive our decisions and actions, and are essential to what makes us human. This motivated us to introduce new interaction methods that will support human values, particularly human well-being. The aim of this thesis is to design new interaction methods that will empower human to have a healthy, intuitive, and pleasurable interaction with tomorrow’s digital world. In order to achieve this aim, this research is concerned with developing theories and techniques for exploring interaction methods beyond keyboard and mouse, utilizing human body. Therefore, this thesis addresses a very fundamental problem, human motion analysis. Technical contributions of this thesis introduce computer vision-based, marker-less systems to estimate and analyze body motion. The main focus of this research work is on head and hand motion analysis due to the fact that they are the most frequently used body parts for interacting with computers. This thesis gives an insight into the technical challenges and provides new perspectives and robust techniques for solving the problem.

BACKGROUND and OBJECTIVES: Low-back overexertion injuries represent a large proportion of fireground “strains, sprains and muscular pains” and are a leading cause of disability and early retirement in firefighters. Given the inherently hazardous and unpredictable nature of many fireground activities, it is often infeasible to implement “task-focused” ergonomic controls and there are limited options to accommodate injured firefighters. Accordingly, effective and practical “worker-focused” injury prevention approaches are needed. Toward this end, four studies were conducted to address the following global thesis objectives: 1) Examine the possible role that firefighters’ personal movement strategies could have on their occupational low-back loading demands and injury potential; and 2) Compare the effects of two different exercise approaches on firefighters’ occupational low-back loading demands and injury potential. STUDY 1: Low-Back Loading Demands during Simulated Firefighting Tasks – Inter-Subject Variation and the Impact of Fatigue and Gender. Background: Non-modifiable fireground duties are considered hazardous for low-back health, but personal movement strategies could modulate low-back loading demands and injury potential. Study objectives were to quantify low-back loading demands during simulated firefighting tasks and to examine the impact of fatigue and gender on the peak loading response. Methods: Ten men and 10 women performed a battery of laboratory-simulated firefighting tasks before and following repeated bouts of a fatiguing stair-climbing protocol. An EMG-assisted three-dimensional dynamic biomechanical model was used to compute peak L4/L5 joint forces during task performance. Results: Peak low-back loading demands varied considerably between subjects and tasks, but 70% of all loading variables examined were of greater magnitudes in male subjects and 40% of all loading variables were of lower magnitudes in both males and females after stair-climbing. Some inter-subject variation in low-back loading was attributed to body size differences, but between- and within-subject differences in movement strategies also contributed to low-back loading variability between subjects and over time. Conclusions: Results of this study suggest that characteristics of individuals, tasks performed, and physical fatigue may influence peak low-back loading demands and injury potential in firefighters. Despite considerable inter-subject variation in the internal low-back loading response to fixed external task and environmental constraints, opportunities to attenuate low-back loading demands through movement behaviour adaptations alone may be limited to only a subset of fireground activities. STUDY 2: Ankle Immobilization alters Lifting Kinematics and Kinetics – Occupational Low-Back Loading Demands and Potential for Injury. Background: Firefighters with lingering lower extremity functional impairments could be forced to move in ways that increase their potential for sustaining occupational low-back lifting injuries. The study objective was to examine the impact of unilateral ankle immobilization on lifting kinematics and kinetics. Methods: With and without their right ankle immobilized, 10 male volunteers performed laboratory-simulated occupational lifting tasks. Together with force platform data, three-dimensional kinematics of the lumbar spine, pelvis, and lower extremities were collected, and a three-dimensional dynamic biomechanical model was used to calculate peak low-back compression and shear loading demands. Results: In comparison to the unaffected conditions, ankle immobilization resulted in less knee (p-values between 0.0004 and 0.0697) and greater lumbar spine (p-values between 0.0006 and 0.3491) sagittal motion when lifting. Associated with this compensatory movement strategy were greater L4/L5 anterior/posterior reaction shear forces (p-values between 0.0009 and 0.2450). However, in a few cases where individual compensatory movement strategies differed from the “group” response (i.e., subjects increased their sagittal knee and hip motion on the affected side), peak L4/L5 joint compressive loads increased while the peak L4/L5 anterior-posterior shear did not change. Conclusions: Distal lower extremity joint dysfunction can alter the way in which individuals move and load their low-backs when lifting. The specific ways in which individuals compensate for personal movement constraints could alter the potential site and mechanism of occupational low-back injury. STUDY 3: FMS™ Scores and Occupational Low-Back Loading Demands – Whole-Body Movement Screening as an Ergonomic Tool? Background: Results of Study 1 suggested that a whole-body movement screen could be used to identify personal characteristics that constrain movement behaviour in ways that impact occupational low-back loading demands and injury potential. The purpose of this study was to examine if Functional Movement Screen™ (FMS) scores could be used to project the low-back loading response to lifting. Methods: Sagittally symmetric and asymmetric laboratory-based lifting tasks were performed by 15 firefighters who scored greater than 14 on the FMS (high-scorers) and 15 size-matched low-scorers (FMS < 14). A three-dimensional dynamic biomechanical model was used to calculate low-back loading demands, and lumbar spine posture was recorded when peak low-back compression was imposed. Results: Regardless of the task performed, there were no differences in peak L4/L5 joint compression (p ≥ 0.4157), anterior/posterior reaction shear (p ≥ 0.5645), or medial/lateral reaction shear (p ≥ 0.2581) loading demands between high- and low-scorers. At the instant when peak compression force was detected, lumbar spine deviation was not different between high- and low-scorers about the lateral bend (p ≥ 0.4215), axial twist (p ≥ 0.2734), or flexion/extension (p ≥ 0.1354) axes. Conclusions: Using the previously established musculoskeletal injury prediction threshold value of 14, the composite FMS score did not project the low-back loading response to lifting. Future attempts to modify or reinterpret FMS scoring are warranted given that several previous studies have revealed links between composite FMS scores and musculoskeletal complaints. STUDY 4: Movement- vs. Fitness-Centric Exercise – Firefighter Fitness, Whole-Body Movement Qualities, and Occupational Low-Back Loading Outcomes. Background: The impact of exercise on firefighter job performance and cardiorespiratory fitness has been studied extensively, but its effect on musculoskeletal loading remains less understood. The aim of this study was to compare various physical fitness, general movement quality, and low-back loading outcomes between groups of firefighters who completed fitness- or movement-centric exercise. Methods: Fifty-four firefighters participated and were assigned to a control (CON), fitness-centric exercise (FIT), or movement-centric exercise (MOV) group. Before and after 12 weeks of exercise, subjects performed a physical fitness test battery, the Functional Movement Screen™ (FMS), and laboratory-simulated firefighting tasks during which low-back loading demands were quantified. Results: FIT and MOV subjects exhibited statistically significant improvements in nearly all measures of physical fitness (i.e., body composition, cardiorespiratory capacity, muscular strength, power, endurance, and flexibility), but FMS scores and occupational low-back loading demands were not impacted in a consistent way across individuals. Conclusions: Improving physical fitness can enhance job performance and prevent cardiac events in firefighters, but it was not clear that 12 weeks of exercise would alter their occupational low-back loading demands. Given variability in individual responses, the short study duration, and limited number and nature of tasks examined, more research incorporating alternative biomechanical and statistical analyses is needed to better understand how individuals adapt to chronic exercise and what impact these adaptations have on occupational movement behaviours, low-back loading demands, and low-back loading capacity. SUMMARY and CONCLUSIONS: Results confirmed that fireground activities are potentially hazardous for low-back health, as simulated occupational low-back loading demands routinely exceeded recommended exposure limits in the studies performed. However, results also indicated that personal movement strategies – possibly influenced by body size, preference, gender, physical fatigue, or distal lower extremity joint dysfunction – could alter occupational low-back loading demands and injury potential. It could not be concluded that occupational low-back loading demands and injury potential would be consistently affected by short-term improvements in physical fitness, nor could the low-back loading response to lifting be projected by scoring above or below 14 on the Functional Movement Screen™. Future research is warranted to examine the low-back loading demands associated with performing non-fireground duties, as opportunities may exist to implement ergonomic strategies to control cumulative low-back loading exposures. Particular attention should be paid to the exercise and training practices of firefighters, as musculoskeletal injuries sustained during these activities are potentially avoidable and could reduce the capacity of the musculoskeletal system to withstand demands imposed during non-modifiable fireground operations.

À quel point les mouvements humains sont-ils optimaux ? Cette thèse aborde cette question en se concentrant particulièrement sur les mouvements en escalade, étudiés ici sous trois aspects complémentaires que sont la collecte expérimentale de séquences de grimpe, l'analyse biomécanique de ces données, et la synthèse de gestes par optimisation temporelle. La marche fut l'objet de nombreux travaux, avec de bons résultats notamment en animation [Mordatch 2013]. Nous nous intéressons ici spécialement au problème original des mouvements d'escalade, dont la diversité et leur caractère multicontact présentent une complexité intéressante pour l'évaluation des caractéristiques du mouvement humain. L'hétérogénéité du répertoire gestuel rencontrée en escalade s'explique par plusieurs facteurs que sont l'évolution sur des parois de formes variées, la multiplicité des niveaux d'expertise des pratiquants, et des disciplines différentes au sein même de l'activité, à savoir le bloc, la difficulté, ou encore l'escalade de vitesse. Notre démarche d'exploration de ce sport se décompose en trois étapes : la collecte de données par une capture de mouvements multicaméra avec marqueurs, couplée à un ensemble de capteurs de force montés sur un mur de bloc en laboratoire ; une analyse du geste par dynamique inverse, prenant exclusivement des données cinématiques pour entrées, basée sur une minimisation des couples internes pour résoudre l'ambiguïté du multicontact, intrinsèque à l'activité d'escalade, validée par comparaison avec les mesures capteurs ; et enfin, l'utilisation d'un critère d'efficacité énergétique pour synthétiser la meilleure temporisation associée à une séquence de déplacements donnés. Les enregistrements expérimentaux se sont fait à l'université McGill qui dispose d'un mur instrumenté de 6 capteurs de forces, et d'un dispositif de capture de mouvements 24 caméras, nous ayant permis de collecter des données sur une population de 9 sujets. L'analyse de ces données constitue la deuxième partie de cette thèse. Le défi abordé est de retrouver les forces externes et les efforts internes à partir uniquement des déplacements du grimpeur. Nous supposons pour cela une répartition optimale des efforts internes. Après analyse, cette répartition s'avère être plutôt uniforme que proportionnelle aux capacités musculaires des différentes articulations du corps. Finalement, dans une troisième et dernière partie, nous nous intéressons à la temporisation des gestes en escalade, en prenant en entrée la trajectoire du grimpeur, éventuellement issue de cinématique inverse pour s'affranchir de la nécessité d'une capture par marqueurs et caméras infra-rouges. En sortie, une temporisation idéale pour cette trajectoire est trouvée. Cette temporisation s'avère réaliste, mais manque d'une modélisation des instants d'hésitation et de prise de décision, ainsi que d'un modèle d'établissements de contact, phénomène présentant un délai temporel non pris en compte pour l'instant. / How optimal are human movements ? This thesis tackles this issue by focusing especially on climbing movements, studied here under three complementary aspects which are the experimental gathering of climbing sequences, the biomechanical analysis of these data, and the synthesis of gestures by timing optimization. Walking has been largely studied, with good results in animation [Mordatch 2013]. We are interested here especially in the original question of climbing motions, whose diversity and multicontact aspect present an interesting complexity for the evaluation of the human motion characteristics. The heterogeneity of climbing gestures can be linked to several factors which are the variety of wall shapes, the multiplicity of climber skill levels, and different climbing categories, namely bouldering, route climbing or speed climbing. Our exploratory approach of this sport consists in three steps: the data collection by multicamera marker-based motion capture, combined with a set of force sensors mounted on an in-laboratory bouldering wall; a gesture analysis by inverse dynamics, taking only kinematic data as inputs, based on the minimization of internal torques to resolve the multicontact ambiguity, intrinsic to the climbing activity, validated by comparison with sensor measurements; and finally, the use of the energy efficiency criterion for synthesizing the best timing associated with a given sequence of movements. Experimental recordings were made at McGill University which has a climbing wall instrumented of 6 force sensors, and a motion capture device of 24 cameras, which allowed us to collect data on a population of nine subjects. The analysis of these data is the second part of this thesis. The addressed challenge is to find the external forces and internal torques from the climber's movements only. To this end we assume an optimal distribution of internal torques. After analysis, the distribution turns out to be rather uniform than proportional to the muscle capacity associated to each body joint. Finally, in a third and last part, we focus on the timing of climbing gestures, taking as input the path of the climber, possibly after inverse kinematics in order to overcome the need for a capture with markers and infrared cameras. As output, an optimal timing for this path is found. This timing is realistic, but lacks of a modelization for hesitation and decision making instants, as well as a model for the contact establishment, with the associated temporal delay currently not taken into account.

Background: Joint stability has been experimentally and clinically linked to mechanisms of knee injury and joint degeneration. The only dynamic, and perhaps most important, regulators of knee joint stability are contributions from muscular contractions. In participants with unstable knees, such as anterior cruciate ligament (ACL) injured, a range of neuromuscular adaptations has been observed including quadriceps weakness and increased co-activation of adjacent musculature. This co-activation is seen as a compensation strategy to increase joint stability. In fact, despite increased co-activation, instability persists and it remains unknown whether observed adaptations are the result of injury induced quadriceps weakness or the mechanical instability itself. Furthermore, there exists conflicting evidence on how and which of the neuromuscular adaptations actually improve and/or reduce knee joint stability. Purpose: The overall aim of this thesis is therefore to elucidate the role of injury and muscle weakness on muscular contributions to knee joint stability by addressing two main objectives: (1) to further our understanding of individual muscle contribution to internal knee joint moments; and (2) to investigate neuromuscular adaptations, and their effects on knee joint moments, caused by either ACL injury and experimental voluntary quadriceps inhibition (induced by pain). Methods: The relationship between individual muscle activation and internal net joint moments was quantified using partial least squares regression models. To limit the biomechanical contributions to force production, surface electromyography (EMG) and kinetic data was elicited during a weight-bearing isometric force matching task. A cross-sectional study design determined differences in individual EMG-moment relationships between ACL deficient and healthy controls (CON) groups. A crossover placebo controlled study design determined these differences in healthy participants with and without induced quadriceps muscle pain. Injections of hypertonic saline (5.8%) to the vastus medialis induced muscle pain. Isotonic saline (0.9%) acted as control. Effect of muscle pain on muscle synergies recruited for the force matching task, lunging and squatting tasks was also evaluated. Synergies were extracted using a concatenated non-negative matrix factorization framework. Results/Discussion: In CON, significant relationships of the rectus femoris and tensor fascia latae to knee extension and hip flexion; hamstrings to hip extension and knee flexion; and gastrocnemius and hamstrings to knee rotation were identified. Vastii activation was independent of moment generation, suggesting mono-articular vastii activate to produce compressive forces, essentially bracing the knee, so that bi-articular muscles crossing the hip can generate moments for the purpose of sagittal plane movement. Hip ab/adductor muscles modulate frontal plane moments, while hamstrings and gastrocnemius support the knee against externally applied rotational moments. Compared to CON, ACL had 1) stronger relationships between rectus femoris and knee extension, semitendinosus and knee flexion, and gastrocnemius and knee flexion moments; and 2) weaker relationships between biceps femoris and knee flexion, gastrocnemius and external knee rotation, and gluteus medius and hip abduction moments. Since the knee injury mechanism, is associated with shallow knee flexion angles, valgus alignment and rotation, adaptations after ACL injury are suggested to improve sagittal plane stability, but reduce frontal and rotational plane stability. During muscle pain, EMG-moment relationships of 1) semitendinosus and knee flexor moments were stronger compared to no pain, while 2) rectus femoris and tensor fascia latae to knee extension moments and 3) semitendinosus and lateral gastrocnemius to knee internal rotation moments were reduced. Results support the theory that adaptations to quadriceps pain reduces knee extensor demand to protect the joint and prevent further pain; however, changes in non-painful muscles reduce rotational plane stability. Individual muscle synergies were identified for each moment type: flexion and extension moments were respectively accompanied by dominant hamstring and quadriceps muscle synergies while co-activation was observed in muscle synergies associated with abduction and rotational moments. Effect of muscle pain was not evident on muscle synergies recruited for the force matching task. This may be due to low loading demands and/or a subject-specific redistribution of muscle activation. Similarly, muscle pain did not affect synergy composition in lunging and squatting tasks. Rather, activation of the extensor dominant muscle synergy and knee joint dynamics were reduced, supporting the notion that adaptive response to pain is to reduce the load and risk of further pain and/or injury. Conclusion: This thesis evaluated the interrelationship between muscle activation and internal joint moments and the effect of ACL injury and muscle pain on this relationship. Findings indicate muscle activation is not always dependent on its anatomical orientation as previous works suggest, but rather on its role in maintaining knee joint stability especially in the frontal and transverse loading planes. In tasks that are dominated by sagittal plane loads, hamstring and quadriceps will differentially activate. However, when the knee is required to resist externally applied rotational and abduction loads, strategies of global co-activation were identified. Contributions from muscles crossing the knee for supporting against knee adduction loads were not apparent. Alternatively hip abductors were deemed more important regulators of knee abduction loads. Both muscle pain and ACL groups demonstrated changes in muscle activation that reduced rotational stability. Since frontal plane EMG-moment changes were not present during muscle pain, reduced relationships between hip muscles and abduction moments may be chronic adaptions by ACL that facilitate instability. Findings provide valuable insight into the roles muscles play in maintaining knee joint stability. Rehabilitative/ preventative exercise interventions should focus on neuromuscular training during tasks that elicit rotational and frontal loads (i.e. side cuts, pivoting maneuvers) as well as maintaining hamstring balance, hip abductor and plantarflexor muscle strength in populations with knee pathologies and quadriceps muscle weakness.

Cette thèse s’inscrit dans un projet à long terme de conception de nouvelle prothèse de l’Articulation Temporo-Mandibulaire (ATM). Afin de faciliter une caractérisation non invasive de l’ATM, elle a conduit à l’élaboration d’un modèle élément finis plan de l’ATM. Le modèle, construit à partir de relevés IRM, intègre le ménisque ainsi que les insertions musculaires et ligamentaires. Il est commandé en déplacements imposés tout d’abord et en efforts imposés ensuite. Les déplacements ont été mesurés par analyse vidéo 3D et les efforts musculaires ont été évalués par EMG au cours de travaux antérieurs réalisés au sein du laboratoire. Le modèle est ici exploité pour simuler un mouvement d’ouverture et un serrage inter-incisives dans trois configurations qui correspondent à des ouvertures de 5 mm, 25 mm et 30 mm. Les résultats de ces simulations, validés par IRM, ont permis de caractériser le rôle du disque articulaire de l’ATM dans la réalisation des déplacements et la transmission des efforts. L’étude souligne la nécessité de rechercher des solutions technologiques de remplacement du disque articulaire lors de la conception d’une nouvelle prothèse. / This study presents a part of a long-term project that aims to design a new prosthesis for the Temporomandibular Joint (TMJ). In order to facilitate a non-invasive characterization of the TMJ, a plane finite element model of the joint has been elaborated starting from MRI images. The model integrates the meniscus as well as the principal ligaments and the main muscular insertions. It has been driven firstly with displacements and then with forces. The displacements have been measured using a 3D motion analysis system and the muscles forces have been taken from anterior former EMG studies led in the laboratory. An opening movement and inter-incisors clenching in three configurations which correspond to openings of 5, 25 and 30 mm have been simulated. The results of these simulations, validated by MRI, made it possible to characterize the function of the articular disk during the movement and the transmission of actions. This study underlines the necessity of seeking technological solutions to replace the meniscus when designing a new prosthesis.

Motion segmentation is an important process for separating moving objects from the background. Common methods usually assume fixed camera, other approaches exist as well, but they are usually very computational intensive. This work presents an approach for scene segmentation to regions with coherent motion, which works faster than similar methods and it is capable of online processing with no prior knowledge of objects or camera. The main assumption is that the points belonging to a single objects are moving together and this applies as well in the opposite direction. The proposed method is based on tracking of feature points and searching for groups with similar motion by using RANSAC-based algorithm. Short-range repair of broken tracks is applied to increase the overall robustness of tracking. Found clusters are subsequently processed to represent separate moving objects.

The thesis deals with the issue of tracking feature points earned from videosequences of hand helded camera. The work is focused on the case of moving camera and static background, and events that are associated with this case and can occur. There is studied the movement of the camera, which is given its direction and speed. The aim of this work is the election and the subsequent implementation of three fundamentally different methods suitable for tracking feature points in case of moving camera and their comparison according to set criteria. On the basis of comparison will be under pre-defined conditions chosen algorithm that is best able to deal with tracing these points.

Kinematic approaches of motion generation use joint angles of a specified kinematic skeleton to describe poses and consider motions as sequences of poses. The progression functions, i.e. the functions describing the angular values of the joints over time are usually obtained by motion capturing. So far, approaches to synthesize these functions have only been able to create motions with strong artificial visual appearance. In this paper we present a novel method for generating gait motions from synthesized progression functions. Our method is based on the key observation that the progression functions of the joints involved in gait motions show certain characteristic shapes. Based on empirical evaluations we describe these shapes for all progression functions needed to generate walking movements. Furthermore, we analyze the variation of the described shapes depending on stride length and walking speed. Polynomial splines are used to define functions that mimic the shapes of progression functions and can be easily controlled via the spline parameters. We develop a model that describes how to change the parameters of the splines according to the rules of shape variation observed on empirical data in order to adjust stride length and walking speed. Our method can be used to generate walking motions of virtual characters with user provided stride length or walking speed. To evaluate our method we compare synthesized gait motions with recorded ones. A numerical evaluation shows that the maximal joint displacement between captured and synthesized motions lies within the range of variability of natural human walking.

Bakgrund: I Sverige är den generella uppfattningen att det vid val av vardagssko är rekommenderat att välja en sportsko framför en canvas tennissko. Tidigare studier har jämfört hur olika skomodeller påverkar gången, men ingen har studerat skillnader mellan sportskor och canvas tennisskor. Syfte: Undersöka hur en sko med instabil läst och platt bindsula (canvas tennissko) samt en sko med en stadig läst, en sula med bra stötdämpning och avrullning (sportsko) påverkar den mediolaterala stabiliteten olika under stödfasen. Metod: Gånganalys på fem kvinnliga deltagare. Kinetisk och kinematisk data samlades in med hjälp av ett 3D-rörelseanalyssystem. Resultat: Rörelseomfånget skiljer sig mer mellan deltagare än skomodeller. Sportskor har ett försumbart lägre rörelseomfång än canvas tennisskor. Sportskor ger mer inverterad gång än Canvas tenniskor. Steglängden och stödfasen (stance time) skiljer inte mellan de två skomodellerna. Slutsats: Fotens rörelseomfång i frontalplanet skiljer sig inte mellan canvas tennisskor och sportskor under stödfasen, men sportskon har en mer inverterad rörelse. / Background: In Sweden it is a general perception that a sports shoe is a better choice than a canvas tennis shoe for everyday use. Previous studies have investigated how different shoe models affect the gait, but none have studied the differences between sport shoes and canvas tennis shoes. Aim: Investigate how a shoe with unstable last and a flat insole (canvas tennis shoe) and a shoe with steady last, a sole with good shock absorbing and roll off (sport shoe) affect the mediolateral stability differently during stance. Methods: Gait analysis on five female participants. Kinetic and kinematic data collected with3D-modionanalysis system. Results: The range of motion differs more between participants than between shoe models. The sport shoe have a negligible lower range of motion than the canvas tennis shoe. Walking in sport shoe shows a more inverted gait than gait in canvas tennis shoe. Step length and stance time are the same in both shoe models. Conclusion: The range of motion and motion pattern of the foot in the coronal plane does not differ between canvas tennis shoes and sport shoes during stance phase, but the sport shoe has a more inverted motion.

No description available.